Unit 3 : Activity 3 : Earth's Rotation : Daily Motion : Equatorial Coordinates : Meridian Diagrams : Unit Exam

Unit 1: How to Point to a Star
Unit 2: Where on Earth Are You?
Unit 3: Earth's Rotation and the Sun's Apparent Motion
Unit 4: Yearly Changes in the Sky
Unit 5: Seasons and Climate
Unit 6: Sundials
Unit 7: Navigation
Unit 8: Ancient Astronomy
Unit 9: Constellations

Activity 3

--Complete this activity prior to proceeding to Unit 3--

Take your "Earth", or any globe of Earth.  Use a small peg, the lid of a pen, or a small figure to represent the observer - you - and put this on your location.  Notice the direction that your head is pointing - for example, "towards the lamp".  This point in your sky is your zenith, the point directly over your head.  Your little figure would be able to see half of the room (if he were as small compared with your Earth as you are compared with the real one).  Look around and make a mental list of what he can and what he cannot see.

The earth turns during the course of the night.  Let your globe turn in the same way as the earth would (as you found in Activity 2):  With the US following Europe which follows Asia which follows the US.  After the earth has made half a turn, keeping the N-S axis of the earth pointing always in the same direction, can your little figure see the same things in your room?  Which objects can he still see, and which can he no longer see?  In the same way, the stars that are "up" for you at one time of night are not the same ones that will be "up" for you later in the night. 

Move your figure around to different parts of the earth and try the same experiment.  You will get very special results if you put your observer on one of the poles of Earth, and other interesting results if he is at the Equator.

If you have two observers, one at each pole, how much of the sky can they both see?

If you have two observers, on opposite sides of the earth at the equator, can they see the same things at the same time?  Can they see the same things but at different times?

In the next two units you'll be looking at a lot of illustrations and diagrams that are based on the situation that you have been modeling with your little figure and the globe.  If you find the drawings confusing, it may help to go back to the globe and try to reproduce the situation being shown in the drawing.

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