The skies this month
February 1: Mercury is visible below the thin crescent moon low in the western skies about 45 minutes after sunset.
February 3: Full moon
February 10: The moon lies in the Milky Way just below Jupiter in the constellation of Gemini. To the left of Jupiter you will find the bright twin stars, Castor and Pollux
February 11: Last quarter moon
The winter triangle
The Milky Way is brilliant this month in Crestone skies. Orion, the Hunter, is halfway up toward the zenith in the south. It contains the unmistakable three stars of his belt. His sword, which contains the Great Nebula of Orion, is hanging from belt. The upper brilliant red star is Betelgeuse and the lower star on the right is Rigel. Follow the three stars of the belt to Sirius, the Dog Star, the brightest star in our northern skies, lying a modest distance of 8.75 light years away. Up above Sirius is the small dog Canis Minor, of which Procyon its brightest star. To the right is the beautiful bright red star Betelgeuse. These three stars form the Winter Triangle.
The winter Milky Way
Lying between Procyon and Betelgeuse is our wintery view of the Milky Way Galaxy, our home in the universe. Our galaxy has spiral arms, and our solar system lies on the inner edge of one of its arms. The summer Milky Way is in the direction of the center of the galaxy, some 27,000 light years away, obscured from our view by gas and dust. But in winter, we are looking away from the center of the galaxy and seeing the nearby stars in our own spiral arm, which is the reason that the region of Orion, Canis Major, Canis Minor, etc is so rich in bright stars.
Following the Milky Way upward, you come to Jupiter, currently residing in Gemini. Above it is the bright star, Capella, in the constellation of Auriga at the top of the sky. Continue to the north, and you will come to the two fuzzy spots of the double cluster of Perseus. Their visibility is one of the great tests for the darkness and clarity of the sky, and they are normally easily visible in the skies of Crestone. Even though each of these clusters contain more than 500 bright, young stars, they lie across the vast expanse of space between our spiral arm and the next one, at a distance of 8000 light years.
Dawn comes to Ceres
We’ve been occupied during the past few month with the European Space Agency’s Rosetta Spacecraft and the comet it is orbiting. Meanwhile, our NASA has been very busy with another kind of exploration. Its spacecraft Dawn, which was launched in September 2007, has been orbiting the asteroid Vesta for 14 months and is now on its way to do the same with Ceres, the largest object in the asteroid belt. It will reach Ceres on March 6, 2015 and then go into orbit for 16 months. Like the erstwhile planet Pluto, Ceres is designated as a dwarf planet. Never before visited by space craft, Ceres may contain an ocean of liquid water under its surface. Plumes of water vapor have been detected from several regions of Ceres. Water means the possibility of life, which we might be able to explore and sample in the future. It is closer to the earth than other floating oceans in the solar system. Take Europa, the moon of Jupiter, for example. It appears to have a huge hidden ocean. Unfortunately, Europa is contained in the radiation belt of Jupiter. High energy electrons and protons are raining down on its surface, making it a very unattractive place for human, or even robotic, exploration. Enceladus, a moon of Saturn, also has lakes of water under its surface, but it is very far away.
Ceres will be the first dwarf planet to be visited by space craft. The second encounter with a dwarf planet will come in July when the New Horizons spacecraft flies past Pluto. Dawn is supposed to undertake a 16-month study of Ceres once it gets into orbit, coming as close as 250 miles to its surface. When the fuel of Dawn is exhausted, it will be left as an artificial satellite orbiting Ceres. Models predicting its orbit have been run for the next hundred years and it appears to have a very stable orbit. It looks like Dawn will become a perpetual artificial satellite of Ceres: something for the ages!
Dawn is arriving at Ceres after a very successful sojourn orbiting Vesta, which is the second largest object in the asteroid belt. This 330-mile-wide rock has the appearance of an underinflated football, which, dare I say, looks slightly like a Patriot’s deflated football. The shape of Ceres is the result of a colossal collision that ripped away a big chunk out of its southern polar region. It is a special place. Vesta appears to have an inner core of iron. With the exception of the four inner planets (Mercury, Venus, Earth and Mars) and Jupiter’s moon Io, Vesta has the highest density of all known objects in the Solar System. Its surface area is approximately the same as that of Pakistan. Temperatures on the surface lie between about relatively balmy -4°F when the sun is overhead, to a low of -310°F at the pole at winter.
A fascinating discovery made by Dawn is the connection between Vesta and a class of meteorites, known as HED, which make up 6% of all meteorites that have fallen on the earth. Pyroxene, a mineral rich in iron and magnesium, is found in these meteorites and measurements of light reflected off the surface of Vesta show the presence of that same mineral. How absolutely wonderful! We don’t need to visit Vesta in the future and bring home some of its surface. Bits and pieces have already arrived and haven’t cost a cent!
It is likely that these meteorites were thrown off Vesta in big impacts at the southern pole. The Rhea Silvia crater measures some 475km in diameter, almost as large as the asteroid itself. About 250,000 cubic miles were excavated from Rhea Silvia, which is enough to fill the Grand Canyon a thousand times over. Some of that excavated material lies scattered across the surface of Vesta outside Rhea Silvia crater. Some have been propelled into space to form other asteroids. And finally, some of those fragments have reached (and will continue to reach) the earth as meteorites. We can estimate the age of surfaces of asteroids by counting the number of impact craters. Few such craters means that the surface is young; lots indicate battering over millennia. The pattern of craters on Vesta reveals that the great hole on its southern pole was gouged out a billion years ago.