Skywatch Line for Monday (Labor Day) and Tuesday September 4th, and 5th, 2023

This is the Dudley Observatory’s Skywatch Line for Monday (Labor Day) and Tuesday September 4th, and 5th, written by Joe Slomka.

The Sun sets at 7:25 PM; night falls at 9:04. Dawn begins at 4:45 AM and ends with the Sun rising at 6:24.

The constellation Aries presents the Moon on both nights. Monday’s 20-day-old rises in the northeast at 9:50 PM, appears 31 arc-minutes diameter, 70% illuminated and sets at 1:09 PM Tuesday. Monday’s Moon rises with Jupiter, only 15° away; as the Moon crosses the sky, the pre-dawn sky now shows it only 6° from the Pleiades (M 45) at 5 AM and sets at 1:09 PM. Tuesday’s Moon rises the Southeast at 10:22 PM; by 5 AM, it is 67° high, 31 arc-seconds, 66% lit and sets at 2:19 PM on Wednesday.

For the last few months, we have been tracking Comet 103P/Hartley. It is now racing through the September sky preparing for perihelion. Hartley is a periodic comet, it orbits the Sun every 6.5 years and appears to contain a lot of water. Hartley glimmers with 8th magnitude in Perseus, 77% illuminated rises at 7:06 PM, highest at 5:13 AM and sets at 3:23 PM. At 8 PM, it is 16° high, but is best seen between Midnight and Dawn when it is 81° highest and about 23° above the Moon and Jupiter. On Tuesday, it lies about 2° above the star Algol, in Perseus. It is visible through a 6 inch or larger telescope. This week, views are hindered by the brilliant Moon and Jupiter, but the sky darkens later next week.

Mars barely hangs on very low on the western horizon; in Virgo, it glows with 1st magnitude, only 3 arc-seconds, 3° high at 8 PM and sets at 8:32 PM. Saturn is much easier, rises in southeastern Aquarius at 7:37 PM, zero magnitude, moderate 19 arc-seconds, 9° highest at 12:55 AM, 6° at 5 AM and sets at 6:09. Neptune, in eastern Pisces, rises at 8:26 PM, glows with 8th magnitude, 2 arc-seconds and highest at 2:20 AM with 45° altitude.

Aries holds Jupiter and Uranus. The Giant Planet rises at 10:22 PM, glimmers with minus 2nd magnitude, a large 44 arc-seconds, 22° at Midnight and 62% at 5 AM. Tuesday evening, the Jovian moon Io’s shadow begins to cross the planet at 7:45 (during dusk), Io itself begins its travel at 8:59 PM, the shadow ends at 9:55 and Io at 11:07. Wednesday, the Great Red Spot (a giant storm) becomes visible at 2:39 AM. Uranus follows by rising at 10:38 PM, shining with 5th magnitude, 3 arc-seconds, 19° at Midnight and 65° highest at 5 AM.

Venus brings up the rear, rising in eastern Cancer at 4:47 AM, blazing with minus 4th magnitude, 47 arc-seconds in size and 9° high at 5 AM. Watch Venus daily and the planet thins from 50 arc-seconds to 33, but the planet’s illuminated surface grows from 11% to 36%.