Stellar Motion

1. Stellar Motion

2. Stellar Motion Apparent Motion • The apparent motion of stars is the motion visible to the unaided eye. • Apparent motion is caused by the movement of Earth. • The rotation of Earth causes the apparent motion of stars sees as though the stars are moving counter-clockwise around the North Star. • Earth’s revolution around the sun causes the stars to appear to shift slightly to the west every night.

3. Stellar Motion Circumpolar Stars • Some stars are always visible in the night sky. These stars never pass below the horizon. • In the Northern Hemisphere, the movement of these stars makes them appear to circle the North Star. • These circling stars are called circumpolar stars.

4. Stellar Motion Actual Motion of Stars • Most stars have several types of actual motion. • Stars rotate on an axis. • Some stars may revolve around another star. • Stars either move away from or toward our solar system.

5. Stellar Motion Actual Motion of Stars • Doppler effect an observed change in the frequency of a wave when the source or observer is moving • The spectrum of a star that is moving toward or away from Earth appears to shift, due to the Doppler effect. • Stars moving toward Earth are shifted slightly toward blue, which is called blue shift. • Stars moving away from Earth are shifted slightly toward red, which is called red shift.

6. Doppler Effect • http://www.youtube.com/watch?v=Kg9F5pN5tlI

7. Stellar Motion The spectrum of a star that is moving toward or away from Earth appears to shift, as shown in the diagram below.

8. Distances to Stars • Light-year the distance that light travels in one year. • Distances between the stars and Earth are measured in light-years. • Parallax an apparent shift in the position of an object when viewed from different locations. • For relatively close stars, scientists determine a star’s distance by measuring parallax. • http://www.youtube.com/watch?v=ewGsiUPeBD4

9. Stellar Brightness • Apparent magnitude the brightness of a star as seen from the Earth. • The apparent magnitude of a star depends on both how much light the star emits and how far the star is from Earth. • Absolute magnitude the brightness that a star would have at a distance of 32.6 light-years from Earth • The brighter a star is, the lower the number of its absolute magnitude.

10. Stellar Brightness The lower the number of the star on the scale shown on the diagram below, the brighter the star appears to observers.

11. Other Components of the Universe

12. Constellations Dividing Up the Sky Constellation one of 88 regions into which the sky has been divided in order to describe the locations of celestial objects; a group of stars organized in a recognizable pattern • In 1930, astronomers around the world agreed upon a standard set of 88 constellations. • You can use a map of the constellations to locate a particular star.

13. Multiple-Star Systems • Over half of all observed stars form multiple-star systems. • Binary stars are pairs of stars that revolve around each other and are held together by gravity. • The center of mass, or barycenter, is somewhere between the two stars.

14. Star Clusters • Sometimes, nebulas collapse to form groups of hundreds or thousands of stars called clusters. • Globular clusters have a spherical shape and can contain up to 100,000 stars. • An open cluster is loosely shaped and rarely contains more than a few hundred stars.

15. Galaxies • Galaxy a collection of stars, dust, and gas bound together by gravity • Answer the questions on your video note sheet. • http://www.discovery.com/tv-shows/other-shows/videos/how-the-universe-works-family-of-galaxies.htm

16. The Milky Way • The galaxy in which we live, the Milky Way, is a spiral galaxy in which the sun is one of hundreds of billions of stars. • Two irregular galaxies, the Large Magellanic Cloud and Small Magellanic Cloud, are our closest neighbors. • These three galaxies are called the Local Group.