2020, August: Jupiter, Saturn in Evening Sky


Jupiter Close up from Hubble Space Telescope
This Hubble Space Telescope view of Jupiter, taken on June 27, 2019, reveals the giant planet’s trademark Great Red Spot, and a more intense color palette in the clouds swirling in Jupiter’s turbulent atmosphere than seen in previous years. The colors, and their changes, provide important clues to ongoing processes in Jupiter’s atmosphere. (NASA Photo)

Jupiter and Saturn shine from the evening sky.  Catch a last glimpse of the morning planet parade with Venus, Mars, Jupiter, and Saturn.

by Jeffrey L. Hunt

Now past their opposition points, Jupiter and Saturn shine from the southeast after sunset.  In the early evening sky, bright Jupiter is to the upper right of Saturn.  During the night, the planetary pair appear farther eastward.

Aim your binocular or small telescope at these planets.  Usually, at least one of the four largest moons is visible near the planet.  With a telescope, Jupiter’s subtle atmospheric bands can be seen.  With Saturn, a hint of a ring might be visible with a binocular, that is easily viewed with a telescope.

Mars follows Jupiter and Saturn later in the evening.  Venus appears during the early morning hours.  The four planets parade across the early morning sky.  Jupiter sets after 4 a.m. CDT on August 1.  By month’s end, Jupiter sets a few minutes past 2 a.m. CDT. 

Viewing the four planets together becomes more difficult as the month progresses.  On August 25, our planet passes between Venus and Jupiter, a so-called Venus – Jupiter opposition.  The planets are on opposite sides of our planet – Venus rises as Jupiter sets.  This is not an observable event, but worth noting to explain the break-up of the morning planet parade.

Early in the month, bright Mercury is low in the east-southeast during morning twilight, but long after Jupiter and Saturn leave the sky in the southwest.

Jupiter and Saturn in the starfield, August 2020.
Jupiter and Saturn retrograde in eastern Sagittarius during August 2020. The motion is described in the daily notes. The stars that make the background of their motion is 56 Sagittarii (56 Sgr, m = 4.8), 50 Sagittarii (50 Sgr, m =5.6), and Pi Sagittarii (π Sgr, m =2.9). The planets are plotted at the end of twilight on August 15, 2020.

In the starfield, Jupiter and Saturn are retrograding – moving westward compared to the stars.  This is an illusion from our faster moving Earth approaching them, passing between Jupiter and Saturn and the sun, and then moving away from them.  Jupiter retrogrades until September 12.  It then resumes its eastward trek toward Saturn.  Saturn’s retrograde ends September 28.  Jupiter overtakes and passes Saturn on December 21, 2020.

A conjunction of Jupiter and Saturn occurs once every 19.6 years.  While not a rare event, the grouping of the two planets is of special note and referred to as a Great Conjunction.

During August, use a binocular to watch Jupiter and Saturn retrograde compared to the dimmer starry background.  The star designations – 50 Sagittarii, 56 Sagittarii, and Pi Sagittarii – certainly are not household names, but frequent looks at the starry background reveals the westward motion of Jupiter and Saturn. Now that the planets are higher in the evening sky, our daily detailed notes should help with tracking the five bright planets.

As the planets retrograde during August, the gap from Jupiter to Saturn widens about the apparent size of the full moon.  This is noticeable without a telescope.  The unaided eye can spot that difference with frequent sightings of the pair.

On the chart above, the four stars are indicated along with the locations of Jupiter and Saturn on August 15.  Before and after the planets are near these points, and certainly can be found with a binocular.

The moon is in the region of these planets during four nights.

 

August 1: In the evening sky, the bright moon is 2.9° below Jupiter and 6.7° to the right of Saturn. The giant outer planet pair is 7.7° apart.

On the evening of August 1, the bright moon is 2.9° below Jupiter and 6.7° to the right of Saturn.

Jupiter, Saturn, Moon, August 2, 2020
August 2: In the evening sky, the bright moon is in the southeast. It is 7.8° to the lower left of Saturn. The Ringed Wonder is 7.7° to the lower left of Jupiter.

On August 2, the gibbous moon is 7.8° to the lower left of Saturn as the evening sky darkens.

Jupiter, Saturn, Moon, August 28, 2020
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.

The moon returns at month’s end.  On August 28, the gibbous moon is 2.2° below Jupiter and 8.3° to the right of Saturn.

Jupiter, Saturn, Moon, August 29, 2020
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, Saturn is 5.7° to the upper right of the bright moon, while Jupiter is 8.3° to the right of the lunar orb.

As the planet parade reaches its conclusion, look for the four bright planets in the morning sky early in the month.  Set your clock for an early rise.  Meanwhile Jupiter and Saturn are easily seen in the evening sky.  The gibbous moon is near them four evenings during August.

(Photos and charts are by the author unless otherwise specified.)

 

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