The crescent moon shines this morning from Leo. During morning twilight, Morning Star Venus and Mercury dance among the stars of Virgo in the east-southeast. Mercury reaches its greatest elongation from the sun. In the evening, Mars shines from the east-southeast. In the south-southwest, Jupiter dances toward Saturn before their Great Conjunction on December 21, 2020.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 6:35 a.m. CST; Sunset, 4:34 p.m. CST. Check local sources for sunrise and sunset times for your location.
International Space Station pass (Chicago, Illinois area) begins at 5:17 a.m. CST 29° up in the west-southwest. Less than a minute later, it reaches its highest point of this pass, 32° up in the southwest. It disappears at 5:21 a.m. CST in the south-southeast at an altitude of 10°. The ISS moves through Orion, below the three belt stars and then above Sirius.
Morning: This morning before sunrise the crescent moon is among the stars of Leo, near a stellar triangle that marks the Lion’s haunches. The lunar arc is 4.8° to the lower right of Theta Leonis (θ Leo on the chart) and over 11° to the upper right of Denebola, the Lion’s Tail. Your fist at arm’s length is about 10° from the thumb knuckle to the pinky finger. To reference the stars, your fist should fit between the moon and the tail star.
Farther east, Venus shines brightly from Virgo, 8.6° above Spica. If you wait until about 45 minutes before sunrise, Mercury makes its fall appearance. It is about 7° to the lower left of Spica and brighter than the star. Use a binocular to initially locate Spica and then Mercury. You’ll need to sight along a natural horizon (no obstructions) with no clouds. Then can you locate Spica and Mercury without optical help?
This is Mercury’s best morning appearance of the year. It is a challenge to see. During the autumn, the plane of the solar system (ecliptic) is tilted favorably to see the planet before sunrise. The angle of the ecliptic is similarly situated for favorable Mercury during springtime evenings.
Mercury is at its greatest separation (greatest elongation) from the sun as seen from Earth. The angle between the sun and Mercury is only 19°, so it appears low in the east before sunrise. That’s the best morning view we’ve had of the planet for the year.
Morning detailed note: One hour before sunrise, the moon (24.7d, 29%) is 49.0° up in the southeast, 4.8° to the lower right of Theta Leonis (θ Leo, m = 3.3), and over 11° to the upper right of Denebola (β Leo, m =2.1). Venus (m = −3.0) – over 18° up in the east-southeast – is to the moon’s lower left. The planet is 8.6° above Spica, while the star is nearly 10° in altitude. Through a telescope, Venus is 12.6” across and 84% illuminated, a morning gibbous. Mercury (m = −0.6) is 6.9° to the lower left of Spica. As morning twilight progresses follow the speedy planet higher into the sky. Mercury is at its Greatest Elongation West (19.1°) at 11:03 a.m. CST.
Evening: During the evening, Mars, Jupiter, and Saturn are bright evening planets. Bright Jupiter is in the south-southwest, less than one-third of the way up in the sky. Dimmer Saturn is 4.2° to Jupiter’s upper left. Jupiter is slowly inching eastward toward Saturn compared to the starry background. The Jovian Giant overtakes the Ringed Wonder on December 21, 2020, in what is called a Great Conjunction. Because the two planets are slow-moving and Jupiter circles the sun in over 11 years and Saturn in nearly 30 years, Jupiter catches up and passes Saturn every 19.6 years. This once-in-a-generation conjunction during 2020 is the closest the two planets have appeared since the year 1623. Of course, other Great Conjunctions have occurred in the nearly 400 years, but none this close.
Use a binocular to make nightly observations of the planets to note their changing position compared to the background stars. In the starfield, Jupiter is 3.2° to the lower right of 56 Sagittarii (56 Sgr on the chart), while Saturn is 2.3° to the lower left of the same star. Jupiter is 2.3° to the upper left of 50 Sagittarii (50 Sgr).
Jupiter sets in the west before 8:45 p.m. CST, about 4 hours after sunset.
Farther east, bright Mars shines from the dim stars of Pisces. It is retrograding – moving westward- near Epsilon Piscium (ε Psc on the chart) and Delta Piscium (δ Psc). Retrograde motion is an illusion as Earth passed Mars last month. This illusion ends on November 13 and the Red Planet begins to move eastward compared to the starry background.
Mars is visible in the east-southeast as the sky darkens. It appears to move across the sky as Earth turns during the night. The Red Planet sets (3:50 a.m. CST) in the west before Venus rises in the east, less than 3 hours before sunrise.
As with other observations of the planets, use a binocular to observe Mars is 3.3° to the lower right of ε Psc and 3.3° below δ Psc.
For more about Mars during November, see this article.
Evening detailed note: One hour after sunset, Jupiter is over 23° up in the south-southwest with Saturn 4.2° to its upper left. In the starfield, Jupiter is 3.2° to the lower right of 56 Sgr, while Saturn is 2.3° to the lower left of the same star. Additionally, Jupiter is 2.3° to the upper left of dim 50 Sgr. Mars is 82.9° of ecliptic longitude east of Jupiter. Mars continues to retrograde, although the pace is slowing, while Jupiter moves eastward. The Red Planet is nearly 27° up in the east-southeast, 3.3° to the lower right of ε Psc and 3.3° below δ Psc.
Read more about the planets during November.
December 28, 2021: The Great Andromeda Galaxy is nearly overhead at the end of the evening twilight.
December 29, 2021: The morning crescent moon approaches Scorpius and Mars. In the evening sky, four evening planets – Venus, Mercury, Saturn, and Jupiter – are lined up in the southwest. Venus is rapidly leaving the evening sky.
November 28, 2021: During twilight this evening, the three bright evening planets – Venus, Saturn, and Jupiter – are on parade in the southwestern sky.
December 28, 2021: Brilliant Venus is quickly slipping from the evening sky. Mercury appears beneath Venus after sunset. This duo is joined by Jupiter and Saturn. In the morning, Mars is near Antares and the moon near Spica.
December 27, 2021: The Red Planet Mars passes Antares this morning before sunrise. At the same hour, the moon is near Spica. The three bright planets – Venus, Saturn, and Jupiter – are in the evening sky.