Sinus Iridum's Golden Handle (evening) (Chris Vaughan, Starry Night Education)

This Week’s Sky: March 22 to 28, 2021

Mars passes Aldebaran this week, as the Moon waxes to full.

Monday, March 22 – Mars and Aldebaran (evening)

Mars and Aldebaran (evening) (Chris Vaughan, Starry Night Education)

In the western sky on the nights surrounding March 20, Mars’ eastern motion along the ecliptic will carry it past a “twin”, the bright, reddish star Aldebaran in Taurus. Mars will outshine the star only slightly, and their colours will be very similar. During the period of closest approach, around March 18-22, the pair will be separated by 7 degrees, with Mars on the upper right (northerly) side of the star. Mars’ better-known twin is the star Antares, the “rival of Mars”, in Scorpius.

Wednesday, March 24 – Sinus Iridum’s Golden Handle (all night)

Sinus Iridum’s Golden Handle (evening) (Chris Vaughan, Starry Night Education)

On Wednesday night, March 24, the pole-to-pole terminator that divides the lit and dark hemispheres of the waxing gibbous Moon will fall to the left (or lunar west) of Sinus Iridum, the Bay of Rainbows. The circular, 155 mile (249 km) diameter feature is a large impact crater that was partly flooded by the same basalts that filled the much larger Mare Imbrium to its right (lunar east). The “Golden Handle” is produced because slanted sunlight is brightening the eastern (right-hand) side of the prominent, curved Montes Jura mountain range (the old crater rim) that surrounds the bay on the top and left (north and west). The rim extends into Mare Imbrium as a pair of protruding promontories named Heraclides and Laplace at the bottom and top, respectively. You can see the feature with sharp eyes – and easily in binoculars and backyard telescopes. Sinus Iridum is almost craterless, but hosts a set of northeast-oriented dorsae or “wrinkle ridges” that are revealed under magnification at this phase.

Friday, March 26 – Comparing the Twins (evening)

Comparing the Twins (Chris Vaughan, Starry Night Education)

While the Moon is bright and the planets are absent, skywatchers can still enjoy viewing bright stars. The twin stars of Gemini, Castor and Pollux, shine high in the western sky after dusk. A closer look with your unaided eyes will reveal that the twins are quite dissimilar. The left-hand (easterly) star Pollux is nearly twice as bright as sibling Castor to its right (west). Pollux’ K0 spectral class gives it a warmer colour than white, A1-class Castor. In a backyard telescope Castor is revealed to be a delightful multiple star system, with several fainter companions distributed around a bright, close-together pair.

Sunday, March 28 – Full Worm Moon (at 18:48 GMT)

Full Worm Moon (Chris Vaughan, Starry Night Education)

The March full Moon, known as the Worm Moon, Crow Moon, Sap Moon or Lenten Moon, always shines in or near the stars of Leo. Full moons always rise in the east as the Sun sets, and set in the west at sunrise. When fully illuminated, the Moon’s geology is enhanced, especially the contrast between the ancient cratered highlands and the younger smoother maria. This full Moon is occurring 1.5 days before perigee, the point in the Moon’s orbit when it is closest to Earth, making this the first of four consecutive supermoons in 2021.

Tuesday, March 30 – Zodiacal light again (after dusk)

Zodiacal light again (Chris Vaughan, Starry Night Education)

At the end of March we receive another opportunity to view the Zodiacal Light – if you live in a location where the sky is free of light pollution. After the evening twilight has disappeared, you’ll have about half an hour to check the western sky for a broad wedge of faint light extending upwards from the horizon and centered on the ecliptic (i.e., below Mars). The viewing period will end with the new Moon on April 11.

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 to tour the universe together.