December 12, 2020: The super crescent moon appears with Venus this morning low in the southeast during early morning twilight. Step outside to take a look!
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.
About an hour before sunrise, the razor-thin crescent moon that is only 6% illuminated is low in the southeast. It is to the upper right of brilliant Morning Star Venus.
If the moon were at its Full Moon phase, we would call this a supermoon, because the lunar orb is at perigee (point closest to Earth) at 2:42 p.m. CST.
We could call this a “super crescent.”
The moon’s orbit is not a circle, but varies in its distance from our planet. The near point is known as perigee, apogee for the farthest.
The moon revolves around Earth every 27.3 days, while the moon phases repeat every 29.5 days – a month, or a “moonth.”
Three or four times a year, the Full Moon phase occurs near the time of perigee. The moon looks about 14% larger in the sky, a phenomenon that is very difficult to measure and to perceive without photography to gauge the size of the moon in the image.
The term “supermoon” has emerged into the popular science scene with social media and traditional media making a big deal out of the full moon’s appearance. The full moon always looks big and bright when near the horizon, a phenomenon known as the moon illusion. The supermoon effect is not easily perceptible.
For our purposes this morning with Venus and a crescent moon together, we’re calling this a “super crescent” moon because it is near perigee and appears near Venus. . (A super crescent is defined here to be when the moon occurs within 24 hours of a Venus – moon grouping, where the moon is within 5°. The next such occurrence is July 26, 2022, when Venus is in the morning sky.)
Venus appears lower in the sky each morning. It is rising 2-3 minutes later each morning, as it slides back into morning twilight. It is approaching its superior conjunction – on the far side of the sun – next year. It then slowly appears in the evening sky later in the year.
This morning Venus rises about 2 hours before sunrise. The moon appears above the horizon about 30 minutes before Venus.
Dress warmly and step outside to spot the pair together low in the southeast during morning twilight.
Photographers can capture the scene with exposures from a fraction of a second to about 5 seconds, depending on the camera’s settings (fast f/stops, high ISO settings need faster exposures).
View “earthshine” – reflected sunlight from Earth’s oceans, continents, and clouds that gently illuminates the night portion of the moon – with a binocular or a bird watching spotting scope.
Photographers can catch earthshine with longer exposures.
Cell phone photographers can attempt to photograph the super crescent with varying results. Hold the camera a steady as possible and zoom in on the scene. Without zoom lens attachments, the moon still appears small. The cameras should capture the crescent and Venus along with the magnificent colors of morning twilight.
The best experience, though, is to step outside on a chilly morning during twilight and view the Venus – moon grouping with just your own vision.
Venus appears with the moon again on January 11, the last Venus – moon grouping of this appearance of the planet in the morning sky during 2020-2021, although it is not a super crescent.
Detailed Note: One hour before sunrise, the crescent moon (27.3d, 6%) is over 13° up in the southeast, 4.2° to the upper right of Venus. In the starfield, the planet is 3.0° to the lower right of γ Lib. The moon is at perigee at 2:42 p.m. CST – 224,826 miles away.
Read more about the planets during December.
Look for the bright rosy star Betelgeuse during February evenings. It makes up the shoulder of Orion the Hunter.
February 19-21: The bright moon moves through the constellation Taurus. Use a binocular to see the starry background with the moon.
February 18, 2021: The moon, waxing toward its First Quarter moon phase, is high in the southwest after sunset. Planet Mars is 3.8° to the upper right of the moon. Mars is parading eastward compared to the starry background in eastern Aries as it heads toward the Taurus border.