Skywatch Line for Monday and Tuesday September 11th, and 12th, 2023

This is the Dudley Observatory’s Skywatch Line for Monday and Tuesday September 11th, and 12th, written by Joe Slomka.

The Sun sets at 7:13 PM; night falls at 8:50. Dawn begins at 4:54 AM and ends with the Sun rising at 6:32.

Monday’s Moon rises in northwestern Cancer at 2:44 AM and sets at 6:10 PM. Tuesday’s Moon shifts to Leo, rises at 3:49 AM and sets at 6:35 PM. Tuesday finds the Moon nearing New. This guarantees only thin slivers of Moonshine in the brightening Dawn and dark skies for night. The Moon rises at 4:52 AM on Wednesday and is accompanied by Regulus 4° away and Mercury 7° away.

Comet Hartley continues its visit, rising in Perseus at 7:44 PM, 75% illuminated and shining with 7th magnitude, highest at 5:42 AM and sets at 3:44 PM. It is best observed after midnight when it is almost overhead and midway between Perseus and Auriga.

A second comet is hurtling through our sky. P2023/Comet Nishimura has suddenly appeared, discovered by a Japanese astronomer. It appears near Leo’s tail (Denebola). Reports show it has a classic tail and blue-green head that is 24% illuminated. It glimmers with 3rd magnitude and brightening. Nishimura will be closest on September 18 and then gradually fade through October. However, its proximity to the western horizon means that one must have an unobstructed view before setting at 8 PM.

Mars ended its appearance. Saturn, in southeastern Aquarius, rises at 6:39 PM, shining with zero magnitude, almost 19 arc-seconds in size, highest at midnight and sets at 5:08 AM. At 8 PM it is 13° high. Saturn’s rings are slowly closing, now only 9° angle, presenting a challenge to observers. There is another challenge; according to NASA astronomers, there is a possibility for “spokes”; to appear on the rings; observers with medium or large telescopes may spot them. Neptune, in eastern Pisces, rises at 7:30 PM, 7th magnitude, 2 arc-seconds, highest at 1:23 AM and sets at 7:12 AM; it is 5° at 8 PM.

Aries hosts Jupiter and Uranus on both nights. Jupiter is brightest with minus 2nd magnitude, large 45 arc-seconds, rises at 9:27 PM, highest at 4:27 AM and is 61° altitude at 5 AM. On Tuesday, a series of events begin with Io’s eclipse beginning at 12:31 AM and ending at 3:49 AM. Io’s shadow begins another transit at 9:39 PM and ends at 11:49 PM. Wednesday, the Great Red Spot (a giant storm) begins its trek at 3:25 AM. Observers have discovered Jupiter’s 12th impact; Jupiter acts as a “magnet”, attracting comets and asteroids that would otherwise threaten the development of life on Earth. An example is 1994’s Comet Shoemaker-Levy 9, which crashed onto Jupiter and left debris that backyard telescopes could see persist for months. Uranus, 7° from Jupiter, rises at 9:43 PM, glows with 7th magnitude, 3 arc-seconds, highest at 4:56 AM, 65 ° high at 5 AM.

Both Venus and Mercury are close to the Sun. Venus rises in eastern Cancer at 3:47 AM, blazing with minus 4th magnitude, 42 arc-seconds, 21% illuminated and 13° altitude at 5 AM. Mercury brings up the rear, rising at 5:52 AM, 2nd magnitude, 9 arc-seconds, 8% illuminated and is 2° high at 6 AM. Observers should take care not to accidently look at the Sun.