Watch Mars disappear behind the Moon tonight

All eyes on Mars

An hour after sunset in the Midwest on Dec. 7, Mars and the Moon are already more than 10° high in the east and stand less than 2° apart, with Mars to the lower left (east) of the Moon. Over the next few hours, they will continue to rise higher above the eastern horizon, nestled among the stars of Taurus the Bull. The pair sits roughly halfway between the bright star Aldebaran (magnitude 0.9), which serves as the Bull’s eye, and Elnath (magnitude 1.7), which marks the tip of Taurus’ western horn. Although Full Moon does not officially occur until 11:08 PM EST, our satellite’s face will already appear fully illuminated to the naked eye.

Occultations occur over only a limited portion of the globe because the celestial geometry must be just right for the Moon to appear to cross in front of Mars. It’s just like an eclipse, which also traces a limited path over the globe. Even if you’re not in the path, it’s worth standing outside under the stars to enjoy the sight of our Moon skimming close to Mars. Again, a telescope or binoculars will show this best, but you should be able to see the bright planet easily without any optical aid.

Shortly before midnight EST, the Full Cold Moon will occur, the last Full Moon of the year. And shortly after midnight EST, Mars will officially reach opposition. Through a telescope, Mars appears 17″ wide — large enough for bigger scopes to show some of the planet’s most prominent geological features. Around midnight, Mare Cimmerium and Mare Elysium should appear near the center of the planet. Look also for its lighter-colored polar caps; the northern cap may even sport a darker region, called the north polar hood, which is now starting to shrink as winter in Mars’ northern hemisphere comes to a close.

So much else to see

About 16° west of the pair is the Pleiades (M45), a nearby open cluster of young stars that is easily visible to the naked eye. Many people see six or seven stars without any optical aid; pull out binoculars or a low-power telescope, however, and many more luminaries will pop into sight. This is a particularly good target for low powers, as larger telescopes will provide a field of view so small that not many stars are visible.

Just southeast of Taurus, closer to the horizon, is Orion the Hunter, familiar to many because of Orion’s three-star belt and bright red shoulder, Betelgeuse. Hanging below the easternmost belt star is Orion’s Sword, which contains the stunning Orion Nebula (M42), one of the nearest star-forming regions to Earth. Visible to the naked eye as a faint, extended glow, Orion’s Nebula is a target you’ll want a telescope for, which allows you to peer into the heart of thick dust clouds where baby stars are born. The stars of the Trapezium Cluster form a small box in the center of the nebula.

Close to the horizon is the brightest star in the sky: Sirius, the nose of the Big Dog in Canis Major. A blazing magnitude -1.4, this star will appear nearly as bright as Mars and may seem to twinkle or dance like mad, particularly earlier in the evening after it’s just risen. This is because you’re looking through more — and more turbulent — air closer to the horizon than the zenith, and all this air “scrambles” the light from Sirius, like looking at a light through water. While this star is clearly visible to the naked eye, binoculars or a telescope may show it twinkling and dancing like a diamond catching the light until it climbs high enough above the horizon.

And there’s one more obvious target in the sky: the Moon itself! The Full Moon is quite bright; using high magnification to look at just a small portion of its surface can help cut down on the glare. Additionally, you can try using a Moon filter or even wearing your sunglasses when looking through the eyepiece. During the Full Moon, the Sun appears directly overhead from the lunar nearby’s point of view. Shadows are at their smallest and contrast is low, but the dark maria (Latin for seasalthough these regions never hosted water) still provide a wonderful landscape to enjoy.

Both the Moon and Mars will remain in the sky until dawn on Dec. 8. So, enjoy this stunning pairing all night, paying particular attention as they not only cross paths but slowly draw apart again — by the time they set, they’re just over 3.5° apart!

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