An introduction to Astronomy

But what specific paths do they take across our sky? When we view stars appearing after sunset, how did they arrive at those positions? In this lesson we will discuss the principles behind the motions. Then in the exercises, we will observe these motions directly using the Starry Night software. We need to see how the motions of the stars are viewed from our local perspective. First, let's review the local coordinate system. The local view places the observer at the center. The zenith is the point directly over the observer's head. And the horizon is the boundary between the earth and sky. Compass points along the horizon are marked N, S, E, and W. Recall that the Celestial Sphere places the Earth at the center and the sphere of stars around it. Recall the special places on the celestial sphere: the North Celestial Pole, South Celestial Pole, and the Celestial Equator. The Earth rotates under the celestial sphere in a counter-clockwise direction as viewed from above the north pole. However, we do not see this motion, instead, we see the stars, moon, sun, etc move in the opposite direction. The stars appear to move in circles centered on the celestial poles. Stars closer to the north celestial pole will make smaller and smaller circles. The north celestial pole itself does not move during earth's rotation. Now we must map the celestial motions onto our local sky. If we lived at the north pole, then the north celestial pole would be directly over our heads. If we lived at the equator then the celestial equator would be directly over our heads and the north celestial pole would appear on our northern horizon. We live slightly more than a third of the way between the equator and the north pole, the north celestial pole appears to be about slightly more than a third of the way up from the north point on our horizon. Our sky motions then map as concentric circles centered at the North Celestial Pole as shown. The Sun, moon, stars and all heavenly bodies follow this general daily motion in our sky. 4 Language Objective: This laboratory introduces the Star and Planet Locator; which is a common tool used in backyard observing. This tool helps approximate the location of constellations and certain stars as they move across the sky during a single night (this is called "daily motion"). In addition, it is possible to approximate the time that stars rise and set, as well as when the best time to observe will be. Background:

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