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Jupiter Opposition Data, 2015-2018

Jupiter Moon positions (Flash plug-in)

Jupiter Conjunctions with other Planets, 2014-20

Jupiter Transit Altitudes, 2015-2018

Jupiter Passage of Bright Stars, Aug 2014 - Oct 2018

Moon near Jupiter Dates, 2018

Jupiter Through the Telescope

The Position of Jupiter, 2009-2011

The Position of Jupiter, 2011-2014

 The Position of Jupiter in the Night Sky:

2014 to 2018

 by Martin J. Powell


Where is Jupiter now? This star map shows the path of Jupiter through Cancer, Leo, Virgo and Libra from September 2014 to November 2018. Click for full-size version, 162 KB (Copyright Martin J Powell, 2014)

The Path of Jupiter against the background stars of Cancer, Leo, Virgo and Libra from September 2014 to November 2018, with positions marked on the 1st of each month (click on the thumbnail for full-size image, 162 KB). Periods when the planet is unobservable (i.e. when it is too close to the Sun, or passes behind it) are indicated by a dashed line; hence the planet becomes lost from view (in the evening sky) in early August 2015 and becomes visible again (in the morning sky) in mid-September 2015.

The chart shows the changing shape of a planet's apparent looping formation as it moves through the zodiac. Having crossed the ecliptic (the apparent path of the Sun, Moon and planets) in a Northward direction in late 2013, Jupiter describes a hybrid loop (half loop, half zig-zag) on the Cancer-Leo  border in 2014-15, followed by three Northward-facing loops as it heads Southward through Leo, Virgo and Libra over the next three years. The star map applies to observers in the Northern hemisphere (i.e. North is up); for the Southern hemisphere view, click here (166 KB).

The faintest stars on the map have an apparent magnitude of about +4.8. Printer-friendly versions of this chart are available for Northern (76 KB) and Southern hemisphere (78 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 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. Night sky photographs of the region can be seen below; descriptions of the deep-sky objects  in Cancer, Leo and Virgo which are marked on the chart can be found here.

Having spent the 2013-14 observing period among the stars of the zodiac's most Northerly constellation of Gemini, the Twins, Jupiter re-appears in the dawn sky in August 2014 in the neighbouring constellation of Cancer, the Crab, positioned not far from the celebrated star cluster named Praesepe or The Beehive (Messier 44 or NGC 2632).

Jupiter imaged by Efrain Morales Rivera in February of 2014. Click for a larger version, 6 KB (Image: Efrain Morales Rivera)Jupiter imaged by Puerto Rican amateur astronomer Efrain Morales Rivera on February 27th 2014 using an 8-inch Ritchey-Chrétien telescope fitted with a CCD camera (click on the thumbnail for a larger image, 6 KB) (Image: Jaicoa Observatory)

Jupiter describes its 2014-15 'hybrid' loop on the Cancer-Leo border, the planet crossing into Leo, the Lion, in mid-October 2014 and attaining its Eastern stationary point in December of that year. The planet retrogrades (moves East to West) back into Cancer in early February 2015 and just 2 days later reaches opposition some 17' (17 arcminutes or 0°.3, where 1 arcminute = 1/60th of a degree) from Cancer's Eastern border. Western stationary point is reached in April 2015, after which the planet resumes direct motion (West to East) and re-enters Leo two months later. Jupiter heads out of view in the evening twilight in early August 2015, the planet passing just to the North of Leo's brightest star Regulus (Greek lower-case letter 'alpha' Leonis, apparent magnitude +1.3) soon afterwards.

Jupiter re-appears in the dawn sky in mid-September 2015, positioned in central Southern Leo, marking the start of the planet's 2015-16 apparition. The planet reaches its January 2016 Eastern stationary point just inside Leo's Eastern border, then retrogrades towards a March opposition positioned just 40' (0°.7) West of the star Sigma Leonis (Greek lower-case letter 'sigma' Leo, mag. +4.0), the rear paw of the Lion. Western stationary point is reached in May 2016, after which the planet resumes direct motion, entering Virgo, the Virgin, in early August. Jupiter becomes lost in the evening twilight during early September, crossing the celestial equator - where the declination is 0° (Greek lower-case letter 'delta' = 0°) - in mid-September. Six days later, the planet passes through its 2016 superior conjunction, when it is positioned directly behind the Sun as seen from the Earth.

Jupiter emerges in the dawn Eastern sky in mid-October 2016, heralding the 2016-17 apparition which sees the planet occupying central Virgo throughout. In early 2017 the planet is positioned around 4° North of the constellation's brightest star Spica (Greek lower-case letter 'alpha' Vir or Alpha Virginis, mag. +1.0) and moving in a South-easterly direction against the background stars. Eastern stationary point is reached in early February, after which the planet turns retrograde and heads North-westwards, passing North of Spica a second time around mid-month. Opposition takes place in early April, positioned just 16' (0°.3) West of the double star Theta Virginis (Greek lower-case letter 'theta' Vir, mag. +4.4). After reaching Western stationary point in June the planet resumes direct motion, heading South-easterly again and passing North of Spica for a third and final time in early September. The 2016-17 apparition ends in early October, as Jupiter sinks into the Western sky at dusk.

Jupiter in central Gemini in January 2014. Click for full-size image, 56 KB (Copyright Martin J Powell, 2014)

Jupiter in Gemini, the Twins photographed by the writer two days before the planet's opposition in January 2014 (click on the thumbnail for the full-size photo, 56 KB). An annotated version of the photo can be seen here (26 KB). Jupiter was positioned in Gemini for a little over a year between 2013 and 2014, reaching its highest point in the zodiac in March 2014. Throughout the period the planet formed a variety of triangle shapes with the constellation's two brightest stars Castor and Pollux.

As 2017 draws to a close, Jupiter re-emerges in the dawn sky and the 2017-18 apparition commences, the planet having just entered the constellation of Libra, the Balance. The entire apparition takes place within the confines of this unremarkable constellation, the planet's Northward-facing loop being described to the North and East of its second-brightest star Zuben Elgenubi (Greek lower-case letter 'alpha' Lib or Alpha Librae, mag. +2.7). In mid-December 2017 Jupiter is a morning object and passes less than a degree North of the star. At the start of 2018 the planet is positioned around 2° East of it, continuing South-eastwards to reach its Eastern stationary point in March. The planet turns retrograde and heads North-westwards, reaching opposition in early May, some 3° East of Zuben Elgenubi. The planet passes North of the star again in early June then reaches its Western stationary point in mid-July. Having resumed direct motion Jupiter proceeds South-eastwards and passes North of Zuben Elgenubi one more time in mid-August. The 2017-18 apparition closes as Jupiter disappears into the evening twilight in early November 2018. Soon afterwards, the King of the Planets leaves Libra and heads into the Southernmost constellations of the zodiac.

[Terms in yellow italics are explained in greater detail in an associated article describing planetary movements in the night sky.]

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Jupiter Opposition Data, 2015 to 2018

Jupiter reaches opposition to the Sun (when it is closest to the Earth and brightest in the sky for any given apparition) every 398.9 days on average, i.e. about 33½ days later in each successive year. For the period covered by the above star map, oppositions take place on February 6th 2015, March 8th 2016, April 7th 2017 and May 9th 2018. Around opposition, the planet is due South at local midnight in the Northern hemisphere (due North at local midnight in the Southern hemisphere).

The apparent magnitude of the planet at opposition during the period of the star chart is -2.4 (in 2015) and -2.3 (in 2016, 2017 and 2018). Jupiter's apparent size (i.e. its angular width as seen from the Earth, measured in arcseconds, where 1 arcsecond = 1/3600 of a degree) at opposition is 45".3 (in 2015) reducing to 44".4 (in 2016), 44".2 (in 2017) and then increasing to 44".8 (in 2018).

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Because of Jupiter's rapid rotation speed, its disk appears as an oblate spheroid through telescopes and high-magnification binoculars (i.e. it appears flattened at the poles and bulged at the equator). The dimension given above is the apparent equatorial diameter of the planet; its apparent polar diameter is about 6.3% less.

Superior conjunction (when Jupiter passes behind the Sun as seen from the Earth) takes place on August 26th 2015, September 26th 2016, October 26th 2017 and November 26th 2018. The planet is not visible from Earth for about two weeks on either side of these dates. At superior conjunction the magnitude fades by one whole magnitude to -1.5 (in 2015, 2016 and 2017) brightening slightly to -1.6 (in 2018) and the planet's apparent diameter is 30".8 (in 2015), 30".5 (in 2016), 30".6 (in 2017) and 31".1 (in 2018).

Data relating to Jupiter's oppositions from 2015 to 2018 are provided in the table below.

Jupiter opposition data for the period 2015 to 2018. Click for full-size image, 41 KB (Copyright Martin J Powell, 2014)

Jupiter opposition data for the period 2015 to 2018 (click on thumbnail for full-size image, 41 KB). The Declination is the angle of the planet to the North (+) or South (-) of the celestial equator; on the star chart, it represents the planet's angular distance above or below the blue line. The angular diameter (or apparent size) of the planet as seen from Earth is given in arcseconds (where 1 arcsecond = 1/3600th of a degree). The Polar Diameter is 6.3% less than the Equatorial Diameter because Jupiter is an oblate spheroid.

Jupiter's opposition distance from Earth slowly increases through to 2017, so that its angular diameter at opposition shrinks slightly year by year. This is reflected in the planet's apparent magnitude (brightness) which fades slightly over the same period. The planet passed through aphelion - its most distant orbital point from the Sun - in February 2017. From 2018, Jupiter's opposition distance from Earth begins to reduce once more. The Tilt (the inclination of Jupiter's rotational axis relative to the Earth's orbital plane) is positive (+) when Jupiter's Northern hemisphere is tipped towards the Earth and negative (-) when its Southern hemisphere is tipped towards the Earth; the maximum value it can attain is ±3°.4.

The Tilt values were obtained from NASA's Jupiter Ephemeris Generator 2.5. All other data was obtained from 'Redshift' and 'SkyGazer Ephemeris' software. The Jupiter images were obtained from NASA's Solar System Simulator. 

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Jupiter Conjunctions with other Planets,

August 2014 to December 2020

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.

Conjunctions between Jupiter and Venus are perhaps the most spectacular of all to view and the most photogenic. Between August 2014 and December 2020 there are eight occasions when these two planets can be seen together. Three of the eight take place when Venus is more than 40° from the Sun. The conjunction of October 26th 2015 is particularly good for Northern hemisphere observers, that of July 1st 2015 is particularly good for Southern hemisphere observers, whilst the conjunction of January 22nd 2019 is good for both hemispheres. The October 26th 2015 conjunction takes place on the very same day as Venus' greatest Western elongation, whilst that of January 22nd 2019 takes place only two weeks after its greatest Western elongation.

Three conjunctions of Jupiter with Mars take place during the period in question, all of them morning events. For Northern hemisphere observers the conjunction of October 17th 2015 is the best, with Venus joining in the spectacle several degrees away. For Southern hemisphere observers the March 20th 2020 conjunction is best, the two planets being positioned almost 70° away from the Sun in the constellation of Sagittarius. This is also the brightest conjunction of the three, with Saturn being positioned not far away. The Jupiter-Mars conjunction of January 7th 2018 is favourable for both hemispheres, the separation between the two planets (12 arcminutes or 0°.2) being the closest of the three.

Jupiter in central Taurus in November 2012. Click for full-size image, 339 KB (Copyright Martin J Powell, 2012)Jupiter reached opposition to the Sun in central Taurus in late 2012 (click on thumbnail for full-size photo, 339 KB). The picture shows the planet in the Western sky before dawn, when it began to sink into the suburban skyglow. Orion is seen at the left of the picture and Auriga is at the upper right. An annotated version of the photo can be seen here (180 KB).

The rarest of the conjunctions during the period is that between the giant planets Jupiter and Saturn in December 2020. Known historically as Great Conjunctions, Jupiter-Saturn conjunctions take place about every twenty years, the last one having been in May 2000. However, they are not always best placed for viewing, sometimes taking place at narrow solar elongations. The most spectacular conjunctions between these two planets occur when they are both within days of opposition, at which time they are particularly bright and visible throughout the night. Such events are very rare however, taking place about every 139 years or so (the next will be in the year 2238). Perhaps the best-known conjunction between Jupiter and Saturn was that in the year 7 BC, in the constellation of Pisces, the Fishes. In the early seventeenth century the German astronomer Johannes Kepler (1571-1630) suggested that this event might have been the origin of the Star of Bethlehem, referred to in St Matthew's Gospel of the Bible. Specifically, this was a triple conjunction - a series of three conjunctions which took place between May and December of that year - which, it is argued, was such an unusual chain of events that the Magi (the 'wise men' or astrologers) gave it a special significance. Critics of this theory say, among other things, that the two planets were too far apart to attract any particular attention, their angular separation at best having been about 1° (about two apparent Full Moon diameters).

The 'Great Conjunction' of December 2020 takes place on the day of Earth's winter solstice, the planets being only 30° away from the Sun in the evening sky. Whilst not ideally placed for viewing and being well past their opposition dates, Jupiter and Saturn are separated by only 6 arcminutes (0°.1), making them excellent photographic targets through the eyepiece of a telescope. After 2020, they will next meet in November 2040 in the constellation of Virgo, the Virgin.

The following table lists the conjunctions involving Jupiter which take place at solar elongations of greater than 15°. In several cases, other planets and/or stars are also in the vicinity and these are detailed. Note that, because some of the conjunctions occur in twilight, the planets involved may not appear as bright as their listed magnitude suggests.

Table listing Jupiter conjunctions with other planets from August 2014 to December 2020. Click for full-size image, 66 KB (Copyright Martin J Powell, 2014)

Jupiter conjunctions with other planets from August 2014 to December 2020 (click on thumbnail for full-size table, 66 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 Jupiter, e.g. on 2016 Aug 27, Venus is positioned 0°.1 North of Jupiter at the time shown. The 'Fav. Hem' column shows the Hemisphere in which the conjunction will be best observed (Northern, Southern and/or Equatorial). The expression 'Not high N Lats' indicates that observers at latitudes further North than about 45°N will find 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 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 will be 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.

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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Constellations of the Zodiac: Photographs

Photograph showing the constellation of Libra, the Balance and the Northern region of Scorpius, the Scorpion. Click for a full-size photo, 57 KB (Copyright Martin J Powell, 2006)___Photograph showing the constellations of Leo, Virgo and Coma Berenices. Click for full-size version, 282 KB (Copyright Martin J Powell, 2011)___Photograph showing the constellation of Cancer and the Northern region of Hydra. Click for full-size version, 187 KB (Copyright Martin J Powell, 2005)

Libra & Northern Scorpius

Leo, Virgo & Coma Berenices

Cancer & Northern Hydra

Chart showing the areas of the 2014-18 star chart which are covered by the photographs. Dashed lines indicate that the photograph extends beyond the boundary of the star chart. Click for full-size image, 53 KB (Copyright Martin J Powell, 2014)

Cancer, Leo, Virgo and Libra  Photographs showing the region of the night sky through which Jupiter passes from mid-2014 to late 2018 (click on thumbnails for full-size versions: 57 KB, 282 KB and 187 KB). The regions of the star chart which are visible in the photographs can be seen by clicking on the thumbnail at left (53 KB). Labelled versions of the photographs can be seen for the Cancer photo (39 KB), the Leo and Virgo photo (62 KB) and the Libra photo (12 KB). For the Cancer photo, stars are visible down to about +8.2; for the Leo and Virgo photo, the limiting magnitude is about +7.0 and for the Libra photo it is also about +7.0. Note that the photographs do not have the same scale because of the varying camera lens settings and image resolutions.

As it slowly moves along the 'celestial highway' known as the ecliptic (the apparent path along which the Sun, Moon and planets move through zodiac) Jupiter passes numerous bright stars; these are listed below, in chronological order:






Deep-Sky Objects

Details of other interesting objects in the region (star clusters, variable stars, nebulae, galaxies, etc) can be found on the Zodiacal Sky: Cancer-Leo-Virgo page.

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Jupiter Transit Altitudes, 2015 to 2018

Jupiter is the largest of the Solar System planets and it can show considerable detail even through modest-sized telescopes. A major factor determining the likelihood of seeing a clear telescopic image is the altitude (angle above the horizon) of a planet at the time of observation. 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.

Jupiter's meridian transit altitude (as seen from any given point on Earth) varies from one year to the next in the course of its 11.8-year journey through the zodiac constellations. Its most Northerly point is attained in Gemini (around 23½° North of the celestial equator) then - some six years later - its most Southerly point is attained in Sagittarius (around 23½° South of the celestial equator). In the intervening years, the planet lies somewhere between these two extremes.

The meridian transit altitude at which an observer sees a planet depends not only upon the constellation in which the planet is positioned at the time, but also upon the observer's latitude. As a result, certain apparitions are more favourable to observers in one hemisphere than to observers in the opposite hemisphere.

In the 2012-14 period, observers at mid-Northern latitudes saw Jupiter at its highest meridian transit altitude for some twelve years, as the planet traversed the Northernmost constellations of the zodiac. From 2015 to 2018, observers here will see Jupiter's transit altitude reduce significantly year by year as the planet heads Southward through Leo, Virgo and Libra, the planet crossing the celestial equator in September 2016.

For Southern hemisphere observers, the 2012-14 period saw Jupiter at relatively low altitudes when it reached meridian transit (due North in the Southern hemisphere) providing less-than-optimal viewing conditions for telescopic observers. From 2015, viewing circumstances from these latitudes will improve year-on-year until the planet reaches its most Southerly declination in Sagittarius in 2020.

Table listing transit altitudes of Jupiter from various latitudes from 2015 to 2018. Click for full-size image, 30 KB (Copyright Martin J Powell, 2014)

Transit altitudes of Jupiter at successive oppositions from 2015 to 2018, as seen from a variety of latitudes (click on thumbnail for full-size table, 30 KB). The Declination (Dec.) is the angle of the planet to the North (+) or South (-) of the celestial equator at the time of the planet's opposition. The Altitude Range is the approximate altitude variation over the course of the apparition, e.g. for the 2015/16 apparition at latitude 40° North, the transit altitude of Jupiter ranges from (55°.9 - 4°.1) = 51°.8 to (55°.9 + 4°.1) = 60°.0. The table demonstrates that, from 2015 through to 2018, Jovian transit altitudes improve for Southern hemisphere observers but worsen for Northern hemisphere observers.

What are the best and worst case scenarios regarding Jupiter's transiting altitude? Northern hemisphere observers witnessed their best case scenario (and Southern hemisphere observers witnessed their worst) in the 2013-14 observing season, when Jupiter was positioned at its most Northerly point in Gemini (see table on the 2011-14 page). Observers at mid-Northern latitudes then saw the planet transit at around 70° high in the sky. Mid-Southern hemisphere observers fared rather worse, the planet transiting at only 30° high (worst case scenario). The next optimal observing time for Southern hemisphere observers will be in 2020, when the planet will be transiting at altitudes of around 80° at mid-hemispheric latitudes (best case scenario). Observers at mid-Northern latitudes will then see Jupiter transiting at altitudes of less than 30° (worst case scenario).

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Moon near Jupiter Dates, 2018

The Moon is easy to find, and on one or two days in each month, it passes Jupiter in the sky. Use the following table to see on which dates the Moon is in the vicinity of the planet:

Moon near Jupiter dates for 2018 (click for full-size image, 37 KB)Moon near Jupiter dates for 2018 (click on thumbnail for full-size table, 37 KB). No dates are shown for December because Jupiter is too close to the Sun to view during this month. 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 are 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 27th at 17:39 UT, Jupiter is 3°.9 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).

Moon near Jupiter dates can also be viewed for 2014, 2015, 2016 and 2017.

Jupiter, Venus and the waxing crescent Moon formed an impressive grouping in the evening sky from Cairo, Egypt on December 1st, 2008. This is the author's simulation of how the event appeared. Click for full-size image, 15 KB (Copyright Martin J Powell, Sep 2007)On December 1st, 2008, Jupiter, Venus and the four-day-old Moon formed an impressive celestial grouping in the evening sky (click thumbnail for full-size image, 15 KB). This is the writer's simulation of how the event appeared to residents of Cairo, Egypt, at the end of evening twilight (around 1810 Local Time), when the group was situated low down in the South-western sky. Venus (at left of picture) was an 'Evening Star' at magnitude -4.0 and Jupiter was at magnitude -1.8 (closing in on the Sun, heading towards superior conjunction) at the time of the event. On the same day, observers in Europe and North-west Africa saw the Moon pass in front of Venus - in an event called a lunar occultation - around local sunset/dusk. The next lunar occultation involving Jupiter will take place in late 2019.

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 Jupiter when seen from some locations than from others. For this reason, the dates shown in the table should be used only for general guidance.

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Position of Jupiter's Four Brightest Moons


Jupiter's four brightest moons (satellites) - namely Ganymede (magnitude +4.6 at opposition), Io (+5.0), Europa (+5.3) and Callisto (+5.6) - can readily be seen through telescopes or steadily-held binoculars. The moons are seen to change their position in relation to each other, along the planet's equatorial plane, from one night to the next. In fact, their motion can be detected in the space of just a few hours.

Because of their low magnification, binoculars may have some difficulty detecting Io since it is the closest of the four moons to the planet; it never lies more than three Jupiter-diameters away. Europa is easier, but Ganymede is the easiest of the four to see. Callisto moves furthest away from the planet but it is also the faintest of the four.

Due to Jupiter's shallow axial tilt (3º.1 to the plane of its orbit), the Jovian moons appear to present a more-or-less linear motion when seen from the Earth (this is in contrast to, say, Saturn with its relatively high axial tilt [26º.7]), which causes its moons to mostly follow apparent elliptical paths around the planet when viewed from the Earth - see Saturn's moon positions). Approximately every six years, when the Earth passes through Jupiter's equatorial plane, the Jovian moons are seen to become involved in mutual occultations (where the moons pass in front of each other) and mutual eclipses (where a moon's shadow falls upon another moon). Numerous mutual events took place in the latter half of 2014 and continued into the first half of 2015.

The following Flash program shows the current position of Jupiter's four brightest moons (based on your computer's clock and Time Zone settings):

The Positions of Jupiter's four brightest satellites in relation to the planet (click to access Flash program, width 655 pixels, 108 KB)

The Positions of Jupiter's four brightest satellites in relation to the planet (click on thumbnail to access Flash program, width 655 pixels, 108 KB; the graphic requires the Adobe Flash Player plug-in to display correctly). Binocular and terrestrial telescope users in the Northern hemisphere should use the default 'Erect Image' (North up, East to the left) setting; Southern hemisphere observers using this equipment will need to click on the 'Inverted' (North down, West to the left) button.

Users of astronomical telescopes in the Northern hemisphere will need to use the 'Inverted' option to match the view in their telescope, whilst those in the Southern hemisphere should use the default ('Erect Image') setting. The 'Mirror Reversed' button applies to astronomical telescopes with a star diagonal attached.

Enter the required values for Date (in the form mm/dd/yyyy) and Time and click on 'Recalculate' to see the position of the moons for any date and time between January 1st 1900 AD and December 31, 2100 AD. The Timezone offset from UT is determined by the settings in your web browser.

Other details shown are the planet's apparent magnitude, its angular size (in arcseconds), its distance from the Sun (in Astronomical Units) and the planet's System II Longitude (the Jovian longitude of the central meridian, i.e. the imaginary line through the centre of the planet's disk from pole to pole). Since Jupiter's outer layers are gaseous, the planet does not rotate as a solid body; in fact the equatorial region (known as System I ) makes one rotation in 9h 50m 30s whilst the rest of the planet (System II) rotates once in 9h 55m 40s. The Great Red Spot is located in System II, at a latitude of about 22° South.

Pressing the 'Display' button generates a list of Jovian satellite phenomena for the selected date - namely transits (when a moon or its shadow passes across the planet's disk), occultations (when a moon passes behind the planet's disk) and eclipses (when a moon enters Jupiter's shadow). All of these events can be observed in telescopes.

The next three transit times of the Great Red Spot (GRS) - i.e. when it crosses the planet's central meridian - are also listed, the GRS itself being displayed on the graphic. Note that the accuracy of these times is dependant upon the Jovian longitude of the GRS, which slowly drifts over time. By default, the program uses a longitude of 98°, however this is now incorrect and the value must be updated in order to provide accurate transit times. As of late 2017, the longitude of the GRS was approximately 282°, so this value should be entered in the 'GRS Longitude' box and the timings recalculated by pressing the 'Display' button. The current longitude of the GRS can be determined from the graph displayed at the JUPOS website.

Times of all events in the program are given in Universal Time (UT) which is equivalent to Greenwich Mean Time (GMT).

The 'Jupiter's Moons' program by John Bartucci is available as a standalone, executable (exe) file which can be downloaded from the The Wilderness Center Astronomy Club website.

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The Position of Jupiter, 2014-18 (Full Desktop Site)

The Naked-Eye Planets in the Night Sky

Planetary Movements through the Zodiac










Copyright  Martin J Powell  July 2014

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