Bellwork 1110 Please turn in your bellwork sheet

Bellwork 11/10 Please turn in your bellwork sheet from last week 1. Choose a star name out of the beaker: 2. Using a computer or your device, look up: • • Temperature Luminosity Color Size (Dwarf, giant, super giant, ect) 3. Then, cut out a circle for each of your stars. 4. Write the information on the star & shade the circle with the star’s color

Properties of Stars What can stars tell us about the universe?

*Side note: • Stellar = relating to a star… • Not the way we use it in common language

Stellar Brightness There are 2 ways we can talk about “brightness” of a star… 1. Apparent brightness • Brightness when viewed from Earth • Decreases with distance

2. Absolute brightness • "True" or intrinsic brightness of a star • Does not depend on distance • Can also be measured in “luminosity” amount of radiation leaving a star Both of these terms are “intrinsic” or “real” quantities

Canis Major (Great Dog) Constellation

How do scientists figure out this intrinsic value? • The distance will always be 10 pc when measuring absolute brightness • Where do the “ 5’s” come from?

Color & Temperature of Stars v. Color and temperature • Hot star • Temperature above 30, 000 K • Emits short-wavelength light • Appears blue • Cool star • Temperature less than 3000 K • Emits longer-wavelength light • Appears red • Between 5000 and 6000 K • Stars appear yellow • e. g. , Sun

Hertzsprung-Russell diagram v. Shows the relation between stellar • Brightness (absolute brightness) and • Temperature v. Diagram is made by plotting (graphing) each star's • Luminosity ( or absolute brightness) and • Temperature

What observations can you make about the HR Diagram?

Let’s “dissect” the HR Diagram a little bit more • HR Diagram Lab – http: //astro. unl. edu/naap/hr/animations/hr. html • End Goals: – 1. Understand how to read/interpret the HR Diagram – 2. Infer how the HR Diagram helps scientists make predictions

Hertzsprung-Russell diagram v. Parts of an H-R diagram • Main-sequence stars • Most stars are on the main sequence • Band through the center of the H-R diagram • Giants (or red giants) • Very luminous • Large • Upper-right on the H-R diagram

Hertzsprung-Russell diagram v. Parts of an H-R diagram • Super Giants • Very large giants are called supergiants • Only a few percent of all stars • White dwarfs • Fainter than main-sequence stars • Small (approximate the size of Earth) • Lower-central area on the H-R diagram • Perhaps 10% of all stars

Spectral Class

What else does the Hertzprung-Russell diagram show us?

http: //aspire. cosmic-ray. org/Labs/Star. Life/support/HR_animated. swf

Properties of stars v. Binary stars • Two stars orbiting one another • Stars are held together by mutual gravitation • Both orbit around a common center of mass • More than 50% of the stars in the universe are binary stars http: //en. wikipedia. org/wiki/Binary_star#/media/File: Orbit 1. gif Why are Binary stars important or worth talking about? ?

Properties of stars v. Stellar mass • Determined using binary stars – the center of mass is closest to the most massive star

Binary stars orbit each other around their common center of mass