Astro Bob A look at celestial happenings in the Northland and beyond Bob King View my profile Click here to view previous posts or additional resources

Brightest asteroid a snap to see in binoculars

Tomorrow we can look forward to seeing one of the thinnest crescent moons ever paired up with Venus and Jupiter low in the western sky at sundown. My enthusiasm for seeing this trio is tempered by a snowy weather forecast. Maybe we'll get lucky, and maybe some of you reading this will have clear skies. I'll have more details in Sunday's blog so stop back again tomorrow. 

The dashed line is the border between Puppis (PUPP-iss) and Canis Major. To find M46 and M47, extend a line through the two stars on either side of Sirius one length (or one outstretched fist) to the left or east. M47 is visible with the naked eye and bright in binoculars. Created with Stellarium

We continue today with our cluster hunt in Canis Major that we began yesterday. Did any of you stand out in the cold to find M41? The sky was very transparent for much of the night from my home, and I could just detect the cluster with the naked eye. Two other clusters I always associate with Canis Major but which aren't actually in the constellation are M46 and M47. They belong to neighboring Puppis, the stern of the ship sailed by Jason and the Argonauts. If you look at yesterday's map of Canis Major you'll see that both clusters are in the band of the winter Milky Way. They're two of the brightest in a region filled with star clusters for scopes of all sizes.

Our three featured binoculars star clusters are (from left): M41, M47 and M46. The small blue dot at the top of M46 is the planetary nebula NGC 2438. Credits: M41 & 47 - NOAO/AURA/ NSF. M46 - Jim Misti

M47 is a bright, loose jangle of some 50 stars stars about a "fist" to the left of Sirius. Just follow the line comprised of the three stars across the top of the constellation. I can easily see about a dozen stars in my 8x40 binoculars. M46 is a different beast altogether -- a mysterious-looking misty spot to the left of M47. My binoculars fail to show individual stars but the contrast between the two clusters is striking. Telescopes have no problem resolving M46 into stars. Though fainter, it's a richer cluster than its neighbor to the west with at least 150 stars plus a bonus planetary nebula pinned to its northern edge. The nebula, called NGC 2438, is most likely superimposed against M46 rather than physically inside it. M46 is a distant 5,400 light years away compared to M47's 1,600 explaining why it looks so much fainter in your binoculars.

Thanks to the bright, naked eye star Gamma Leonis, Vesta will be easy to find in binoculars in the coming nights. The circle represents the approximate circle of sky you'll see in binoculars. The yellow crosses show the asteroid's position each night. Use the wide-angle map below to help you find Gamma. Created with Chris Marriott's SkyMap software.

During the remainder of this month and into early March, sky watchers with binoculars have a great opportunity to see the brightest asteroid of them all -- 4 Vesta. Vesta was the fourth asteroid discovered (hence the number) and was found by astronomer Heinrich Olbers on March 29, 1807. It's 329 miles across and orbits within the asteroid belt at an average distance from the sun of 220 million miles. This month Vesta is at opposition to the Earth (making a close approach) and shining at 6th magnitude. From a dark sky site, it's very faintly visible to the naked eye but any pair of binoculars will show it easily. Heck, I walked right out of the house last night without dark-adapting my eyes, pointed my 8x40s at Vesta and voila -- there it was!

Gamma Leonis is the bright star in the bend in the "Backwards Question Mark" of Leo that you'll point your binoculars at to seek Vesta. Right next to it is 40 Leo. You can use the Big Dipper to get you there. This map shows the sky about 9-9:30 p.m. as you look east. Created with Stellarium

The word asteroid means "starlike". Only the very largest telescopes can discern the shapes of a few of them, otherwise the asteroids are all much too small to look any different from stars. Yet they do betray their membership in the solar system in one obvious way. Asteroids move in orbits around the sun like the planets so you'll be able to watch Vesta progress westward through Leo night by night.

Tomorrow we'll take a closer look at Vesta and learn among other things, how we discovered pieces of it lying around of all places right here on Earth.

Posted by: rking@duluthnews.com on 2/13/2010 at 11:21 AM | Comments (0) | Permalink | Edit

Tags: daily updates, canis major, star cluster, astro bob, life, moon, sirius, puppis, m46, m47, vesta, asteroid