Oct23b-2020-at-10-pm-Lunar-X
Lunar X (Chris Vaughan, Starry Night Education)
This Week’s Sky: October 19 to 25, 2020

After the Orionids peak before dawn October 21, look for features on the Moon as it waxes past quarter.

Wednesday, October 21 pre-dawn – Orionids Meteor Shower peak

Orionids Meteor Shower peak (Chris Vaughan, Starry Night Education)

The annual Orionids meteor shower is produced when the Earth plows through a cloud of small particles dropped by repeated passages of Comet Halley in its orbit. The shower runs from September 23 to November 27 and will peak between midnight and dawn on Wednesday, October 21. At that time the sky overhead will be moving directly into the densest region of the particle field, producing 10-20 fast meteors per hour. The meteors can appear anywhere in the sky, but will seem to be travelling away from the constellation of Orion. On the peak night, the young, crescent Moon will set during evening — leaving the overnight sky dark for meteor-watching.

Thursday, October 22 evening – Half-Moon near Jupiter and Saturn

Half-Moon near Jupiter and Saturn (Chris Vaughan, Starry Night Education)

The Moon’s monthly visit with the gas giant planets Jupiter and Saturn will occur in the southwestern sky after dusk on Thursday, October 22. The waxing, half-illuminated Moon will form a neat triangle below the two planets – bright Jupiter to the Moon’s upper right, and somewhat dimmer Saturn positioned to the Moon’s upper left. The trio, which will set in late evening, will offer a lovely wide field photo opportunity when composed with some interesting foreground scenery.

Friday, October 23 evening – Dwarf planet Ceres changes direction

Dwarf planet Ceres changes direction (Chris Vaughan, Starry Night Education)

On Friday, October 23, the dwarf planet Ceres will complete a retrograde loop (red path with dates:time) that began in July – causing it to temporarily cease its motion through the background stars. On this night, the magnitude 8.6 object will be located in the lower part of the southern evening sky – about a fist’s diameter to the upper right (or 9.5 degrees to the celestial northwest) of the very bright star Fomalhaut. After tonight, Ceres will resume its regular eastward motion through the stars.

Friday, October 23 at 13:23 GMT – First quarter Moon

First quarter Moon (Chris Vaughan, Starry Night Education)

When the Moon completes the first quarter of its orbit around Earth at 9:23 a.m. EDT (or 13:23 GMT) on Wednesday, October 23, 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 ones to see the lunar terrain when it is dramatically lit by low-angled sunlight.

Friday, October 23 at 10 p.m. EDT – Lunar X

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 Parbach, la Caille, and Blanchinus are illuminated from a particular angle of sunlight, they form a small, but very obvious X-shape. The phenomenon called is pareidolia — the tendency of the human mind to see familiar objects when looking at random patterns. At approximately 10 p.m. EDT on Friday, October 23, the Lunar X is predicted to peak in intensity — but the phenomenon will be visible for approximately two hours on either side of that time. This event should be visible anywhere on Earth where the Moon is shining in a dark sky during that time window. Simply adjust for your difference from the Eastern Time zone. For the Americas, the Moon will be positioned low in the southwestern sky. 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 prominent round crater Werner sits to its lower right.

Saturday, October 24 evening – Rupes Recta (the Straight Wall)

Rupes Recta, the Straight Wall (Chris Vaughan, Starry Night Education)

On Saturday evening, October 24, 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 Straight Wall, a feature that 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, which sits in the lower third of the Moon’s Earth-facing hemisphere. The feature is always prominent a day after first quarter and day before last quarter. For reference, the very bright crater Tycho sits due south of the Straight Wall.

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 AstroGeo.ca to tour the universe together.

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