The Venus Evening Apparition
by Martin J. Powell
The Paths of Venus and Mercury through the zodiac constellations during the latter part of Venus' evening apparition in 2018 (click on the thumbnail for the full-size image, 176 KB). The earlier part of the apparition appears in the star chart below. Positions are plotted for 0 hrs Universal Time (UT) at 5-day intervals. For Venus, apparition data for the dates shown in bright white (at 10-day intervals) are included in the table below.
Wherever a planet was too close to the Sun to view, the path is shown by a dashed line (- -). For Mercury, both evening and morning apparitions are included. Hence Mercury's evening apparition drew to a close in late July 2018. It then became lost from view in the evening twilight as it headed towards inferior conjunction with the Sun. The planet then re-emerged in the dawn twilight in mid-August for a morning apparition which lasted through to early Sepetmber. Because Mercury is only ever seen in twilight, many of the fainter stars shown in the planet's vicinity may not have been visible when the planet itself was observed.
The positions at which Mercury and Venus attained greatest elongation from the Sun are indicated by the letters 'GE', with the solar elongation angle in brackets. The June/July evening apparition of Mercury favoured Southern hemisphere observers (who should refer to the Southern hemisphere chart (180 KB) for a more appropriate orientation) whilst the morning apparition of August/Sepember favoured Northern hemisphere observers. The position at which Venus attained greatest brilliancy for this apparition (apparent magnitude = -4.6) is shown by the letters 'GB'.
Click here (124 KB) to see a 'clean' star map of the area (i.e. without planet paths); a printable version can be found here (59 KB).
The faintest stars shown on the chart have an apparent magnitude of about +4.8. Printer-friendly versions of this chart are available for Northern (80 KB) and Southern hemisphere (81 KB) views. Astronomical co-ordinates of Right Ascension (longitude, measured Eastwards in hrs:mins) and Declination (latitude, measured in degrees North or South of the celestial equator) are marked around the border of the chart.
Star names shown in yellow-green were officially adopted by the International Astronomical Union (IAU) in 2017. The two such star names shown on this chart were drawn from Chinese mythology (more details are given in the main text).
Following superior conjunction on January 9th 2018 (when it passed directly behind the Sun in central Sagittarius) Venus moved into Capricornus, the Sea-Goat,, on January 17th. The planet emerged into the dusk sky in early February 2018 as an 'Evening Star', low down in the WSW soon after sunset. Observers at Equatorial latitudes were the first to see it, with Tropical and mid-Northern/Southern latitudes viewing the planet about a week or so later. At mid-Southern latitudes, low altitude (angle above the horizon) and twilight delayed the first appearance of the planet until around early March. When it first appeared in the dusk sky the planet was moving steadily North-eastwards along the ecliptic (the apparent path of the Sun, Moon and planets), pulling away from the Sun at a rate of about 0°.25 per day.
Venus and Mars in the dusk sky in February 2017, photographed by the writer five days after Venus reached peak brilliancy. Mars is to the upper left of Venus (click on the thumbnail for the full-size picture, 290 KB).
As typifies a Venusian evening apparition, the planet was slow to emerge from the twilight glow, taking several weeks to gain a significant altitude at any given time after sunset. During the 2018 evening apparition it would be the Northern hemisphere which first saw Venus attain its highest point in the sky after sunset (in local mid-Spring), the Southern hemisphere witnessing this about three months later (in local mid-Winter). Details of the planet's direction and altitude (at 30 minutes after sunset) for various latitudes are listed in the table below and they are also shown in the form of horizon diagrams.
2 0 1 8 February
Venus entered Aquarius, the Water Bearer, on February 8th, positioned at a distant 1.695 Astronomical Units (AU) from the Earth (253.6 million kms or 157.6 million statute miles), a distance which would continually reduce over the next eight months, through to the end of the apparition.
At around 1630 UT on February 16th, observers located in South-western Africa were able to witness the slender, waxing crescent Moon passing in front of Venus, blocking it from view, in an event known as a lunar occultation. The planet's narrow solar elongation (or simply elongation, its angular distance from the Sun) of just 9° meant that the event took place in twilight, positioned only a short distance above the Western horizon (a map showing the visibility and timings of this event can be seen by following the link in the 'Moon near Venus Dates' section below).
Venus reached an elongation of 10º East of the Sun on February 20th. When seen through a telescope, Venus showed a broad gibbous phase of about 98% at this early stage in the apparition (i.e. 98% of the disk was illuminated). The planet shone at an apparent magnitude (mag.) of -3.9 and measured only around 10" across (i.e. 10 arcseconds, where 1" = 1/60th of an arcminute or 1/3600 of a degree). However, its low altitude, great distance from the Earth and small apparent size made it a difficult object to observe telescopically, with no detail being discernible in its clouds.
On February 21st Venus passed 0º.6 South of Neptune (mag. +7.9) in a planetary conjunction which was too close to the Sun for both planets to be observed. A planetary conjunction occurs when two planets attain the same celestial longitude, so that they appear close together in the night sky. Although this particular conjunction was not observable, there would be four observable planetary conjunctions involving Venus during its 2018 evening apparition (three with Mercury and one with Uranus), of varying viewing difficulty. Three of the four would take place in March.
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2 0 1 8 March
Venus entered the constellation of Pisces, the Fishes, along its South-western border on March 2nd. Around this time the planet Mercury (mag. -1.2) entered the evening sky in the first of three paired apparitions between Venus and Mercury which took place during Venus' 2018 evening apparition (a paired apparition being when the two planets are visible together for a prolonged period of time, either in the morning sky or the evening sky). This particular apparition of Mercury was favourable for viewing in the Northern hemisphere, from where the ecliptic presented a steep angle to the Western horizon after sunset at this time of year. Over the course of the first few days of March, Mercury gained on slower-moving Venus by about 0°.5 per day; it was positioned 1°.7 West of Venus on March 2nd, 1°.3 WNW of the planet on the 3rd and 1°.1 North-west of it on the 4th. At around 18 hours UT on March 5th Mercury passed 1°.4 North of Venus in a difficult planetary conjunction which was viewable from latitudes North of the Southern Tropics. For more details on this and the other planetary conjunctions involving Venus in 2018, see the planetary conjunctions section below.
After conjunction Mercury, having dimmed slightly to magnitude -1.0, carried on North-eastwards, being 1°.9 NNE of Venus on March 7th, 2°.3 North-east of it on the 8th (when Mercury entered the Chart 1 coverage) and 2°.7 North-east of it on the 9th.
On March 9th Venus crossed the celestial equator (where the declination of a celestial body is 0°) heading Northwards, positioned some 3° East of the Sun's Vernal Equinox position (known historically as the First Point of Aries) where celestial longitude measurement originates (ecliptic longitude = 0° and Right Ascension = 0h 0m 0s). The planet now set between one and 1½ hours after sunset at Northern latitudes, one hour after sunset at Equatorial latitudes and 40 minutes after sunset at mid-Southern latitudes. Being positioned so close to the celestial equator at this time, the planet set due West across the inhabited world.
Venus entered the Chart 1 coverage on March 10th, at which time Mercury was positioned 3°.1 to the North-east of Venus. The elusive planet was 3°.4 North-east of Venus on March 11th and 3°.7 North-east of it on the 12th, when Venus reached a solar elongation of 15° East.
Table of selected data relating to evening apparition of Venus during 2018 (click on the thumbnail for the full-size image, 67 KB). The data is listed at 10-day intervals, corresponding with the dates shown in bright white on the star charts 1 and 2. The data for the table was obtained from 'MegaStar', 'Redshift 5' ,'SkyGazer Ephemeris' software and the 'BAA Handbook 2018'. The Venusian disk images were derived from NASA's Solar System Simulator.
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On March 12th Venus made a brief exit from the zodiac, entering the constellation of Cetus, the Whale at 14 hours UT, cutting diagonally across its North-western corner. The planet reached 15° East of the Sun on the same day.
Venus re-entered Pisces at 16 hours UT on March 14th, after some 50 hours in the company of the Whale. Mercury, now magnitude -0.5, was positioned nearly 4° North-east of planet at this time. The two planets attained a maximum separation of 4°.1 on March 15th, the same day on which Mercury reached its greatest elongation from the Sun (18° East). Mercury's apparent motion was now slowing as it approached its Eastern stationary point, allowing Venus to catch up with it over the next few days. At 01 hours UT on March 18th the pair again met in conjunction, Venus swiftly passing 3°.9 to the South of Mercury in central Southern Pisces. Being only two weeks since the pair last lined up, this conjunction was also only visible at latitudes North of Southern Tropics. At about 2115 UT that same day, Mercury, Venus and the crescent Moon lined up, visible low down in twilight from the central Northern Atlantic Ocean. Mercury reached its Eastern stationary point, 5° to the North-west of Venus, on March 23rd. Mercury's elongation rapidly reduced over the next few days and the planet became lost from view in the dusk twilight by month's end.
On March 23rd Venus passed 0.°6 South of the double star Revati ( Psc or Zeta Piscium,, mag. +5.2), a name which is derived from the ancient Hindu lunar mansions. She was the daughter of King Kakudmi in Hindu mythology and a consort of the god Balarama (the elder brother of Krishna). The name was formerly adopted in 2017 by the Working Group on Star Names (WGSN), a newly-established division of the International Astronomical Union (IAU). Since 2016 the WGSN has been cataloguing and standardizing the star names used by the international astronomical community, the names being entered into the 'IAU Catalog of Star Names'. In order to accommodate a wider diversity of global culture, they have adopted some names from mythologies other than Arab, Greek and Roman, whose star names dominate the night sky. In the words of the IAU, the new names "were drawn largely from the Australian Aboriginal, Chinese, Coptic, Hindu, Mayan, Polynesian and South African peoples". Although they are considered to be 'new' (in the sense that they are unfamiliar to Western culture) the names have of course been known to their respective cultures for hundreds or thousands of years. The other four 'newly-named' stars which appear in the star chart will be discussed below, along with a number of better-known star names (proper names) for which the IAU have now introduced standardized spellings.
Now in the 'tail' region of the Fishes, Venus passed just 4'.5 (0°.075) South of Uranus (mag. +5.9) shortly after midnight UT on March 29th in a difficult-to-view planetary conjunction which was only visible between latitudes 38° North and 10° South. As they passed each other in the sky, Venus lay at a distance from Earth which was only one-twelfth of that to Uranus and its apparent motion was 22 times faster than that of the gas giant. Uranus was now at the end of its 2017-18 apparition and would move into Aries in late April, having spent some nine years in Pisces.
At around 2140 UT on the same day, Venus passed 1°.1 North of the star Torcular ( Psc or Omicron Piscium, mag. +4.2), also known as Torcularis Septentrionalis, positioned in the tail of the Northern Fish. The fanciful name was a translation of a Greek word meaning 'winepress'. However, this was a mistranslation of the original Greek word which meant 'flax', i.e. the cord that tied the two Fishes' tails together. In 2017 the name Torcular was formerly standardized by the IAU.
Venus entered the constellation of Aries, the Ram, on March 30th, passing 9°.5 South of the star Sheratan ( Ari or Beta Arietis, mag. +2.6) on March 31st.
2 0 1 8 April
As March gave way to April, Venus became more readily visible to Northern hemisphere observers, hanging low over the Western horizon and setting between 1½ to 2 hours after sunset. Now at a more comfortable solar elongation of around 20°, the brilliant-white planet began to catch the attention of millions of people as they made their Westbound journeys homeward from workplaces, colleges and schools. Viewed from the Southern hemisphere, however, the planet would not become especially prominent until May.
Venus passed 9°.2 North of the double-star Alrescha ( Psc or Alpha Piscium, mag. +3.8) in neighbouring Pisces on April 2nd, a name which was standardized by the IAU in 2016 (the star having previously been known as Al Rischa, Alrisha or Al Rescha). It comprises two blue-white components of magnitudes +4.1 and +5.1, separated by an angular distance of 1".8 on a roughly East-West orientation. Telescopes of at least 75 mm (3 in) aperture are required to split the pair.
The planet passed a wide 10°.9 to the South of Aries' brightest star Hamal ( Ari or Alpha Arietis, mag. +0.2) on April 3rd, crossing the ecliptic heading Northwards on April 12th. On the same day Venus passed 10º.8 South of the star Bharani (41 Ari or 41 Arietis, mag. +3.6), another name which was adopted by the IAU in 2017. Bharani is the name of the second lunar mansion in Hindu astrology and it is - quite appropriately in the present context - ruled by Shurka (Venus). The planet passed 1º.6 South of Botein ( Ari or Delta Arietis, mag. +4.3), the Ram's Easternmost bright star, on April 17th.
Venus entered Taurus, the Bull, on April 19th. Four days later (April 23rd) the planet passed 3°.7 South of the open star cluster known as the Pleiades (pronounced 'PLY-add-eez' or 'PLEE-add-eez') or The Seven Sisters (Messier 45), perhaps the best-known star cluster in the night sky. Now sinking into the evening twilight, the cluster is not best seen at this time of year. Under dark skies the seven brightest stars in the group can be seen with the naked-eye and they are often considered to be a good test of visual acuity; they are Alcyone ( Tau or Eta Tauri, mag. +2.9), Atlas (mag. +3.6), Electra (mag. +3.7), Merope (mag. +4.2), Taygete (mag. +4.3), Pleione (mag. +5.1v) and Celaeno (mag. +5.5). The planet took about 64 hours to traverse the 1° angular distance between the cluster's brightest Western star (Electra) and its brightest Eastern star (Atlas).
On April 26th Venus passed 8°.8 North of the eclipsing binary star Tau (Lambda Tauri), whose magnitude varies from ca. 3.5 to 4.0 over a period of four days. Given its prominent position at the 'heart' of the Bull figure, it is perhaps surprising that the star carries no proper name, although a 17th-century Egyptian star catalogue names the star Sadr al Tauri, the Latin translation of which is Pectus Tauri ('the Bull's chest').
Between April 30th and May 3rd Venus passed several degrees North of another, much larger star cluster known as the Hyades, a distinct 'V'-shaped grouping of stars forming the head of the Bull. Also known by the designations Caldwell 41, Collinder 50 and Melotte 25, the cluster comprises around 400 stars spread over an area of about 5° of the sky. It is the nearest star cluster to the Earth, lying at a distance of about 153 light years (where 1 light year = 63,240 AU). Believed to be around 625 million years old, the cluster is rich in double stars and variable stars. At the apex of the 'V' is the star Prima Hyadum ( Tau or Gamma Tauri, mag. +3.6) which, before standardization by the IAU, was known variously as Primus Hyadum or Hyadum I. Venus passed 6°.7 North of the star on April 30th.
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2 0 1 8 May
Early on May 1st Venus passed 4°.9 North of the star Secunda Hyadum (1 Tau or Delta-1 Tauri, mag. +3.7), a triple star system positioned about half-way along the Northern arm of the Hyades cluster. Before IAU standardization, this star was alternatively called Secundus Hyadum or Hyadum II.
The Hyades cluster is not limited to the 'V'-shape which is visible to the naked eye; the true cluster extends several degrees away from the 'V' in all directions. Venus passed two 'detached' stars of the cluster over the course of the same day (May 1st), both of which are positioned to the North of the 'V'. At about 1645 UT the planet passed 15' (0°.25) North of the star Tau (Kappa Tauri), a double star with components of magnitude +4.2 and +5.2. The star was photographed during a scientific expedition to view an eclipse in Brazil in May 1919 and, when its apparent position was shown to have shifted slightly during totality because of the Sun's gravity, it demonstrated that Albert Einstein's general theory of relativity was correct. Four hours later (21 hours UT) on May 1st Venus passed 13' (0°.2) South of the star Tau (Upsilon Tauri, mag. +4.3), a variable star with a very small brightness fluctuation of between magnitudes +4.2 and +4.3 over a period of 3½ hours.
Also positioned along the Northern arm is the star Ain ( Tau or Epsilon Tauri, mag. +3.5), marking the base of the Bull's Northern horn. An extra-solar planet or exoplanet (a planet outside our Solar System) was detected orbiting this star in 2007. Named Ameratu after the Shinto goddess of the Sun, it orbits the star at a distance of 1.9 AU over a period of 645 days. The planet, whose technical designation is Epsilon Tauri b, is believed to have a mass equivalent to 7.6 Jupiter masses. Ain is the brightest Taurean star which is currently known to have an exoplanet, and Venus passed 3°.5 North of the star at around 0740 UT on May 2nd. At the same moment, Venus passed 6°.8 North of the star Chamukuy (2 Tau or Theta-2 Tauri, mag. +3.4), the brightest of the Hyades' 'true' members, positioned about half-way along the Southern arm of the cluster. The name is that of a small bird in Yucatec Mayan culture and it was adopted by the IAU in June 2017. The star forms a naked-eye yellow-white double with 1 Tau (Theta-1 Tauri, mag. +3.8), positioned some 337" (5'.6 or 0°.09) to the North.
In early May, observers at high-Northern latitudes saw Venus attain its highest altitude after sunset for the 2018 apparition. This was because, from these latitudes, the ecliptic presented a high angle to the Western horizon at the point in the zodiac where Venus was positioned at this time. At latitude 60º North some 30 minutes after sunset, the planet was positioned 14º above the WNW horizon, being visible for three hours thereafter. Meanwhile, observers at mid-Southern latitudes were only just beginning to see Venus attain a significant altitude at dusk. At 45º South the planet was only 7º high in the North-west at 30 minutes after sundown. From these latitudes the planet would not be seen at its best until late August.
Occupying the South-eastern corner of the Hyades cluster is the orange-red star Aldebaran ( Tau or Alpha Tauri, mag. +0.9), marking the 'eye' of the Bull. 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 at a much closer distance of 68 light years. Venus passed 6°.5 North of Aldebaran on May 3rd.
Another star which is not part of the cluster is Tau (Tau Tauri, mag. +4.2), which is amusingly referred to as Tau Tau! Positioned at the 'bend' of the Bull's Northern horn, it is a multiple-star system and part of an obscure open cluster known as Alessi 51. Venus passed 18' (0°.3) North of the star on May 4th. Four days later the planet passed 2°.4 North of the Easternmost bright member of the 'true' Hyades cluster, Tau (Iota Tauri, mag. +4.6). Positioned between the Bull's horns, it is a remarkable 9°.5 to the ENE of the familiar 'V'-shaped asterism.
In mid-May Venus reached an elongation of 30° East of the Sun and a brightness of magnitude -4.0. On May 13th the planet passed 4°.0 South of the star Elnath ( Tau or Beta Tauri, mag. +1.6), which is located at the tip of the Bull's Northern horn. The name was standardized by the IAU in 2016, previous versions of the name being spelled Al Nath, El Nath or simply Nath. The star also neatly completes the six-sided figure comprising the stars of Auriga, the Charioteer, located to the North-east of Taurus. For this reason, for many centuries the star was considered to have a shared identity, the German lawyer and cartographer Johann Bayer (1572-1625) giving the star a second designation of Gamma Aurigae ( Aur). When the IAU formally defined the constellation boundaries in 1930 the latter designation mostly fell out of use, although it still appeared in some star atlases as recently as the 1980s. With the introduction of the IAU's star-name catalogue, the designation has now been formally dropped.
The star marking the tip of the Bull's Southern horn is Tianguan ( Tau or Zeta Tauri, mag. +2.9v), another 'new' name adopted by the IAU in 2017. The name derives from Chinese astronomy, in which the star is known as the Celestial Gate, part of an asterism (small group of stars) contained within a mansion called Bì Xiù ('the Net'). Venus passed 3°.6 North of Tianguan on May 15th.
Venus left Taurus and entered Gemini, the Twins on May 19th, passing 1°.8 North of the star 1 Gem (1 Geminorum, mag. +4.2), marking the foot of the Northern twin, on May 20th. 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. Venus passed about 44' (0°.75) North of the cluster's centre between 08 hours and 15 hours UT on May 21st.
On May 22nd the planet attained its highest declination (angle above the celestial equator) for this apparition of +25° 3' 15" (+25°.05416 in decimal format). Venus then set at its most Northerly point along the horizon, an effect which was more pronounced the further North in latitude an observer was situated. For example, at the Equator (latitude 0°) the planet set in the WNW at this time whilst at 60° North the planet set in the NNW, some 35° further North along the horizon. The high Northern declination also meant that the planet remained visible in the evening sky for longer in the Northern hemisphere: a little over three hours at latitude 60° North but only two hours at 45° South. Later on May 22nd Venus passed 2°.5 North of the star Propus ( Gem or Eta Geminorum, mag. +3.5v), also referred to as Tejat Prior or Praepes before IAU standardization in 2016.
On May 24th, Venus passed 2°.5 North of the star Tejat ( Gem or Mu Geminorum, mag. +3.0v), which marks the Northern twin's knee. Before IAU standardization the star was known by several other names: Tejat Posterior, Nuhatai, Calx and Pish Pai! Four days later (May 28th) the planet passed 15.'5 (0°.25) South of Mebsuta ( Gem or Epsilon Geminorum, mag. +3.0) which is positioned at the groin of the Northern twin.
At around 1220 UT on May 31st Venus formed an isoscelene triangle with Gemini's two luminaries Castor ( Gem or Alpha Geminorum, mag. +1.6) and Pollux ( Gem or Beta Geminorum, mag. +1.1) positioned to the ENE of the planet. The long sides of the triangle measured a little over 10° and the angular distance of the short side (from Castor to Pollux) is 4°.5. The temporary celestial triangle pointed South-westwards towards Orion. This celestial geometry was visible from South-east Asia and the Eastern Indian Ocean.
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2 0 1 8 June
At midnight UT on June 1st Venus passed 4°.0 North of the optical double star Mekbuda (Gem or Zeta Geminorum, mag. +3.9v), positioned at the right knee of the Southern twin. The planet passed 2°.1 North of the star Wasat ( Gem or Delta Geminorum, mag. +3.5) on June 4th.
By early June, Venus was showing a phase of around 80% and was appearing slightly gibbous through telescopes, having enlarged in apparent size to around 13". Observers at mid-Northern latitudes now saw the planet at its highest altitude after sunset for the 2018 apparition. At latitude 40º North, some 30 minutes after sunset, Venus was positioned 21º high in the WNW, setting 2½ hours after the Sun. A correspondence of celestial mechanics and spherical astronomy meant that Venus now set around 2½ hours after sunset from across the inhabited world (see direction and altitude table below).
At any given interval after sunset, observers at all latitudes had seen Venus creep Northwards along the horizon since the planet's emergence into the evening sky in February. From high Northern latitudes the planet's Northward motion ceased in early June (it occurred in late May from the Equator and Northern Tropical latitudes; around mid-June from mid-Southern latitudes). Soon afterwards Venus headed back along the horizon (Southwards) and continued to do so through to the end of the apparition. When the position of Venus in the local evening sky is plotted for each day of the apparition at one half-hour after sunset (see horizon diagrams below), the resulting profiles at latitudes South of about 45º North are seen to have broader and more rounded peaks. Hence during the 2018 evening apparition, Southern latitudes saw the planet higher in the sky for a longer calendar period than in the Northern hemisphere. From mid-Southern latitudes in particular, Venus covered a much greater span in azimuth (compass bearing) over the course of the apparition (from North-west in mid-June through to WSW in mid-October).
On June 6th Venus passed 8°.1 South of the aforementioned Castor, which is Gemini's second-brightest star. On June 7th the planet passed 11°.0 South of the star Jishui ( Gem or Omicron Geminorum, mag. +4.9), another star name adopted by the IAU in 2017. The star is positioned close to the constellation's Northern border with Lynx. According to astronomy writer (and WGSN member) Ian Ridpath, Jishui, along with another star named Jixin, 'represent[ed] a supply of water for winemaking or brewing and a pile of firewood for cooking.' The source of the water was the Northern River (Beihe), formed in the Chinese night sky by the stars Castor, Pollux and nearby Gem (Rho Geminorum, mag. +4.2).
The planet left the Chart 1 coverage on June 8th. At around 2010 UT on the same day Gemini's brightest star Pollux, Gem (Kappa Geminorum, mag. +3.5) and Venus formed a line 4°.7 in length, aligned roughly celestial North and South. The line was visible at dusk from South-eastern Europe, central Northern Africa and the South-eastern Atlantic Ocean. The angular distance between Pollux and Gem is 3°.6 and that between Gem and Venus was 1°.1. Extending the line some 18° to the South of Venus brought one very close to the bright star Procyon ( CMi or Alpha Canis Minoris, mag. +0.5) in the constellation of Canis Minor, the Lesser Dog. Venus passed 1°.1 South of Kappa Geminorum itself on June 8th.
The following day (June 9th) the planet passed 4°.7 South of Pollux. At 18 hours UT on June 11th, as Venus reached 18 hours in Right Ascension ( i.e. 270° East of the Vernal Equinox position), Castor, Pollux and Venus formed a line some 10°.6 in length, orientated SSE-NNW. This alignment was visible at dusk from a narrow strip running SSW from the Caspian Sea to Namibia. The line pointed towards the head of Hydra, the Water Snake, positioned 20° to the SSE of Venus.
Venus entered Cancer, the Crab - the faintest of the zodiac constellations - on June 12th. The following day the planet entered the Chart 2 coverage.
The Paths of Venus and Mercury through the zodiac constellations for the earlier part of Venus' evening apparition in 2018 (click on the thumbnail for the full-size image, 199 KB). The latter part of the apparition is shown in the star chart above. Planet positions are plotted for 0 hrs Universal Time (UT) at 5-day intervals. Wherever a planet was too close to the Sun to view, the path is shown by a dashed line (- -). Hence Mercury became difficult to view in late March (as it headed towards inferior conjunction with the Sun) and in late May (as it headed towards superior conjunction with the Sun). For Venus, apparition data for the dates shown in bright white (at 10-day intervals) are included in the table above. For Mercury, both evening and morning apparitions are included. The positions at which Mercury attained greatest elongation from the Sun are indicated by the letters 'GE', with the solar elongation angle in brackets; it is Eastern (E) in the evening and Western (W) in the morning (the elongation of Venus is Easterly throughout the chart coverage). Note that the March evening apparition of Mercury shown on the chart favoured Northern hemisphere observers, whilst the April/May morning apparition favoured Southern hemisphere observers (who should refer to the Southern hemisphere chart (203 KB) for a more appropriate orientation). Because Mercury is only ever seen in twilight, many of the fainter stars shown in the planet's vicinity may not have been visible when the planet itself was observed.
Planetary conjunctions of Venus with Mercury and Venus with Uranus took place on March 18th and March 29th respectively; these are indicated on the chart by the symbol (for more details see the planetary conjunctions section below). The path of Uranus on this chart (in South-eastern Pisces) is shown only as a guide; a more detailed finder chart for this planet can be found on the Uranus page.
Click here (147 KB) to see a 'clean' star map of the area (i.e. without planet paths); a printer-friendly version can be found here (74 KB).
The faintest stars shown on the chart have an apparent magnitude of about +4.8. Printer-friendly versions of this chart are available for Northern (93 KB) and Southern hemisphere (94 KB) views. Astronomical co-ordinates of Right Ascension (longitude, measured Eastwards in hrs:mins) and Declination (latitude, measured in degrees North or South of the celestial equator) are marked around the border of the chart.
Star names shown in yellow-green were officially adopted by the International Astronomical Union (IAU) in 2017. The five such star names shown on this chart were drawn from Chinese, Hindu and Mayan mythology (more details are given in the main text below).
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On June 15th Venus passed 12°.6 North of Cancer's brightest star Altarf ( Cnc or Beta Cancri, mag. +3.5), at the South-western corner of the constellation's lambda-shaped () figure. The name, which is not in common usage, is derived from the Arabic for 'the End', i.e. the end of the Crab's leg. As of January 2018, the name had not been approved by the IAU. There is a case to be made for potential confusion, however, since the similarly-named star Alterf ( Leo or Lambda Leonis, mag. +4.3), meaning 'the View', is positioned only 22° to the North-east in neighbouring Leo [Note added August 2018: the IAU approved Beta Cancri's proper name as Tarf in June 2018].
From around mid-June, Mercury (mag. -0.8) entered the evening sky at the start of an apparition which was favourable to Southern hemisphere observers. The planet approached Venus from the WNW, gaining on it by about 0°.6 per day. Closest approach between the two planets would be reached in early July.
From June 19th-20th Venus passed 0°.7 North of the star cluster commonly known as Praesepe (pronounced 'pree-SEE-pee') or the Beehive Cluster (M44 or NGC 2632). Under dark, rural skies it is visible to the naked-eye as a hazy patch of light and in city locations it is easily seen in binoculars. Venus took some 22 hours to traverse the angular width of the cluster, commencing its passage at around 1745 UT on June 19th and completing it at around 1545 UT on June 20th.
On June 21st Venus passed between the stars Asellus Borealis ( Cnc or Gamma Cancri, mag. +4.6) and Asellus Australis ( Cnc or Delta Cancri, mag. +3.9), passing a little under half-way between them at around midnight UT. The distance between the two stars - measured from North to South - is 3º.3. The planet passed a sizeable 7º.3 North of Acubens ( Cnc or Alpha Cancri, mag. +4.3), at the South-eastern corner of the constellation, on June 24th.
Venus reached an apparent disk size of 15" on June 24th and an elongation of 40° East on June 28th. The planet moved from Cancer into Leo, the Lion on June 29th, where it would remain throughout the month of July.
2 0 1 8 July
On July 3rd Venus passed 5°.8 North of the star Subra ( Leo or Omicron Leonis, mag. +3.5), marking the paw of the Lion's foreleg. Between July 4th and 12th Venus was positioned South of the asterism commonly known as the Sickle of Leo, at the Western end of the constellation, which appears to the naked-eye as a backward question-mark (). The planet passed 8°.5 South of the star Ras Elased Australis ( Leo or Epsilon Leonis, mag. +2.9), at the upper North-western end ('pointed end') of the sickle, on July 4th. Every Australis (Southern) star in the night sky must have a Borealis (Northern) equivalent, and in this case it lies 2°.6 to the North-east - at the top of the sickle's blade - as Rasalas ( Leo or Mu Leonis, mag. +3.9) which, before its name was standardized by the IAU in 2016, was also known as Ras Elased Borealis.
Far to the South of Venus, some 29° away in the constellation of Hydra, the Water Snake, is the star Zhang (1 Hya or Upsilon-1 Hydrae, mag. +4.1), a name adopted by the IAU in 2017 and named after a Chinese lunar mansion. In Chinese astronomy the constellation of Zhang comprised three stars which we know today as Lambda Hydrae ( Hya) Mu Hydrae ( Hya) and of course, Upsilon-1 Hydrae (1 Hya). It represented an outstretched net, possibly for catching birds in flight.
Around early July, observers at Northern Tropical latitudes saw the 'Evening Star' attain its highest altitude after sunset for the 2018 apparition. At latitude 20º North Venus was positioned 28º high in the West at 30 minutes after sunset, setting 2½ hours after the Sun. At high-Northern latitudes, however, Venus' altitude after sunset had rapidly fallen since its high-point in early May, the planet now being visible for just 1½ hours after sunset. Elsewhere the planet was setting two hours after sunset (at mid-Northern latitudes), 2¾ hours after sunset (at Equatorial latitudes), three hours after the Sun (at Southern Tropical latitudes) and 3¼ hours after the Sun (at mid-Southern latitudes).
On July 8th at around 22 hours UT Venus was positioned at precisely 1.00 AU from the Earth, i.e. the same distance as the average distance of the Earth from the Sun (149.5 million kms or 92.9 million statute miles). The distance between Venus and the Earth was reducing at an average daily rate of about 1.13 million kms (704,800 statute miles) at this point in the apparition. On the same day Mercury (mag. +0.4), which had been an evening object since mid-June, came to within 15°.9 of Venus, the pinkish-orange planet being positioned to the WNW of Venus; they did not reach conjunction on this occasion. Mercury reached greatest elongation (26° East) on July 12th. The waxing crescent Moon passed the two planets between July 14th and 16th. Mercury remained visible in the dusk sky through to the end of July.
Venus passed 1°.1 North of Leo's brightest star Regulus ( Leo or Alpha Leonis, mag. +1.4) on July 9th. Regulus is positioned less than 0°.5 North of the ecliptic so it is occasionally occulted by planets and - more frequently - by the Moon. Venus last occulted Regulus in July 1959 and will next occult the star during its morning apparition in October 2044.
On July 12th Venus passed 7°.9 South of the star Algieba (1 Leo or Gamma-1 Leonis, mag. +2.3), at the base of the Lion's neck (although the name is Arabic for 'the forehead'). It is a double star with golden-yellow components (1 Leo and 2 Leo) of magnitudes +2.3 and +3.6, separated by an angular distance of 4".7. The pair are about 130 light years from Earth and they orbit each other in a period of 554 years. The star is easily split in small telescopes and is considered to be one of the finest double stars in the night sky. In 2009 an exoplanet was detected orbiting Algieba, named Gamma-1 Leonis b. The exoplanet's mass is equivalent to 8.8 Jupiter masses and it orbits the star at a distance of 1.2 AU in a period of 428 days.
Venus passed 1°.4 South of the star Leo (Sigma Leonis, mag. +4.0), at the foot of the Lion's hind leg, on July 27th. Around this time Venus reached its highest altitude after sunset as seen from Equatorial latitudes. Here the planet stood 34º above the Western horizon (about one-third the way 'up the sky') at 30 minutes after sunset, remaining visible for almost three hours thereafter. From Equatorial latitudes, twilight is brief throughout the year, so the planet was mostly seen in its true brilliant splendor against a fully dark sky.
By contrast, as July came to a close, observers at high-Northern latitudes were the first to bid farewell to the planet as it slipped into the bright summer dusk twilight.
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2 0 1 8 August
Now brightening more significantly, Venus entered Virgo, the Virgin or Maiden, on August 1st, shining at magnitude -4.2. The planet crossed to the South of the ecliptic later that same day.
On August 4th Venus passed 1°.0 South of Zavijava ( Vir or Beta Virginis, mag. +3.6), at the back of the Maiden's head. Before standardization by the IAU in 2016 the star was also known by the names Zavijah, Zavyava or Alaraph. On August 6th the planet crossed the celestial equator heading Southwards, meaning that the planet now set due West across the inhabited world, just as it had done back in early March. On August 13th Venus passed 2°.6 South of the star Zaniah ( Vir or Eta Virginis, mag. +3.8).
From early to mid-August, observers at Southern Tropical latitudes saw Venus at its best for the 2018 evening apparition. Half an hour after sunset, the planet was positioned 38º above the Western horizon, setting almost 3½ hours after the Sun. In fact, when considered in terms of the planet's visual impact and its ease of viewing, the 2018 evening apparition of Venus was best seen overall from Southern Tropical latitudes.
On August 12th at around 10 hours UT the distance between the Earth and Venus was the same as that between the Sun and Venus, at 0.7271 AU (108.7 million kms or 67.5 million miles). Seen from far above the Earth's North pole, the Earth, Venus and the Sun now appeared to formed an isoscelene triangle in space, with Venus positioned at the apex.
On August 17th at 1558 UT, Venus reached its greatest elongation from the Sun for this apparition (45°.92 East) in South-western Virgo. It was positioned 4°.3 SSW of the star Porrima ( Vir or Gamma Virginis, mag. +2.9) and 13°.5 WNW of Virgo's brightest star, Spica ( Vir or Alpha Virginis, mag. +1.0). At this point, telescopes showed Venus' disk half-illuminated (phase = 0.50 or 50%), which is often referred to as the moment of dichotomy. The planet now had an apparent diameter of 24".4 and it shone at magnitude -4.3. Although the greatest elongation from the Sun took place on August 17th, Venus was in fact positioned at 45°.9 elongation for a ten-day period from August 13th through to the 22nd. When seen from a point far above the Solar System, the Earth, Venus and the Sun would now formed a right-angled triangle in space, with Venus positioned at the 90° angle.
Venus at Dichotomy imaged by Stefano Quaresima (Rome, Italy) in June 2015 using a 406 mm (16-inch) Schmidt-Cassegrain reflector telescope fitted with an ultraviolet filter to reveal subtle cloud detail (click on the thumbnail for a larger image, 3 KB). (Image: Stefano Quaresima / ALPO-Japan).
Whilst the time of greatest elongation is normally considered to be the best time to observe Venus, in this particular apparition observers at mid-Northern latitudes found the planet to be low down in the sky after sunset and caught in the long summer twilight, being visible for only about 1¼ hours (50° North) and 1½ hours (40° North) after sundown. Unlike the situation three months earlier, Venus' position in Virgo meant that the planet was now on the descending (Southward) section of the ecliptic. Seen from mid-Northern latitudes, the ecliptic now presented a shallow angle to the local horizon after sunset, placing the planet low down in the sky. Already lost from high-Northern latitudes, the viewing window for Venus from mid-Northern latitudes rapidly shortened over the coming weeks. Further South, Venus set 2¼ hours after the Sun (at Northern Tropical latitudes), 2¾ hours after the Sun (at Equatorial latitudes), 3¼ hours after sunset (at Southern Tropical latitudes) and four hours after sunset (at mid-Southern latitudes). At 30 minutes after sunset the planet stood highest in the sky (38°) when seen from Southern Tropical latitudes. In stark contrast, at 30 minutes after sunset Venus appeared just 6° above the horizon when seen from latitude 50° North.
For telescopic observers of Venus, a high placement of the planet in the sky after sunset - whether or not this takes place around greatest elongation day - is of little benefit. Because of the planet's glare when seen against a darkening sky, coupled with the Earth's troublesome atmospheric turbulence at low altitudes, most telescope users observe the planet in full daylight, when it is high above the horizon and more easily seen against a brighter sky. Of course, extreme caution must be taken when attempting to observe any of the planets in daylight and the Sun must be positioned at a safe angular distance from the planet and be fully shielded from view.
For a few days around greatest elongation, telescopic observers often attempt to determine the precise moment when the terminator (the line separating the light and dark sides of the planet) appears perfectly straight, essentially dividing Venus into two perfect halves. Solar System geometry suggests that this should occur on greatest elongation day, however it often does not and the precise reason for this was not understood until quite recently. Observers often report the straight terminator a few days earlier or later than the greatest elongation date (early in evening apparitions and late in morning apparitions). Hence in the current apparition, telescopic observers could have expected to see a 50% phase on or around August 14th. This is commonly known as the phase anomaly or Schröter's Effect (the latter coined by the late Sir Patrick Moore after the German astronomer Johann Schröter, who first observed the effect in 1793). The phenomenon is thought to be due to Venus' dense atmosphere scattering the sunlight. Blue light scatters more readily than red light (which is why the sky on Earth appears blue) and this effect is also seen on Venus when it is observed using coloured eyepiece filters. The phase anomaly is much more evident when the planet is observed through a blue filter, whilst the anomaly is less evident when seen through filters of other colours, e.g. red or yellow.
Soon after midnight UT on August 18th, Venus passed just 9' (0°.1) North of the star 25 Virginis (mag. +5.8), which the planet will occult during its evening apparition on the same calendar date eight years hence, in 2026. At 1740 UT on the same day the planet passed 2°.0 North of the star Vir (Chi Virginis, mag. +4.6), a star which was found to have an exoplanet in 2009. Named Chi Virginis b, the planet is thought to have a mass equivalent to 11 Jupiter masses, orbiting Chi Virginis at a distance of 2.1 AU in a period of 835 days. Chi Virginis is the brightest Virgoan star currently known to have exoplanets.
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On August 19th Venus passed 4°.9 South of the aforementioned star Porrima, named after one of the Roman goddesses of prophecy. It is a binary star comprising components of magnitude +3.4 and +3.5, appearing to the naked-eye as a single star of magnitude +2.9. The pair orbit each other in a period of 169 years, their separation varying greatly throughout. The pair came closest together around 2006, when they were just 0".4 apart, making them difficult to separate in anything but the largest of telescopes. Currently 2".7 apart, the pair are widening and will be easy to separate in amateur telescopes from around 2020, aligned North-South in relation to each other. Before IAU standardization in 2016 Porrima was also known as Arich, a name whose origin appears to be shrouded in mystery.
In late August, observers at mid-Southern latitudes finally got their opportunity to see Venus at its highest and best for the 2018 apparition. At 35º South, some 30 minutes after sunset, Venus was placed 38º high, setting over 3½ hours after the Sun. Southern hemisphere observers, now deep into local Winter, saw Venus against the backdrop of a truly dark sky, the planet shining like a distant arc-lamp above the Western horizon.
Venus passed 4°.8 South of the double star Vir (Theta Virginis, mag. +4.4), located at the base of the Maiden's neck, on August 28th, then on August 31st the planet passed 6°.7 North of the star 61 Virginis (mag. +4.7), a star which, in 2009, was found to have two - and possibly three - exoplanets. All three planets (61 Virginis b, c and d) orbit the star at a distance which would place them within the equivalent orbit of Venus in our own Solar System. The innermost planet (b) orbits the star in just 4 days and is most likely rocky (terrestrial) in nature, whilst the other two are considered more likely to be gas giants, similar in composition to Uranus and Neptune. At 28 light years distant, 61 Virginis is one of the closest stars to Earth which is known to have exoplanets.
2 0 1 8 September
From early September Venus began to move in towards the Sun, its elongation now reducing, with telescopes showing a crescent phase and a rapidly enlarging apparent disk size. On September 2nd the planet passed 1°.4 South of the aforementioned Spica ( Vir), a blue-white star which dominates the South-eastern region of the constellation. During September the apparent size of the Venusian disk enlarged by 1½ times, from 29".5 (on September 1st) to 46".0 (on September 30th). Having started the month at almost greatest elongation distance, Venus would end the month some 11° closer to the Sun.
On September 11th Venus passed 2°.0 North of 89 Virginis (mag. +4.9), another star which the planet will occult at a future date - in this case, during its evening apparition on September 20th 2042.
The planet Jupiter (mag. -1.7), now in the final weeks of its 2017-18 apparition, had spent the past year in neighbouring Libra (the Balance) and was positioned less than 20° East of Venus during the latter half of September. It was 18° East of Venus on September 11th and 15° East of it on September 19th. The two planets would come closest together on September 28th, when they were 13°.8 apart.
Venus passed 9°.3 South of the 'newly-named' star Kang ( Vir or Kappa Virginis, mag. +4.2) on September 22nd. In Chinese astronomy Kang was a constellation and a name given to the second lunar mansion. Derived from 'Kàng Xiù' meaning 'Neck', the constellation represented the neck of a Blue Dragon, formed by the stars Kappa Virginis, Vir (Lambda Virginis or Khambalia, mag. +4.5), Vir (Iota Virginis or Syrma, mag. +4.1) and Vir (Phi Virginis, mag. +4.8). At this time of year, the star Kang is only visible to observers located South of about latitude 40° North, positioned low in the WSW (Northern latitudes) or West (Southern latitudes) at dusk.
On September 25th Venus attained its greatest brilliancy for this apparition at magnitude -4.6, positioned just 1°.2 from the border with Libra. The planet's greatest brilliancy occurs when the percentage of the illuminated portion of the disk (phase) and its angular size combine to best visual effect. In 2018 this took place when the planet was 23% illuminated (phase = 0.23), its angular diameter was 42".3 and its solar elongation was 37°. For observers at mid-Northern latitudes, however, the planet's greatest brilliancy in 2018 was not seen against a truly dark sky because the planet was low down and bathed in the bright dusk twilight; from 40° North it was only 3° above the WSW horizon at one half-hour after sunset. Southern hemisphere observers, on the other hand, saw Venus in its true majestic brilliance in a dark sky above the Western horizon; from latitude 35° South the planet stood some 28° high at 30 minutes after sunset.
2 0 1 8 October
From around early October, steadily-held binoculars detected the crescent of Venus soon after sunset, as the planet languished low in the Western sky. Telescopes showed a large, thin crescent at this point, about 15% illuminated. The crescent was greatly disturbed by turbulence in the Earth's atmosphere and was split into the rainbow colours by an effect called dispersion (an example of how dispersion appears through a telescope can be seen here).
As the Venusian crescent continued to enlarge it also became more slender, such that the dark (non-illuminated) side of the planet was well-displayed when seen from the Earth. With the aid of eyepiece filters, telescopic observers now began their search for the mysterious and elusive Ashen Light, a faint glowing of the night side of Venus which has no clear explanation. First observed in 1643 by the Italian astronomer Giovanni Riccioli (1598-1671), the effect is best observed when Venus is at a narrow crescent phase and is seen against a fully dark sky. An obstruction known as an occulting bar can be placed in the telescope eyepiece, thus blocking the glare of the planet's crescent and allowing the unlit portion of the disk to be seen with greater ease. The Ashen Light is thought to be caused either by the planet's surface glowing red hot (due to its extremely high surface temperature) or by electrical activity in the planet's dense atmosphere. Intriguingly, reports of the Ashen Light have been rare in recent years, though it is difficult to say whether this is the result of improved observing equipment (i.e. eliminating contrast effects caused by poor optics) or a true reduction in activity of a genuine phenomenon.
The Ashen Light sketched by two British observers some sixty years apart (click on the thumbnail for the full-size image, 23 KB). (Left) By V. A. Firsoff in January 1958, observed using 165 mm (6½-inch) and 320 mm (12½-inch) reflector telescopes and (Right) by Tim Wetherell in February 2017, observed through a 178 mm (7-inch) refractor telescope. The images show the planet's apparent size correctly in relation to each other (Images: (Left) British Astronomical Association and (Right) Tim Wetherell / StargazersLounge.com.
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When Venus entered Virgo at the beginning of August it was moving at a daily angular motion of about 1°.0, but by the time it entered Libra on October 1st its motion had slowed to less than 0°.2 per day. Its path through the sky had deviated Southward, carrying it several degrees away from the ecliptic. During the first week of October Venus became lost from view from mid-Northern latitudes, whilst in the Southern hemisphere the planet's altitude at any given time after sunset rapidly fell away over the coming days, dropping by about 1° per day (see horizon diagrams below).
Venus reached its stationary point in South-western Libra at around 04 hours UT on October 5th, at which point its prolonged period of direct (West to East) motion ceased. Having moved just 13' (0°.21) into Libra, the planet then commenced retrograde (East to West) motion, turning back towards Virgo and re-entering that constellation at its extreme South-eastern corner on October 8th. Now 7°.3 South of the ecliptic and heading directly into the Sun's glare, the planet's period of visibility from Earth was drawing to a close.
In mid-October Mercury (mag. -0.4) entered the evening sky for the third and final paired apparition with Venus in 2018, in this case favouring Southern hemisphere observers. On October 13th Mercury was 8°.4 to the NNW of a slowly retrograding Venus, gaining on the planet by about 1°.8 per day. Over the coming week, Mercury would escort Venus in the dusk sky, seeing it through to the end of its apparition.
Venus' solar elongation reduced to 20° East on October 14th. At around 15 hours UT on the same day, Mercury (mag. -0.3) passed 6°.8 to the North of Venus (now mag. -4.2) in the final planetary conjunction of the 2018 apparition. Mercury was 6°.6 North of Venus on October 15th, 6°.2 NNE of the planet on the 16th and 6°.5 North-east of it on the 17th, by which time Venus' elongation had reduced to 15° East of the Sun. Observers at Northern Tropical latitudes lost sight of the planet in the bright dusk twilight from mid-October, with Equatorial latitudes following only days afterwards.
In the closing days of the apparition, Southern hemisphere observers with exceptionally good eyesight may now have attempted to observe the crescent of Venus with the naked-eye soon after sunset. Whilst this may seem extraordinary, the planet's apparent size of around 58" brought it very close to the generally-accepted resolution of the human eye, i.e. 1' (one arcminute, or 1/60th of a degree). Because the planet was now so close to the Sun, glare was no longer a problem because the planet was seen in bright twilight through to its setting, reducing contrast and theoretically allowing the crescent to be discerned more easily. Telescopically, the last observers to view the planet saw a large, thin and rippling crescent, just a few percent illuminated.
Mercury (mag .-0.2) was 7°.2 North-east of Venus on October 18th, 9°.6 ENE of it on the 19th and 11°.1 ENE of it on the 20th. Jupiter (mag. -1.6) was now 30° East of the Sun and 20° East of Venus. At around 13 hours UT on the 20th, Mercury was positioned between the two bright planets, forming an isoscelene triangle, with long side 20° and short sides of 10°.5.
Venus' elongation reduced to just 10° East of the Sun on October 21st, with Mercury now 12°.8 to its East, by which time Venus had disappeared from view from Southern Tropical latitudes.
By the fnal week of October Venus had sunk into the twilight glare and had become lost from view from all locations, bringing the 2018 apparition to a formal end. The planet reached inferior conjunction (passing between the Earth and the Sun) in South-eastern Virgo on October 26th, when it was positioned 6º.3 South of the Sun's centre (ecliptic latitude = -6º.3) and lay at a distance of 0.272 AU (40.7 million kms or 25.3 million statute miles) from Earth. The period of non-visibility was brief, however; by month's end Venus was seen rising as a 'Morning Star' in the Eastern sky shortly before the Sun, heralding a new morning apparition (2018-19) which lasts through to July 2019.
[Terms in yellow italics are explained in greater detail in an associated article describing planetary movements in the night sky.]
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Venus Conjunctions with other Planets
Four planetary conjunctions involving Venus were observable during the evening apparition of 2018, no single event of which was visible worldwide.
There were three conjunctions between Venus and Mercury during the apparition, none of them being particularly easy to view and all of them taking place in twilight. Conjunctions between these two planets typically happen two or three times a year but many of them are too close to the Sun to observe; even when they are visible they are often difficult to see because of their narrow solar elongation.
The first conjunction between the pair, on March 5th 2018, took place very early in the apparition when they were positioned just 14° from the Sun. Mercury was positioned 1°.4 North of Venus in a difficult planetary conjunction which was viewable from latitudes North of the Southern Tropics. From latitude 60° North the pair were positioned at an altitude of just 4° in the West when Mercury (the fainter planet) came into view, the event being visible for about 40 minutes before setting. At the Equator the planets were 7° high in the West and visible for about 30 minutes. At latitudes further South the altitude at which Mercury appeared, and the duration for which it was visible, progressively reduced until the pair were not seen at all South of about 25° South.
Venus and Mercury in the dusk sky, painted by Oli Froom at Beachy Head, East Sussex, England, UK in January 2015 (click on the thumbnail for a larger image, 13 KB). The full-size painting can be seen at the Astronomy Sketch of the Day website.
The second conjunction between Venus and Mercury, on March 18th 2018, took place only two weeks after the first and during the same Mercury apparition. Consequently, much like the earlier event, it was only visible from the Northern hemisphere and as far South as the Southern Tropics. The separation between the two was a relatively wide 3°.9. As Mercury came into view in the dusk twilight the pair stood about 6° above the Western horizon at latitude 60° North, 10° high at 30° North and 5° high at 15° South. Owing to the planets' slightly Northern declination the pair were visible for slightly longer at Northern latitudes than at locations further South: from 50 minutes (60° North) to 24 minutes (15° South) before setting. Uranus was unspectacularly placed 12° to the ENE of the pair and was only visible with optical aid.
The conjunction of October 14th 2018 was the widest of the four during the period (6°.8) and it was only visible from the Southern hemisphere. As Mercury came into view in the dusk sky the planets stood between 8° (Equator) and 10° (45° South) in the WSW, visible for between 36 minutes and 55 minutes before setting, respectively. It was technically the easiest of the four conjunctions of 2018 to view, with Jupiter adding further interest to the event, some 17° to the East of Venus.
Venus and Uranus were involved in a close but difficult conjunction on March 29th 2018. Only latitudes between the Equator and the mid-Northern hemisphere were able to observe it, the planetary pair being positioned between 4° and 6° above the Western horizon as Uranus came into view. Nowhere was the pairing visible for more than about 35 minutes before they set.
Uranus is a tricky object to observe whenever it is involved in conjunctions with Venus because Uranus is only just visible to the naked-eye and Venus is, of course, the brightest of the naked-eye planets. Consequently the glare caused by Venus' brilliance (mag. -3.8) made it difficult to see the much fainter Uranus (+5.9) beside it. Binocular observers in particular may find it easier to position Venus just outside the binocular field of view so that Uranus may be more comfortably seen. Twilight quickly renders Uranus unobservable (even through binoculars), so any conjunctions taking place less than about 20° from the Sun will be difficult or impossible to see; this particular one was just below that limit, at 19°.
Conjunctions between Venus and Jupiter are arguably the most spectacular to view, though none took place during this particular apparition.
The four planetary conjunctions with Venus which were viewable during the 2018 evening apparition are summarised in the table below.
Venus conjunctions with other planets during the 2018 evening apparition (click on the thumbnail for the full-size table, 35 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 Venus, e.g. on 2018 Mar 18, Mercury was positioned 3°.9 North of Venus at the time shown. The 'Fav. Hem' column shows the Hemisphere in which the conjunction was best observed (Northern, Southern and/or Equatorial). The expression 'Not high N Lats' indicates that observers at latitudes further North than about 45°N would most likely have found the conjunction difficult or impossible to observe because of low altitude and/or bright twilight.
In the 'When Visible' column, a distinction is made between Dusk and Evening visibility; the term Dusk refers specifically to the twilight period after sunset, whilst the term Evening refers to the period after darkness falls (some conjunctions take place in darkness, others do not, depending upon latitude). The 'Con' column shows the constellation in which the planets were positioned at the time of the conjunction.
To find the direction in which the conjunctions were seen on any of the dates in the table, note down the constellation in which the planets were located ('Con' column) on the required date and find the constellation's setting direction for your particular latitude in the Rise-Set direction table.
The table is modified from another showing Venus conjunctions with other planets from 2015 to 2020 on the Venus Conjunctions page.
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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Moon near Venus Dates,
February to October 2018
The Moon is easy to find, and on one or two days in each month, it passes Venus in the sky. Use the following tables to see on which dates the Moon passed near the planet between February and October 2018:
Moon near Venus dates for the evening apparition of 2018 (click on the thumbnail for the full-size table, 27 KB). The Date Range shows the range of dates worldwide (allowing for Time Zone differences across East and West hemispheres). Note that the dates, times and separations at conjunction (i.e. when the two bodies were at the same Right Ascension) are measured from the Earth's centre (geocentric) and not from the Earth's surface (times are Universal Time [UT], equivalent to GMT). The Sep. & Dir. column gives the angular distance (separation) and direction of the planet relative to the Moon, e.g. on May 17th 2018 at 18:09 UT, Venus was positioned 4°.8 North of the Moon's centre.
Because Venus never appears more than 47° from the Sun, the Moon always shows a crescent phase whenever it passes the planet in the sky: a waxing crescent during evening apparitions and a waning crescent during morning apparitions.
On December 1st, 2008 observers in Europe and North-west Africa witnessed the four-day-old Moon passing in front of Venus (in an event called a lunar occultation) around local sunset/dusk (click on the thumbnail for the full-size image, 16 KB). This photograph of the event was taken by the writer from the south-western United Kingdom. Venus had just emerged from behind the Moon after being hidden from view for about 90 minutes. Depending upon the angular size and phase of Venus at the time of any given occultation, it can take anything from several seconds to more than a minute for the planet to become completely obscured by the passing Moon, and the same time to re-appear. This is in contrast to a star, which, being a very distant point of light, disappears behind the Moon more or less instantaneously.
During the same evening, Venus, Jupiter and the crescent Moon formed an impressive celestial grouping in the sky, whose appearance varied somewhat depending upon the observers' location and the time of viewing. The grouping was nicknamed 'the smiley face' conjunction and many photos of the event were taken by the general public worldwide.
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 have appeared closer to Venus 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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Direction, Altitude & Visibility Duration
of Venus after Sunset,
March to October 2018
The following tables give the direction and altitude (angle above the horizon) of Venus at 30 minutes after sunset, together with the duration of visibility of the planet after sunset, for the 2018 evening apparition. An explanation of abbreviations in the tables is given in the box below. For the sake of convenience, the table is split into Northern and Southern hemisphere latitudes (the Equator is included in both tables to allow interpolation of the data for observers situated at Equatorial latitudes). The tables should have proved sufficient to locate the planet in twilight, allowing telescope users to have viewed the planet in comfort (because of Venus' brilliance, glare becomes a problem when the planet is seen through the eyepiece against a dark sky). Direction and Altitude diagrams are also provided below for intermediate latitudes of 55° North, 35° North, 30° South and the Equator.
The tables allow one to find the highest altitude in the sky which Venus attained for any given latitude during the 2018 evening apparition, and in which direction it was seen. For example, observers situated at latitude 40° North (a mid-Northern latitude) found the planet highest in the sky (at 30 minutes after sunset) in mid-June 2018, when it was seen at an altitude of 21° towards the West-North-west (WNW). The duration column shows that the planet was viewable for about 2½ hours after sunset.
Direction & Altitude (30 minutes after local sunset) and Visible Duration of Venus for Northern hemisphere latitudes and the Equator for the evening apparition of 2018 (click on the thumbnail for the full-size table, 105 KB). For Southern hemisphere latitudes and the Equator, click here (100 KB). To find your latitude, visit the Heavens Above website, select your country and enter the name of your nearest town or city using the 'Town Search' facility.
The table column headings are as follows:
Dir = compass direction of Venus,
Alt = angular altitude (elevation) of Venus (degrees above the horizon; a negative value of Alt means Venus was below the horizon). Altitudes are accurate to within ±1°.
Dur = the approximate visibility duration of Venus after local sunset (in hrs:mins). An italicised duration means that Venus was seen under twilight conditions through to its setting, i.e. it was not seen against a truly dark sky (twilight in this case refers to nautical twilight, which ends when the Sun is more than 12° below the horizon). A hyphen (-) indicates that Venus set in daylight. Durations are accurate to within ±5 minutes.
Note that the directions and altitudes refer to the planet's position at 30 minutes after local sunset. To find the time of local sunset at your own location, select your country/town from the drop-down menu at the Time and Date.com website. The approximate time at which Venus set can be found by adding the visibility duration on a particular date (column Dur) to the time of local sunset on the same date. To find the direction in which Venus set on any given date for a particular latitude, note down the constellation in which the planet was located on the required date (column headed Con) then find its setting direction for your latitude in the Rise-Set direction table.
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Direction & Altitude Diagrams (Horizon Diagrams)
for the 2018 Evening Apparition
The following diagrams show an observer's Western horizon (from due South to due North) for latitudes of 55° North (a high-Northern latitude), 35° North (mid-Northern), the Equator and 30° South (mid-Southern). The path of Venus is plotted in the sky at 30 minutes after local sunset throughout the 2018 evening apparition with the planet's direction and altitude marked along the horizontal and vertical axes, respectively. Essentially, these diagrams show the same information as in the above look-up tables, but in an illustrative format, for the Equator and three intermediate latitudes.
Below: Paths of Venus in the Evening Sky (30 mins after sunset) for the 2018 evening apparition, as seen by observers at latitudes 55° North, 35° North, the Equator and 30° South (click on a thumbnail for a full-size image, ca. 130 KB each). The letters GE refer to the planet's greatest elongation (followed in brackets by its angular distance from the Sun) and the letters GB refer to the planet's greatest brilliance point (followed in brackets by its apparent magnitude).
The azimuth (Az, along the bottom of each diagram) is the bearing measured clockwise from True North (where 0° = North, 90° = East, 180° = South, etc.). The altitude (Alt) is the angle measured vertically from the local horizon (the horizon itself is 0° and the point directly overhead is 90°). Azimuth and altitude are co-ordinates which are used for high-accuracy tracking of objects across the sky; in astronomy it is mainly used for setting telescopes which are fitted with altazimuth mounts.
To determine the planet's position in the sky with higher accuracy, an overlay grid is provided for each diagram. The overlay grids are marked at 10° intervals in azimuth and altitude (the dates are removed for clarity). For example, at latitude 30° South on July 1st 2018, at 30 minutes after sunset, Venus was found at azimuth = 313° (i.e. in the North-west) and altitude = 28°.
The Path of Venus in the Evening Sky (plotted for 30 mins after sunset) during 2018 for an observer at latitude 55° North. Click here (123 KB) for the overlay grid.
The Path of Venus in the Evening Sky (plotted for 30 mins after sunset) during 2018 for an observer at latitude 35° North. Click here (112 KB) for the overlay grid.
The Path of Venus in the Evening Sky (plotted for 30 mins after sunset) during 2018 for an observer at the Equator (latitude 0°). Click here (109 KB) for the overlay grid.
The Path of Venus in the Evening Sky (plotted for 30 mins after sunset) during 2018 for an observer at latitude 30° South. Click here (97 KB) for the overlay grid.
Although the dates indicated in the above diagrams refer specifically to the year 2018, Venus has an 8-year cycle of apparitions such that its position in the evening sky in 2018 will repeat very closely in the evening sky of 2026. The writer refers to this particular evening apparition as Apparition A; for more details, see the accompanying article describing The Venus 8-year Cycle.
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Copyright Martin J Powell February 2018
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