The Last Month in Astronomy

DEC-13-2010 •Voyager Leaving• Voyager 1 has been traveling for 33 years. Finally it is out so far that the solar wind has no outward motion. It is nearing 11 billion miles from the sun. The solar wind is still present but the interstellar wind is pushing it sideways. http://www.jpl.nasa.gov/news/news.cfm?release=2010-415

DEC-09-2010 •WISE Colors• The supernova remnant IC 443 has shown some unusual coloration when imaged by WISE, the Wide-field Infrared Survey Explorer. The infrared image was given representational colors (please don’t say false-colored) and it shows that half of the shell has a different density and color and elemental makeup than the other half. It seems unlikely that the progenitor star was different in one half than the other so the difference must be due to differences in the material around the supernova. http://www.nasa.gov/mission_pages/WISE/multimedia/gallery/pia13449.html

DEC-02-2010 •Billions and Billions• No, Carl Sagan never actually said that. But he was trying to tell us how many stars there are in the universe. The math is fairly simple. If our galaxy has 4 x 10^11 stars and let’s say that is typical and there are 10^11 galaxies, then you end up with 4 x 10^22 stars or 4 septillion. It turns out that number is a little low, maybe by a factor of 3. That’s the conclusion of Pieter van Dokkum (Yale) and Charlie Conroy (Harvard). They look at elliptical galaxies such as the very large ellipticals found in the Virgo and Coma clusters. What they found is that the percentage of red dwarf stars is much greater than we have in the Milky Way galaxy. If these elliptical galaxies are typical, then these galaxies have 20 times as many red dwarfs as do spiral galaxies. http://www.skyandtelescope.com/news/111192389.html

NOV-30-2010 •Planet Steam• The star Gliese-Jahreiss 1214 is a dim M class star 40 light years away. It has a planet that is 6.5 Earth masses which was discovered in 2009. The planet, GJ1214b, is seen to transit its star once every 38 days and its atmosphere can be studied spectroscopically. That spectrum indicates that the upper atmosphere is dominated with water vapor or clouds. Because it is detected during a transit, the diameter can be estimated and thus the density which turns out to be 1/3 of the Earth’s. That low density rules out a gas giant. http://www.skyandtelescope.com/news/111070634.html