Skywatch Line for Monday and Tuesday October 4th, and 5th, 2021

This is the Dudley Observatory’s Skywatch Line for Monday and Tuesday October 4th, and 5th, written by Joe Slomka.

The Sun sets at 6:31 PM; night falls at 8:05. Dawn begins at 5:24 AM and ends with the Sun rising at 6:58.

Monday’s Moon rises at 4:28 AM in Leo, 32 arc-minutes in size, and sets at 6:05 PM; this is the Old Moon which poses a challenge to the observer to spot a thin 3% crescent in the brightening sky. Tuesday’s New Moon now inhabits Virgo, but is not visible, hiding in the Sun’s glare.

The variable star Algol, in Perseus, is at its dimmest at 11:23 PM on Tuesday, 41° up in the East.

The Zodiacal Light, faint glowing of our Solar System’s dust, will be visible for the next two weeks. In the pre-dawn rural sky, it appears like a pyramid stretching from southeastern Cancer to Taurus.

Venus is still the “Evening Star”, hanging low in the western sky and setting at 8:09 PM. This month, Venus approaches Earth. Binoculars and telescopes reveal that it sets progressively later and brighter. Its apparent size becomes bigger, from 19 arc-seconds to 26 arc-seconds, but its crescent decreases from 62% to 48% lit.

Once you are finished observing Venus, swing eastward to see Saturn and Jupiter already well up in southeastern Capricornus. Saturn rises first, shines with zero magnitude, 17 arc-seconds, 24° high by 7 PM, highest at 8:37 PM, and sets at 1:24 AM. Brilliant Jupiter, is next. It blazes with minus 2nd magnitude, almost 46 arc-seconds, 21° high by 7 PM, highest at 9:40 PM and sets at 2:45 PM. Tuesday, telescopic viewers can witness the Jovian moon Io begin to cross the planet’s face at 9:19 PM, followed by its shadow at 10:20. The whole event ends with the shadow leaving at 4:38 AM. This month, both planets are still in retrograde, which means that they are backing up, but will stop and begin to creep closer to each other.

Neptune, next, lies 28° to Jupiter’s left. In Aquarius, it glows with 7th magnitude, a tiny 2 arc-seconds, highest at 11:28 PM and sets at 5:14 AM. Uranus, bringing up the rear in Aries, rises at 7:46 PM, shines with 5th magnitude, almost 4 arc-seconds, highest at 2:48 AM and sets during daytime. Beginners should obtain sky charts from astronomy magazines or apps.

Since both Saturn and Jupiter inhabit Capricornus, let us contemplate this unusual constellation. By nightfall, Capricornus, Aquarius, Pisces and Cetus dominate the southern sky. All are water-based. Capricornus is a unique constellation: The Sea-Goat. The creature has the head of a goat, but the body of a fish. This part of the Zodiac is truly ancient; Sumerians identified it as early as 1600 BC. A royal seal, from the town of Ur, is on display in the Boston Museum. The seal bears the image of Capricornus, just as it is pictured today. Boundary markers of Mesopotamian kings also depict Capricornus as we do. The source of this animal is a mystery. A people far removed from any large body of water invented it. The Goat-Fish was associated with the god Ea, the master of creation and the god of the underwater seas, including fresh water springs. Ea resembles the Roman god Neptune. In 1846, the astronomer Galle discovered Neptune in Capricornus.

The constellation inspired several English words. To caper is to frolic like a goat; when people change their minds, they are called capricious. The famous island of Capri was named “the isle of goats.” Cornucopia is a horn of plenty.

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