Category: Feature

2020, August 15: Moon, Venus Pair, Artistic Sight in Morning Sky

(In the image above, 2020, July 17: The crescent moon, Brilliant Venus, and Aldebaran shine from the eastern during early morning twilight.)

Venus and the moon make a spectacular scene before sunrise on August 15.  Artists and photographers can create inspiring interpretations of the view.

by Jeffrey L. Hunt

Venus sparkles in the eastern sky before sunrise during the summer and autumn months.  During the moon’s monthly journey, it moves past this brilliant planet.  During August, the moon makes a close pass with Venus, creating the inspiring scene.  From North America, the thin lunar crescent, that is about 15% illuminated, is 3.6° to the upper left of the brilliant planet.

Venus and Moon, August 15, 2020
August 15: The crescent moon is 3.5° to the upper left of Venus.

At mid-northern latitudes on August 15, Venus rises over three hours before sunrise.  By an hour later, the Venus – Moon pair is over 15° in altitude in the eastern sky.  Early risers may have to find a spot away from trees, houses, and other obstructions to see Venus and the moon in the eastern sky.

As the morning progresses and the sky brightens, Venus and the moon rise higher in the sky.

Crescent Moon, Venus, Aldebaran, July 17, 2020
2020, July 17: The crescent moon, Venus, and Aldebaran in the eastern sky before sunrise.

Each stage of morning twilight presents spectacular views of the celestial pair shining in the eastern sky and varying opportunities to capture the view with a camera.

The pair can be photographed with cameras that have time exposure settings.  Exposures can range from fractions of a second through a few seconds.  By varying the exposure times, a suitable image can be captured.

The longer the exposure, the more the moon’s nighttime side appears in the photo.  This gentle illumination known as “Earthshine,” is from sunlight reflected from Earth’s clouds, continents, and oceans.  It softly illuminates the night portion of the moon.

The waning crescent moon, July 14, 2020.
2020, July 14: The moon is in the eastern sky. It is 23.4 days past its New phase and 37% illuminated. It is a thick waning crescent phase.

At some lunar phases the sunlight reflected from the moon illuminates Earth’s terrestrial features.  This is bright enough to create shadows on the ground.

The moon and Venus may be visible after sunrise and well into the morning.

Coincidentally, the Venus – Moon grouping occurs at the same time that Sirius is making its first appearance in the morning sky before sunrise.  About 45 minutes before sunrise, Sirius is above the horizon in the east-southeast.

On September 14, the moon passes Venus again, but the moon is farther away and the pair is lower in the sky.

The August 15 grouping of Venus and the crescent moon is the best grouping during Venus’ current appearance in the morning sky, because the two are visible together for over 3 hours before sunrise.

For more about the sky in August, click here.

(Photos and charts by the author.)

 

 Feature Articles:

2020, August 15-16: Helical Rising of Sirius

The first appearance of Sirius low in the east-southeast during mid-August 2020.

2020, August 15-16: The helical rising of Sirius is the star’s first appearance in the morning sky before sunrise.

The helical rising (annual first appearance) of Sirius in the morning sky is a spectacular sight.  During 2020, this occurs in mid-August.

(Reported sighting of Sirius from 33.8° north latitude with a binocular, August 6, 2020.)

(Author saw Sirius, with a binocular through a broken  cloud deck, 29 minutes before sunrise on August 12, 2020. To see it without optical assistance in a few mornings, see the description below.) 

by Jeffrey L. Hunt

The spectacular appearance of a bright star in the morning before sunrise is an impressive sight. While very low in the sky, the star twinkles against the brightening hues of morning twilight.

The first morning appearance of a star in the eastern sky before sunrise is known as the “heliacal rising” of the star.

The first morning appearance of Sirius attracts attention. The brightest star in the sky, it can be found near the horizon before we see other bright stars.

In the lore of earlier generations, the heliacal rising of Sirius was thought to cause “dog days.” It’s coincidental that the “Dog Star” first appears in the morning sky during the hot days of the year.

Observing the first morning appearance of a bright star is a challenging feat. This requires a perfectly clear sky to the horizon and a vantage point to see the natural horizon, free from trees, buildings, houses, and other obstructions.

A Sky and Telescope magazine article described the circumstances of the date of the heliacal rising of Sirius. The author described that when the sun is about 8° below the horizon and Sirius is 3° in altitude in the east-southeast sky, the star should be first visible. For this writer’s latitude (41.7° North), no single date meets the criteria. The best pair of days is August 15, 2020, and the following morning. On the former morning, Sirius is slightly lower than 3° and on the morning of the latter it is slightly higher than the visible limit.

The chart above shows the sky 42 minutes before sunrise on August 16, 2020. Bright Venus and the crescent moon are high in the east.

Betelgeuse, Procyon, and Sirius – while they are part of their own constellations – make a large equilateral triangle, known as the Winter Triangle. The trio is prominent in the evening sky during the colder months in the Northern Hemisphere.

Procyon is sometimes translated as “before the dog.” It rises about 25 minutes before Sirius, so it rises before the Dog Star.

For beginners, start looking in the morning sky about August 12. Locate Betelgeuse and Procyon. A binocular may help you initially find the stars. Venus is nearly above Procyon, although the planet is much higher in the sky. On the diagram, Procyon is only 8° in altitude; that’s about one-tenth of the way up in the sky from the horizon to overhead (zenith). Betelgeuse is higher, about one-third of the way up in the sky, at about the same altitude as brilliant Venus. Once you see the two stars, you can visualize the scale of this large celestial triangle.

After you recognize Procyon and Betelgeuse, look each clear morning to continue to find the visible pair. Then scale the other two sides of the Winter Triangle, Betelgeuse – Sirius and Procyon – Sirius, and attempt to look for the nighttime’s brightest star very low in the east-southeast sky.

For observers north or south of this writer’s location, shift the helical rising date one or two days earlier for the southern United States and similar latitudes. Add one to two days for locations farther north.

When do you first see Sirius? Respond in the comments section of this article.

Read the Venus as a Morning Star, 2020-2021 article.

Recent Articles

2020-2021: Brilliant Planet Venus as a Morning Star

Venus in Orion, August 12, 2020
2020, August 12: Venus is 2.7° to the lower right of Eta Geminorum (η Gem) and 2.5° to the lower right of Mu Geminorum (μ Gem).

Brilliant Morning Star Venus shines brightly in the morning sky during 2020 and early 2021.

by Jeffrey L. Hunt

Click here for our semi-technical article about the apparition of Venus during 2020-2021.

Bookmark this page and check back frequently for images and updates.

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Slideshow of Venus images

Articles:

Venus makes a grand entrance into the morning sky after its inferior conjunction on June 3, 2020, at 12:44 p.m. CDT. It races into the morning sky and a week after conjunction it rises at Civil Twilight, 32 minutes before sunrise. After mid-June, Venus gleams from low in the east-northeast sky during mid-twilight. By early July, Venus is at its greatest brightness, rises before the beginning of twilight, and appears higher in the sky as sunrise approaches.

During July, Venus moves through the Hyades, with an Aldebaran conjunction on July 12. Watch the planet move through the star cluster with a binocular, during several mornings leading up to the Venus – Aldebaran conjunction.

On July 19, the lunar crescent and five planets are simultaneously spread across the sky with Jupiter low in the western sky and Mercury low in the eastern sky. Venus, Mars, and Saturn are scattered between them.

During August, Venus leaves Taurus, passes through the club and arm area of Orion and into Gemini. On August 15, see the moon join Venus.

Other highlights of the Venus apparition include a grouping with the Beehive cluster in mid-September that includes the crescent moon on September 14; two mornings in October when Venus is about 0.5° from Regulus; a widely spaced Venus – Spica conjunction during mid-November; and an extremely close conjunction with Beta Scorpii in December. Mercury makes an appearance during November, but the gaps with Venus are very wide. At the end of the apparition, Venus passes Mercury, Saturn, and Jupiter. Although they are near the sun, attempt to view the Venus – Jupiter Epoch (close) Conjunction during the day.

Venus reaches its superior conjunction on March 26, 2021, then slowly moves into the evening sky.

Recent Articles

2020, October 13: Mars at Opposition

 

Mars
The Red Planet from the Mars Global Surveyor shows the effects of a global dust storm (NASA)

Mars is at opposition, October 13, 2020.

by Jeffrey L. Hunt

Link to pdf of this article.

Mars reaches opposition on October 13, 2020, among the dim stars of southeastern Pisces. At opposition, Mars is biggest and brightest. Unlike some Internet memes, it is not as big as the moon. It shines as a bright star in the sky all night long.

Mars has captured our attention. It’s reddish appearance in the sky has cast it as a warrior in several cultures. After the inventions of larger telescopes, Mars brought the attention of many observers. Public announcements of possible civilizations there likely spurred the growth of science fiction writing and storytelling.

While Mars is close to Earth, it appears small even through a telescope. Through a telescope’s eyepiece, it appears as a red-ochre globe. A polar cap and some darker equatorial markings might be visible. At times, Mars surface cannot be seen when dust storms engulf the planet. For those with a telescope, Sky & Telescope’s Mars profiler shows what is visible on the surface on any date and time.

Mars Retrograde 2020
This chart shows the apparent motion of Mars compared to the starry background, during a 168-day interval that includes the planet’s opposition.

The Mars opposition occurs at the end of a span of 91 days, with the three Bright Outer Planets (Jupiter, Saturn, and Mars) passing their oppositions. Jupiter and Saturn are at their oppositions during a span of 6 days in July 2020.

Mars’ opposition occurs 72 days after it passes its orbital point closest to the sun (August 2, 2020), known as a planet’s perihelion, while the previous opposition occurred 49 days before perihelion (September 15, 2018). The July 27, 2018, event was called a “perihelic” opposition.

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Slideshow of images for Mars Opposition 2020

 

Mars and Earth in their orbits near the opposition of Mars 2020
This chart views the motions of Earth and Mars from north of the ecliptic during the same time interval as the retrograde chart above.

 

The accompanying charts show two perspectives of the planet’s motion from July 21, 2020, to January 5, 2021. The first chart shows the apparent motions of Mars as seen against the starry background in southeastern Pisces. The second chart shows the view of a section of Earth’s orbital path and Mars’ orbit as viewed from above the solar system.

Celestial Brightness

In the notes in this article, the “m” numbers are measures of the planets’ and stars’ brightness. The lower the number, the brighter the celestial object. The sun has the lowest value (−26.5) on this scale. Afterall it is so bright it creates daytime on our planet and shines on the moon and other planets in its system. The planets’ brightness changes as their distances from Earth vary.

Each full digit numeric change on the magnitude scale equals a change of 2.5 times (2.512x). From the beginning of the sequence to its brightest, Mars brightness increases 25 times, a dramatic, but easily observed change of brightness. As we move away from Mars in start the new year, the planet’s brightness decreases about ten times from its brightest light. So, like an excellent golf score, the lower the number the brighter the “star.”

All Planets in Morning Sky

As the sequence opens, five naked eye planets are in the morning sky, along with Uranus, Neptune, and Pluto. At about 40 minutes before sunrise, the bright planets span nearly 168° of ecliptic longitude, stretching from horizon to horizon. Mercury (m = 0.4), a day before its greatest elongation, is quite low in the east-northeast. Use a binocular and find a clear horizon. Brilliant Venus (m = −4.6) is about 20° up in the east, to the lower left of Aldebaran. Mars (m = −0.9) is over 45° up in the south-southeast. Farther westward along the ecliptic, Saturn (m = 0.1) is about 10° up in the southwest. Bright Jupiter is 6.4° to Saturn’s lower right. Because Mercury is low in the sky, start looking for Jupiter about an hour before sunrise. Work your way eastward across the sky to find Mercury with a binocular 10-20 minutes later. I’ve seen Jupiter just a few degrees above the horizon without optical assistance. It might be possible to see all of them in the sky together.

Mars at Opposition

Here’s what to look for:

  • July 21, 2020: This is the first day displayed on the charts. See the text above for a description of the menagerie of morning planets. Bright Mars (m = −0.9) is moving eastward against the starry background. As midnight approaches, the Red Planet is 5° up in the east.
  • August 2: Mars (m = −1.1) is at perihelion, 1.38 AU from the sun, its closest point to the sun in its orbit. As midnight approaches, it is 10° up in the east.
  • August 4: Mars (m = −1.2) passes 0.4° to the upper left of a star with the catalog name 89 Piscium (89 Psc, m = 5.1). The star is dim. Use a binocular to see Mars with the starfield.
Mars and Moon, August 8, 2020
As midnight approaches the moon is 2.0° to the lower right of Mars that is about 13° in altitude in the east.
  • August 8: As midnight approaches the moon (19.5 days past the New phase, 73% illuminated) is 2.0° to the lower right of Mars (m = −1.3) that is about 13° in altitude in the east.
  • August 22: Mars (m = −1.6) passes 0.5° to the upper left of Nu Piscium (ν Psc, m = 4.4). Four hours after sunset, Mars is nearly 18° in altitude in the east.
  • September 5: Four hours after sunset, the moon (18.1d, 86%) – over 20° up in the east – is 0.7° below Mars (m = −1.9).
  • September 9: Mars (m = −2.0) begins to retrograde; four hours after sunset, it is nearly 25° up in the east-southeast. See the first chart above Retrograde motion is an illusion. To early astronomers, this was the cosmological problem of the time. Those who thought Earth was at the center of all motion used a series of circles needed to get the planets to move westward compared to the starry background. For observers who thought all the planets revolved around the sun, Mars seems to move backwards when our faster moving planet catches, overtakes, and moves past the Red Planet. Mars and all objects in the solar system beyond it seem to back up for a period of time, then resume their eastward motion compared to the starry background as we move past. This is more obvious for the bright planets, especially Mars. The issue of Earth’s place in the solar system was not finalized until after the invention of the telescope and precision instruments were developed to measure our planet’s revolution around the sun.

For those with further interest, the variable star Mira (ο Cet) is predicted to reach its brightness. This paragraph describes more Mira’s brightness prediction and its location to Mars Predicted dates for the brightest phase range from mid-September to late in the month. The brightest magnitude is uncertain, ranging from 2.0 to 4.0. On September 15, Mira is about 12° to the lower left of Mars. For the latest observations of Mira’s brightness, check with the American Association of Variable Star Observers (https://www.aavso.org/).

Mars and Moon, October 2, 2020
Three hours after sunset, Mars is 24° up in the east-southeast. The bright gibbous moon is 1.3° to the lower right of the planet.
  • October 2: Three hours after sunset, Mars (m = −2.5) is 24° up in the east-southeast. The bright gibbous moon (15.7d, 98%) is 1.3° to the lower right of the planet.
  • October 6: Earth and Mars (m = −2.6) are at their closest. The planet passes 0.4° to the lower right of Mu Piscium (μ Psc, m = 4.8). Use a binocular to see the dimmer star with Mars. Three hours after sunset, the Red Planet is over 25° in altitude in the east-southeast.
  • October 13: Earth is between Mars and the sun. When the sun sets, Mars is rising in the eastern sky. Around midnight (about 1 a.m. during Daylight Saving Time), Mars is in the south. Mars sets in the western sky at sunrise. Mars and sun are opposite in the sky. Mars is at opposition, 1.43 AU from the sun and 0.419 AU from Earth. Three hours after sunset, the planet is over 30° up in the east-southeast.
  • October 23: Mars (m = −2.4) passes 0.6° to the lower right of 80 Piscium (80 Psc, m = 5.5). Use a binocular to see the star with Mars. Two hours after sunset, Mars is over 25° in altitude in the east-southeast.
Mars and the moon, October 29, 2020
Two hours after sunset, the bright moon is nearly 26° up in the east-southeast. Mars is 4.8° to the upper right of the gibbous moon.
  • October 29: Two hours after sunset, the bright moon (13.2d, 98%) is nearly 26° up in the east-southeast. Mars (m = −2.2) is 4.8° to the upper right of the gibbous moon.
  • November 13: Mars’ (m = −1.7) retrograde ends. Mars begins to move eastward compared to the starry background. Two hours after sunset, the planet is nearly 40° up in the southeast.
Mars and the moon, November 25, 2020
At the end of evening twilight, Mars is over 40° in altitude in the southeast. The moon is 5.1° to the lower left of Mars.
  • November 25: At the end of evening twilight, Mars (m = −1.3) is over 40° in altitude in the southeast. The moon (10.8d, 84%) is 5.1° to the lower left of Mars. (The end of twilight occurs about 100 minutes after sunset.)
  • December 4: Mars (m = −1.0) passes 1.0° below Epsilon Piscium (ε Psc, m = 4.2). Use a binocular to track Mars compared to the dimmer starry background. At the end of evening twilight, Mars is over 45° in altitude in the southeast.
  • December 12: Mars (m = −0.7) passes 0.6° above Zeta Piscium (ζ Psc, m = 5.2). Another dim star. You’ll likely need a binocular to see the star. At the end of evening twilight, find the Red Planet 50° up in the southeast.
  • December 21: Forty-five minutes after sunset, Mars (m = −0.5) is nearly 48° up in the southeast. The half-full moon (7.3d, 50%), over 40° up in the south-southeast, is about 24° to the lower right of Mars. This is the evening of the once-every-generation Great Conjunction of Jupiter (m = −2.0) and Saturn (m = 0.6). The conjunction is about 14° in altitude above the southwest horizon. Mar and Jupiter are nearly 83° apart.
Mars and the moon, December 23, 2020
At the end of evening twilight, Mars is 55° up in the south-southeast. The moon is 5.6° to the lower left of Mars.
  • December 23: At the end of evening twilight, Mars is 55° up in the south-southeast. The moon (9.3d, 69%) is 5.6° to the lower left of Mars.
  • December 31: Mars (m = −0.2) passes 1.0° to the lower left of Pi Piscium (π Psc, m = 5.5). A binocular is needed to see the dim star and the planet together. At the end of evening twilight, Mars is nearly 60° in altitude in the south-southeast.
  • January 5, 2021: This is the last day displayed on the charts. At the end of evening twilight, Mars (m = −0.1) is 60° in altitude in the south-southeast.

The sequence ends with Jupiter and Saturn approaching their solar conjunctions. The giant planetary pair is 15 days past the December 21, 2020, Great conjunction. Jupiter is 1.7° east of Saturn. During mid-twilight, Jupiter is about 6° up in the southwest. Along with Mercury, Jupiter and Saturn are less than 20° east of the sun. Mars is over 85° of ecliptic longitude from Jupiter. In the morning sky, Venus is about 5° up in the southeast during morning twilight. While the sun is between them, Venus is over 37° in ecliptic longitude from Jupiter.

What’s Next for Mars

Mars heads toward brighter starfields during 2021. During March, it passes the Pleiades and the Hyades, and moves between the Bull’s horns in mid-April. Mars strolls through the Beehive Cluster in late June, although the pair is low in the west-northwest during evening twilight. During mid-July, Venus passes Mars in the western evening sky. Later in the month, Mars passes Regulus with Venus higher in the sky, although the Mars – Regulus pair is very low in the sky during mid-twilight. Then, Mars makes a slow slide into evening twilight. It reaches its solar conjunction on October 7, 2021. The next opposition is December 7, 2022. Mars is farther away, 0.549 AU. This is followed by the January 15, 2025, opposition, when the Martian distance increases to 0.734 AU.

1623: The Great Conjunction of Jupiter and Saturn

The Starry Sky
(NASA Photo)

The 2020 Great Conjunction of Jupiter and Saturn is the closest conjunction of these giant planets since their conjunction in 1623.

by Jeffrey L. Hunt

Was this conjunction observed?

The Jupiter – Saturn conjunction of 1623 occurred in the wake of the invention of the telescope, so observing was in its infancy; yet, the sky was full of planetary activity. A partial lunar eclipse (April 15, 1623) was visible throughout the Americas and in Central Europe, where the moon was setting as the eclipse reached its 90% magnitude. Venus passed Jupiter and Saturn in late June and Mercury passed the planetary pair less than two weeks later, when the planets were about 22° east of the sun. With the inner planets in the vicinity of the impending Great Conjunction and Mars reaching opposition (July 4, 1623), surely sky watchers were observing the planets’ locations to test and revise their planetary motion equations.

By the time of the Great Conjunction on July 16, 1623, the planetary pair was less than 13° east of the sun. By Civil Twilight, the pair was near the horizon at mid-latitudes. Without optical help, the conjunction likely went unobserved, even for those with recently minted telescopes. Even then, the observer needed some luck to find the conjunction.

In later years, two British publications stated that the 1623 conjunction was not observed. In 1886, the Monthly Notices of the Royal Astronomical Society state that the February 8, 1683, Jupiter – Saturn conjunction was the first observed “since the invention of the telescope” and that the 1623 passing went unobserved. The same statement was written in the Journal of the British Astronomical Association in 1897. Perhaps the conjunction was observed without optical aid and recorded from more southerly latitudes, when the planets were higher in the sky.

Did the two British publications make the statements out of parochialism, rather than from factual observations made around Europe regarding the first Great Conjunction observed with a telescope, or was this the first time that the conjunction fit into an eyepiece since the telescope’s invention? The February 24, 1643, conjunction was visible in the western sky during mid-twilight as well as the October 16, 1663, conjunction. At the second conjunction the planets were about 10° up in the southwest at one hour after sunset. However, at both conjunctions, the planets were nearly 1° apart. At the 1683 conjunction, the planets were close, about 0.2° apart, twice the separation of the upcoming event. While the two previous conjunctions were visible to the naked eye and individually in a telescopic eyepiece, the 1683 conjunction was the first observed with both planets simultaneously in an eyepiece. With a separation of 0.1°, the 1623 conjunction would have fit into telescopes eyepieces of that generation, but certainly those early telescopes were unwieldy to steer and hold steady, and the telescope operator needed some persistence during the days preceding the conjunction to follow the converging planets into bright twilight while they had sufficient altitude to observe them. So, while the British publications are accurate about viewing the planets simultaneously through a telescope, the two preceding conjunctions were visible to the unaided eye and individually through a telescope, and this does not speak to the issue as whether the 1623 conjunction when unobserved across all of humanity.

In recent times, Great Conjunctions occurred February 18, 1961; followed by a triple conjunction of the two planets in 1980-81; and the last occurred May 30, 2000, although this was difficult to observe.

Read the Great Conjunction of 2020 Article.

2020: December 21: The Great Conjunction of Jupiter and Saturn

Jupiter and Saturn, August 12, 2020
2020, August 12: Saturn is 8.1° to the lower left of the Giant Planet. In the starfield, Jupiter is 1.4° to the right of 50 Sagittarii (50 Sgr), while Saturn is 2.4° to the lower left of 56 Sagittarii (56 Sgr).

December 21, 2020: Jupiter passes Saturn in a close conjunction, a once-in-a-generation Great Conjunction. This Jupiter – Saturn conjunction is the closest Great Conjunction since 1623.

Read more about the August 2020 planets.

by Jeffrey L. Hunt

Once a generation, Jupiter catches and passes Saturn. This is known as a Great Conjunction.  Both planets move slowly around the sun because of their distance from our central star.  A Jupiter year is nearly 12 Earth-years long while Saturn revolves around the sun in nearly 30 years.  A Jupiter-Saturn conjunction is rare enough for observers to take notice of this unique pairing.

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Click through the gallery of Jupiter and Saturn images.
(Bookmark this page to return to see updates in this gallery.)

See our detailed article about the Great Conjunction here(updated May 28, 2020)

Jupiter takes nearly 20 years to move past Saturn, travel around the sun, and catch Saturn again.  When Jupiter catches Saturn on December 21, 2020, they will be very close, only 0.1° apart!  This is the closest conjunction since the Great Conjunction of July 16, 1623!  The next Great Conjunction is October 31, 2040, when the two planets are 1.1° when they are low in the east-southeast before sunrise.

December 2020

Look low in the southwest, one hour after sunset.  Bright Jupiter is easy to locate.  Dimmer Saturn is nearby, to Jupiter’s upper left.

On December 16, the crescent moon enters the scene. One hour after sunset, the crescent moon (2.3 days past its New phase, 7% illuminated) joins the planets. It is over 6° up in the southwest, about 5° below Jupiter. The Jupiter – Saturn gap is 0.5°.  This is about the apparent diameter of the moon.

Jupiter - Saturn 2020 Great Conjunction

Each night thereafter, Jupiter closes more on Saturn, until conjunction evening when they are 0.1° apart.  This is close enough to see them in through at a telescope’s low power. Here is the detailed note for conjunction evening:

  • December 21: Jupiter – Saturn Great Conjunction! One hour after sunset, Jupiter is about 12° up in the southwest, 0.1° to the lower left of Saturn. They are 30° east of the sun. Both fit into the eyepieces of modest telescopic powers. Jupiter’s Galilean Satellites are nicely lined up along the equatorial plane of the planet. Ganymede, Io, and Calisto are east of Jupiter, and Europa is west of the planet. Titan is nicely placed to the northwest of Saturn. After the conjunction, Jupiter moves eastward along the ecliptic, separating from Saturn. Each evening the planetary pair appears lower in the sky.
Telescope view of Jupiter and Saturn, December 21, 2020
Jupiter and Saturn are close enough to appear together through a telescope’s low power eyepiece. Saturn’s rings and Jupiter’s four brightest and largest moons are visible as well.

Through a telescope with an eyepiece that is in the 50x-60x magnification range, Jupiter and Saturn are visible in the same field.  Saturn’s rings are easy to locate.  Jupiter’s four largest and brightest moons – Io, Europa, Callisto, and Ganymede – are evident as well.  On closer inspection, some of Jupiter’s cloud bands are visible.  Some telescopes invert the view compared to the diagram shown here.  Others flip the image left to right.  So the actual view through a telescope may look differently than what is shown here.

The half-full moon is higher in the south-southeast.  Mars is to the left of the moon, over halfway up in the sky in the southeast.  Four bright solar system objects are in the sky – moon, Jupiter, Mars, and Saturn.

Angular Sizes

Moon image by NASA

When viewing the sky, the actual sizes of objects are difficult to determine because there is no depth perception.  We measure objects by their apparent angular size.  Apparent is how large they seem to our eyes.  Angular size is measured in degrees, like the way a protractor measures angles.  The moon appears to be about 1/2° in diameter.  At the Great Conjunction, Jupiter and Saturn are 0.1° apart.  This seems to be close, but they are easily distinguished from each other.  The image above shows the angular size of the moon and 0.1° of angular size on the moon.  The large circular feature is the largest lunar feature, the Imbrium Basin, easily visible without a binocular or telescope.  So the planets are close together, but they do not appear as a “single star” at the conjunction.

Detailed Motion of Jupiter and Saturn

The image at the top of this article shows a close conjunction of Venus and Jupiter.  Notice the separation of the two planets.  At the 2020 Great Conjunction, Jupiter and Saturn are closer than this August 27, 2016 conjunction.

Jupiter and Saturn, their apparent motion in the sky 2020
2020: The apparent motions of Jupiter and Saturn compared to the background stars.

In 1961, the Jupiter – Saturn conjunction occurred in the morning sky, about 2° below 56 Sagittarii. (Note the star’s location on the accompanying chart, nearly 5° west of the Capricornus – Sagittarius border.) The 2020 conjunction occurs about 6° farther eastward, just east of the constellations’ border.

The chart above shows the motions of the planets against the background stars.  Two apparent motions occur to the Bright Outer Planets – Mars, Jupiter, and Saturn.  As Jupiter and Saturn emerge from their solar conjunctions, early in 2020, they appear higher in the sky when weekly observations are made.  They somewhat match the annual westward march of the stars.  This is caused by the earth’s revolution around the sun.  The stars are a calendar.  Over several human lifetimes, the same star is in the same position at the same time and same date each year.

The second motion is a combination of the planets’ slow orbit around the sun, especially for Jupiter and Saturn, since they don’t appear to move far during a year and Earth.  Jupiter and Saturn appear to move eastward (direct motion) compared to the starry background.  During the next year they are among a faint starfield in eastern Sagittarius and western Capricornus.  As our planet catches up and passes between them and the sun (opposition), they appear to move westward (retrograde motion) compared to the stars — retrograde motion.  After Earth passes them, Jupiter and Saturn seem to resume their direct motion compared to the background that moves farther west and rise earlier as the seasons progress.

Jupiter finally catches Saturn in late December for this Great Conjunction. On the chart, notice that Mars passes Jupiter and Saturn during late March 2020.

Read about the 1623 Jupiter – Saturn Great Conjunction here.

Monthly Summaries of What to Watch

(Bookmark this page to return for monthly updates of the planets’ locations.)

Recent Articles

A Perseid Meteor
A Perseid meteor, photographed with a camera that views the entire sky. (NASA photo)

2020, August 11-12: Peak Perseid Meteors

The Perseid Meteor shower peaks on the night of August 11-12, but it is dimmed by a thick waning crescent moon. Even with the moon’s presence, bright meteors are visible.