November 30, 2020: The Great Conjunction countdown: 21 days. Jupiter continues to close in on Saturn. Rusty Mars is in the eastern sky. The bright moon is in the sky nearly all night.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 6:58 a.m. CST; Sunset, 4:21 p.m. CST. Check local sources for sunrise and sunset times for your location.
Jupiter continues to close in on Saturn in the south-southwest after sunset. The gap between the two planets is 2.2°. Jupiter is overtaking Saturn in a slow-moving conjunction. Bright Jupiter is to the lower right of Saturn. Both planets are brighter than any star in the region.
In the sky a conjunction occurs when the moon or planet passes another celestial object in celestial longitude.
The sky has a coordinate system that mimics the earth’s coordinate system of longitude and latitude. The plane of the solar system, known as the ecliptic, marks the “equator.” Planets can be north or south of the solar system’s plane.
In the sky we see the combined motions of the planets’ revolutions around the sun that is combined with our planet’s orbital speed. We see the planets usually move eastward compared to the distant stars.
While the sun, moon, stars and planets rise in the east and set in the west, the planets appear to move eastward compared to the distant stars. As an example, look at the photos in the article for November 2020 for Venus. Notice how the planet has moved compared to the star Spica.
Sometimes, when Earth passes the outer planets, they appear to reverse their eastern direction and go backwards (westward) compared to the stars. This is an illusion from our faster moving planet passing the slower-moving outer planets. After a while the planets reverse their directions and start eastward again. Mars reversed its direction on November 13 and started marching eastward again compared to the stars.
Besides celestial latitude, the coordinate system has longitude. A conjunction occurs when the planet and the other celestial object have the same celestial longitude.
The Jupiter – Saturn conjunction occurs on December 21, when Jupiter’s celestial longitude matches Saturn’s.
While seemingly close together in our sky, the two planets will “not merge into a single star” in the sky. The separation between them is about the apparent size of the Imbrium Basin on the moon. The feature is thought to be a very large impact crater that was filled in from the bottom with lava that hardened as dark rock. Imbrium is easily visible on the moon to the unaided eye. The photo above shows the apparent separation of Jupiter and Saturn that is projected on the moon.
The actual conjunction occurs (Jupiter has the same celestial longitude) a few minutes after noon Central Time when the planets are in the daytime sky for North America and South America.
By the time the sun sets, Jupiter is already past Saturn, but they are still very close. By the time the planets are visible after sunset in the Central Time Zone, the separation only opens about 3% from its exact conjunction time.
While Jupiter and Saturn are in the south-southwest, Mars is in the east-southeast. It looks like a bright rusty star.
The bright moon is in the east during the early evening sky in front of the stars of Taurus. The star Aldebaran is about 7° to the right of the lunar orb. Block out the moon to see the brightest star in Taurus.
For more about Mars during November, see this article.
Detailed note: One hour after sunset, the moon (15.8d, 100%) is very low in the east-northeast, 7.5° to the left of Aldebaran. Mars is 38.0° up in the east-southeast. In the starfield, the Red Planet is 1.3° to the lower right of ε Psc, 1.8° to the upper right of 80 Psc, and 3.4° to the lower left of δ Psc. Jupiter is 80.9° of ecliptic longitude west of Mars and 2.2° to the lower right of Saturn that is nearly 21° in altitude in the south-southwest. Great Conjunction countdown: 21 days. Among the stars, Saturn is 3.6° to the upper left of 56 Sgr and 4.6° to the lower right of σ Cap. Jupiter is 2.1° to the lower right of 56 Sgr and 4.8° to the upper left of 52 Sgr.
Read more about the planets during November.
January 26, 2021: Visible high in the south after sunset, Mars is in Aries heading for an early March conjunction with the Pleiades star cluster.
Depending on the latitude, the time of equal light and equal darkness occurs during early February.
January 22-24, 2021: The bright gibbous moon moves through Taurus during the evening.