Skywatch Line for Monday and Tuesday, August 6th and 7th, 2018

This is the Skywatch Line for Monday and Tuesday, August 6th and 7th.

The Sun sets at 8:09 PM; night falls at 10:03. Dawn breaks at 4:00 AM and ends with the Sun rising at 5:53.

The parade of bright evening planets continues; it spans 120º across the sky. Venus, in Leo, blazes with minus 4th magnitude 13º low on the western horizon. This month, Venus brightens and grows larger in our instruments, but thins its crescent from 57% to 40%; it also closes in on Spica. Venus sets at 9:54 PM.

Jupiter, in Libra, radiates with minus 2nd magnitude and appears about 25º altitude in the South. It also fades and shrinks this month. While binoculars permit views of the giant planet and its moons; telescopes permit more detailed sights. On Tuesday, telescopic observers can see the Great Red Spot (a giant storm) at 9:00 PM. Later that night, they can also see the moon IO begin its trek across the planet at 10:29 PM, at 10:32 the moon Europa reappears from behind Jupiter, at 10:38 the moon Ganymede’s shadow departs Jupiter and, finally, Europa disappears into Jupiter’s shadow. Jupiter sets at 11:46 PM.

Saturn, moderately low in Sagittarius, glows with zero magnitude; it fades and shrinks slightly this month. Still, views of the planet and its glorious rings never fail. It is best observed at 10:07 PM and sets at 2:39 AM.

Mars, in Capricornus, is at its brightest and biggest since 2003. It currently outshines Jupiter, because it just came closest to Earth last week; but during August it fades and shrinks a little. Its low altitude and ongoing planet-wide dust storm means uncertain viewing conditions. Mars’ South Polar Cap, a mixture of water and dry ice, is shrinking due to onset of Martian Spring. The Red Planet is best observed at 12:13 AM and sets at 4:27.

Neptune, in Aquarius, rises at 9:24 PM and lies about 1½º from the star Phi Aquarii. The blue-green planet shines with 7th magnitude and appears a tiny 2.3 arc-seconds. It is best studied at 3:02 AM. Uranus, in Aries, shines with 5th magnitude and is larger with 3.6 arc-seconds in size. Uranus rises at 11:03 PM. Both Neptune and Uranus require detailed sky charts.

The 25-day-old Moon, in Taurus, blazes with minus 7th magnitude and exhibits 22% crescent. It rises at 1:42 AM on Tuesday. Wednesday, finds it in Orion, dimmer with 6th magnitude and a 13% crescent. It rises at 2:35 AM near Orion’s Club.

Since Mars is prominent in Capricornus, let us consider this strange 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; the 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 underground seas, including fresh water springs. Ea resembles the Roman god Neptune. In 1846, the astronomer Galle discovered the planet Neptune in Capricornus.

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