If you step outside tonight you’ll see a bright waxing gibbous moon below the Great Square of Pegasus. Far to the moon’s lower right shines Fomalhaut, the only bright star in the southern half of the sky during early evening hours.
While the moon looks smooth and pasty to the naked eye, binoculars will show its biggest craters and rough, crinkly surface especially if you direct your gaze along the terminator, the curving border separating the bright, sunlit portion of the moon from the part that’s still in darkness.
Tonight’s 9-day-old moon features an arc of four prominent lunar craters just this side of the terminator: Plato, Copernicus, Tycho and Clavius. Plato, the northernmost and 68 miles across (109 km), looks like an oval swimming pool only instead of water it’s filled with dark, titanium-rich lava that solidified some 3.8 billion years ago.
Dropping south we next encounter Copernicus (58-miles / 93 km). Though smaller than Plato, it looks far more impressive because the crater sits at the center of a great corona of rays. Lunar rays form when material blasted out by an impact fall back to the surface to create long chains of secondary craters. Seen from 240,000 miles away in binoculars and telescope they look like wispy white tendrils.
Copernicus is a bowl 2.3 miles (3.75 km) deep that was blasted out in the not-to-distant past 800 million years ago. I know that sounds like a lot of years but compared to 3.84 billion years for Plato, Copernicus is a youngster. If you have a scope, look inside and around the the crater to see and appreciate how rugged and relatively fresh it is.
Continuing along the arc we meet Tycho (53 miles / 86 km), the largest fresh crater on the near side of the moon. The asteroid that excavated it struck the moon about 108 million years ago during the heyday of the dinosaurs. Sharply-defined walls and a pointed central mountain peak reflect its youth. Even without water and air, erosion happens all over the moon. The temperature extremes of the lunar day-night cycle break down the rocks, while bombardment of the surface by solar particles and radiation gradually “sandpapers” them to a powdery finish.
Like Copernicus, Tycho’s wears a crown of rays best seen around full moon.
Our last stop is Clavius, the third largest crater on the visible side of the moon. Measuring 140 miles across or about the distance between Duluth, Minn. and Minneapolis, this 4-billion-year-old scar is so huge it’s riddled with dozens of younger craters easily visible in a small telescope. Glide down the arc tonight and see all four craters.
I thought I’d put together an updated tableau of the four bright morning comets Encke, ISON, Lovejoy and C/2012 X1. Encke will meet up with Mercury this weekend a few days before Comet ISON does the same on Nov. 17. Speaking of ISON, it’s developed two very clear tails the past few days – one of dust and the other gas. I’ll have a map in Friday’s blog to help you find the two. Meanwhile, Lovejoy has quietly slipped into Leo the Lion and C/2012 X1 is approaching the bright star Arcturus. There is a lot happening before sunrise!
That includes the return of the space station passes for many northern hemisphere locations. I’ve listed bright passes for the Duluth, Minn. region below. Click over to Heavens-Above or Spaceweather’s Satellite Flyby page for times for your city.
* Weds. morning Nov. 13 starting at 5:44 a.m. in the southwest and traveling to the northeast. Brilliant pass high in the southern sky.
* Thurs. Nov. 14 at 6:31 a.m. Nice bright pass halfway up across the northern sky.
* Fri. Nov. 15 at 5:45 a.m. passes almost directly overhead. Brilliant!
* Sat. Nov. 16 at 6:31 a.m. halfway up across the northern sky.
* Sun. Nov. 17 at 5:45 a.m. Another pass halfway up in the northern sky
* Mon. Nov. 18 at 6:31 a.m. in the northern sky