Figure 1: Jupiter appeared in the morning sky in the fall of 2016.
(There are many details in this article about Jupiter’s 2017-2018 appearance. Bookmark it to return in the future.)
Jupiter last appeared in the morning sky in the fall of 2016 (Figure 1). It appeared in front of the stars of Virgo, with a triple conjunction of Spica.
Jupiter begins a 397-day appearance on October 26, 2017, at its solar conjunction. During this appearance it has a triple conjunction with the star Zubenelgenubi, the brightest star in Libra, conjunctions with Mars and Venus, and another close approach of Venus in 2018.
While the stars of Libra are not among the brightest stellar gems, the two brightest can be found from most street-lit areas.
Zubenelgenubi (“The Southern Claw”) and Zubeneschamali (“The Northern Claw”) may have been part of Scorpius. Today some charts show the scorpion holding the scales in its claws.
In their book “Short Guide to Modern Star Names and Their Derivatives,” Paul Kunitzch and Tim Smart state, “The stars of Libra were interpreted by the Babylonians as ‘the Claws of the Scorpion’, and alternately (perhaps at a more recent stage) they were made an independent constellation,’the Balance'” (p. 43).
Zubenelgenubi and Zubeneschamali lie nearly midway between Spica and Antares. Jupiter had a triple conjunction with Spica during its last apparition. Spica is distinctly blue and Antares is reddish. Spica lies near the ecliptic with the planets and moon passing it frequently. Antares is about 5 degrees south of the ecliptic. Planets can pass a few degrees away from it and the moon can pass relatively close.
Jupiter generally moves with the westward movement of the stars. After its solar conjunction, it appears in the eastern sky morning sky. Each week it appears noticeably higher in the east; this is from the earth’s revolution around the sun. Each morning it appears higher in the sky as Earth rotates. A few months after its first appearance, it appears south near sunrise. Then it appears farther west near the horizon at sunset. It then rises the east at sunset. Again it appears higher and more westward each week from Earth’ revolution. Late in its appearance Jupiter starts the evening in the west and as the weeks pass it disappears into the sun’s brilliant glare, completing its apparition.
In addition to its annual westward march, it moves it against the background stars. Generally, the planets appear to move eastward against the starry background. On occasions they seem to stop and backup, at a later date to resume their eastward planetary movement again.
A Triple Conjunction
A triple conjunction occurs when a planet appears to pass a star or another planet three times during a single appearance. There are multiple definitions of a conjunction: The simplest is the closest separation between a planet and another celestial object. Two others are based on coordinate systems: the solar system plane (ecliptic) and the plane of the earth’s equator (equatorial). Coordinate systems have specific names for longitude and latitude. In these systems conjunctions occur when the star’s longitude is the same the planet’s changing longitude as it revolves around the sun. One could say that an airplane flying across the country is in conjunction with a city when its longitude matches the city’s longitude. For our purposes a star’s celestial coordinates are constant while the planet’s coordinates change as it revolves around the sun.
Figure 2: The celestial equator and the ecliptic.
Since the ecliptic is angled with the celestial equator by 23.5 degrees, a planet’s ecliptic longitude and equatorial longitude are not the same. For this article, the triple conjunction occurs in the ecliptic coordinate system. The charts in this article showing Jupiter’s long-term apparent motion are graphed with coordinates based on the ecliptic (Figure 2).
Jupiter begins its morning appearance on October 26, 2017 when the planet is behind the sun in solar conjunction.
Jupiter completes one solar orbit about every 11 earth years. Because Jupiter slowly lumbers through its orbital path, it does not travel far among the stars during the earth’s annual path around the sun.
Figure 3: Jupiter’s solar conjunction, October 26, 2017. The sun’s
bright glare blocks us from viewing Jupiter as the planet is
in the sky during daylight hours.
Notice that time is displayed on the chart (Figure 3). Noon is defined as the line extending from Earth to the sun and beyond. Any celestial object near that line appears in the sky with the sun and in the south when the sun is south (noon). Midnight is the opposite direction. Any star or planet appearing near the midnight line is in the sky nearly all night long, appearing in the south around midnight. (Clearly, by definition, the sun cannot appear in the sky at midnight.) Mercury and Venus, being inside our planet’s orbit are frequently near the noon line or with 47 degrees of it. They appear in either the eastern morning sky or western evening sky. The outer planets can appear anytime in the sky and they are not restricted by lying inside our planet’s orbit.
Jupiter in the Morning Sky
Figure 4: Jupiter rising in the eastern sky compared to sunrise. The Giant Planet has conjunctions with Venus and Mars.
Jupiter then begins its appearance in the morning sky, initially rising during twilight. By early November, it rises about an hour before sunrise. The chart above shows the rising times of Jupiter, the star Spica, Venus, Mercury, and the moon (circles) compared to sunrise (Figure 4). (As the moon heads towards its new phase, it rises later –closer to sunrise — each morning.) The astronomical twilight line represents the time when the sky is as dark as it every gets naturally. As the sky brightens, the ground can be discerned from the sky: Nautical twilight. So named because at sea the horizon clearly separates the water from the sky. At Civil Twilight, the sky is bright, most details of terrestrial features can be identified. Street lights normally turn off during the time between Civil Twilight and sunrise (or turn on during evening Civil Twilight).
Jupiter rises earlier each day, appearing higher in the eastern sky as sunrise approaches. On November 13, Venus and Jupiter meet for an Epoch Conjunction.
Figure 5: An Epoch Venus-Jupiter Conjunction
On this morning, brilliant Venus and bright Jupiter shine from low in the east-southeastern sky (Figure 5). The pair is only about 5 degrees above the horizon. Venus is twice as bright as Jupiter. On the morning before the conjunction, November 12, Venus is slightly less than one degree above Jupiter. Spica is nearly 13 degrees to the upper right of Venus; Mars is 23 degrees; and the moon is 55 degrees above Venus. For more about this conjunction read this article.
The challenge in seeing this conjunction is having a good eastern horizon and looking about 45 minutes before sunrise. The above chart shows the sky at 45 minutes before sunrise in the Chicago area.
The next Venus-Jupiter conjunction is during the morning of January 22, 2019. While not a close conjunction, the planets in this widely spaced conjunction are far apart visually, but easily seen as they rise about 3 hours before sunrise and appear in low in the southeastern sky as morning twilight begins.
Figure 6: Jupiter’s Retrograde loop compared the stars of Libra and Scorpius and the ecliptic.
Because Jupiter moves slowly through its orbit, our planet catches and passes the planet about every year. The chart above (Figure 6) shows Jupiter’s apparent path among the stars with its retrograde occurring between the Scorpion’s claws. Scorpius is to the lower left of Jupiter with its bright star Antares. The green line on the chart represents the ecliptic, the solar system’s plane.
Figure 7: Detail of the retrograde loop of Jupiter and its triple conjunction with Zubenelgenubi.
Looking closer at the region of the sky where Jupiter appears reveals that it does not have many bright stars. The chart (Figure 7) shows Jupiter’s apparent motion from November 30, 2017 through October 14, 2018. Dates on the chart indicate the triple conjunction dates with Zubenelgenubi and Jupiter’s opposition.
Figure 8: Jupiter in the morning sky with the Claws of the Scorpion.
The first date (November 30, 2017) on the chart (in Figure 7) shows bright Jupiter in the east-southeastern sky with Spica and Mars at 6 a.m. CST. Jupiter is approaching Zubenelgenubi for the first time with the first conjunction about three weeks away. Jupiter is about 4.5 degrees to the upper left of its target star (Figure 8).
Figure 9: Jupiter’s first conjunction with Zubenelgenubi.
By December 21, Jupiter moves eastward to about one-half degree (the apparent diameter of the moon) of the star. (This was about the same separation when Venus passed Regulus during September 2017 (Figure 9). See this article for a photo that shows the separation of Venus and Regulus.)
Figure 10: The Jupiter-Mars conjunction
Jupiter continues to rise earlier each morning. By New Year’s Day Jupiter rises nearly 4.5 hours before the sun. On January 7, Mars passes Jupiter (Figure 10). (Mars is moving faster eastward among the stars than Jupiter.) In this close conjunction, the planets are separated by only 0.3 degree! Jupiter is nearly 20 times brighter than Mars. By this morning, Jupiter is nearly 3 degrees past Zubenelgenubi.
The planetary pair is also very close on the previous morning (January 6), only slightly more distant. Either morning has the two planets close together.
Mars is at opposition on July 27, 2018. For more information about the two-year appearance of Mars, see this article. The next conjunction of Jupiter and Mars is March 20, 2020 when the pair is nearly 1 degree apart with Saturn about 7 degrees to the left of the conjunction.
Figure 11: Jupiter, Mars and the Moon, January 11, 2018
A few days after the Jupiter-Mars conjunction, the moon moves through the region and makes one of its closest passes near Jupiter during this appearance as viewed from the Western Hemisphere. The waning crescent moon is about 4 degrees from Jupiter (Figure 11).
Figure 12: Jupiter reaches its western quadrature (90 degrees from the sun) on February 10, 2018.
As Earth moves toward Jupiter, Jupiter and the nearby stars appear slightly higher each morning, noticeably higher in week. By February 10, Jupiter rises around midnight and appears in the south as dawn approaches. It is at quadrature, 90 degrees from the sun (Figure 12). The westward march of the celestial sphere continues.
Figure 13: Jupiter stops moving eastward and begins to retrograde, March 8, 2018.
On March 8, 2018, Jupiter appears to stop moving eastward and appears to move backward compared to the starry background. At this time Jupiter is 8 degrees from Zubenelgenubi and the moon is 13 degrees to the left of Jupiter (Figure 3).
Jupiter in the Evening Sky
Figure 14: Jupiter reaches opposition on May 8, 2018 and appears in the sky all night.
As the mornings pass, Earth catches up to and moves between Jupiter and the sun on May 8, 2018 (opposition). Jupiter is about 400 million miles away. Its large size and highly reflective clouds make it gleam in our night sky.
At opposition, Jupiter rises in the southeast at sunset and moves westward during the night from our planet’s rotation. By midnight it is in the south and it sets in the southwest at sunrise (Figure 14).
Figure 15: Jupiter’s second conjunction with Zubenelgenubi, June 3, 2018
After opposition, Jupiter rises before sunset and shines from the southeast as the sky darkens. By early June, Jupiter rises nearly 2.5 hours before sunset, shining from the southeast as night falls. After opposition, Jupiter continues to retrograde. By June 3, it passes Zubenelgenubi again for the second conjunction by nearly one degree (two apparent full moon diameters — Figure 15). Extend an arm and your index finger on that hand. Your finger will nearly cover both the planet and the star; that’s one degree.
Figure 16: This chart shows Jupiter setting in the western sky compared to the time of sunset.
Jupiter continues to appear farther to the west each evening at sunset, By early July it begins setting 5 hours after sunset; it is graphed on the setting chart as displayed above (Figure 16). The chart shows the stars, planets, and moon setting in the west after sunset with the three phases of twilight.
Figure 17: Jupiter stops retrograding on July 17, 2018
After Earth passes Jupiter, it stops retrograding and resumes its eastward motion against the sidereal backdrop. The chart (Figure 17) shows Jupiter in the south-southwest at around 10 p.m. on July 17. Jupiter is setting earlier each night; it is beginning a very slow fade into the western sky that lasts until November. Jupiter and Zubenelgenubi are now about 2 degrees apart.
Figure 18: Jupiter appears at its eastern quadrature in the evening sky on August 6, 2018
By August, Jupiter rises during the day and is in the south at sunset. On August 6, Jupiter and the sun are 90 degrees apart in the sky (Figure 18). And this Giant Planet sets about 3.5 hours after sunset.
Figure 19: Jupiter passes Zubenelgenubi for the third conjunction during the planet’s apparition, August 16, 2018.
The third conjunction with Zubenelgenubi occurs on August 16 when Jupiter passes about 0.5 degree above the star (Figure 19). The triple conjunction is now complete in one Jupiter apparition.
Figure 20: Venus and Jupiter appear in the western sky, but there is no conjunction.
This chart shows them 16 degrees apart.
By late summer Jupiter appears near brilliant Venus which is completing its 2018 evening apparition. On the setting chart above (Figure 16), Venus sets about 2 hours after sunset — at the end of twilight on July 7 — while Jupiter sets over 3 hours later. As the weeks progress, Jupiter sets earlier and Venus continues to set around 2 hours after sunset. A conjunction looks imminent, but Venus then quickly dips into the sun’s blinding glare. The chart above shows Jupiter and Venus on September 15 when Venus sets about an hour after sunset (Figure 20). The pair is 16 degrees apart. They get as close as about 14 degrees, but Venus is setting during bright twilight.
Figure 21: Jupiter fades quickly into the western horizon. This is the last date
charted on the retrograde charts earlier in this article.
The retrograde charts (Figure 6 and Figure 7) show the last plotted date as October 14. On this day Jupiter sets about 90 minutes after the sun. At the chart time above, Zubenelgenubi and Zubenelgenubi are low in the western sky. (Likely Zubenelgenubi is visible only through binoculars and telescopes when viewed with a clear horizon). Jupiter is about 9.5 degrees past its point of triple conjunction and nearly 16 degrees west of Antares (Figure 21).
Jupiter is on course for a 2020 conjunction with Saturn. On this chart (Figure 21) these planets are 38 degrees apart. Conjunctions between these two planets are infrequent. After 2020, the next conjunction is November, 2040. The last one was May 2000.
Jupiter revolves around the sun every 11.8 earth years; Saturn revolves every 29.5 years. Because each move slowly around the sun, it takes Jupiter about 20 years to catch Saturn. (In 1981 there was a triple conjunction of the two planets!)
Figure 22: Jupiter reaches its solar conjunction on November 26, 2018.
Jupiter slowly disappears into bright sunlight and heads for conjunction on November 26, 2018 (Figure 22), completing its 2017-2018 appearance and triple conjunction between the Claws of the Scorpion.
Watch Jupiter slow creep eastward and catch a slower moving Saturn during the next few years.
Appearances with the Moon
Jupiter appears with the Moon on these dates (Central Time):
- November 16, 2017 — 6 degrees (d)
- December 14, 2017 — 4d
- January 11, 2018 — 4d
- February 8, 2018 — 6d
- March 7, 2018 — 3.5d
- April 3, 2018 — 6d
- April 29, 2018 — 5.5d
- May 27, 2018 — 6d
- June 23, 2018 — 4d
- July 20, 2018 — 3.5d
- August 18, 2018 — 7.5d
- September 13, 2018 — 4d
- October 11, 2018 — 3d
- November 8, 2018 — 3d (during bright twilight
Jupiter, a gleaming celestial gem, can be seen shining among the dimmer stars of Libra, nearly midway between Spica and Antares. During this appearance it has a triple conjunction with Libra’s brightest star Zubenelgenubi, Venus and Mars. During 2018 Jupiter and Venus have a far encounter when they are about 14 degrees apart. Take a look at the movement of Jupiter compared to the starry background and as it starts in the eastern morning sky and then disappears into the sun’s glare in late 2018. Watch the distance between Jupiter and Saturn close during the next few years for their infrequent celestial conjunction.