Juno at opposition
Published on Apr 10, 2007 at 4:52 pm.
No Comments.
Filed under asteroids.
Today, Earth is between the asteroid 3 Juno and the Sun. That means that the asteroid appears opposite the Sun in the sky, as seen from Earth. We call this orientation “opposition” for obvious reasons. At opposition, a body rises at sunset and sets at sunrises. It is highest in the sky in the middle of the night. This is when a body is closest and brightest as seen from Earth. Currently Juno appears to be in the constellation Virgo, as seen from Earth. It isn’t really bright, but it is a bit brighter than magnitude 10 right now, and within reach of good binoculars in dark skies, but you have to know what you are looking for. It will look like a very dim star.
The number “3″ signifies that Juno was the third asteroid discovered. It is not the largest asteroid, ranking about tenth in size. However, it was discovered before its larger cousins in part because of luck, and in part because it has a higher albedo (reflectivity) than the others, making it a bit brighter. It also has a rather elliptical orbit, bringing it somewhat closer to us than some of the other main belt asteroids. It is a rocky asteroid (Type S), but it may have some unusual surface qualities because it does have a higher albedo than other rocky asteroids. Juno is about 150 miles across and somewhat irregular in shape. Interestingly, Juno, along with several of the other asteroids first discovered in the Nineteenth Century, was originally classified as a planet. Astronomy textbooks from the middle of the Nineteenth Century list over a dozen planets. But, no matter how big of a telescope was used on them, they stayed just dots in the telescope, indicating that they were quite small compared with the other planets. Eventually, this fact, together with the discovery of a lot more of these bodies, led astronomers to reclassify it as something else. Officially, they are referred to by astronomers as “minor planets,” but to the layman, they will always be “asteroids.” So, Pluto fans, you can take some comfort, I suppose, in the fact that Pluto wasn’t the first object to be demoted from planetary status.
Several years ago, Sallie Baliunas and her colleagues managed to get some infrared images of 3 Juno using the 100 inch Hooker telescope at Mount Wilson Observatory when Juno was particularly close to Earth, showing its not-quite-round shape. It appears to have a chunk missing from it, too, probably due to an impact with another body. These are the best images ever collected of Juno, and are only possible using a technique called “adaptive optics” which can somewhat compensate for distortion in an image due to convection and turbulence in Earth’s atmosphere. The impact that carved the chunk out of Juno also would have thrown debris all over the Solar System. Undoubtedly, many of the stony meteorites that we find on Earth are really pieces of Juno. Unfortunately, we can’t really be sure which meteorites come from Juno.
-Astroprof
