General Astronomy, 29:61
Fall, 2004
Observational Exercise ...Observations of Uranus, Neptune, and Vesta

I. Introduction
By this time in the semester, students have heard and read much about planets, but haven't seen any unless they have risen before dawn. This observing exercise is intended to remedy that. All semester long, Uranus and Neptune, the two furthest major planets, have been in the evening sky. However, since neither is visible to the naked eye (at least in town), they have not been obvious.

In addition, the most conspicuous example of an interesting class of objects, the asteroids, has also been in the evening sky. This is Vesta, a minor planet 600 kilometers in diameter. Vesta hovers near naked eye visibility sometimes. It is a very interesting asteroid; among other reasons for its appeal is the fact that you can see pieces of it in the Smithsonian Museum of Natural History in Washington, D.C.

This is not a strenuous lab activity; it is intended to sharpen your observing skills rather than illustrate subtle processes from physics. I hope you will appreciate the following.

1. You will be able to see faint, starlike images move with respect to the background stars over a period of weeks. This will be your clue that these are solar system objects, orbiting the Sun and moving with respect to the Earth.
2. These observations will give you an intuitive sense of how vast are distances in the solar system. Uranus and Neptune are planets considerably larger than the Earth. However, their distances of 19.9 and 30.2 astronomical units from Earth (at the present time), respectively, render them no more than faint points of light. Think about their distances as you look at them.
3. Asteroids have some extremely interesting properties, and they have probably played a major role in the geological history of the Earth. Having Vesta in the evening sky is one of your best chances to see one.

II. What to do
First, you need to prepare for your observations. This involves finding the position (celestial coordinates) of the objects, and locating them on a good star chart that you can use in the observing session. Later, we will make the observations with binoculars or a small telescope.

There are two ways of doing this preparation.

IIA. Method A. Use of planetarium programs
This is probably the best way to do it. Use a program such as Starry Night Pro, or other with which you are familiar. Have it find Uranus, Neptune, and Vesta for you. Have it generate a star chart which is a few degrees across (comparable to the field of view of a pair of binoculars), and have it plot stars down to magnitude 8 or 9. This is about the limit of binoculars. Even if you use Starry Night Pro to find the objects for you, it is advisable to use the star charts from Method B. below to plot it and use for the actual observations.

IIB. Method B. Use of star charts
Star charts from the Skalnate Pleso atlas will be available. This set of star charts is just about ideal for this sort of exercise because the faintest stars plotted are about as faint as what you see in good binoculars. The star charts will have grid lines corresponding to right ascension and declination. The coordinates for our objects are:

Table 1: $\ast$ Distance for Vesta is at closest approach

Object	Right Ascension	Declination	Distance (a.u.)
Uranus	22$^{h}$20.5$^{m}$	-11$^{\circ}$ 10$^{'}$	19.88
Neptune	21$^{h}$01.0$^{m}$	-17$^{\circ}$ 04$^{'}$	30.24
Vesta	23$^{h}$16.5$^{m}$	-15$^{\circ}$ 26$^{'}$	1.36$^{\ast}$
$\delta$ Aquarius	22$^{h}$54.9$^{m}$	-15$^{\circ}$ 48$^{'}$	--

The coordinates for $\delta$ Aquarii are included for the following reason. The coordinates given here are for the present time. The Skalnate Pleso chart was drawn up with right ascension and declination for the year 1950. Due to the precession of the Earth, there is a small but easily detectable shift in the coordinates of the background stars during this 50 year period. $\delta$ Aquarii will help you determine the amount you have to shift the positions in the table to plot them on the star chart.

Use these charts to find the parts of the sky where the three objects are. Try to find the ``star the shouldn't be there''. That will be Uranus, Neptune, or Vesta as the case may be. Uranus will be the easiest to find, Neptune the most difficult.

Plot each of the objects on the star chart, or make your own drawing of the star field and where you find the planet. One point you should note is how bright the planet is relative to nearby stars. Write this information on the form you use for other observations.

Keep these records, which could be on the back of this document. We will repeat the observations in three weeks to a month. By that time, the objects should have moved relative to the background stars. After the second observation, turn in your observing forms to your teaching assistant.