Unit 2 : Activity 2 : The Terrestrial Coordinate System : Longitude and Time Zones : Earth Clock : 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 2: The Earth Rotates

--Complete this activity prior to proceeding to Unit 2--

Astronomers use the word "rotate" to mean "spin about an axis through the object".  The Earth rotates once every day (every 24 hours).  (We save the word "revolve" to mean "goes in an orbit around something else";  the Earth revolves around the Sun once every 365 1/4 days.) 

Holding your Earth from Activity 1 only at the poles (or using the built-in support, if you are using a commercial globe), try to figure out which way it should spin.  Suppose you are standing in Iowa, near the middle of the US.  New York is east of you, and San Francisco is west of you.

Looking at your globe from above the North Pole, with the red dot marking Iowa, where is the sun when it is rising?

Blue Globe Marked With Red Dot and Arrow Pointing East

The sun rises along the eastern horizon, that is, along the horizon that is in the same direction from the Ames observer as New York is. This picture represents where the sun would be at sunrise. Play around with your globe and a source of light until you are convinced that this is the right answer!

Later in the day the sun will be high in the sky. Finally, the sun will set along the western horizon. 

Now try putting a flashlight, lamp, or laser-pointer in one place, representing the source of sunlight, and spinning the globe so that the morning comes before noon and noon before evening.  It may help you to put the cap of a pen or a small peg or figure on the globe at Ames and to picture what he or she is seeing.  Which way does the globe spin?  Does the US chase Europe, or the other way around?  To remember how it goes you might make up a story about China chasing Japan, or Hawaii chasing California.

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