Wednesday, December 1 – Neptune stands still (evening)
On Wednesday, December 1, the distant, blue planet Neptune will complete a retrograde loop that has been carrying it slowly westward through the stars of northeastern Aquarius since late June. After pausing tonight, Neptune will return to its regular eastward motion. From dark sky locations the magnitude 7.9 planet can be observed in good binoculars and backyard telescopes for several hours after dusk. Search for the planet several finger widths to the upper left (or 3 degrees to the celestial east-northeast) of the medium-bright star Phi Aquarii (inset). The trio of stars named Psi Aquarii will sit below them. The planet and those stars will appear together within the field of view of binoculars (green circle).
Thursday, December 2 – Old Moon and Mars (pre-dawn)
In the southeastern sky before dawn on Thursday, December 2, the slim crescent of the old Moon will shine a palm’s width to the upper right (or 7 degrees to the celestial northwest) of magnitude 1.6 Mars. Use binoculars (green circle) to look for the bright double star Zubenelgenubi (or Alpha1,2 Librae) positioned just to the moon’s lower right. Half a day later, observers in most of Mongolia, northeastern China, parts of eastern Russia, Japan, most of Micronesia, northern Polynesia, and Hawaii can see the moon occult Mars. On Friday morning, the moon will drop to Mars’ lower left.
Friday, December 3 – Venus at maximum brightness (evening)
On Friday, December 3, the evening planet Venus will achieve maximum brightness for its current lengthy evening apparition. Astronomers call this event “greatest illuminated extent”. The term refers to the optimum combination of the planet’s apparent disk size (41 arc-seconds) and its illuminated phase (26%) sending a maximum amount of reflected sunlight towards Earth. That evening, Venus will shine at a spectacular magnitude –4.66. Venus’ crescent phase (inset) will be apparent in any telescope or spotting scope, good binoculars, or even to very sharp, unaided eyes – but ensure that the sun has fully set before using optical aids.
Friday, December 3 – Comet Leonard passes Messier 3 (post-midnight)
A comet discovered on January 3, 2021 by G.J. Leonard is predicted to grow to naked-eye brightness during December, and then pass the Sun at perihelion on January 3. In the first few days of December, Comet C/2021 A1 (Leonard) will rise around midnight. Each night it will travel rapidly eastward near the bright star Arcturus (red path). Although the comet will brighten each day, it will also be drawing closer to the dawn Sun, so make an effort to see it sooner than later. During the wee hours of Friday, December 3, Comet Leonard will pass very close to the bright globular star cluster Messier 3 in Canes Venatici. Both objects should be bright enough to see in binoculars from dark sky locations, and will be telescope-close (green circle) for several hours. On the following night, the comet will pass the fainter globular cluster NGC 5466, also known as the Snowglobe Cluster.
Read more about Comet Leonard in this article by Chris Vaughan.
Saturday, December 4 – New Moon and Antarctic total solar eclipse (at 07:43 GMT)
On Saturday, December 4 at 2:43 a.m. EST or 07:43 GMT, the December new Moon will occur. At its new phase, the Moon is travelling between Earth and the Sun. Since sunlight can only reach the far side of the moon, and the Moon is in the same region of the sky as the Sun, the Moon becomes completely hidden from view for about a day.
This new Moon will also produce a total solar eclipse visible inside a narrow track that crosses west Antarctica and the Ross Sea, with maximum eclipse occurring at 2:33:26 a.m. EST. The partial eclipse will be visible over the rest of Antarctica, South Africa, Tasmania and the South Atlantic. This new Moon will occur only two hours before the Moon reaches perigee, producing high tides around the world.
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the Universe together.