Apparent motions of the Celestial Objects

1. Apparent motions of the Celestial Objects Do Not Write What is in Yellow 

2. Definitions • Celestial sphere: Imaginary sphere encircling Earth on which all object in the night sky appear • Celestial object: Object in the sky outside Earth’s atmosphere; the sun, moon, stars, planets • Terrestrial: Objects that are a part of Earth, such as rocks, oceans, and clouds

3. Motions • The sun, moon, planets, stars or any distant object seems to rise in the east and set in the west- this is an illusion: the Earth is the object that is moving • The apparent motion of objects occurs at a rate of 15 degree per hour, which is the rate that earth rotates • Daily Motion: the movement of a celestial object over a 24-hour period • Day: Average interval of time during which the sun passes from its highest point on one day to its highest point on the next; ~24 hours

4. Zenith: The point on the celestial sphere that is directly above the observer.

5. From Different Perspectives • Mid-Latitudes: Stars appear to move from east to west in circular paths • North Pole: Stars appear to move in a circle

7. Star's Path Through the Sky The Earth rotates, causing the stars to appear to rise and set. Remember that the Sun is a star. It rotates/spins in place but does not revolve/orbit

8. Information • Sundials were used to tell time using the apparent movement of the sun • The passing of hours is indicated by the movement of the shadow • Days are short during the winter because we are pointed away from the sun so the sun is below the horizon most of the day • Sundials • More on sundials

11. Path of the Planets • Planets do not remain in fixed positions among the stars • Planets change their position from night to night • Each planet has its own unique motion • Sometimes they appear to drift west, other times east • “Planet” = Wanderer

12. The Moon • The moon revolves around Earth in about 27 days • The moon rises about 50 minutes later each evening • The path of the moon varies from higher to lower depending on the time of year • The moon’s path is similar to the sun’s as it looks like it rises and sets

13. Apparent Motions of the Sun • The sun appears to rise in the east, travel in an arc across the sky and set in the west • The greater the length of the sun’s path over an area, the more hours of daylight • In the spring and fall, the sun rises due (exactly) east and sets due west • In the summer, the sun rises north of east and sets north of west • In the winter, the sun rises south of east and sets south of west

15. Changes in the Altitude of the Sun at Noon • The sun is always highest at local solar noon • Only between the latitudes of 23.5 degrees North and 23.5 degrees South can the noon sun be directly overhead