2020, December 12: Jupiter Closes Gap to Saturn, Mars in East

Jupiter and Saturn, December 12, 2020
2020, December 12: One hour after sunset, Jupiter and Saturn are in the southwest. The Jupiter – Saturn gap is 0.9°.

December 12, 2020: The Great Conjunction countdown: 9 days!  Jupiter and Saturn are in the southwest after sunset.  The Jupiter – Saturn gap is 0.9° this evening.  Farther east rusty Mars marches eastward in Pisces.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 7:09 a.m. CST; Sunset, 4:20 p.m. CST.  Check local sources for sunrise and sunset times for your location.

Jupiter is less than 1° from Saturn this evening.  This distance is about the same apparent size as two full moons.

With early sunsets, be sure to spot the pair in the southwest starting about 45 minutes after sunset and for the next 90 minutes as the planets appear lower in the sky. Jupiter sets nearly 3 hours after sunset.

In the sky, we perceive the separation and the sizes of objects differently from what we do during the day.  We have no depth perception in the starry sky, so without more information, stars appear bright or dim.  The moon and sun appear “large.”

The planets appear as stars.  To the earliest astronomers, the distant worlds were stars that had the power to move.  Most of the stars were “fixed” in their constellations.  The planets – the wanderers – moved through a band of constellations known as the zodiac – the circle of animals.

With the aid of telescopes and robot spacecraft (and 12 astronauts who have walked on the moon), we know more details about these places, their actual sizes and other characteristics.

In round numbers, Jupiter is about half a billion miles away.  Saturn is nearly double that figure.

From Earth, with our eyes alone, Jupiter and Saturn appear close together in the sky, less than 1° in angular separation.

Through a telescope, Jupiter’s moons appear as well as clouds and storms.  At Saturn, its rings gleam from sunlight and some moons are visible.

In the sky we see them close together this evening.

The Great Conjunction of Jupiter and Saturn is 9 days away!

Mars, December 12, 2020
2020, December 12: One hour after sunset, Mars is in the southeast, 0.6° to the upper left of Zeta Piscium (ζ Psc) and 2.4° to the lower left of Epsilon Piscium (ε Psc).

Farther east, Mars is marching eastward among the dim stars of Pisces.  Actually, the stars are much farther away than Mars, but we still use terms like, “Mars is in Pisces” or “Mars is among the stars.”  These statements are from our perceptions, in that we cannot tell with our eyes alone the details and distances of the stars and planets.

Mars is the “rusty” star about halfway up in the southeastern sky after sunset.  It appears to move across the sky as our planet rotates.  The planet sets in the west after 2 a.m. CST.

The Red Planet is 0.6° to the upper left of Zeta Piscium (ζ Psc on the chart).  The planet is 2.4° to the lower left of Epsilon Piscium (ε Psc).

Read about Mars during December.

Detailed note: One hour after sunset, Jupiter is nearly 16° in altitude above the southwest horizon.  Saturn is 0.9° to the upper left of Jupiter.  Great Conjunction Countdown: 9 days. Farther eastward, Mars is nearly halfway up in the sky in the southeast. The Red Planet passes 0.6° to the upper left of ζ Psc.  The planet is 2.4° to the lower left of ε Psc.

For more about the Great Conjunction, read our feature article. This is the closest Jupiter – Saturn conjunction since 1623.

Read more about the planets during December.

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