References:

Introduction:

If you watch the nightly weather on TV, you will often note the time of sunrise and sunset. If you pay attention, you will see it change as the year progresses. In this exercise, we wish to examine the change in the sunrise and sunset time. In addition we will check the compass position of the sunrise and sunset also. As we do so, we wish to see what the correlation is between these investigations and the changing of the seasons.

In your reading, you will have noted that the seasons are due to the tilt of Earth's axis. Another affect this will have is an alteration in the altitude of the sun at noon. So, in addition, we will investigate the altitude of the sun at noon as well as the time of noon. Keep in mind that "noon" to an astronomer is the time the sun is due South. Is this at 12:00? Does the time change during the year?

Finally, we wish to investigate what changes our observations would have if we changed our location on Earth. What would be different in Argentina? at the poles?

Procedure:

This lab will utilize Starry Nights to view the positions of the sun at various places on the earth and at various times of the year. Starry Nights is on the CD included with the Kaufmann text. It runs on Windows and Macintosh computers. Under the Help menu is a choice for the Manual. I suggest you take some time and run through the manual first. Warning: Some commands discussed in the manual cannot be performed on the Freeman edition of Starry Nights. You will need to just ignore those commands. They are not utilized in this exercise.

If you like Starry Nights and wish to order the full version, please contact me first. There are a few other pieces of software I like better, and some of them are cheaper.

A note about the movies linked below. The avi movies can be played with Windows Media Player. If you have Window 9x you should have no problem with them. The mov extension is for QuickTime Player. These are generally larger files. You may want to click on the avi file even if you have a Macintosh computer. My Mac automatically launched QuickTime when I clicked on the avi file and interpreted the movie quite nicely. The rm format is for RealPlayer. I included it because they are very small files. However, compression has basically made them useless for fine detail like letters and numbers. They will give you a general idea of mouse motion though. 

Open Starry Nights. The first time you start Starry Nights you are asked to set the home location. Choose the triangle next to North America, then choose USA, and then choose Casper, WY. I apologize to those of you who do not live in Casper. But it makes all the answers uniform as I grade them. If you have already made your location elsewhere, please click on the location button of the tool palette and change it to Casper as indicated above. (See the attached movie: location.avi (1.4 MB), location.mov (2.0 MB), or location.rm (0.24 MB)) A typical Starry Nights screen is below. The tool and time palettes may be in other locations. You can drag them to wherever you would like. I apologize for the lack of clarity in the picture.

Under the WINDOW menu, make sure that TOOLBAR and TIME are checked. These will control our location on the earth and the time of day. We will also control the time of year. We will use this window to step through the time of day. A time step of ten minutes should work fine. You can change it to about three minutes for more accurate times when you are near the goal position. The buttons that look like VCR controls will be used to step through time. We will be able to watch the position of the sun in the sky. There is a daylight savings time toggle on the time controller. This is a little circle that is empty or filled with a sun. Leave it empty so as not to worry about altering the time for daylight savings.

Complete the exercise by filling in the table provided. Assume today is June 1. At what time does the sun rise and set? Consider the sun to be rising or setting when it is something near a half circle on the horizon. (See the attached movie for an example of sunrise. Note that the sun rises at 8:37 AM in the movie. But be careful, daylight savings time was not off in the movie, so 8:37 AM is not the correct time. sunrise.avi (282 KB), sunrise.mov (484 KB), sunrise.rm (50 KB)) What is the general compass position of the sunrise and sunset? A rough estimate is ok for this. Say something like "South", or if its between NE and E you would write "ENE." At what time is the sun on the meridian? If you cause the program to face due South (click the "S" icon) or due North if you are looking from the southern hemisphere you will have the meridian in the middle of the screen. The sun is on the meridian at local noon. (See the attached movie for an example of the sun on the meridian. Note that the sun is on the meridian at 12:10 PM in the movie. I even passed the meridian and used the rewind button to go back to the meridian. meridian.avi (353 KB), meridian.mov (3.5 MB), meridian.rm (235 KB)) Note its height above the horizon. Measure it on your screen using a ruler. Measure the distance from the "ground" on screen to the middle of the sun. If it is not visible because it is too high, simply say "off screen." This number will vary from monitor to monitor but it will give you an idea of changes.

(Note about Starry Nights: The altitude in degrees of the sun is not readable since a horizon grid is unavailable. The same is true for precise compass directions.)

Repeat the above questions for March 20, June 20, September 20, and December 20. Repeat all the readings for the following cities: Anchorage, AK; Managua, Nicaragua; Buenos Aries, Argentina. Then choose a spot on the North and South polar regions. Note the movement of the sun and stars in these last 2 locations.

Write a conclusion to discuss what you learned from this lab. What surprises did you find? The conclusion of a laboratory experience is the most important part of a laboratory exercise. Please write a thoughtful and insightful discussion.

This page was last updated on 05/30/01.