Skywatch Line for Monday and Tuesday October 25, and 26th, 2021

This is the Dudley Observatory’s Skywatch Line for Monday and Tuesday October 25, and 26th, written by Joe Slomka.

The Sun sets at 5:57 PM; night falls at 7:32. Dawn begins at 5:47 AM and ends with the Sun rising at 7:22.

The waning Moon visits Gemini on both nights. Monday’s Moon rises at 8:58 PM, in the Northeast, 76% illuminated, 29 arc-minutes in size and sets at 1:07 PM on Tuesday. Tuesday’s Moon rises at 9:48 PM, almost the same size, 68% lit and sets at 1:54 PM on Wednesday.

Venus persists as the “Evening Star” in the constellation Ophiuchus. By Civil Twilight (6:26 PM), Venus, low in the southwest, blazes with minus 4th magnitude, 24 arc-seconds, 53% lit and 12° high. At 7 PM it descends to 8° and sets at 8 PM.

Saturn and Jupiter still share Capricornus, in the Southwest. Saturn rose first. It shines with zero magnitude, 17 arc-seconds, highest at 7:15 PM and sets at 11:58 PM. Jupiter, 15° east of Saturn, flashes with minus 2nd magnitude, appears much larger than Saturn, highest at 8:17 PM with 32° high and sets at 1:21 AM. Monday, at 9:48 PM, telescopic observers can witness the Jovian moon Ganymede begin to cross the planet’s face; however, Jupiter sets before Ganymede exits. Note that Venus, Saturn and Jupiter share the Southwestern sky; best time is 7 PM.

Neptune, 28° East of Jupiter, occupies Aquarius, glowing with 7th magnitude, 2 arc-seconds, highest at 10:03 PM with 42°, and sets at 3:49 AM. Uranus inhabits Aries, 52° below Neptune. It glimmers with 5th magnitude, rises at 6:21 PM, appear 3 arc-seconds, 28° high by 9 PM, is highest at 1:23 AM and sets during daytime.

Elusive Mercury appears in eastern Virgo, rises at 5:46 AM, twinkles with zero magnitude, appears 6 arc-seconds, 60% lit and is 12° high in the East at Civil Dawn (6:53 AM). It is now best positioned for  Northern Hemisphere residents to see it.

Monday, Mercury is at Maximum Western Elongation, meaning farthest from the Sun – 18.4°. Let us examine Mercury, a planet of extremes. Mercury is the Roman name for the Greek god Hermes. The son of Zeus and Maia, he was the guardian of commerce and the messenger of the gods, announcing the will of the gods to people. It is the closest planet to the Sun and the smallest, only 4879 km (3032 mi) wide and nearly the hottest (Venus is hotter). Temperatures exceed 400°C (751°F). Mercury orbits the Sun every 87.9 days, but its day is 58.6 earth-days long. It travels across the Ecliptic, the path of the Sun, Moon and planets, but its 7° inclination means that it is always just above and below that imaginary line. Mercury is visible only shortly before or after sunrise or sunset. Like Venus, Earth and Mars, Mercury is a rocky planet, composed mostly of calcium oxide and magnesium oxide. It doesn’t have an atmosphere, but has a tenuous gas blanket that is so thin that atoms don’t collide. It is buffeted by micro meteor barrages and the constant solar wind. This “atmosphere” is unstable and brightens when large meteors impact. Mercury is visible low in the East into early November.

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