The Mars Apparition of 2017-2019
by Martin J. Powell
The path of Mars against the background stars from February to December 2018, shown at 10-day intervals (click on the thumbnail for the full-size image, 202 KB). During this apparition Mars describes a Southward-facing loop against the background stars, quite unlike the 'zig-zag' that it described during the planet's previous apparition in 2015-17. The path of Saturn in Sagittarius is also shown, marked at the beginning of selected months over the same period; the two planets pass each other in the morning sky in early April 2018 (for more details see the planetary conjunctions section below). The star map applies to observers in the Northern hemisphere (i.e. North is up); for the Southern hemisphere view, click here (206 KB).
The faintest stars shown on the map have an apparent magnitude of about +4.8. Printer-friendly versions of this chart are available for Northern (95 KB) and Southern hemisphere (96 KB) views. Astronomical co-ordinates of Right Ascension (longitude, measured Eastwards in hrs:mins from the First Point of Aries) and Declination (latitude, measured in degrees North or South of the celestial equator) are marked around the border of the chart. Click here (160 KB) to see a 'clean' star map of the area (i.e. without planet path); observers may wish to use the 'clean' star map as an aid to plotting the planet's position on a specific night - in which case, a printable version can be found here (79 KB). Photographs of this region of the night sky can be seen below.
At superior conjunction on July 27th 2017 (when it passes directly behind the Sun in the constellation of Cancer, the Crab), Mars is positioned 2.6554 Astronomical Units (AU) from Earth (397.2 million kms or 246.8 million miles). Mars reaches its most distant point from Earth (known as the apogee or, in the case of Mars, the apoareion) for this apparition several days later on August 5th, when it lies at a distance of 2.6581 AU (397.6 million kms or 247 million miles). Were it to be visible from Earth at this time, its apparent magnitude would be +1.7 and its apparent size only 3".5 (i.e. 3.5 arcseconds, where 1" = 1/60th of an arcminute or 1/3600 of a degree). Mars enters the constellation of Leo, the Lion, on August 17th, becoming visible in the bright dawn twilight from Northern Tropical latitudes by month's end.
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In early September Mars becomes visible from Equatorial and Northern latitudes, rising in the ENE between an hour (20° North) and 1¼ hours (50° North) before sunrise. The 2015-17 apparition truly gets underway as Mars reaches a solar elongation of 15° West on September 11th, when Southern Tropical latitudes also begin to view the planet. The Red Planet is slowly pulling away from the Sun at a rate of just 0°.3 per day. From latitudes further South, low altitude (angle above the horizon) and twilight delay the appearance of the Red Planet until early October (35° South) and early November (45° South).
At this early stage in the apparition, Mars appears as a feeble, pale-orange 'star', shining about as bright as the star Alhena ( Gem or Gamma Geminorum, mag. +1.9), at the foot of Gemini's Southern Twin. Mars barely gains any significant altitude before disappearing into the brightening dawn twilight. Telescopically the planet is a disappointing sight, its low altitude and tiny apparent size frustrating most attempts to obtain a steady and clear view of the planet's surface.
Mars at Opposition imaged by Ed Grafton (Houston, Texas, USA) at the planet's previous very close passage to the Earth in August 2003 (click on the thumbnail for a larger image, 28 KB). Grafton used a 14-inch SCT telescope fitted with a CCD camera. The feature at centre-right is Solis Lacus, often called the 'Eye of Mars'; it also appears in a sketch by UK astronomer Paul Abel below (Image: Ed Grafton / ALPO-Japan).
In mid-September Mars experiences the first of eight planetary conjunctions which take place during the planet's 2017-19 apparition. A planetary conjunction takes place whenever any two planets attain the same celestial longitude, such that they appear close together in the night sky. On September 16th the planet Mercury (currently magnitude -0.7) passes just 0°.05 to the North of Mars in a difficult-to-observe conjunction which is only visible from the Northern hemisphere and Equatorial latitudes. Mercury is now about half-way through its third morning apparition of 2017, there being seven apparitions in total this year (four in the morning and three in the evening). For more details on this and the other planetary conjunctions invoving Mars during the 2017-19 period, refer to the planetary conjunctions section below.
Two days after the Mars-Mercury conjunction, on September 18th, from most parts of the world the waning crescent Moon is seen to pass near Mars in the dawn sky. From Wake Island and Minami-Tori-shima in the North-western Pacific Ocean, however, the Moon is seen to pass in front of the planet - blocking it from view - in an event called a lunar occultation (for a map and timings of this event follow the link provided in the Moon near Mars Dates section below). On the same day Mars (mag. +1.8), Mercury (mag. -0.9) and the crescent Moon form a tight grouping (within 1°.8) at around 2120 UT when seen from Eastern Russia, Eastern China, the Korean peninsula and Japan. From the Bonin Islands to the South of Japan, the Moon is seen to pass mid-way between Mars and Mercury at around 1930 UT (0430 local time on September 19th). Mercury is itself occulted by the Moon at around the same time, an event visible in twilight from South-eastern China and Taiwan. Adding to the spectacle is the 'Morning Star' Venus, shining brilliantly at magnitude -3.8, positioned 11° to the WNW of the trio.
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Mercury speeds on Eastwards over the following days, heading back towards the Sun, as Venus approaches Mars from the West. At around 1930 UT on September 23rd the three planets form a line beneath the belly of the Lion figure, 14° across and equally spaced apart. All three planets are currently positioned around 1° degree North of the ecliptic (the path of the Sun, which the Moon and planets follow very closely).
By late September Mars has reached 20° West of the Sun and is rising in darkness from higher Northern latitudes, meaning that the planet now rises in darkness from across the Northern hemisphere. Mars rises 2¼ hours ahead of the Sun at latitude 60° North, 1¾ hours before the Sun at latitude 40° North and 1¼ hours before sunrise at the Equator. At Southern Tropical latitudes Mars rises in twilight about an hour before sunrise whilst at 35° South the planet rises in twilight only about 45 minutes before the Sun. The planet's position in South-eastern Leo, around 7° North of the celestial equator (where the declination of a celestial body is 0°), means that it rises in the East from most of the inhabited world, with the exception of high-Northern latitudes (i.e. further North than about 55° North) where the planet rises in the ENE. Before disappearing from view in the brightening dawn sky, Mars attains an altitude of 9° at latitude 60° North, 13° at 40° North and 11° at the Equator.
Since late September Venus has been closing in on slower-moving Mars at an apparent daily rate of 0°.6 against the background stars. At around 1325 UT on October 5th the 'Morning Star' (mag. -3.8) passes just 0°.2 North of the Red Planet (+1.8) in the second planetary conjunction of the apparition. Only 0°.3 to the NNE of the pair is the fourth-magnitude star Sigma Leonis ( Leo, mag. +4.0), at the foot of the Lion's hind leg. The conjunction is a relatively good one to observe from the Northern hemisphere. By 1400 hours UT on the same day, the three celestial bodies form a line 33' (0°.55) across from North to South.
As Mars begins to appear in the dawn sky from mid-Southern latitudes, the Red Planet reaches aphelion (its most distant point from the Sun) on October 7th, at a distance of 1.666 AU (249.2 million kms or 154.8 million miles). It enters the constellation of Virgo, the Virgin, five days later on October 12th.
Over the next month Mars passes the brighter stars which make up the Southern part of the Virgin figure. The planet passes 0°.5 North of the star Zavijah ( Vir or Beta Virginis, mag. +3.6) on October 18th, crossing to the South of the celestial equator on October 26th. On October 30th the planet passes just 14' (0°.23) South of the star Zaniah ( Vir or Eta Virginis, mag. +3.8) then 1º.8 South of the double star Porrima or Arich ( Vir or Gamma Virginis, mag. +3.5) on November 9th. Mars passes 0º.7 South of the star Theta Virginis ( Vir, mag. +4.4) on November 21st. One week later (November 27th) it passes 3º.3 North of the constellation's brightest star Spica ( Vir or Alpha Virginis, mag. +1.0), Mars being about 0.7 magnitudes fainter than the bright, blue-white star.
By mid-December Mars is rising in darkness from most of the inhabited world, its solar elongation having extended to 50°W. The Red Planet now rises around 5 hours before the Sun at latitude 60º North; 4 hours before the Sun at 40º North; 3½ hours before sunrise at the Equator and 2¾ hours before sunrise at 35º South. From Equatorial and Tropical latitudes Mars is still rising in the East but elsewhere it is rising in the ESE. At 60° North the planet attains a respectable 17° altitude before the dawn twilight envelops it. At 40° North the planet attains an altitude of 31°; at the Equator it reaches 41° whilst at 35° South the planet reaches 24° high.
On December 18th Mars passes 2º South of the star Kappa Virginis ( Vir, +4.1) before exiting Virgo and entering Libra, the Balance (or Scales) on December 21st. Mars is slowly approaching the much brighter planet Jupiter (mag. -1.7) to its South-east, gaining on the giant planet by about 0°.5 per day. Jupiter, currently in Western Libra, has recently emerged into the dawn sky at the start of its 2017-18 apparition.
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On January 2nd 2018 Mars passes 0°.6 North of Libra's second-brightest star Zuben Elgenubi ( Lib or Alpha Librae, combined mag. +2.8), a double star comprising components of magnitude +5.2 (1 Lib) and +2.7 (2 Lib) separated by a distance of 3'.8 (3.8 arcminutes, where 1' = 1/60th of a degree). The name Zuben Elgenubi means 'Southern claw', a relic of the pre-Roman days when the stars in this region of the sky were considered part of Scorpius, the Scorpion, positioned just to the South-east.
On January 7th Mars (mag. +1.4) and Jupiter (-1.7) meet in central Libra in a close planetary conjunction, the pair being separated by an apparent distance of just 0°.2. With a solar elongation of 58° it is well seen worldwide and it is arguably the best of the eight conjunctions which take place during the current Martian apparition. The two planets are easily contained within a telescope field of view, Mars having increased in apparent size to 5" (but small nonetheless) and Jupiter, almost seven times larger at 33" across, providing a contrasting visual treat.
Jupiter now left behind it, Mars passes 3º.7 South of the star Zuben Elakrab ( Lib or Gamma Librae, mag. +4.0) on January 20th (the name Zuben Elakrab meaning 'Northern claw'). The planet passes 2º.8 South of the star Theta Librae ( Lib, mag. +4.1), near the Eastern border of the constellation, on January 27th.
Mars enters Scorpius on January 31st, passing 0º.4 South of the double star Graffias (1 Sco or Beta-1 Scorpii, combined mag. +3.9) on February 1st. The two blue-white components (1 Sco and 2 Sco) are magnitudes +2.6 and +4.9, separated by 13".7 and easily seen in small telescopes. Beta-1 Scorpii is itself also double, having a tenth-magnitude companion positioned less than an arcsecond away, separable only in larger telescopes. Later on February 1st, starting around 1910 UT, Mars passes North of the two Omegan stars Jabhat al Akrab (1 Sco or Omega-1 Scorpii, mag. +3.9) and Omega-2 Scorpii (2 Sco, mag. +4.3). The two stars are separated in the night sky by 0º.24 and, together with the stars Jabbah ( Sco or Nu Scorpii, mag. +4.0) to their North-east and Dschubba ( Sco or Delta Scorpii, mag. +2.2) to their South-west, they form an eye-catching asterism in the Northern region of the Scorpion. Mars' passage of the Omegan stars takes around 5½ hours, the planet passing 0º.4 North of 1 Sco at 1910 UT and 0º.6 North of 2 Sco the following day (February 2nd) at 0040 UT. Mars passes 1º South of Jabbah, a multiple star with brighter components of magnitude +4.0 and +6.3, on February 3rd.
Now approaching the Eastern border of Scorpius, Mars passes 4º.7 North of the variable star Alniyat ( Sco or Sigma Scorpii, mag. +2.9) on February 7th. Mars enters the 'non-zodiac' constellation of Ophiuchus, the Serpent-Bearer, on February 8th. The ecliptic crosses the Southern end of the constellation, an 18º.5 wide strip of sky sandwiched between Scorpius and Sagittarius.
On February 10th Mars passes 5º.2 North of the Scorpion's brightest star Antares ( Sco or Alpha Scorpii, mag. +1.0v). Antares is unmistakable in that it scintillates (twinkles) orange-red, rivalling the colour of the Red Planet. Indeed, the name Antares derives from the ancient Greek 'anti Ares' meaning 'rival of Mars' (Ares being the ancient Greek god of War). The brightness of the two celestial bodies differs on this occasion by only 0.3 magnitudes (Mars being the brighter of the two), allowing for a good naked-eye comparison of their colours.
Mars enters the star chart coverage (above) on February 13th, positioned 6º.7 North of the star Sco (Tau Scorpii, mag. +2.8). The planet's passage through the constellations during the early part of the 2017-19 apparition (i.e. pre star chart) is summarised in the table below:
Table showing the position and apparent magnitude of Mars for the early part of the 2017-19 apparition (click on the thumbnail for the full-size table, 21 KB). The magnitudes, diameters and solar elongations listed here refer to the middle of the period in question. In this and the tables which follow, the rising and setting directions of the constellations listed can be found by referring to the zodiacal constellation rise-set direction table.
By late February twilight is beginning to interfere with observation of Mars from higher Northern latitudes as the Northern hemisphere Spring equinox approaches. From 60º North latitude the planet is visible for only about 2½ hours before the dawn twilight envelops it.
On February 26th Mars passes 6º.8 South of the star Sabik ( Oph or Eta Ophiuchi, mag. +2.5), then 2º.1 North of Ophiuchus' Southernmost bright star Theta Ophiuchi ( Oph, mag. +3.2) on March 3rd. The planet leaves the constellation on March 11th when it enters Sagittarius, the Archer.
Mars crosses to the South of the ecliptic on March 16th. The planet's ecliptic crossing at this point is significant because it determines the shape of the loop described during the months around its opposition (see below). If a superior planet is positioned well to the South of the ecliptic at the time of its opposition to the Sun, the loop described by the planet against the background stars will be South-facing. Likewise, planets positioned well to the North of the ecliptic at opposition describe North-facing loops (for more information on the loops and zig-zags described by the planets in the night sky, see the Planet Movements page).
Mars reaches magnitude +0.5 on March 19th, technically making it a zeroth-magnitude object. On that same day the planet passes two gaseous nebulae, one visible in small telescopes and the other to the naked-eye; Mars is positioned between the two nebulae at around 0930 UT. From 0050 UT to 1025 UT the planet passes 0º.4 South of Messier 20 (M20 or NGC 6514), also known as the Trifid Nebula, its brightest region being roughly elliptical in shape and measuring 29' by 27'. Seen through telescopes under dark skies, three dark dust lanes can be seen, from which the nebula gets its name. At the centre of the nebula is a double star comprising components of 7th and 8th magnitude. From 01 hours UT on March 19th to 11 hours UT (March 20th) Mars passes 0º.8 North of M8 (NGC 6523), also known as the Lagoon Nebula. With apparent dimensions of 90' by 40' and an integrated magnitude of about +5 it is visible to the naked eye as a hazy patch of light under truly dark skies. Telescopes reveal a dark lane through its centre and a star cluster (NGC 6530) in the Eastern half of the nebula, comprising around two dozen stars of 7th magnitude and fainter. Mars is now seen amidst the backdrop of a very star-rich region of the Milky Way, positioned about 6º degrees away from the galactic centre.
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Over the next four weeks Mars passes the numerous bright stars which define the shape of Sagittarius' Archer figure. The constellation's famous asterism, the Teapot, is bounded by eight stars which, taken counter-clockwise, are: Nash, Kaus Meridionalis, Kaus Borealis, Phi Sagittarii, Nunki, Tau Sagittarii, Ascella and Kaus Australis. The Teapot is supposedly pouring its contents over the tail of the Scorpion and the steam rising from its spout is said to be marked by a particularly dense and misty stretch of the Milky Way. The path of Mars in 2018 passes just to the North of the teapot. The passage begins on March 20th, when Mars passes 7º North of the star Nash or Al Nasl ( Sgr or Gamma Sagittarii, mag. +3.0), at the Western end of the asterism, marking the top of the Teapot's spout.
Gibbous Mars sketched by British amateur astronomer Paul Abel in March 2016 using an 8-inch Newtonian reflector telescope at 200x magnification (click on the thumbnail for a larger image, 4 KB). The planet was in the first half of its 2015-17 apparition and measured 11".5 in diameter (Image: Paul G Abel / ALPO-Japan).
On March 24th Mars reaches Western quadrature, when the planet is positioned 90° West of the Sun. The Martian disk now appears 8".0 across and it shines at magnitude +0.4. Theoretically, when seen from the Earth, Mars should now show its minimum illuminated phase, such that it appears significantly gibbous when seen through telescopes (in this case, 88% illumination). However, the eccentric nature of the Martian orbit is such that true minimum phase does not occur until April 12th, by which time its phase has reduced slightly further to 87%.
Since a 90° Western elongation equates to a visible period of (90°/15° per hour) = 6 hours before sunrise, one might expect Mars to now be rising six hours ahead the Sun across the inhabited world. However, the planet's high Southern declination at this time means that this is not the case; in fact, observers at Southerly latitudes see the planet for a longer period before sunrise than observers at Northerly latitudes. At latitude 60° North, Mars rises just 2½ hours before sunrise; at 40° North the planet rises 4½ hours before sunrise; at the Equator it rises 6 hours before the Sun and at 35° South it rises 7¼ hours before the Sun. Directionally, Mars rises towards the South-east at mid- and high latitudes and towards the ESE at Equatorial and Tropical latitudes.
On March 26th Mars passes 6º.3 North of the star Kaus Meridionalis ( Sgr or Delta Sagittarii, mag. +2.7) which marks the centre of the Archer's bow. On March 28th the planet passes 10º.8 North of Kaus Australis ( Sgr or Epsilon Sagittarii, mag. +1.8) which marks the bottom of the Archer's bow. On March 29th the planet passes 1º.8 North of the orange star Kaus Borealis ( Sgr or Lambda Sagittarii, mag. +2.8) which marks the top of the Archer's bow (and the top of the Teapot asterism). On April 1st Mars passes 21' (0º.35) North of the relatively bright globular cluster M22 (NGC 6656) which is considered to be one of the finest globulars in the night sky. Its integrated magnitude is about +5.9 and it has an apparent diameter of 24'. It is just visible to the naked-eye from dark sites, is easily seen through binoculars and is a spectacular sight through telescopes.
At around 1150 UT on April 2nd Mars (+0.2) passes 1º.2 South of the planet Saturn (+0.5) in a relatively wide conjunction which is best seen from the Southern hemisphere. Saturn is slowly brightening as it approaches opposition in late June, its wide-open rings making it a nice telescopic sight. Mars is currently moving Eastwards against the background stars at a rate of about 0º.6 per day, compared with Saturn's snail-pace motion, in the same direction, of just 0º.03 per day as it approaches its Eastern stationary point. Later that same day, at about 21 hours UT, Mars passes just 1'.9 (0º.03) South of the star SAO 187080, a pulsating variable of magnitude 5.8 which the planet will occult in March 2035.
Over the next ten days Mars passes the four stars which form the 'handle' of the apparent Teapot in the sky. The planet passes 3°.5 North of Phi Sagittarii ( Sgr, mag. +3.1) on April 5th; 2°.9 North of the constellation's second-brightest star Nunki ( Sgr or Sigma Sagittarii, mag. +2.0) on April 9th; 6°.5 North of Ascella ( Sgr or Zeta Sagittarii, mag. +2.6) on Apil 13th and finally, 4º.4 North of Tau Sagittarii ( Sgr, mag. +3.3) on April 15th.
Mars reaches 10".0 in angular diameter in mid-April, positioned about 100° West of the Sun. The planet is now brightening significantly with each passing week, its pale orange coloration seemingly more obvious than in the preceding months. For telescopic observers, the planet is now at a sufficient apparent size for significant surface detail to be seen and for a regular observing campaign to begin. Unfortunately for telescopic observers in the Northern hemisphere, Mars' position at the far South of the zodiac means that the planet crosses the observer's meridian (due South) at a relatively low altitude, so that atmospheric turbulence interferes with observation of the planet throughout this period of the apparition. For observers at high-Northern latitudes, low altitude is not the only problem. By late April, observers North of about 60º North latitude lose sight of Mars by naked-eye in the bright summer twilight, which now lasts throughout the night. Observers in these high latitudes do not see Mars again until around mid-June, by which time the planet will have moved on Eastwards into Capricornus, the Sea Goat.
Table of selected data relating to the brighter part of the Mars apparition of 2017-19 (click on thumbnail for full-size table, 146 KB). The data is listed at 10-day intervals, corresponding with the dates on the star map.
The Central Meridian Longitude (provided for telescopic observers) is the Martian longitude which appears at the centre of the disk when seen from the Earth at the time indicated (0h Universal Time, or 0h GMT). A Martian longitude map by Damian Peach showing the surface features can be seen at the BAA Mars Section website (note that the map is shown with South up, matching the inverted view seen through astronomical telescopes). For example, when CM = 290°, Syrtis Major appears at the centre of the disk. The Central Meridian Longitude increases by 14°.6 every hour, so this allowance should be applied for observations at other times (if the result is greater than 360°, subtract 360° to obtain the correct longitude).
Those wishing to observe Mars telescopically should consider downloading the free 'Mars Previewer II ' software by Leandro Rios, available as a ZIP file at Sky & Telescope.
The data for the table was obtained from 'RedShift 5', 'MegaStar 5', 'SkyGazer Ephemeris' , 'Mars Previewer II' software and Mars Ephemeris Generator 2.6. The Martian disk images were derived from NASA's Solar System Simulator. The Martian disks appear at the same scale as those in the Mars Opposition data table here.
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Having left the bulk of the brighter stars of Sagittarius behind it, Mars continues on its Eastward course, passing 2°.2 South of Albaldah ( Sgr or Pi Sagittarii, mag. +2.9), marking the Archer's head, on April 16th. The North-eastern region of Sagittarius, through which Mars travels over the following four weeks, has numerous stars of 4th magnitude or fainter. Amongst them are the stars 52 Sagittarii (mag. +4.6) and 62 Sagittarii (mag. +4.5), both positioned to the South of the ecliptic. The planet passes 2° to the North of 52 Sgr on April 28th. 62 Sagittarii is one of a group of four 4th-magnitude stars, within 2° of each other, named the Terebellum. The name is a Latin translation of an original Greek word meaning 'four-sided figure', allotted to this star group by Claudius Ptolemy (ca. 100-170 AD) in his famous star catalogue, the Almagest. The Terebellum are positioned at the rump of the Archer and include the stars 58 Sgr or Sgr (Omega Sagittarii, mag. +4.7), 59 Sgr (mag. +4.7) and 60 Sgr (mag. +4.8). Mars passes around 4° North of the group between May 8th and May 12th, passing 5°.4 North of 62 Sgr, the most Southerly and Easterly star of the group, on May 12th.
In late May, Mars is positioned 120° West of the Sun, has brightened to magnitude -1.0 and its apparent diameter has reached 14". At around 0540 UT on May 14th, the planet passes 17' (0°.28) South of the globular cluster M75 (NGC 6864). This distant and compact 8th-magnitude cluster has an apparent diameter of only 6' and lies just 0°.3 from the Eastern edge of the constellation. Eighteen hours later Mars leaves Sagittarius and enters Capricornus, the Sea-Goat, where it will spend the brightest part of its 2017-19 apparition.
On May 21st Mars passes 9º.3 South of the star Al Giedi ( Cap or Alpha Capricorni), an apparent double star comprising the stars Prima Giedi (1 Cap or 1 Capricorni, mag. +4.2) and Secunda Giedi (2 Cap or 2 Capricorni, mag. +3.6). The stars are not physically related, since they lie at very different distances from the Earth; the closeness of the two stars is therefore a line-of-sight effect. Through telescopes, however, each star is seen to be double. The fainter component of Prima Giedi is of 9th-magnitude and is not physically related to it. Secunda Giedi has an 11th-magnitude component, part of a true binary system but which is itself double. Al Giedi is therefore a 'double double' star or, more technically, a multiple star system. Mars passes 7º.1 South of another double star, Dabih ( Cap or Beta Capricorni, mag. +3.1), on May 23rd. It is a yellow star with a blue companion of magnitude +6.1, positioned 3'.5 to the West, visible in binoculars and small telescopes.
With the arrival of June, the Red Planet's apparent motion against the stars has slowed considerably, from 0º.6 per day (when it passed Saturn in early April) to just 0º.2 per day. By mid-June Mars has returned to naked-eye view from higher Northern latitudes, low down over the South-eastern horizon, although it is seen in continuous twilight. Because it is now high summer in the Northern hemisphere the twilight will not begin to recede from these latitudes until August.
Mars passes 3º.3 North of the star Psi Capricorni ( Cap, mag. +4.1), at the foot of the Sea Goat, on June 14th. On June 28th Mars' Eastward motion ceases as the planet reaches its Eastern stationary point, positioned 3º to the NNE of Psi Capricorni. Mars is now moving slightly Southward, but by the start of July its motion becomes retrograde (Westward), a situation which will continue over the next two months. On July 12th the planet passes Psi Capricorni again, this time moving in the opposite direction than previously and 2º closer to it (a consequence of the Southward motion).
Mars reaches opposition to the Sun at 0507 UT on July 27th, at which point it is directly opposite the Sun in the sky (solar elongation = 180°) and technically at its brightest for this apparition. The planet is positioned 3º.3 West of Psi Capricorni and 11º SSE of Dabih. This is not, however, Mars' closest point to the Earth during this apparition; because of the eccentricity of its orbit, Mars' perigee (or periareion, its closest point to Earth) is reached four days later - on July 31st - when it is 0.3849 AU distant (57.6 million kms or 35.7 million miles), i.e. about 177,700 kms (110,400 miles) closer than on opposition day. The Red Planet now shines at a brilliant magnitude of -2.77 and its apparent size is 24".2 (double the size it was in mid-May and triple the size it was in late March). Mars is slowly moving South-westward against the stars of Capricornus at a rate of about 0º.3 per day. Although the planet's brightest moment takes place on July 31st, it shines at magnitude -2.7 for a 17-day period from July 21st through to August 6th.
At opposition, a superior planet rises around sunset, is visible throughout the night and sets around sunrise. Its highest point in the sky is reached when it crosses (transits) the observer's meridian at local midnight (due South at midnight in the Northern hemisphere; due North at midnight in the Southern hemisphere). For telescopic observers of the planet, the current apparition is particularly favourable in the Southern hemisphere, where Mars transits the meridian at high altitude (at latitude 25º 30' South the planet transits at the zenith, directly above the observer's head). It is much less favourable for telescopic observers in the Northern hemisphere, the more so the further North one is located. At latitude 60º North, for example, Mars' altitude barely reaches 5º at meridian transit - and since opposition coincides with the Northern hemisphere summer, the planet is seen in twilight throughout the night. A list of meridian transit altitudes and directions of the planet at opposition for various latitudes over several Martian oppositions is given in the table below.
Prior to 2018, Mars last reached opposition in Scorpius in May 2016 (click on the thumbnail to see the full-size version, 91 KB). This photograph of the event, taken by the writer, shows the Red Planet two days after opposition day. Mars (magnitude -2.0) was positioned a short distance North-west of the star Dschubba (Delta Scorpii, mag. +2.3). Saturn, then in Ophiuchus, is just within shot on the left. The pale glow in the lower part of the photo is from moonlight (the Moon was only a couple of days past Full). The photo was taken facing South at around midnight local time, Click here (150 KB) to see an annotated verson of the photograph.
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On opposition day, the Red Planet is experiencing Autumn (Fall) in its Northern hemisphere and Spring in its Southern hemisphere. The planet's Southern Pole is tipped towards the Earth at an angle of about 11º, giving us a good view of its Southern Polar Cap (SPC). Mars is positioned at a heliocentric longitude of 304º ( = 304°) and the areocentric longitude of the Sun (Ls) is 218°. The Martian Year is 34, the Martian Month is 8 and opposition day equates to Sol Number 436 on Mars. The equivalent Earth date on Mars - called the Martian Date (MD) - is November 1st. All the terms given in this paragraph are explained in more detail on the Martian seasons page.
The 2018 opposition of Mars is the best since August 2003. At the current opposition Mars is 0.7 magnitudes brighter (nearly two times brighter) than it was at its previous opposition in May 2016 and its apparent disk diameter is about one-third larger. In fact, it is the largest apparent disk size that the planet will show to the Earth before the year 2035. Such close oppositions to Earth are known as perihelic oppositions, since they take place when Mars is close to the perihelion position of its orbit (for more details, see the Mars Oppositions page).
Later on opposition day, a further spectacle awaits observers across much of the world (with the exception of the Northern and central Americas). At 1824 UT the Full Moon enters the Earth's umbral shadow, marking the start of the umbral phase of a total lunar eclipse, with maximum eclipse taking place at 2021 UT. The eclipsed Moon is positioned several degrees to the NNW of Mars, an event which provides an excellent opportunity for astrophotographers. Due to the effect of parallax, the angular separation between the two celestial bodies depends upon the observer's location on Earth. The separation between Mars and the Moon varies on this occasion from 5º.8 (at higher Northern latitudes) to 7º (at mid-Southern latitudes), the best views of the pairing being from Eastern Africa and central Asia (for more details follow the link in the Moon near Mars Dates section below). This is the only occasion during either the 20th or 21st centuries on which a total lunar eclipse has coincided with a Martian opposition day.
Mars and its moons Phobos and Deimos Sketched at the planet's 2003 opposition by French astronomer Nicolas Biver from Ablis, France (click on the thumbnail for a larger image, 51 KB). Biver used a 16-inch (41 cm) telescope at a magnification of 700x under poor seeing conditions but with good sky transparency (Image: Nicolas Biver / ALPO Japan).
Martian Moons Observing Challenge
During this close opposition, observers equipped with medium and large-sized telescopes may attempt to observe Mars' two natural satellites, Phobos and Deimos. Considered by most scientists to be asteroids captured in the Martian gravity, they were discovered within a week of each other in August 1877 by Asaph Hall using a 26-inch (66 cm) refractor at the US Naval Observatory in Washington, D.C.. They are named after the sons of Ares, god of war, with whom, according to ancient Greek mythology, they accompanied into battle. The names were suggested to Hall by Henry Madan (1838–1901), a Science Master from Eton, UK.
Both moons are irregularly shaped and are relatively small in size. Phobos measures 26 kms by 18 kms (16 by 11 miles) and it orbits Mars in just over 7½ hours at an average distance of 9,377 kms (5,827 miles) from the planet. Deimos measures just 16 kms by 10 kms (10 by 6 miles) and it orbits the planet in just over 30 hours at an average distance of 23,460 kms (14,580 miles). Much like our own Moon, both Phobos and Deimos continually present the same face towards Mars.
Phobos and Deimos are notoriously difficult to observe from Earth due to their tiny sizes, their faint magnitudes and, most significantly, the overwhelming glare produced by Mars. At this opposition, however, Phobos reaches magnitude +10.4 (it averages around +11.3 at opposition) and Deimos reaches magnitude +11.5 (average around +12.4 at opposition). They are best observed under excellent seeing conditions when they are close to their greatest Eastern and Western elongations from the planet. Phobos will be seen extending to about 33" to East and West of the planet (about 1.3 apparent Mars diameters distant) whilst Deimos will be seen extending to about 84" to East and West of the planet (about 3½ apparent Mars diameters distant).
Due to the Martian glare it is essential to obscure the planet in some way whilst attempting to search for the moons. One method is to use an occulting bar, which can be produced using a narrow strip of aluminium foil attached to the rear of the eyepiece, as described in an article at Sky & Telescope from Mars' 2007 opposition. Since the moons orbit to East and West of Mars, the bar should be aligned along celestial North and South to prevent the moons from being blocked by the occulting bar itself.
What size of telescope is required to see the Martian moons? Most amateurs who have successfully observed them have used large instruments, typically 18 inches (45 cm) or larger. Former NASA engineer Greg Crinklaw observed the moons during the exceptionally close approach of Mars in 2003 using an 18-inch telescope but believes that he may have spotted Deimos in a telescope as small as 6 inches (15 cm). "Could it be done in a 4-inch?" he asks, "I really think it might be possible with the right observer under just the right conditions. Doing so would be a real feat!". Crinklaw has much useful advice on attempting to observe the moons (dating from the 2005 opposition) on his website SkyHound.com.
Ideal times to observe the two moons simultaneously (when they are both at, or close to, their greatest elongations from Mars) in the days around closest approach to Earth are listed in the accompanying table (19 KB).
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Opposition having passed, the solar elongation changes from Westerly to Easterly and the angle reduces below 180°. By August 3rd - one week after opposition - Mars' solar elongation has reduced to 170° East of the Sun.
Moving retrograde, Mars begins to pass the stars it had passed over two months ago, except in reverse order. On August 5th Mars passes Dabih again, at an angular distance which is 4°.3 further South than on the previous occasion. Three days later it passes 13°.8 South of Al Giedi, some 4°.5 further South than on the previous occasion.
On August 16th Mars attains its most Southerly declination for this apparition, at -26° 29' 52" (-26°.497 in decimal format), which is the furthest South the planet will be positioned before July 2033. The planet now sets at its most Southerly position on the local horizon. Typically this will be towards the South-west at latitudes far away from the Equator and towards the WSW at Equatorial latitudes. The planet's high-Southern declination dramatically affects the duration which it spends above the horizon at any given latitude. Mars now sets 5 hours after the Sun at 60º North, 8 hours after the Sun at 40º North, 10½ hours after the Sun at the Equator and 12½ hours after the Sun at 35º South.
At around 08 hours UT on August 24th, the Red Planet's South-westerly motion carries it across the Capricornus boundary and back into Sagittarius. On August 28th Mars reaches its Western stationary point, positioned 1º.7 North-east of fourth-magnitude 62 Sagittarii and 2º.1 ENE of the remaining three Terebellum stars. Mars' motion now turns direct or prograde (Eastwards) once more and the planet begins to head back towards Capricornus, having moved just 6' (0º.1) over the boundary into Eastern Sagittarius. The planet re-enters Capricornus on September 1st.
Mars reaches perihelion (its closest orbital position to the Sun) on September 16th, at a distance of 1.3814 AU (206.6 million kms or 128.4 million miles) from the Sun. The fact that its perihelion passage should occur only 47 days after its closest approach to Earth reflects just how favourable this particular opposition has been.
Mars at the 2003 Opposition imaged independently by two Italian amateur astronomers on the same day, showing the differing details resolved by different telescope apertures under similar observing conditions (click on the thumbnail for larger image, 15 KB). In both cases the planet was around 29° above the local horizon (Images: Paolo R Lazzarotti / Ferruccio Zanotti / ALPO-Japan).
Moving direct, Mars passes 11°.8 South of Al Giedi again on September 17th, a little closer than the previous passage owing to the planet's slight Northward motion during the stationary point turn. Likewise on September 19th Mars passes 9°.3 South of Dabih, some 2°.1 closer to the star than on the previous occasion. The planet passes 3º.6 North of Psi Capricorni on October 6th, this time a little further away than on its previous passage. As Mars heads into central Capricornus, it leaves behind the ghost of an apparent loop that it has described in the night sky over the last four months: Southward-facing, measuring 10º.6 wide by 2º.3 high and orientated ENE-WSW.
Mars continues on an uneventful passage of the stars of central and Eastern Capricornus over the next month. The planet passes 2º.5 South of Theta Capricorni ( Cap, mag. +4.0) on October 17th, 1º.3 South of Iota Capricorni ( Cap, mag. +4.3) on October 25th, 4º.7 North of Zeta Capricorni ( Cap, mag. +3.8) on October 27th and 21' (0º.35) North of Nashira ( Cap or Gamma Capricorni, mag. +3.7) on November 2nd. Finally, on November 5th it passes 32' (0º.53) North of the constellation's brightest star, Deneb Algiedi ( Cap or Delta Capricorni, mag. +2.9v). It is an eclipsing binary, meaning that a smaller component revolves around the parent body, causing the star's brightness to fluctuate in a regular cycle. In the case of Deneb Algiedi, however, the fluctuation is between magnitudes 2.8 and 3.1 - a difference which is barely perceptible to the naked-eye - over a period of 24½ hours.
By early November Mars has faded back to 'minus zeroth magnitude' (-0.5) and its apparent diameter has reduced to 12" - only half that at its closest approach back in late July. The planet enters Aquarius, the Water-Carrier, on November 11th, passing 22' (0º.36) North of the star Iota Aquarii ( Aqr, mag. +4.2) on November 14th. On November 15th the planet attains its minimum illuminated phase for this apparition, at 85.7%, with the planet shining at magnitude -0.3, its apparent diameter being 10".5 and its solar elongation 96º East (Eastern quadrature, when the planet should theoretically show minimum phase at a solar elongation of 90º, takes place 2½ weeks later on December 3rd). Unlike at Western quadrature, the illuminated part of the planet's disk faces Westwards (not Eastwards, as before) because it is now positioned to the East of the Sun when seen from the Earth. Mars now sets 8 hours after the Sun at latitude 60° North, 7 hours after the Sun at 40° North, 6 hours after sunset at the Equator and 5½ hours after sunset at 35° South. The planet sets in the WSW from higher Northern latitudes but in the West from elsewhere. South of latitude 12º South, the planet transits the local meridian before coming into view. North of 12º South, the planet has not yet reached the meridian as it comes into view.
Mars is now moving against the background stars at a daily rate of 0º.6, a little faster than at the same period before opposition. On November 18th the planet passes 4º.5 South of the star Ancha ( Aqr or Theta Aquarii, mag. +4.1) in central Aquarius. Between November 21st and 27th the planet is positioned about 11º South of the so-called 'Steering Wheel' asterism, in the Northern part of the constellation. At the centre of the 'wheel' is the star Zeta Aquarii ( Aqr, mag. +3.7) with the stars Sadachbia ( Aqr or Gamma Aquarii, mag. +3.9), Eta Aquarii ( Aqr, mag. +4.0) and Pi Aquarii ( Aqr, mag. +4.8) encircling it. It is one of several asterisms spread across the zodiac which beginner astronomers should familiarise themselves with, in order to aid constellation identification.
In early December Mars' apparent magnitude returns to positive (+0.0). The planet passes 0º.7 South of the star Lambda Aquarii ( Aqr, mag. +3.9), positioned at the handle of the Waterman's amphora, on December 4th and 7º.8 North of the star Skat ( Aqr, or Delta Aquarii, mag. +3.3), at the base of the amphora, on December 5th.
80mm Table Top
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On December 7th Mars (+0.1) has a very close conjunction with the planet Neptune (+7.9), passing just 2'.2 (0º.03) North of the distant planet at around 1445 UT. The conjunction is visible worldwide, the two planets being positioned a significant 88º East of the Sun. Although not quite as close as the Red Planet's previous conjunction with Neptune at the start of 2017, this is nonetheless a spectacularly close event, the two planets being easily contained within the field of view of even the smallest of telescopes. Neptune is only a few months past opposition and has faded by only 0.1 magnitudes since then. This an ideal opportunity for those who have never seen our most distant Solar System planet to locate it with relative ease, using Mars as a bright locator-beacon.
From December 14th through to the 26th, Mars, is positioned about 7º South of the Circlet of Pisces at the Western end of Pisces, the Fishes. The Circlet comprises six stars of fourth and fifth magnitude; under light-polluted conditions it is likely that some or all of them will not be seen with the naked-eye.
On December 13th Mars passes 18' (0º.3) North of the star Phi Aquarii ( Aqr, mag. +4.2) and, on December 15th, just 1'.4 ( 0º.023) South of the star 96 Aquarii (96 Aqr, mag. +5.7), a double star with a magnitude +10.4 companion located 10" distant. Both of these stars lie quite close to the ecliptic and, like the Omegan stars in Scorpius (see above), they are sometimes occulted by passing planets. Mars will next occult 96 Aquarii in 2032.
Having already passed South of the Circlet, Mars enters Pisces itself on December 21st.
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Less than an hour into the new year, Mars passes 7º.2 South of the star Omega Piscium ( Psc, mag. +4.0) and, only minutes later, crosses the celestial equator ( = 0°) heading Northwards. The planet is now positioned 41'.4 (0º.7) away from the First Point of Aries or Vernal Equinox (Spring Equinox) point, i.e. the direction in which the Sun appears against the background stars when its declination is 0° on its Northward path through the ecliptic. Mars leaves the star chart coverage (above) on the same day.
Mars passes to within 5' (0°.08) of the Piscean border with Cetus, the Whale, at around 0040 UT on January 12th, then crosses the ecliptic heading Northwards on January 15th. Now 75° East of the Sun, the planet's apparent diameter has shrunk still further to 7" and it has faded to magnitude +0.6. It is nonetheless brighter than any of the stars which surround it within the boundaries of Pisces.
The Red Planet passes 2º.2 South of the star Delta Piscium ( Psc, mag. +4.4), positioned about half-way along the Southern Fish's body, on January 21st, then 57' (0º.95) South of the star Epsilon Piscium ( Psc, mag. +4.3) on January 26th. On January 31st the planet passes 32' (0º.5) North of the double star Zeta Piscium ( Psc), another star which lies close to the ecliptic. Easily split in small telescopes, its components are of magnitudes +5.2 and +6.3, separated by a distance of 23". Mars passes 5º.3 South of Eta Piscium ( Psc, mag.+3.6) on February 7th. On February 12th the planet passes 2º.2 North of the star Torcularis Septentrionalis ( Psc or Omicron Piscium, mag. +4.2) in the tail of the Northern Fish. The name is a translation of a Greek word '' meaning 'winepress'. However, this was a mistranslation of the original Greek word '' meaning 'flax', i.e. the cord that tied the two fishes' tails together.
At around 04 hours UT on February 13th Mars enters Aries, the Ram, then later that same day passes 1º North of the planet Uranus in the sixth planetary conjunction of the 2017-19 apparition. The conjunction is visible worldwide but it slightly favours Northern hemisphere observers. At magnitude +5.8, Uranus is at the limit of naked-eye visibility whilst Mars has faded to mag. +1.0. Uranus, now in the final stages of its 2018-19 apparition, fully entered Aries only in the previous week, having spent almost nine years in Pisces.
The Solis Lacus region of Mars sketched by Paul Abel in January 2017 using an 8-inch Newtonian reflector at 312x magnification (click on the thumbnail for a larger version, 4 KB). Nearing the end of its 2015-17 apparition, the planet was 60° East of the Sun and just 5".7 in diameter (Image: Paul G Abel / ALPO-Japan).
Mars passes 7º South of Mesarthim ( Ari or Gamma Arietis, mag. +3.9) on February 15th, another double-star easily resolved in small telescopes. It comprises two white stars of magnitudes +4.6 and +4.7, separated by 7".5. On February 16th Mars passes 8º.5 South of the star Sheratan ( Ari or Beta Arietis, mag. +2.6). Five days later (21st) Mars passes 10º South of Aries' brightest star Hamal ( Ari or Alpha Arietis, mag. +2.0). Mars' uneventful passage through this small constellation continues with the passage of two fourth-magnitude stars in the Eastern half of the Ram: 3º.5 to the South of the double star Epsilon Arietis ( Ari, mag. +4.3) on March 12th and 1º South of Botein ( Ari or Delta Arietis, mag. +4.3) on March 17th.
At around 0030 UT on March 22nd Mars comes to within 3'.5 (0º.06) of the Taurean border, passing just to the North-west of 'step' in the boundary line, positioned about half-way down Aries' Eastern side. The planet enters Taurus, the Bull, on March 23rd.
Between March 29th and 31st Mars passes around 3°.2 South of the constellation's most famous star grouping known as the Pleiades (pronounced 'PLY-add-eez' or 'PLEE-add-eez'), also called the Seven Sisters (M45). The planet takes about 37 hours to traverse the 1° angular distance between the cluster's brightest Western star (Electra, mag. +3.7) and its brightest Eastern star (Atlas, mag. +3.6). From April 11th to 16th Mars passes around 5°.5 North of a much larger star cluster called the Hyades, a distinct 'V'-shaped grouping of stars which form the head of the Bull. At the apex (Western end) of the 'V' is the star Hyadum I ( Tau or Gamma Tauri, mag. +3.6); Mars passes 6°.8 North of this star on April 11th. Hyadum II (1 Tau or Delta-1 Tauri, mag. +3.7) is a spectroscopic binary positioned roughly mid-way along the Northern arm of the 'V' (the Bull's forehead); Mars passes 5° North of this star on April 12th.
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Positioned a few degrees North of the Hyades is a grouping of stars of between 4th and 6th magnitude which straddle the ecliptic. At the North-eastern corner of the group are the stars Upsilon Tauri ( Tau, mag. +4.3) and 72 Tauri (mag. +5.5). Mars passes 7' (0°.11) South of Upsilon Tauri at around 1215 UT on April 13th, then at around 2040 UT that same day, 15'.6 (0°.26) South of 72 Tauri. Mars will come to within 4" (0°.001) of this star in March 2036.
At the South-eastern corner of the Hyades, marking the 'eye' of the Bull, is the orange-red star Aldebaran ( Tau or Alpha Tauri, mag. +0.9). Its coloration derives from the fact that it is a red giant star. Most of the Hyades stars comprise a genuine cluster, moving through space together, however Aldebaran is not part of the group: it is a foreground star, positioned much closer to the Earth than the cluster. Mars passes 6°.6 North of Aldebaran on April 16th. By this time it has faded below the threshold of second magnitude (+1.5) and its apparent diameter has reduced to 4".5. Now fainter than Aldebaran, it appears as an ordinary 'star' with an orange tint, almost indistinguishable from many of the stars around it, at least without the aid of a telescope.
At the 'bend' of the Bull's Northern horn is another multiple-star system, Tau Tauri ( Tau, mag. +4.2), amusingly referred to as Tau Tau! Mars passes 18' (0°.3) North of the star at around 04 hours UT on April 19th.
By late April the solar elongation of Mars has reduced to 40° and twilight begins to interfere with observation of the planet as seen from latitudes North of about 60° North. At these latitudes the planet is visible for around 4½ hours before setting in the North-west, the planet being in twilight throughout. Elsewhere the planet is setting in darkness, towards the North-west (at mid-Northern and mid-Southern latitudes) and to the WNW (Equatorial and Tropical latitudes). At latitude 40° North, Mars sets about 3½ hours after sunset and at the Equator it sets around 2¾ hours after sunset. At mid-Southern latitudes the planet sets 2¼ hours after the Sun. The altitudes of the planet, as it becomes visible in the dusk twilight, are: 18° at 60° North, 28° at 40° North, 30° at the Equator and 15° at 35° South.
On May 4th Mars passes 4°.3 South of the star Al Nath or El Nath ( Tau or Beta Tauri, mag. +1.6) which marks the tip of the Bull's Northern horn. The star also carries the name Gamma Aurigae ( Aur) since, apart from defining one of the Bull's horns, it also neatly completes the six-sided figure comprising the stars of Auriga, the Charioteer, located to the North-east of Taurus. Mars passes 3°.3 North of Zeta Tauri ( Tau, mag. +2.9v), which marks the tip of the Bull's Southern horn, on May 8th. On May 12th there is another close encounter with a double star, when Mars passes just 2'.5 (0°.04) South of 132 Tauri (mag. +4.8). It has components of magnitude +4.9 and +9.0, separated by 4".8.
From mid to late May, Mars passes the North-eastern section of the constellation of Orion, the Hunter. Specifically, the stars in this region of the constellation are depicted as being the hunter's club. On May 14th the planet passes 4°.3 North of the star Chi-1 Orionis (1 Ori, mag. +4.4) then on May 17th, 4°.4 North of the star Chi-2 Orionis (2 Ori, mag. +4.6). In between passing these two stars, Mars enters Gemini, the Twins, and soon afterwards attains its most Northerly declination for this apparition ( = +24° 33' 35" or +24°.559), the most Northerly declination attained by the planet since 2008 and before 2021. Mars now sets at its most Northerly point along the local horizon, the actual point of setting depending upon the observer's latitude. This will be towards the North-west at higher Northern latitudes and towards the WNW at most other inhabited latitudes.
About 45 minutes after attaining its most Northerly declination, Mars passes 1°.3 North of the star 1 Gem (1 Geminorum, mag. +4.2), which marks the foot of the Northern twin. A short distance North-east of 1 Geminorum is the open star cluster M35 (NGC 2168). The cluster has an apparent diameter of 30' (about the size of the Full Moon) and it contains over 400 stars (!) It can be glimpsed with the naked-eye as a misty patch of light on a dark, clear night. Mars passes about 15' (0°.25) North of the cluster's centre on May 19th at around 19 hours UT. On May 21st the planet passes 2° North of the star Propus or Tejat Prior ( Gem or Eta Geminorum, mag. +3.5v) and on May 24th, 2° North of Tejat Posterior ( Gem or Mu Geminorum, mag. +3.0v), which marks the Northern twin's knee.
In late May, observers situated at high Northern latitudes are the first to bid farewell to the Red Planet as it slips into the dusk twilight. Over the next month the 'observing window' for Mars also reduces considerably for observers at mid-Northern latitudes.
Mars passes 8° North of the star Alhena ( Gem or Gamma Geminorum, mag. +2.0), at the foot of the Southern Twin, on May 29th and on June 1st, 0°.9 South of the star Mebsuta ( Gem or Epsilon Geminorum, mag. +3.0), at the 'groin' of the Northern Twin. On June 8th the planet passes 3°.2 North of the star Mekbuda ( Gem or Zeta Geminorum, mag. +3.9), the 'left knee' of the Southern Twin and on June 14th, 1°.3 North of the star Wasat ( Gem or Delta Geminorum, mag. +3.5), at the 'groin' of the Southern Twin.
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Around mid-June the planet Mercury emerges into the dusk sky in its second evening apparition of 2019. The planet speedily approaches Mars from the West, gaining on the Red Planet by about 0°.8 per day at this time. It is positioned 5° to the WNW of Mars on June 12th, 4° to the WNW of it on June 13th, 3° to the WNW of it on the 14th and 2° to the WNW of it on the 15th. By June 17th Mercury (+0.3) is 1° to the North-west of Mars (+1.8), passing 0°.2 North of the Red Planet in conjunction at around 1430 UT on June 18th. The narrow solar elongation of 24° East, coupled with the two planets' position in Eastern Gemini, mean that this evening conjunction is only visible South of mid-Northern latitudes. At about 15 hours UT on the same day Mars, Mercury and the star Castor ( Gem or Alpha Geminorum, mag. +1.9) form a line 9° long from North to South, visible at dusk from India. Later, at around 19 hours UT, the planetary duo form a 5°.8 line with Gemini's brightest star Pollux ( Gem or Beta Geminorum, mag. +1.3), orientated North-east/South-west, visible at dusk from Northern Libya. Mars passes 9° South of Castor on the following day (19th).
At 2040 UT on June 22nd Mars, the star Kappa Geminorum ( Gem, mag. +3.5) and Pollux form a line 5°.5 in length from North to South, with Mercury (+0.5) positioned 2°.1 to the ESE of the Red Planet. The line is seen in dusk twilight from North-western Africa. Mars passes 1°.9 South of Kappa Geminorum early on June 23rd and 5°.5 South of Pollux several hours later. Mercury also reaches greatest elongation (25° East of the Sun) later the same day.
Mars heads into Cancer, the Crab, on June 28th. At around 01 hours UT on June 29th, Pollux and Castor appear to 'point the way' to Mars, the three forming an 11°.6 line from NNW to SSE, directed towards the head of the Water Snake (Hydra), located to the South of Cancer. This line is viewable at dusk from the North-western Caribbean.
In late June Mercury is positioned a few degrees to the South-west of Mars. Mercury's apparent motion has slowed as the planet turns Southward, allowing Mars to catch up with it over the next week or so. The waxing crescent Moon passes between the two planets on July 4th, as Mars passes 11°.8 North of the star Altarf ( Cnc or Beta Cancri, mag. +3.5). At around 14 hours UT on July 7th Mars passes 5°.8 North of Mercury in the final planetary conjunction of the apparition, visible with difficulty only from the Northern Tropics Southwards. Mercury reaches its Eastern stationary point on the same day, after which it turns retrograde and heads back towards the Sun.
By early July Mars has been from lost from view from mid-Northern latitudes. Further South, the planet's narrowing solar elongation, its low altitude and the local twilight have reduced the 'observing window' of the planet to just 1¼ hours from 40º North latitude and 1½ hours from latitudes South of the Equator. Mars is now setting in the WNW in the Northern hemisphere and in the West in the Southern hemisphere. At latitude 40° North Mars stands just 5° above the horizon when it first becomes visible at dusk; elsewhere the altitude of the planet at dusk reduces day by day as its solar elongation falls below 20°. At the Equator the planet stands 12° high as it comes into view at dusk, whilst at 35° South it is only 8° above the horizon.
With its return to central Cancer, Mars has now completed a full circuit of the zodiac since the start of its 2017-19 apparition nearly two years earlier. From July 12th to 14th the planet passes through the star cluster known as Praesepe (pronounced 'PRE-SEEP-EE'), designated M44 or NGC 2632, passing a little to the South of the cluster's centre. However, being just 16° from the Sun, the cluster is too faint and too low in the sky after dusk to be visible from any location on Earth.
Mars' passage through the constellations during the latter (i.e. post star chart) period of the 2017-19 apparition is summarised in the table below:
Table showing the position and apparent magnitude of Mars for the latter part of the 2017-19 apparition (click on thumbnail for full-size table, 24 KB). As in the first table, the magnitudes, diameters and solar elongations refer to the middle of the period in question.
As Mars' solar elongation falls below 15º East of the Sun in late July, the planet finally becomes lost from view from across the inhabited world, bringing the 2017-19 apparition to a close. The planet enters Leo, the Lion, on July 30th, where it has a close conjunction with Venus a few weeks later on August 24th. The conjunction is not visible from Earth, however, since the planets are positioned just 3º fom the Sun. Venus is now entering the evening sky at the start of its 2019-20 apparition as an 'Evening Star'.
Mars returns to its most distant point from the Sun (aphelion) on August 26th, at a distance of 1.666 AU (249.2 million kms or 154.8 million miles), some 22½ months (one Martian sidereal period) after its previous aphelion passage. Two days later on August 28th, Mars reaches its most distant point from Earth (apogee) at 2.6753 AU (400.2 million kms or 248.6 million miles) distant.
The planet remains out of view - lost in the solar glare - for a little over a month as it continues Eastwards on the far side of its orbit from the Earth. Mars reaches superior conjunction (passing behind the Sun as viewed from the Earth) in Southern central Leo on September 2nd, when it is 2.6747 AU (400.1 million kms or 248.6 million miles) from Earth. Were the planet to be visible from Earth at this time, it would shine at magnitude +1.7 and appear just 3".5 across.
Mars becomes visible from the Earth again in the Eastern sky at dawn from around early October 2019, when it is first glimpsed from Northern Tropical latitudes. This heralds the start of the 2019-21 apparition, which will see Mars reach opposition in Pisces in October 2020.
[Terms in yellow italics are explained in greater detail in an associated article describing planetary movements in the night sky.]
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Mars Conjunctions with other Planets,
2015 to 2017
Viewed from the orbiting Earth, whenever two planets appear to pass each other in the night sky (a line-of-sight effect) the event is known as a planetary conjunction or appulse. Not all planetary conjunctions will be visible from the Earth, however, because many of them take place too close to the Sun. Furthermore, not all of them will be seen from across the world; the observers' latitude will affect the altitude (angle above the horizon) at which the two planets are seen at the time of the event, and the local season will affect the sky brightness at that particular time. A flat, unobstructed horizon will normally be required to observe most of them.
Alas, most conjunctions involving Mars are unspectacular to view because the planet is usually positioned far away from the Earth - and is therefore not particularly bright - whenever they take place. Those involving Venus will always take place at solar elongations of less than 47° from the Sun, whilst those involving Mercury will always take place at less than about 27° from the Sun. In both of these instances twilight is often a problem, the lighter sky diminishing the visual impact of the conjunction (Mars looking like an ordinary, pale-orange star). Without doubt, Mars' most spectacular conjunctions take place when it is within a few months of opposition - and therefore very bright - at which times they involve either Jupiter or Saturn; these events are however very rare. Most conjunctions between Mars and Jupiter (or Mars and Saturn) occur at elongations of less than 90°, when Mars is far from its brightest in any given apparition. The 2017-19 apparition has two relatively favourable conjunctions involving these two giant planets: a Saturn conjunction taking place at an elongation of 94° and a Jupiter conjunction taking place at an elongation of 88°. In the case of the Saturn conjunction, Mars shines at a relatively bright magnitude of +0.2.In the 2017-19 period there are eight visible planetary conjunctions involving Mars; four in the morning and four in the evening. Five of them are either close or very close conjunctions. Their visibility favours the Northern and Southern hemispheres in roughly equal measure. Three of the eight involve the planet Mercury - in stark contrast with Mars' 2015-17 apparition, which had no visible conjunctions with the elusive planet.
Perhaps the most interesting Martian conjunction of the 2017-19 apparition is that with Saturn in the morning sky on April 2nd 2018, the brightnesses of Mars and Saturn differing by just 0.3 magnitudes. The two planets are separated by 1º.2, much closer together than their previous conjunction in the evening sky in August 2016. The 2018 event takes place in central Sagittarius so it favours Southern hemisphere observers. The near-90° solar elongation means that Mars and Saturn are close to the meridian as they disappear from view in the dawn twilight. At the moment of their disappearance, the pair are positioned close to the zenith (directly overhead) at 25° South, 78° above the horizon at 35° South and 68° above the horizon at 45° South. Despite the relatively wide solar elongation, low altitude affects observation from mid- and high-Northern latitudes. This is caused by the dual effect of the planets' high Southerly declinations and the shallow angle of the ecliptic to the local horizon before sunrise at this time of year. At latitude 60° North the planets are placed just 5° above the SSE horizon as they disappear from view. At 50° North they are 15° above the SSE horizon at disappearance; at 30° North they are 36° above the Southern horizon whilst at the Equator they are 66° above the SSE horizon.
On the morning of January 7th 2018 there is a close conjunction of Mars with Jupiter in central Libra. The event is more favourable to Southern hemisphere observers although there are also good views from the Northern hemisphere. From both hemispheres the planets reach a respectable altitude before the much fainter Red Planet disappears from view in the dawn twilight. From 60° North latitude the pair reach 13° in altitude in the South before Mars is lost from view, whilst at latitude 40° North they attain an altitude of 31° before the Red Planet is lost from view. From the Southern hemisphere the altitudes attained in the Eastern sky are: 48° high at 15° South; 44° high at 25° South; 37° high at 35° South and 28° high at 45° South. With a separation of 12' (0°.2) both planets are easily contained within the field of view of a telescopic eyepiece.
The conjunction between Mars with Venus on the morning of October 5th 2017 is a relatively good one for Northern hemisphere observers. Taking place quite early in the Red Planet's apparition, the event is seen in twilight from latitudes South of about 20° South and is not visible at all South of about latitude 33° South. The solar elongation of the event is only 23°, so altitudes attained above the Eastern horizon at Mars' disappearance are nowhere higher than about 15°. The event is made more interesting - at least for observers equipped with optical aid - because of the proximity of the fourth-magnitude star Sigma Leonis ( Leo) a short distance away from the pair.
Both conjunctions of Mars with the outer planets Uranus and Neptune take place in the evening at wide solar elongations. That with Uranus in Aries on the evening of February 13th 2019 is well-placed for Northern hemisphere observers, the planets being positioned 36° in altitude towards the South-west at latitude 60° North as Uranus comes into view in the dusk twilight. The altitudes and directions at other latitudes are: 47° in the South-west at latitude 40° North; 52° in the West at 20° North; 46° in the WNW at the Equator and 20° in the WNW at 35° South.
The conjunction with Neptune in Aquarius on December 7th 2018 is visible worldwide, the pair being separated by a very small 2'.3 (0°.03). Mars can easily be spotted by the naked-eye in the dusk twilight but Neptune typically requires between 30 and 50 minutes of additional time before the sky is dark enough for the planet to be seen through binoculars. Consequently the altitude of the two planets falls considerably by the time both can be seen together. When they first become visible, the pair are placed 22° high in the SSE at 60° North and 52° high in the South at 30° North. In the Southern hemisphere, they stand 68° high in the WNW when they become visible at 15° South and 46° high in the WNW at 35° South. However, Neptune (mag. +7.9) is 28 times further away than Mars (+0.1) at the moment of conjunction and 1,300 times fainter, so the glaringly-bright Red Planet needs to be positioned outside the eyepiece field-of-view in order to more comfortably observe its distant partner.
All three of the Martian conjunctions with Mercury are difficult to observe, no single event being visible worldwide. The September 16th 2017 event has the narrowest solar elongation of the visible conjunctions of the 2017-19 apparition and it is the only one of the three which is visible from the entire Northern hemisphere. But even here the altitudes attained by the two planets are very low as they disappear from view in the dawn twilight: just 6° high at 60° North and 8° high at 30° North. Twilight and low altitude prevent visibility of this conjunction at latitudes South of about 17° South. Much more evident, some 11° to the WNW of the pair and shining at magnitude -3.8, is the planet Venus, now more than half-way through its 2017 morning apparition and easily seen from both hemispheres.
The best Mercury-Mars conjunction for Southern hemisphere observers is that on June 18th 2019, the planets being separated by just 14' (0º.23) and positioned 24° East of the Sun. As the pair come into view in the dusk sky they stand 15º high in the WNW at latitude 15° South, 13º high in the North-west at 25° South, 11º high in the North-west at 35° South and 7º high in the North-west at 45° South. The conjunction is not visible North of mid-Northern latitudes.
The widest conjunction of the 2017-19 period is that between Mercury and Mars on the evening of July 7th 2019. It takes place during the same morning apparition of Mercury as that on June 18th. The planets are separated by nearly 6°, so wide that many might dismiss it as being a conjunction at all. Only visible South of latitude 30° North, the pair are less than 10º above the WNW horizon as they come into view at dusk.
The following table lists the conjunctions involving Mars during the 2017-19 apparition which take place at solar elongations of 15º or greater. Where other planets are also in the vicinity, details are given. Note that, because some of the conjunctions occur in twilight, the planets involved may not appear as bright as their listed magnitude suggests.
Mars conjunctions with other planets from September 2017 to July 2019 (click on thumbnail for full-size table, 41 KB). The column headed 'UT' is the Universal Time (equivalent to GMT) of the conjunction (in hrs : mins). The separation (column 'Sep') is the angular distance between the two planets, measured relative to Mars, e.g. on 2018 Jan 7, Jupiter is positioned 0°.2 North of Mars at the time shown. The 'Fav. Hem' column shows the Hemisphere in which the conjunction is best observed (Northern, Southern and/or Equatorial). The expression 'Not high N/S Lats' indicates that observers at latitudes further North than about 45°N (or further South than about 45°S) will find the conjunction difficult or impossible to view because of low altitude and/or bright twilight.
In the 'When Visible' column, a distinction is made between Dawn/Morning visibility and Dusk/Evening visibility; the terms Dawn/Dusk refer specifically to the twilight period before sunrise/after sunset, whilst the terms Evening/Morning refer to the period after darkness falls/before twilight begins (some conjunctions take place in darkness, others do not, depending upon latitude). The 'Con' column shows the constellation in which the planets are positioned at the time of the conjunction.
To find the direction in which the conjunctions are seen on any of the dates in the table, note down the constellation in which the planets are located ('Con' column) on the required date and find the constellation's rising direction (for Dawn/Morning apparitions) or setting direction (for Dusk/Evening apparitions) for your particular latitude in the Rise-Set direction table.
A table of planetary conjunctions involving Mars from 2016 to 2020 can be seen here (67 KB).
Although any given conjunction takes place at a particular instant in time, it is worth pointing out that, because of the planets' relatively slow daily motions, such events are interesting to observe for several days both before and after the actual conjunction date.
There are in fact two methods of defining a planetary conjunction date: one is measured in Right Ascension (i.e. perpendicular to the celestial equator) and the other is measured along the ecliptic, which is inclined at 23½° to the Earth's equatorial plane (this is due to the tilt of the Earth's axis in space). An animation showing how conjunction dates are determined by each method can be found on the Jupiter-Uranus 2010-11 triple conjunction page. Although conjunction dates measured along the ecliptic are technically more accurate (separations between planets can be significantly closer) the Right Ascension method is the more commonly used, and it is the one which is adopted here.
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The Southern Zodiac: Constellation Photographs
Eastern Aquarius & Western Pisces
Sagittarius & the Southern Zodiac
Ophiuchus, Sagittarius, Capricornus and Aquarius (click on thumbnails for full-size versions: 201 KB, 49 KB and 183 KB). Photographs showing the region of the night sky through which Mars passes during 2018 (click on the images for their full-size equivalents). In the Aquarius photo stars are visible down to an apparent magnitude of about +7.5. In the Capricornus photo the limiting magnitude is about +7.1 whilst that of the Sagittarius photo it is about +8.1. Note that the three photographs do not have the same scale because of the differing camera lens settings and image resolutions.
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Moon near Mars Dates,
September 2017 to July 2019
The Moon is easy to find, and on one or two days in each month, it passes Mars in the sky. The following tables list the dates on which the Moon passes near the planet between September 2017 and July 2019:
Moon near Mars dates for the period from September 2017 to July 2019 (click on thumbnail for full-size table, 122 KB). The Date Range shows the range of dates worldwide (allowing for Time Zone differences across East and West hemispheres). Note that the Date, Time and Separation of conjunction (i.e. when the two bodies are at the same Right Ascension) are measured from the Earth's centre (geocentric) and not from the Earth's surface. All times are Universal Time [UT], which is equivalent to GMT. The Sep. & Dir. column gives the angular distance (separation) and direction of the planet relative to the Moon, e.g. on April 7th 2018 at 18:16 UT, Mars is positioned 3°.1 South of the Moon's centre. The Moon Phase shows whether the Moon is waxing (between New Moon and Full Moon), waning (between Full Moon and New Moon), at crescent phase (less than half of the lunar disk illuminated) or gibbous phase (more than half but less than fully illuminated).
The Moon moves relatively quickly against the background stars in an Eastward direction, at about its own angular width (0º.5) each hour (about 12º.2 per day). Because it is relatively close to the Earth, an effect called parallax causes it to appear in a slightly different position (against the background stars) when seen from any two locations on the globe at any given instant; the further apart the locations, the greater the Moon's apparent displacement against the background stars. Therefore, for any given date and time listed in the table, the Moon will appear closer to Mars when seen from some locations than others. For this reason, the dates shown in the table should be used only for general guidance.
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Mars Meridian Transit Altitudes,
2001 to 2020
Mars is one of only two Solar System planets whose surface details can be seen through modest-sized telescopes (the other being Mercury, whose small size and low altitude often precludes a clear view). For the naked-eye observer, apart from the increased likelihood of obstruction from trees and buildings, a planet's low altitude is generally of little consequence, however for the telescopic observer, high altitude is essential in order to minimise the effects of turbulence, atmospheric dimming and light pollution (skyglow) which prevails near the horizon. Consequently, telescopic observers consider high altitude transits (when a celestial body crosses the observer's meridian, reaching its highest point in the sky) as more favourable than low altitude transits. As a general rule, telescopic observation is best done when a celestial body's altitude is greater than about 30°; hence observation in the couple of hours after rising or before setting is best avoided, unless there is no other alternative.
In general, high-Northerly oppositions (in Taurus or Gemini) are best seen from the Northern hemisphere and high-Southerly oppositions (in Scorpius, Ophiuchus, Sagittarius or Capricornus) are best seen from the Southern hemisphere. Mars' last most Northerly opposition took place in Gemini in December 2007, when observers at mid-Northern latitudes saw the planet transit at around 60° to 70° high in the sky, providing optimal conditions for viewing through telescopes. Mid-Southern hemisphere observers fared rather worse, the planet transiting at around 20° to 30° high. Mars' next most Northerly opposition will be in December 2022, when it will be positioned in Taurus (its subsequent opposition in January 2025 will also be high, on the Gemini/Cancer border). After the 2001 opposition, observing circumstances for Northern hemisphere observers gradually improved as the planet ascended the ecliptic at each successive opposition. Following its high opposition in Gemini in 2007, the planet began to descend the ecliptic once more, a process which continued through its next few oppositions in Leo (2012), Virgo (2014) and Scorpius (2016).
Mars' last most Southerly opposition took place in Ophiuchus in June 2001, when observers at mid-Southern latitudes saw the planet transit at around 70° to 80° high in the sky; mid-Northern hemisphere observers saw it transit at just 20° to 30° high. Although the July 2018 opposition sees Mars in more Northerly Capricornus, the planet is 6°.5 to the South of the ecliptic, positioning it only about 1° further North than it was at the 2001 opposition. Southern hemisphere observers, having experienced a few rather poor oppositions altitude-wise (in 2005, 2007 and 2010), saw observing circumstances improve in recent oppositions, the planet appearing far to the South (i.e. at a higher transit altitude) at both the 2016 and 2018 oppositions.
Meridian Transit altitudes of Mars at successive oppositions from 2001 to 2020, as seen from a variety of latitudes (click on thumbnail for full-size table, 53 KB).
The planet's best (brightest) oppositions take place when it is positioned in Aquarius, as it was in 2003. During these times Southern hemisphere observers benefit from a high transit altitude; conversely, observers at mid-Northern latitudes must contend with less-than-ideal transit altitudes (< 35°). Observing circumstances improved for Northern hemisphere observers after the planet's 2001 opposition (when it was positioned at a high-Southerly declination in Ophiuchus) but they began to worsen after 2007.
Meanwhile, the Martian disk as seen through the telescope shrank after the 2003 opposition but began to increase from the 2014 opposition.
The varying transit altitude of Mars at each opposition is not the only factor which affects the ability to see the planet's surface details through telescopes; there is also the question of its hugely varying apparent size as seen from the Earth. This is the result of the planet's eccentric orbit, which brings it closer to the Earth at some oppositions than at others. For more details, see the Mars oppositions 2012-2027 page.
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Copyright Martin J Powell August 2017
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