Stars and Galaxies

1. Stars and Galaxies Stars

2. Constellations • Ancient Greeks, Romans, and other early cultures observed patterns of the stars in the sky and called them constellations. • They imagined that they represented mythological characters, animals, and familiar objects.

4. From Earth, a constellation looks like spots of light arranged in a particular shape against the dark night sky. However in space stars in the constellation have no relationship to each other.

5. Absolute and Apparent Magnitudes • Absolute Magnitude of a star is a measure of the amount of light it gives • Apparent Magnitude of a star is a measure of the amount of light received on Earth • Sirius and Rigle are two stars, Sirius looks brighter than Rigle from Earth. Is it because Sirius is brighter or because Sirius is closer?

6. Measurement in Space • How do scientist measure the distance to stars? • Scientists use a method called parallax which is the apparent shift of an object when viewed from two different positions.

8. Light-year • A light-year is the distance that light travels in one year. • Light travels at 300,000 km/s or about 9.5 trillion km in one year.

9. Properties of Stars • Color of a star indicates the temperature of the star, hot stars are blue-white color and cool stars are orange or red in color. See the different colors of the stars, can you pick out the cool ones? The hot ones?

10. Star composition • Astronomers study the composition of the stars by observing their spectra.

11. Spectra • When fitted to a telescope a spectroscope acts like a prism and spreads light out in a rainbow band called a spectrum. • The dark lines are caused by elements in the atmosphere absorbing some light. • Each element absorbs certain wavelengths, producing a certain pattern of dark lines. This can be used to identify which elements are in a star’s atmosphere.