RANDY L. PHELPS

This is the "Motions on the Celestial Sphere" Exercise

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Purpose:                    The purpose of this exercise is to illustrate the daily motions of stars/objects on the celestial sphere as seen                                   from various locations on the Earth, specifically 1. the Earth's Poles, 2. the Earth's equator and 3. intermediate                                   latitudes on the Earth.

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Instructions:             1. Look over the "Applet Description" below to see what you will be doing in the exercises.   Please note that                                      the figures shown on this page are not themselves the applet, but are only diagrams intended to help you                                      see what you will be doing once you begin!
                                 2. When you understand the use of the parameters, go to the bottom of this page to the section marked                                     "Exercises".   There are three exercises for you to do.  Click on the one you wish to do, and follow the                                      instructions for that exercise.  Be sure to do all three exercises! _____________________________________________________________________________________________________________

Applet Description:   The following figure shows a graphical representation of the applet you will be using.  In the exercises below,                                   you will change parameters shown to explore the motions of objects on the celestial sphere at the indicated                                   locations on the Earth. 

Note: The graphics below are not interative. The equivalent ones in the exercises are.

The Use of the Applet

The parameters which you may change by typing in the respective windows, and then hitting the "Enter" key are:

                                  Geographic longitude:   Edit to give the desired longitude^a
                                         Geographic latitude:      Edit to give the desired latitude^a
                                           Date:                          Edit month, date and year
                                  Time:                          Leave as is - no need to change
                                  Right ascension:           Leave as is - we will not go into this
                                  Declination:                 Change as described in the exercises

a. Latitude and Longitude of Sacramento must be found by your own research

The tasks which you may control by clicking in the respective windows are:

                                  Reset                           Resets the parameters to the defaults
                                         Rotation/Pause             Begins the simulation, or pauses it
                                                                                                                                                                      once it is running
                                         Emphasize                   Brings up a menu which allows you                                                                                                                                           to highlight a feature of the celestial
                                                                                                                                          sphere for clarity

Your viewing perspective relative to the observer (point O in the scene) can be changed by adjusting the scroll bars. 

It is probably best to leave these settings where they are, but one can play with them if one desires.  Remember that the Reset bar will take you back to the default perspective:

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Exercises: 1. Motions of the sky as seen from the Earth's Poles
                2. Motions of the sky as seen from the Earth's Equator
                3. Motions of the sky as seen from intermediate latitudes on the Earth

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Applet Copyright: The Applet used in this exercise was written and provided by Walter Fendt and is copyrighted by him.  The right of commercial use remains with that author.