View the Lunar X (Chris Vaughan, Starry Night Education)

This Week’s Sky: March 15 to 21, 2021

The Moon takes centre stage this week, meeting Uranus and the Moon before showing off its Lunar X and then meeting Messier 35.

Tuesday, March 16 – Crescent Moon near Uranus (evening)

Crescent Moon meets Uranus (Chris Vaughan, Starry Night Education)

In the western sky on Tuesday evening, March 16, the young crescent Moon will be positioned several finger widths to the lower left (or 3.5 degrees to the celestial southwest) of the planet Uranus – allowing both objects to share the field of view of binoculars (red circle). Normally, visits by the Moon make seeing magnitude 5.8 Uranus more difficult – but the 12-per-cent-illuminated crescent Moon won’t be excessively bright. Alternatively, note the brighter stars near the Moon that night, such as Menkar in Cetus (to the Moon’s upper left) and Hamal and Sheratan in Aries (to the Moon’s upper right) and then use them to locate slow-moving Uranus on a subsequent moonless night.

Friday, March 19 – Moon and Mars (evening)

Moon and Mars (Chris Vaughan, Starry Night Education)

In the southwestern sky after dusk on Friday, March 19, look for the reddish, medium-bright dot of Mars shining several finger widths to the lower right (or 3 degrees to the celestial northwest) of the waxing crescent Moon. The two objects will appear together in the field of view of your binoculars (red circle). The duo will set together in the west after about 1 a.m. local time.

Saturday, March 20 – March Equinox (at 9:37 GMT)

March Equinox (Chris Vaughan, Starry Night Education)

On Saturday, March 20 at 9:37 GMT (or 5:37 a.m. EDT) the Sun will cross the celestial Equator travelling north, marking the vernal equinox in the Northern Hemisphere and the beginning of northern spring. Days and nights will be of equal length on that day, and the Sun will rise due east and set due west.

Saturday, March 20 – View the Lunar X (at 22:30 GMT)

View the Lunar X (Chris Vaughan, Starry Night Education)

Several times a year, for a few hours near its first quarter phase, a feature on the Moon called the Lunar X becomes visible in strong binoculars and backyard telescopes. When the rims of the craters Purbach, la Caille, and Blanchinus are illuminated from a particular angle of sunlight, they form a small, but very obvious X-shape. The Lunar X is located near the terminator, about one third of the way up from the southern pole of the Moon (at 2° East, 24° South). The ‘X’ is predicted to peak in intensity at about 6:30 p.m. EDT on Saturday, March 20. That will be in waning daylight for observers in the eastern Americas – but you can observe the Moon in a telescope during daytime, if you take care to avoid the Sun. The ‘X’ will persist until about 8 p.m. EDT. This event should be visible anywhere on Earth where the Moon is shining, especially in a dark sky, between 21:00 and 23:59 GMT.

Sunday, March 21- First quarter Moon near Messier 35 (at 14:40 GMT)

First quarter Moon near Messier 35 (Chris Vaughan, Starry Night Education)

When the Moon completes the first quarter of its orbit around Earth at 10:40 a.m. EDT (or 14:40 GMT) on Sunday, March 21, the relative positions of the Earth, Sun and Moon will cause us to see it half-illuminated – on its eastern side. At first quarter, the Moon always rises around noon and sets around midnight, so it is also visible in the afternoon daytime sky. The evenings surrounding first quarter are the best for seeing the lunar terrain when it is dramatically lit by low-angled sunlight. By the time the sky fully darkens in the Americas, the Moon’s eastward orbital motion (green line) will have carried it about four finger widths to the upper left (or four degrees east) of the prominent open star cluster in Gemini known as Messier 35 or the Shoe-Buckle Cluster. That cluster’s stars, which are visible in binoculars (red circle), are located to the right of Tejat and Propus, the medium-bright stars that mark Castor’s toes.

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.