Skywatch Line for Friday, October 11, through Sunday, October 13, written by Sam Salem
This is Dudley Observatory’s Skywatch Line for Friday, October 11, through Sunday, October 13, written by Sam Salem.
On Friday, Sun rises at 7:07am and sets at 6:18pm; Moon rises at 3:33pm.
The bright waxing gibbous Moon will hang near Saturn in the east after sunset on Sunday evening. They’ll set a few hours before dawn. Saturn’s rings are closing now. By March of 2025, they’ll be so perfectly edgewise that, for a time, they’ll disappear.
In October, red Mars slides by the twin stars of Gemini, Castor and Pollux. The red planet is now rising before midnight and can be seen in the sky before dawn. It’s getting brighter, as Earth sweeps up from behind Mars in the race of the planets around the Sun. Earth will pass between Mars and the Sun in January. Then Mars will be opposite the Sun, at its once-in-two-years opposition. Watch, as Mars brightens over the coming months and shifts rapidly toward the evening sky.
Venus, magnitude –3.9, gleams low in the west-southwest as evening twilight fades. It sets around twilight’s end. You can use Venus as a twilight guidepost for locating Comet Tsuchinshan-ATLAS (C/2003 A3) this weekend. It’s almost three fists to Venus’s lower right, right, or upper right depending on the date and your latitude. Comet Tsuchinshan-ATLAS swung through perihelion on September 27th, passing 0.39 a.u. from the Sun. Now, it emerges low into the Northern Hemisphere’s evening-twilight sky with its head likely to be shining at around magnitude 0 or brighter.
Start trying for the comet on Friday evening, but it might not be easy yet. The comet’s head will be about 28°, almost three fist-widths, to the right of Venus, and probably somewhat lower depending on your latitude. It will appear tiny and maybe not as quite bright as Arcturus, which is sparkling at magnitude 0 some two fists to the comet’s upper right. The view will continue to improve every evening after that, and the tail will swing around upward. The comet shouldn’t start losing brightness for about a week.
On Saturday, Comet Tsuchinshan-ATLAS stands higher, about 8° above the west horizon 30 minutes after sunset. Bring binoculars, sixty minutes after sunset, as a few stars are beginning to come out. At that time, the Comet’s head is still 5° above the horizon’s west point. The Comet’s head sets around twilight’s end, but as darkness becomes complete the long dust tail may be detectable extending fairly far, depending on your light pollution.
On Sunday, the comet ‘s head is still a fine 9° high or so 60 minutes after sunset. It appears just about midway from Venus to Arcturus. By now it is predicted to grow a thin, faint anti-tail pointing opposite the main tail. An anti-tail can appear when Earth passes through the plane of a comet’s orbit and we see a thin, broad sheet of its dust debris edge-on. At twilight’s end, the comet is still a couple degrees over the horizon. However, when it’s that low, atmospheric extinction dims it considerably. The comet is now 20° left or lower left of Arcturus.