Rocky objects that orbit the Sun that are too small to be called planets and too large to be called dust are called asteroids. "Asteroid" means star-like, which describes their appearance through a telescope. Although they look like stars from Earth they move around the sky just as the planets do, and are sometimes called "minor planets". Most orbit in a region between Mars and Jupiter called the "Asteroid Belt". Many movies depict the asteroid belt as a crowded place with dozens of tumbling boulders in plain view at any time. Actually, if you were riding on a typical asteroid the nearest asteroid to you would appear as a very faint star. Asteroids rarely pass within a million miles of each other! The largest asteroid, Ceres, was the first discovered in 1801, and is called "1 Ceres". It is about 1000 km (600 miles) in diameter. The brightest asteroid from Earth is 4 Vesta (the 4^th asteroid discovered), which, at a favorable opposition, can just be seen with the naked eye in a dark sky. Vesta’s surface is considerably brighter than most asteroids. Eros is an unusual asteroid because it passes close to Earth and is shaped sort of like a shoe!

When asteroids collide with a larger body, such as the Earth or Moon, they produce craters (not to mention large booms!) such as those visible on the Moon, or the meteor crater outside of Winslow Arizona. Smaller objects merely create bright flaming trails in our sky (meteors), whistling sounds, and sometimes smash mailboxes. There is only one recorded case of a meteor striking a person. This unfortunate woman was vacuuming her home when a meteor came crashing through the roof (it severed a 2 x 10 along the way), the upstairs floor, and struck her in the leg. Fortunately all of the wood slowed it down so that it only gave her a severe bruise.

Many of the meteors that land (called meteorites once they’re on the ground) are made of nearly pure iron! These objects can be cut and polished to look like the finest steel! Iron meteorites are important clues. They indicate that there was an object in the solar system that was big enough to melt (so that all of the iron could sink to the center of it), yet small enough to have cooled and solidified inside. This means that it was probably between 500 and 1500 miles in diameter. The object probably met its doom in a terrible collision with another similar object. The pieces from this collision were scattered into all different kinds of orbits around the Sun. Occasionally Earth meets up with one and allows us to examine what used to be the core of an ancient object. Other meteorites are called "stony" and "chondrite" meteorites. It is believed that the stony meteorites, and perhaps some of the chondrites came from the mantle and crust of the ancient objects that broke up. It is also believed that many of the asteroids are remnants of this big collision, although some may date back to the formation of the solar system.

1. To become aware of what asteroids are, where they are, and what they look like through a telescope.

2. To learn how to use a computerized telescope.

1. A DETAILED sketch of the star field containing the asteroid with the asteroid identified.

3. Notes that describe the color and brightness of the asteroid, and why you are certain that you have found it.

4. Answers to questions.

1. Find a more detailed star atlas on line, in a library, borrow one from a friend, or make an enlarged copy of the appropriate map from your atlas.

2. With a sharp pencil, mark the location of the asteroid on the chart for the dates given in the table below.

3. Draw a faint smooth curve through the marks you have made.

4. Estimate the location of the asteroid on the night you will be observing it and mark it.

5.  Read the instructions on how to use a computerized telescope.

Positions of the Asteroid 4 Vesta for 2010

Date             R.A.        Dec.    Magnitude

January 4            10 H 41.7 M         +14 D 21’           7.1

January 14          10 H 41.3 M         +15 D 11’           6.9

January 24          10 H 38.0 M         +16 D 19’           6.6

February  3         10 H 31.9 M         +17 D 39’           6.4

February  13       10 H 23.5 M         +19 D 05’           6.2

February  23       10 H 13.8 M         +20 D 25’           6.2

March 5              10 H 04.3 M         +21 D 31’           6.3

March 15            09 H 56.1 M         +22 D 17’           6.5

March 25            09 H 50.4 M         +22 D 39’           6.7

April 4                09 H 47.7 M         +22 D 40’           6.9

April 14              09 H 48.1 M         +22 D 20’           7.1

April 24              09 H 51.4 M         +21 D 44’           7.2

May 4                09 H 57.4 M         +20 D 54’           7.4

May 14              10 H 05.5 M         +19 D 51’           7.5

 

1.  Sketch the appearance of the asteroid in the star field and try to determine if you can see any hint of color from it. 

2.  For extra credit, you can try to find this asteroid using the map that you made before the lab.  You will use the technique called "star-hopping" which involves starting with a star that you can find in the finder scope and "hopping" from star to star until you get to the asteroid.  Please ask me to explain this in more detail at the beginning of class if you intend to try for this extra credit.

1. Describe the appearance of the asteroid, including its color and brightness.

2. How do you know it is an asteroid?

3. What is the difference between an asteroid and a star? Why do they look the same?

4. How do you know that other objects are stars and not asteroids?

5. Where are most of the asteroids located?

6. Describe the motion of the asteroid on your star chart that you plotted from the positions that were given.

7. What is happening? (Hint: is an asteroid an inferior or superior "planet"?)