Skywatch Line for Monday July 12th and Tuesday July 13th, 2021

This is the Dudley Observatory’s Skywatch Line for Monday and Tuesday July 12th, and 13th, written by Joe Slomka.

The Sun sets at 8:33 PM; night falls at 10:43. Dawn begins at 3:18 AM and ends with the Sun rising at 5:29.

The waxing Moon occupies Leo on both nights. Monday, the Moon rose during daylight and sets at 10:40 PM, 9% illuminated and 30 arc-minutes in size. Tuesday, the Moon also rises during daylight and sets at 11:08 PM, fatter with 16% lit and 31 arc-minutes. By 9 PM, the Moon is about 6° high in the West on Monday; Tuesday finds it 22° high.

Leo entertains Venus and Mars; both rise during daytime. Venus becomes apparent first, blazing with minus 3rd magnitude, a moderate 11 arc-seconds in size and setting at 10:03 PM. Mars shines with 1st magnitude and appears only 3 arc-seconds in size. While Venus is very low, but obvious, the new observer may be hunting for Mars. To the naked eye, it may not appear. However, with binoculars or telescope, the observer will see that they are about one half of a degree apart – a close conjunction. Both rise, set and remain nearby at almost the same time on both nights. In addition, the Moon is also neighboring, creating a spectacular sight. Mars is winding down its yearlong appearance; it continues to descend nightly while Venus rises higher.

Saturn is the first of a planetary procession. Rising in Capricornus, the Ringed Planet rises at 9:37 PM, shines with zero magnitude and appears a moderate 18 arc-seconds in size; by 10 PM it is 4° high and by 11 PM its 12°. Jupiter, in Aquarius, is next, rising at 10:30 PM, sparkles with minus 2nd magnitude and a large 46 arc-seconds; by 11 PM it is 12° high and 20° at Midnight. By 11 PM, both planets are well placed for observation: Saturn for its rings and Jupiter for its varied views. Tuesday at 11:17 PM, telescopic observers can witness Jupiter’s moon Io reappearing from being eclipsed. Wednesday, they can view the Great Red Spot and, at 2:20 AM, they can watch the moon Callisto begin to march across Jupiter’s face.

Neptune, 21° below Jupiter, is third on parade, rising in Aquarius at 11:20, glowing with 8th magnitude and a small 2 arc-seconds in size. Uranus is the last to rise, at 1:20 AM in Aries; it shines with 5th magnitude, 3 arc-seconds, 7° high by 2 AM and 51° below Neptune. Mercury may present a challenge; it rises, in Gemini, at 4:08 AM, shining with minus 4th magnitude 6 arc-seconds and about 57° lit. However, the rapidly brightening Dawn sky may wash out the view.

The Saratoga Racing season begins on July 15th. As appropriate for the upcoming racing season, two horses appear by midnight. The largest horse is, of course, Pegasus. The smallest is Equuleus. This dim constellation is easy to find. Pegasus soars upside down and is easily identified as a Great Square. Two thin chains sweep northward from the upper left. If one follows across the chain, binoculars reveal a large hazy oval; this is revealed, in telescopes, to be the Andromeda Galaxy – about two and a half million light years distant. You can see it with the naked eye under rural skies. Pegasus’ neck flows from the lower right corner and angles up. Equuleus is the small angular line of stars West of the Pegasus’ nose. A globular star cluster, M 15, lies halfway between Pegasus’ nose and Equuleus. This too is easily seen in binoculars.

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