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This Week in the Sky, Part 1-January 29-31, 2023

January 29, 2023

​The Lunar Straight Wall (evening) On Sunday evening, January 29, the pole-to-pole terminator boundary 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. This feature is very obvious in good binoculars and backyard telescopes. 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 – that’s the large dark region in the lower third of the moon’s Earth-facing hemisphere. The Straight Wall is always prominent a day or two after first quarter, and again just before third quarter. For reference, the prominent crater Tycho is located due south of the Straight Wall.

​January 30, 2023

​Bright Moon vs Mars (overnight) On Monday night, January 30, the waxing gibbous moon will once again shine close enough to the bright reddish dot of Mars for them to share the view in a backyard telescope. After dusk in the Americas, look high in the southern sky to see the moon positioned a short distance to Mars’ southwest. Through the night, the moon’s eastward orbital motion will carry it closely past the red planet while the diurnal rotation of the sky alters the angle between them. Observers located in the southern USA, Mexico, Central America and northern South America can see the moon occult Mars around 06:00 UT on January 31. Use an app like Starry Night to determine the start and end times where you live.

​Mercury at Greatest Western Elongation (before sunrise) On Monday, January 30, Mercury reach its widest separation of 25 degrees west of the Sun, and maximum visibility for its current evening apparition. With Mercury positioned close to the tilted morning ecliptic in the southeastern sky, this appearance of the planet will be a relatively good one for both Northern and Southern Hemisphere observers. The optimal viewing times at mid-northern latitudes will start around 6:15 a.m. local time. Viewed in a telescope the planet will exhibit a waxing, slightly gibbous phase, and the medium-bright star Omicron Sagittarii will shine nearby.

​January 31, 2023

​The Brightest Star (evening) Sirius clears the neighbourhood trees and houses before mid-evening in late January. Also known as the Dog Star and Alpha Canis Majoris, it is the brightest star in the sky (after the sun). The star will climb to its highest point, about a third of the way up the southern sky, around 10 p.m. local time. If you are walking through your darkened house in the middle of the night, this star might catch your eye out a window because it never climbs very high for mid-northern latitude observers. Sirius is a hot, blue-white, A-class star located only 8.6 light-years from the sun. Its extreme brightness and low position in the sky combine to produce spectacular flashes of colour as it twinkles. A very large telescope may allow you to see Sirius B, a faint white dwarf companion located 10 arc-seconds from Sirius.


The information presented here is taken from my personal copy of Starry Night 8 Pro Plus, all rights belong to Starry Night Education/Simulation Curriculum.

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