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Dress warm for the viewing of December's Cold Moon!
This month's lunar display will give space gazers several reasons to cast their eyes to the sky —because not only will it mark the last full moon of the year, but a particular planet will pass by it as well.
Known as the lunar occultation of Mars, the full moon will briefly obscure the Red Planet in the night sky. Viewers will be able to see Mars approach the moon, pass behind it and come out on the other side.
The celestial spectacle is surely unique, but it isn't necessarily rare. In fact, a lunar occultation of Uranus just took place on Dec. 5 and was visible from parts of Asia, Northern Africa, Northern Europe and Greenland.
Lunar occultations may seem few and far between for the average sky watcher due to the moon's exact positioning in the sky and the viewer's location on Earth. "Each occultation is visible from only a small portion of Earth's surface, so it's not super common for any particular spot on Earth to see them frequently," according to NASA.
Here's everything to know about December's full moon, including when it peaks and how to spot it.
Why is December's full moon called the Cold Moon?
Historically, many of the nicknames we use for full Moons come "from Native American, Colonial American, or other traditional North American sources passed down through generations," according to The Old Farmer's Almanac.
Historically, people used full moons and nature's corresponding signs as a way to track the seasons. Since December's full moon rose when the weather began to drop tremendously, Native Americans — specifically the Mohawk tribe, per the publication — referred to it as the Cold Moon.
Other common names include the Frost Exploding Trees Moon (Cree), Snow Moon (Haida, Cherokee), Moon of the Popping Trees (Oglala) and Winter Maker Moon (Western Abenaki).
When to view the Cold Moon?
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December's Cold Moon will reach its fullest phase (and peak illumination) on Wednesday, Dec. 7 at 11:09 p.m. ET — but if you don't feel like staying up late to catch a glimpse, you don't have to! In fact, the Cold Moon — like every other full moon — will appear its biggest before it reaches its peak.
The best time to watch the moon is when it begins to rise, just before sunset at around 4:01 p.m. ET. The suggested location? Any place where you can watch it rise over the horizon. This is due to the Moon Illusion, a trick that makes our brains perceive the moon at its biggest near the horizon compared to when it appears smaller high in the sky.
Fortunately, if you miss the moonrise and peak illumination, lunar lovers will have an extra long time to spot December's moon because it will remain above the horizon for a longer period of time. This is because the winter solstice is nearing on Dec. 21, marking the shortest day and longest night of the year.
(To find the exact time that the moon will appear in your area, consult the Almanac's Moonrise Calculator.)
When will Mars pass by the Cold Moon?
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The moon isn't the only active astronomical object this month! Thanks to an extraterrestrial event known as the lunar occultation, Mars will be in close proximity to December's full moon. Viewers will be able to watch the Red Planet as it passes behind the full moon on Dec. 7 approximately one hour after sunset.
Although binoculars and telescopes are unnecessary, as the phenomenon can be viewed with the naked eye, the Griffith Observatory in Los Angeles, California will host a free online livestream of the lunar occultation of Mars on Dec. 7 (weather permitting).
The livestream will begin at 9:00 p.m. ET, but Mars won't pass behind the moon until 9:31 p.m. ET. The Red Planet will then reappear roughly one hour later.
When is the first full moon of 2023?
The first full moon of 2023 will take place on Jan. 17 at 6:48 p.m. ET. It is known as the Wolf Moon.