Astro Bob: Mars hides behind the moon … again!
For observers in the southern U.S. the moon will cover Mars on Monday night, Jan. 30. Elsewhere we'll see a very close conjunction.
Last month, the full moon took the liberty of blotting Mars from the sky for up to an hour or more from some locations. Maybe you were lucky enough to have clear skies to watch the event. At the time I thought Mars might be bright enough to follow right up to the moon's edge without optical aid. I was wrong. At least my eyes wasn't up to the task. Through binoculars and telescopes it was amazing.
The size difference between the two bodies as well as their color contrast made for a delightful and informative sight. Watching the planet "rise" from behind the moon when it returned to view was the highlight.
This time around, observers in most of the U.S. will witness the waxing gibbous moon pass close to Mars in conjunction on Monday night, Jan. 30. Although they'll be near one another all night, they'll squeeze closest around 12:30 a.m. (Jan. 31) for the East Coast; 11:30 p.m. for the Midwest; 10:30 p.m. for the mountain states and 9-9:30 p.m. for the West Coast. For U.S. and Canadian observers the moon will slide below (south) of Mars.
Here's a sampling of cities and approximate local times when moon and planet will be closest. Separations are in arc-minutes. For reference, one full-moon-diameter is equal to 1/2° or 30 arc-minutes. For convenience, we use the prime symbol (′) as shorthand for arc-minutes. If Mars and the moon are 10′ apart that's equal to one-third of a full-moon-diameter — a tight separation when viewed with the naked eye.
Duluth, Minn. — 11:30 p.m., 11′
Minneapolis — 11:30 p.m. 9′
Fargo — 11:30 p.m., 10′
Chicago — 11:48 p.m., 8′
Philadelphia — 12:50 a.m. (Jan. 31), 9′
Memphis — 11:48 p.m., 1′ (visible in binoculars / telescope)
Denver — 10:25 p.m., 3′
Seattle — 9:05 p.m., 11′
If you're reading this and live south of the double green line shown in the map, the moon will completely cover (occult) Mars. That includes the cities of Montgomery, Oklahoma City, Albuquerque, Las Vegas, Los Angeles and part of Hawaii. An interactive version of the map is available at poyntsource.com/New/Google/Mars_2023_Jan_31.htm .
The planet will disappear at the dark, nighttime edge of the moon and return to view along the bright, sunlit side. Go to lunar-occultations.com/iota/planets/0131mars.htm for a list of cities and times of its disappearance and reappearance. Be aware that the times shown are in UT or Universal Time. Subtract 5 hours for EST; 6 hours for CST; 7 hours for MST and 8 hours for PST.
How close will you be able to follow Mars up to the moon's edge with just your eyes? Good question! That depends on sky conditions and how good you are at fishing out a point of light from the lunar glare. Since its last occultation Mars has faded a good bit. In early December it shone at -1.9 magnitude (brighter than Sirius). This time around it's more than a magnitude fainter at -0.3.
My guess is that observers who live where the planet passes 10′ or less from the moon will temporarily lose sight of it with the naked-eye. Binoculars and small telescopes should show Mars right up to the moon's edge no problem.
No matter what, we'll all get to see a really great conjunction.