Each Monday I pick out the northern hemisphere’s celestial highlights (mid-northern latitudes) for the week ahead, but be sure to check my main feed for more in-depth articles on stargazing, astronomy, eclipses and more.
What To Watch For In The Night Sky This Week: March 15-21, 2021
This week begins with a beautiful two-day old Moon in post-sunset skies. Take an evening walk and look west for a slim crescent. However, this week’s highlight is the waxing crescent Moon’s journey past a famous star cluster, the planet Mars and a red supergiant star.
Monday, March 15, 2021: A super-slim crescent Moon
If you’re really lucky tonight you’ll be able to glimpse a 6%-lit crescent Moon—just a couple of days after its New Moon phase—low down on the western horizon just after dusk.
Tuesday, March 16, 2021: A crescent Moon and ‘Earthshine’
Higher up in the sky tonight yet only 11%-lit, the crescent Moon will tonight display “Earthshine—sunlight being reflected from Earth and on to the Moon—for a short time after sunset before it sinks into the western horizon. Look to the darker limb of the Moon, preferably with binoculars.
Wednesday, March 17, 2021: A crescent Moon and ‘Earthshine’
A second chance to see “Earthshine” tonight as an 18%-lit crescent Moon continues to wax as it moves further from the Sun on its orbit of the Earth.
Thursday, March 18, 2021: A crescent Moon near Mars and the Pleiades
Look southwest after dark and you’ll see a 26%-lit crescent Moon close to the famous Pleiades open cluster (a misty patch to naked eyes).
Binoculars will help you see both “Earthshine” on the Moon—sunlight reflected from Earth back on to the lunar surface—and the famous “Seven Sisters” stars (and many more less bright stars in binoculars).
The Moon and the Pleiades will form a kind of celestial square with Mars and bright star Aldebaran—a red supergiant star and the eye of Taurus, the bull.
Friday, March 19, 2021: The Moon meets Mars
Tonight the Moon makes a move on Mars. Now 34%-lit, the Moon and Mars will be separated by a mere 2° while Aldebaran will be in the same 5° region of the night sky.
Saturday, March 20, 2021: Vernal northward equinox
Spring is here. An equinox marks the day when the midday Sun crosses the equator, conferring equal night and day for the entire planet.
Today’s vernal or northward equinox marks the beginning of astronomical fall or autumn in the southern hemisphere and astronomical spring in the northern hemisphere.
Sunday, March 21, 2021: First quarter Moon
Today the Moon reaches first quarter having completed 25% of its monthly orbit around the Earth. Its face visible to us on Earth is thus 50% illuminated. Next comes its full Moon phase.
Asterism of the week: the Big Dipper/Plough/Saucepan
High in the northern sky this week is the Big Dipper/Plough/Saucepan—a sure sign that spring has sprung—but it’s not a constellation. Seven stars comprise the famous handle-and-cup shape.
The handle is Alkaid, Mizar, Alioth and Megrez, with the cup made from Megrez, Phecda, Merak and Dubhe. However, this simple shape is not a constellation, but an “asterism”—a familiar shape of stars.
The Big Dipper is actually the core of a vast constellation called Ursa Major, the Great Bear.
Times and dates given apply to mid-northern latitudes. For the most accurate location-specific information consult online planetariums like Stellarium and The Sky Live. Check planet-rise/planet-set, sunrise/sunset and moonrise/moonset times for where you are.
Wishing you clear skies and wide eyes.