Introduction:

In another exercise, it was discovered that the time the sun crossed the meridian was dependent upon the longitude of the observer. In this exercise, the latitude of the observer will be altered to see what affect this has upon the position of the sun at local noon. Recall that local noon is when the sun crosses the meridian and that it also marks the point in the sky where the sun will be at its highest angle on that day.

Procedure:

Start up Cybersky. For the sake of consistency, set the longitude and latitude to 106 W degrees and 43 degrees N respectively by using Options/Location. Click on the "Add" button. Create a location called "Workbook" and enter in the coordinates above. This location will be 7 hours behind UT. This is roughly the location of Casper, WY. Alter the date to February 20, 2001. Also make sure that daylight savings time is not utilized by unchecking the box in the Time/Local Time dialog box. It will be helpful to turn off the star names, constellation names, grids, etc. Make sure the planets and sun are still visible though. If there are planets so close to the sun as to be a nuisance, change the date until the sun is mostly alone and not obscured. A date change of a year may be the most helpful so that time of year is still consistent.

Set the sun to local noon, position the cursor over the sun. On the data bar at the right of the Cybersky window is a set of numbers. The first two numbers under "Equatorial Coordinates" are Right Ascension and Declination respectively. The next two under "Horizontal Coordinates" are compass azimuth (South should be nearly 180 degrees) and angular altitude (the one we are interested in here). Note that if the sun is on the meridian, the azimuth should be nearly 180 degrees when the cursor is over the sun.

1) For the coordinates we started with, what is the angular altitude of the sun?

2) Change the longitude to 122 W degrees by editing the "Workbook" location (122 W degrees is near Portland, OR). Move the time until the sun is on the meridian. What is the angular altitude of the sun?

3) Change the longitude to 7 E degrees (near Nice, France). Move the time until the sun is on the meridian. What is the angular altitude of the sun?

4) Change the longitude to 125 E degrees (near Changchun, China). Move the time until the sun is on the meridian. What is the angular altitude of the sun?

5) What is the relationship between longitude and altitude of the sun?

Return to a longitude and latitude of 106 degrees W and 43 degrees N respectively. Return the sun to the meridian. Is the altitude of the sun the same as it was before? If not, you may have changed the date somehow. Return to the proper date and time.

6) Alter the latitude to 50 degrees N (near Regina, Canada). What is the altitude of the sun here? How much did it change? How much did the latitude change in angle?

7) Alter the latitude to 53 degrees N and the longitude to 113 degrees W (near Edmonton, Canada). You may need to change the time slightly to get the sun on the meridian. What is the altitude of the sun? How many degrees did it change from the last measurement? How many degrees in latitude did you change? How many degrees in longitude did you change? You should have discovered earlier that longitude changes are not related to altitude changes.

Alter the latitude to the values in the table below. Find and record the altitude of the sun in each case.

8) What trends do you find in this data? Is there a strong relationship between the angular alteration in latitude and the angular alteration in altitude? If so, what is the relationship?

Now we will go to the southern hemisphere. Change your latitude to 45 degrees S. The sun is not apparent. Do a search for the sun by selecting Search/Solar System Object from the pull down menu and selecting the sun from the dialog box.

9) What change do you notice? What is the facing on the horizon?

Alter the latitude to the values in the table below. Find and record the altitude of the sun in each case.

10) What trends do you find in this data? Is there a strong relationship between the angular alteration in latitude and the angular alteration in altitude? If so, what is the relationship?

extra credit) What mathematical equation might give the correct value?

This page was last updated on 02/21/01.