Lots of news in the world of astronomy this week. First, let’s do some updates. Supernova SN 2011fe in the Pinwheel Galaxy (M101) appears to have peaked at magnitude 10.0 according to my own estimates over the past few nights using charts available from the American Association of Variable Star Observers. That makes it the 6th brightest supernova ever seen outside the Milky Way system.
We’re now headed for full moon, so the galaxy appears faint to invisible in most telescopes. Don’t let that stop you. SN 2011fe is so bright, you can star-hop to it without the need to even see the galaxy! Recent observations show that debris is expanding away from the supernova explosion at some 12,000 miles per second. I updated the finder chart for a third time to help get you there. Click HERE to see it and a telescopic map.
Tomorrow morning (Sept. 9) the bright planet Mercury is in conjunction with Regulus, Leo the Lion’s brightest star. If you’re up around 6 a.m. and have a great view to the east, try to spot the pair low in the sky far to the left of the stars Procyon and Sirius. Mercury should be fairly easy to see with Regulus requiring a little more effort. Keep your binoculars handy.
Some of you have e-mailed me asking what’s happening lately with Comet Elenin. It’s still rather faint — around 9th magnitude — and the comet’s coma continues to fade and spread out as the nucleus disintegrates. Well-known Japanese comet observer Seiichi Yoshida’s new light curve, which is a prediction of of the comet’s future brightness based on current and past behavior, shows Elenin only reaching 8th magnitude in October at brightest. That would make it faintly visible in binoculars under rural skies.
The comet reaches perihelion or closest distance to the sun this Saturday at 44.6 million miles or about half Earth’s average distance from the sun. Everyone eager to see Elenin when it pops into the morning sky next month hopes it survives the additional heating and more powerfully-felt solar gravity at perihelion. If so, perhaps the comet will be bright enough to see in the Solar and Heliospheric Observatory’s C3 coronagraph a couple weeks before we see it in the dawn sky. Comet Elenin should be in the instrument’s field of view from September 24-28.
Weather forced NASA to scrub today’s launch of the Gravity Recovery and Interior Laboratory (GRAIL) mission to the moon and re-schedule it for early tomorrow morning. Two identical spacecraft will be sent to orbit in tandem around the moon for several months. Using a microwave signal, the distance between the two probes can be measured with great precision. By watching that distance expand and contract as the pair fly over the lunar surface, researchers will be able to map the moon’s underlying gravity field.
“These measurements will tell us a lot about the distribution of material inside the Moon, and give us pretty definitive information about the differences in the two sides of the Moon’s crust and mantle. If the density of crustal material on the lunar far side differs from that on the near side in a particular way, the finding will lend support to the ‘two moon’ theory,” according to David Smith, GRAIL’s deputy principal investigator at MIT.
The two-moon theory is a recent attempt to explain why the farside of the moon is so different from the nearside. The farside is covered in mountainous highlands and saturated with craters, while the nearside is dominated by vast, lava-filled impact basins or ‘seas’. The seas are the dark blotches that comprise the face of the ‘man in the moon’ most noticeable around the time of full moon.
Martin Jutzi and Erik Asphaug of the University of California at Santa Cruz believe that two moons formed when Earth was struck by a Mars-sized asteroid early in its history. The resulting debris from the collision may have created a larger body that would ultimately become the moon and a smaller moon that later collided in a more gentle fashion with the larger body. Instead of gouging out a huge crater, it went splat on what’s now the lunar farside, coating it with a thick layer of debris. It’s an intriguing idea, and one scientists hope the GRAIL mission may provide more evidence for. To read more on the topic, take a look at this NASA release.