The Observations

If you already know the night sky, the observations can be taken in one clear stretch of about 2.5 hours in one night. If you need to take time to recognize what stars you are seeing, it will take longer.

The two sets of observations of the Northern Sky should be taken within a couple nights of each other, with the first set at least two hours before the second (that is, don't go out at 10 PM on both nights; if the first set was made at 10 PM on one night, the second set should be made at midnight or later on that or subsequent night). Errors increase as the number of nights between observation sets increase. Also, the two sets of observations of the stars near the horizon need to be done within several nights. The second set should be at least one hour clock time later than the first.

For both timed sets of observations, the results improve slightly if more than the minimum of time is allowed between sets (i.e., three hours is better than two hours).

One night plan:

1. The Northern Sky. Measure the altitude of Polaris. Measure the altitude and separation from Polaris for two stars east of Polaris and two stars west of Polaris. Stars that are close to Polaris produce better results than very distant stars.
2. The Horizon. Go around the horizon and measure the altitudes of about ten stars as close to the horizon as possible. (Don't measure anything above 45 degrees altitude). Try to make them equally spaced around the horizon as possible. You must be able to identify each star on the SC-1 chart. Note that the SC-1 chart does not include the northern sky.
3. Measuring a constellation. Choose four or more stars, these may be in the same constellation or in adjacent ones. You should draw a sketch of what the pattern looks like. Measure the separation of each star from each other. You may use the cross-staff or your calibrated hand/fist.
4. Repeat the Horizon measurements. If at least an hour has passed since you started the first set of horizon measurements, go around the horizon again in the same direction as you went the first time. Your goal is to measure the altitudes of stars closest to the horizon, therefore you may measure a different set of stars. Again, you must be able to identify these stars on the SC-1 chart.
5. Complete the constellation measurement or take a break.
6. Repeat the Northern Sky observations. If at least two hours has passed since the first set of observations, measure the altitude of each star (including Polaris) and the separations of the other stars from Polaris. You must use the same stars as you did the first time.

Use graph paper to plot your measurements of the stars around the north pole and of the constellation.
For the horizon measurements, draw your circles around each star with a different color for each set of observations. Check the scale for the circles against the scale on the left or right side of the SC-1 chart. If you aren't sure about how to draw a tangent to these circles, check with your instructor. Use pencil.

You can learn more about celestial spheres at this NASA web site