Astronomy

2020, August 28-29: Jupiter, Saturn, Moon in Evening Sky

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2020, February 18: The moon is near Mars before sunrise.

The bright moon appears near Jupiter and Saturn on the evenings of August 28 and August 29.

by Jeffrey L. Hunt

Four bright planets – Jupiter, Saturn, Mars, and Venus – are visible between sunset and sunrise.

The planets appear as overly bright stars in the sky.

Bright Jupiter appears in the southeastern sky after sunset.  Dimmer Saturn is to the Giant Planet’s lower left.

Of all the celestial objects, the moon moves fastest eastward compared to the stars.  It travels through one orbit in less than 30 days as it nearly displays all its phases.

August 28: In the evening sky, Jupiter is 2.2° above the moon. Saturn, 8.3° to the left of Jupiter, is 8.8° to the upper left of the moon.

On the evening of August 28, the lunar orb, distinctly a gibbous shape (83% illuminated), is low in the south-southeast.  Bright Jupiter is 2.2° above the moon and Saturn is 8.3° to the left of Jupiter.

August 29: One hour after sunset, Saturn is 5.7° to the upper right of the moon and 8.3° to the left of Jupiter that is over 13° to the upper right of the gibbous moon.

On the next evening (August 29), the moon is farther eastward and with a larger phase (90% illuminated).  Saturn is 5.7° to the upper right of the gibbous shape and 8.3° to the left of Jupiter.  The Giant Planet is over 13° to the upper right of the moon. 

Now over a month after our planet passed between Jupiter and Saturn (opposition), these planets are easily visible in the evening sky.

When held steadily, a binocular can reveal any number of Jupiter’s four largest moons.   A small telescope can show stripes in Jupiter’s clouds.  A careful inspection of Saturn with a small telescope reveals its ring and perhaps a cloud band or two in its atmosphere.

Because of the planets’ stellar appearance, the earliest astronomers recognized these special stars had the power of movement, compared to the multitude of “fixed” stars in the constellations.

Normally, the planets appear to move eastward compared to the starry background. As Earth approaches them in its celestial orbit; moves between them and the sun; and recedes from the worlds, the planets appear to move backwards or retrograde compared to the starry background.

Jupiter and Saturn are retrograding in front of the stars of Sagittarius.  Jupiter’s eastward direction resumes on September 12, while Saturn returns to its eastward direction on September 28.

Jupiter then approaches and passes Saturn on December 21, 2020, in a once-in-a generation Great Conjunction.  Of the large count of Great Conjunctions during the centuries, this is the closest conjunction since the grouping in 1623.

Mars rises later in the evening and it is well up in the east as midnight approaches.  At this time, Jupiter and Saturn are in the southwestern sky. 

Mars begins its retrograde direction on September 9.  Earth passes between the Red Planet and the sun on October 13, 2020.  Near opposition, Mars outshines everything in the night sky except for Venus and the Moon.

Venus rises before morning twilight begins and it is “that bright star” in the east before sunrise. Venus, Mars, and Saturn are in the sky together shortly after Venus rises, but the Ringed Wonder shortly disappears below the horizon.

Saturn is no longer visible in the sky with Venus after early September as Venus moves eastward more rapidly than Saturn, that is still retrograding at that time.

Then Venus and Mars are in the morning sky together until November when Mars sets as Venus rises.

2020, August 21: Jupiter is 2.4° to the lower left of Pi Sagittarii (π Sgr) and 2.2° to the lower right of 50 Sagittarii (50 Sgr). On for the next few weeks, watch Jupiter move closer to π Sgr and farther from 50 Sgr.

The photo above shows Jupiter and Saturn on the evening of August 21, 2020.

Look at the starfield around Jupiter and Saturn with a binocular.  Jupiter is to the lower left of Pi Sagittarii (π Sgr on the photo) and to the lower right of dimmer 50 Sagittarii (50 Sgr).  Jupiter continues to move to the right (west) compared to the stars, moving closer to π Sgr and a little farther from 50 Sgr.

Meanwhile, Saturn is moving westward below 56 Sagittarii (56 Sgr).  By the end of September Saturn is nearly below the star.

Here is a daily summary about the planets during August and September.

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