The Night Sky, written b astronomers from the East Tennessee State University Department of Physics and Astronomy, appears o the last Sunday of the month previewing upcoming events for East Tennessee sky watchers.
July brings warmer weather and more time outdoors, and many reasons to look at the night sky. While you are waiting to enjoy the fireworks on the 4th take a moment to look at the full moon, which should be shining in the east. The July full moon has several names. The English tradition called it the Hay Moon, but it is also known as the Buck Moon (for the new antlers growing on young bucks) or the Thunder Moon (for the frequent thunderstorms at this time of year.)
Later in the month, nature will be providing its own, less ostentatious fireworks with the Delta Aquariid meteor showers. This is relatively long-lasting meteor shower, lasting from approximately mid-July through early August, with the peak on the 28th or 29th The meteors will be most visible in the early morning before dawn, streaking from the South across the sky.
Up beyond the Earth’s atmosphere, NASA’s Dawn probe is about to enter a new phase in its mission to explore the asteroids. Launched in 2007, it arrived to orbit around the small Solar System body Vesta last July. At the end of this month, or early next month, it will finish its current study and head off o its three-year journey to the largest asteroid, the dwarf planet Ceres.
Ceres orbits the sun between Mars and Jupiter, and was discovered on the first day of 1801. It was originally classified as a planet. But soon other objects near Ceres were discovered, and within a few decades it became clear that it was not the same kind of object as the other planets known at the time. In fact, the material in what is now called the Asteroid Belt is probably the same that formed the other planets, but it was strongly perturbed and never coalesced into a single body. After about 50 years and many new objects were discovered, astronomers realized that Ceres and its companions deserved recognition as a new type of object, and were reclassified as asteroids.
If you think this sounds familiar, you’re right. A hundred or so years later, the same thing happened again. Pluto was discovered in 1930 and classified as planet. But within the past several decades it has become clear that Pluto is actually much smaller than originally thought, smaller even than the Earth’s Moon. Many other objects were also discovered at approximately the same distance from the Sun. Like the Asteroid Belt, they are also remnants of the disk that formed the planets, but never went through the final stages of formation that would have made them into one larger object.
The issue of what to call Pluto was brought to head when new object was discovered that was larger and further out than Pluto. Since this object had at least as much claim to the name of planet as Pluto, astronomers either had to continue to add objects that were very different from the first eight planets, or re-evaluate the terminology. The words we use to describe things can either clarify or obscure, depending o whether they represent real categories or not, and it’s the job of scientists to increase understanding of the universe. So when the International Astronomical Union met in 2006, they defined three new categories of object: planet, dwarf planet, and small Solar System body. By these definitions, Pluto is dwarf planet (as is Ceres.) This in no way changes Pluto’s importance to astronomers. A NASA probe is on its way to Pluto now, and will give us unprecedented knowledge of its structure and history. Calling Pluto a dwarf planet is not a demotion, but rather a reflection of our improved understanding of this fascinating world.
The ETSU Powell Observatory open houses are on hiatus for the summer. They will resume in the fall.
This month’s Night Sky was written by Dr. Tabetha Hole, Postdoctoral Research Fellow at the Department of Physics and Astronomy. She can be reached at [email protected]. Astronomy-related information for the public, including a link to the ETSU astronomy open houses, can be found at http://www.etsu.edu/physics/astronomy.htm.