The Lunar Straight Wall (Chris Vaughan, Starry Night Education)

This Week’s Sky: November 23 to 29, 2020

Watch the Moon this week as it passes near Mars. At the start of next week, look for a penumbral lunar eclipse.

Monday, November 23 – The Lunar Straight Wall (evening)

The Lunar Straight Wall (Chris Vaughan, Starry Night Education)

On Monday evening, November 23, the pole-to-pole terminator that divides the lit and dark hemispheres of the waxing gibbous Moon, will fall just to the left (or lunar west) of Rupes Recta, also known as the Lunar Straight Wall. The rupes, Latin for “cliff”, is a north-south aligned fault scarp that extends for 65 miles (110 km) across the southeastern part of Mare Nubium, which sits in the lower third of the Moon’s Earth-facing hemisphere. The wall, which is very easy to see in good binoculars and backyard telescopes, is most prominent a day or two after first quarter, and also the days before last quarter. For reference, the very bright crater Tycho is located due south of the Straight Wall.

Wednesday, November 25 – Bright Moon meets Mars (evening)

Bright Moon meets Mars (Chris Vaughan, Starry Night Education)

In the southeastern sky after dusk on Wednesday, November 25, the waxing gibbous Moon will be located a slim palm’s width below (or 5 degrees to the celestial south of) reddish Mars. The Moon and Mars will cross the sky together until well after midnight. By then, the diurnal rotation of the sky, and the Moon’s eastward orbital motion, will shift the Moon to Mars’ left, in the western sky.

Thursday, November 26 – Sinus Iridum’s Golden Handle (all night)

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

On Thursday night, November 26, 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 flooded by the same basalts that filled the much larger Mare Imbrium to its right (lunar east) – forming a rounded, handle-shape on the western edge of that mare. You can see it with sharp eyes – and easily in binoculars and backyard telescopes. The “Golden Handle” is produced when slanted sunlight brightly illuminates the eastern side of the prominent, curved Montes Jura mountain range that surrounds the bay on the top and left (north and west), and by a pair of protruding promontories named Heraclides and Laplace to the bottom and top, respectively. Sinus Iridum is almost craterless, but hosts a set of northeast-oriented dorsae or “wrinkle ridges” that are revealed under magnification at this phase.

Saturday, November 28 – Neptune changes course (evening)

Neptune changes course (Chris Vaughan, Starry Night Education)

On Saturday, November 28, the distant, blue planet Neptune will complete a retrograde loop that has been carrying it westward through the stars of Aquarius since late June. After today, Neptune will resume its regular eastward motion (red path). From dark sky locations the magnitude 7.9 planet can be observed all evening in good binoculars and backyard telescopes – if you know where to find it. Search about a thumb’s width to the upper left (or 44 arc-minutes to the northeast) of the medium-bright star Phi Aquarii. Both the planet and the star will appear together in the field of view of a telescope at low magnification (red circle).

And in a preview for next week…

Monday, November 30 – Full Beaver Moon and penumbral lunar eclipse (maximum at 9:44 GMT)

Full Beaver Moon and penumbral lunar eclipse (Chris Vaughan, Starry Night Education)

The November Full Moon, traditionally known as the Beaver Moon or Frost Moon, always shines in or near the stars of Taurus and Aries. Full moons occurring during the winter months in North America will climb as high in the sky as the summer noonday Sun and cast similar shadows. This full Moon’s orbital motion (green line) will carry it into Earth’s outer shadow, producing a penumbral eclipse that will be visible in its entirety across most of North and Central America, and northern Asia. The Moon will first contact the shadow at 07:32:22 GMT. At greatest eclipse at 09:44:02 GMT, approximately 83 per cent of the Moon’s disk will be within the Earth’s southern penumbral shadow. The subtle darkening of the Moon’s right-hand (northern) limb will be visible only within about 30 minutes of greatest eclipse. The eclipse will end at 11:53:26 GMT. South America and northern Europe will only see the early stages, while Australia, Southeast Asia, China, and parts of Russia will only see the latter stages.

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.