February 2010

Tony Martinez

Each month I will describe sights of interest in the night skies of South Carolina. These sights will be broken down into three sections; what you can see with the naked eye, with binoculars, and with a small telescope. The best time to view the night sky is at and around the times when the Moon is not visible, what is known as a New Moon; which will occur this month on February 13^th. For February, your best viewing nights will be from February 3^rd through February 19^th. The Star chart below is set for Florence, SC on February 15^th at 9 pm.

Vesta:

I am going to make a guess that anyone who reads this column and enjoys amateur astronomy has seen most if not all the common night time objects except one, asteroids, primarily because they can be quite difficult to find. If you have not yet seen an asteroid, this is a good month to start. The asteroid to locate is called Vesta.

Vesta is an irregular shaped “rock” with a diameter of about only 330 miles, at a distance of over 100 million miles; quite a challenge for an amateur! Vesta is formally called 4 Vesta because it was the 4^th asteroid discovered. Vesta was discovered in 1807 and is the second largest asteroid; Ceres is the largest with a diameter of about 600 miles. Also, Ceres unlike Vesta is large enough to be spherical, and is therefore classified as a dwarf planet along with Pluto. However, Vesta does hold the honor of being the brightest asteroid, which will also make it easier for you to see. Below is Hubble’s view of Vesta.

Here is another interesting Vesta fact. In October 1960, some men mending fences in Australia saw a large meteor fall to earth. Eventually the site of this meteor’s impact was located, and pieces of the meteor were recovered. It was later determined that this meteor was a piece of the asteroid Vesta! How did they know it really came from Vesta? A scientific method known as infrared spectroscopy is used to scan certain objects and give a type of “fingerprint” of the material. It was found that telescopic infrared spectroscopy of Vesta was a “fingerprint” match of the Australian meteorite. Years later, observation of Vesta by the Hubble telescope showed a massive crater covering a large portion of Vesta; likely the source of the meteorite. Over the years, many other Vesta meteorites have been discovered around the world. These Vesta meteorites are called HED meteorites; a name derived from their chemical composition.

So how did astronomers over the last 200 years discover asteroids? In the beginning, it was totally by chance. An astronomer may have been studying a particular star or other object for several hours or nights. In the process, it was noted that one of the “stars” in the field of view moved. This moving speck of light turned out to be one of many small pieces of rock, which we now call asteroids. The astronomers were also able to determine that these asteroids were in an orbit around the Sun, between the orbits of Mars and Jupiter. Once astronomers were aware that these objects existed, they started to look for new asteroids. The discovery of new asteroids moved slowly until the development of astrophotography at the end of the 19^th century. At that time, several astronomers had discovered a total of 323 asteroids. In 1891 when an astronomer Max Wolf began using astrophotography he discovered another 248 just by himself! By the late 1900’s, a total of a few thousand asteroids were discovered. The next “giant leap” occurred with the use of digital astrophotography combined with computerized analysis. Just one asteroid searching team called LINEAR has alone discovered over 97,000 new asteroids! Below is an image of some dwarf planets beyond the orbit of Pluto, and some asteroids compared to the size of the Earth, note the size of Vesta.

So now it is your turn, and you only have one asteroid to find this month. Why did I choose this month? Since these are tiny and somewhat difficult objects to see, it is good to have a marker in the sky to help out. On February 16th, Vesta moves between the stars Algieba and 40 Leonis in the constellation of Leo the Lion. On that night, Leo will be well above the horizon by 9 pm. Algieba is easily seen and is part of the backwards question mark forming the front of Leo. The chart below shows the location of Algieba in the Leo question mark.

When you look at Algieba with simple binoculars, you will see the star 40 Leonis below and to the right. The charts below show the position of the asteroid Vesta in relation to these two stars over a period of three nights.

So on these nights, at about 8 pm, use a pair of binoculars to locate these two stars and Vesta. Next, make a sketch of the objects you see. Then check again at 10 or 11 pm, and see if the object you thought was Vesta moved. If you are not sure, keep your sketch, and check that location the next night. With luck, you should be able to make your first asteroid sighting. Over the months I will tell you about any other easy to find asteroids.

Naked Eye Sights: Observe as Orion begins its departure in the West while the main constellation of spring, Leo, arrives in the southeast.

Binocular Sights (7 to 10 power): Main target this month is the asteroid Vesta. In addition, the great sights such as the Pleiades and the Orion Nebula are still visible.

Telescope Sights (60-100mm): Mars is now high in the sky. If you have been waiting for the return of Saturn, it is visible in the east after 10 pm at the end of the month. Saturn’s rings will slowly open up throughout 2010.

See you next month!