See A Lunar Crater Arc Tonight / 4-comet Tableau / Space Station Flybys

Tonight’s gibbous moon features a lovely arc of large craters visible in binoculars beginning with Plato on down to Clavius. Credit: Christian Legrand and Patrick Chevalley’s Virtual Moon Atlas

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.

The waxing gibbous moon shines high in the southern sky below the Square of Pegasus during early evening hours tonight. Stellarium

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.

Clockwise from top left: Comets 2P/Encke on Nov. 4, ISON (Nov. 12), C/2012X1 (Nov. 6). and Lovejoy (Nov. 10) . All four comets are visible  in 50mm and larger binoculars from a dark sky site. Comet ISON’s dust and gas tails are now very obvious. Credits: Damian Peach (Encke and X1) and Michael Jaeger (ISON and Lovejoy).

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

8 Responses

  1. Brian Larmay

    These clouds are killing me. I have not imaged anything in the last three months.
    Seeing these incredible comet images add to the frustration.

    Sorry to whine, but withdrawal is taking its toll.


    1. astrobob

      Hi Brian,
      I’ve been there and know exactly how you feel. Sorry to hear about your skies. I wish you better conditions soon! We went through a long spell of clouds from the end of Oct. through the first week of Nov. Only recently have we gotten a couple clear-partly clear nights, most of them under threat of clouds later in the night.

      1. Brian (a different Brian)

        Hi Astro Bob,

        I hope the following is useful to you and your readers.

        Environment Canada publishes forecasts of the clouds, seeing conditions, sky transparency, and ground weather for astronomy in N. America in the Analyses and Modelling section of their website at

        Here’s what the top-page says:

        This web site gives access to up-to-date meteorological forecasts in order to provide astronomers with information to plan their sky observation activities. The forecasts cover North America and are produced by the numerical weather prediction models that execute at the Canadian Meteorological Center.The following forecast parameters are available in real time: forecasts of cloud, surface winds, temperatures and humidity as well as more specific parameters such as seeing forecasts and sky transparency.

        Cloud forecast
        Cloud forecasts at hourly intervals up to 48 hours.These forecasts can be interpreted in the same way as satellite pictures in the visible spectrum.

        Seeing forecast
        Seeing forecasts at 3-hourly intervals up to 48 hours. The “seeing” is the term used in astronomy to quantify the steadiness or the turbulence of the atmosphere. The detailed observation of planets, planetary nebulae or any celestial object requires excellent seeing conditions.

        Sky transparency forecast
        Sky transparency forecast at hourly intervals up to 48 hours.Observing deep sky objects such as faint galaxies and nebulae requires excellent sky transparency. Astronomers evaluate sky transparency based on the magnitude of the faintest star visible to the unaided eye. Sky transparency varies with airmass type.

        Weather forecast near the ground
        Wind, temperature and humidity forecasts near the ground surface for the next 48 hours.

  2. Edward M. Boll

    Plans for Thursday morning viewing, dashed with call to work. I have to get out Friday, or it will be Monday again before I have another chance. We are loosing Encke and ISON fast to the twilight. ISON was on Nov. 8 only mag. 8.1, average of last 7 reports. At that time it was only about .77 AU from the Sun. If it would have brightened as predicted, it should have been about about 2 magnitudes brighter.By using the slower brightening model, I have predicted a magnitude of -2.6 at about 8 million miles from the Sun, which will occur on the early evening of the 27th in the USA.

    1. astrobob

      Good luck – hope you see it soon! I’ll be out tomorrow morning, my last shot for a few days because of snow in the forecast.

  3. allison

    Is it possible that Comets Lovejoy and LINEAR are switched/mislabeled in the 4-comet montage? I think that’s Lovejoy at bottom left and LINEAR at bottom right.

    Going to try to see all of those, plus C/2013 V3 (Nevski) tonight (I’ve previously seen all but LINEAR and Nevski). Might try for C/2013 N4 (Borisov) also!

    1. astrobob

      Thanks for pointing out the error. I switched photos and forgot to update the caption. It’s correct now. You’ll have a blast with all those comets. Nevski is much brighter than expected and probably in outburst. I saw it this morning at mag. 9.7.

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