2020, August 4: Jupiter, Saturn Bright Evening Stars



Jupiter and Saturn, August 4, 2020
2020, August 4: About 70 minutes after sunset, Jupiter is 0.8° to the lower right of 50 Sagittarii (50 Sgr) and 3.6° to the lower left of Pi Sagittarii (π Sgr). Meanwhile, Saturn is 2.8° to the lower left of 56 Sagittarii (56 Sgr).

Look for bright Jupiter and Saturn in the southeast during the hours following sunset.

by Jeffrey L. Hunt

Jupiter and Saturn are low in the southeastern sky during the hours following sunset. They appear as overly bright stars.  Jupiter is to the upper right of dimmer Saturn. This evening they are 7.8° apart.  The pair continues to retrograde in eastern Sagittarius as the gap between them grows. 

Retrograde is an illusion that appears when Earth overtakes, passes, and moves away from planets that revolve around the sun farther from our central star than our home planet.  Normally, planets appear to move eastward when compared to the starry background.  While they rise in the east and set in the west during a 24-hour period from Earth’s rotation, these planets seem to move eastward compared to the stars. This occurs because of the mutual revolution of Earth and the planets around the sun.

Earth passed Jupiter on July 13 and Saturn a week later.  This giant planet duo retrogrades until next month.  When they resume their eastward motion, Jupiter overtakes and passes Saturn on December 21, 2020 in what is known as a Great Conjunction.

Jupiter revolves around the sun in 11.8 years and Saturn in 29.5 years.  Jupiter overtakes and passes Saturn in our sky every 19.6 years.  While the great conjunction is not rare, it occurs at intervals of once every generation.  This year’s conjunction is the closest passing of the two planets since 1623.

Each night at the same hour Jupiter and Saturn are farther westward in the sky.  The December conjunction occurs in the southwest sky.

If you’re up early enough tomorrow morning, catch Jupiter and Saturn before they set at 4 a.m.  At that hour bright Mars is in the southeast and brilliant Venus is in the east.

Here is a daily summary about the planets during August.

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