Chapter 25Chapter 25Section 1: Stars

Stars and Galaxies Stars and Galaxies ObjectivesObjectivesDiscuss constellationsUnderstand the difference

between apparent and absolute magnitudes

Describe parallax

ConstellationsConstellationsObserved patterns of stars in the sky

◦88 Constellations recognized by IAUAppear to move, but it is Earth in

motion◦As Earth orbits the sun, we have different

views of the stars◦Summer/winter constellations

Circumpolar constellations surround the north pole and stay in view all year◦Seem to move because of the rotation of

Earth about its axis◦ Time lapse - Circumpolar stars around alertness tower – You

Tube◦ Circumpolar Stars-Northern Autumn Sky - YouTube

Some familiar Some familiar constellationsconstellationsBig Dipper (part of constellation

Ursa Major)OrionCassiopeia

Star PropertiesStar PropertiesMagnitude – brightness of stars

◦ Absolute magnitude – measure of the actual amount of light the star gives off

◦ Apparent magnitude – measure of the amount of light received by Earth

Measurement ◦ Parallax—measure of shift in position when object

viewed from different positions Use geometry to determine distance Closer object has larger parallax

◦ Light year – distance that light travels in one year◦ 9.5 trillion km

◦ Nearest star Proxima Centauri is 40 trillion km away 4.2 Light years

Star PropertiesStar PropertiesColor of a star indicates its

temperature◦ Hot is blue/white◦ Cold is red/orange