Skywatch Line for Monday September 13th and Tuesday September 14th, 2021

This is the Dudley Observatory’s Skywatch Line for Monday and Tuesday September 13th, and 14th, written by Joe Slomka.

The Sun sets at 7:21 PM; night falls at 8:59. Dawn begins at 4:58 AM and ends with the Sun rising at 6:34.

The Moon reaches First Quarter on Monday at 4:39 PM; it rises at 2:20 PM, sets at 11:17 PM and appears 51% illuminated, 32 arc-minutes in size and 21° high at 7:21 PM Tuesday. It rises at 3:28 PM, 20° high, 63% lit and sets at 12:13 AM, Wednesday. Monday, Antares, the Moon, Saturn and Jupiter enliven the southern sky with the Milky Way separating the Moon and Saturn.

Venus and Mercury persist low in the western sunset, both in Virgo. Venus is brightest and easiest to spot. Both rose in the morning and set during Civil Twilight. Venus blazes with minus 4th magnitude, is a moderate 16 arc-seconds and sets at 8:34 PM. Mercury glows with zero magnitude, 7 arc-seconds, 57% lit and sets at 7:49 PM. Mercury is at greatest elongation (most distant) from the Sun, but hugs the horizon.

Meanwhile, Saturn and Jupiter are already moderately high in Capricornus, having risen during afternoon. Saturn glimmers with zero magnitude, a moderate 18 arc-seconds, highest at 10 PM and sets at 2:49 AM. Jupiter flashes with minus 2nd magnitude, twice as large as Saturn, highest at 11 PM and sets at 4:16 AM. Both are easily located in the southern sky and present great binocular and telescopic views.

Neptune is at Opposition, residing in Aquarius, glimmering with 7th magnitude, a tiny 2 arc-seconds, highest at 12:56 AM and sets at 7:10 PM. “Opposition” means that Neptune, Sun and Earth are aligned; this also means the Neptune is up all night. However, its small size and dullness means that the observer should have a star chart to find the planet amid similar appearing stars. It is 27° to Jupiter’s lower left. Uranus, in Aries, brings up the rear, rising at 9:10 PM, shining with 5th magnitude, 3 arc-seconds, highest at 4:13 AM and sets during daytime; it is 31° high at Midnight, another planet which requires a chart.

If we look south at about 10:00 PM, a hazy white band of light seems to stretch from the North Pole to horizon. This band is commonly called “The Milky Way” (Latin: Via Lactea). Examination of the Milky Way with binoculars or telescopes reveals it to be a continuous band of stars or clouds of dust or gases. Our galaxy is a gigantic thin pinwheel, with several arms. Our planet is located in one of these arms. When we look at the Milky Way, we are seeing through this arm out into space. From Lyra to Sagittarius the Milky Way seems to divide in two. A giant dust cloud causes this “Great Rift”. We can see these dust clouds on other galaxies. If we follow the Milky Way to the southern horizon, we come upon the constellation Sagittarius. The center of our galaxy is located in that constellation, but we cannot see it due to dense star and dust clouds.

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