Bell Ringer Monday, March 26th Grab your notebook and open to the next available page. 1. What was something interesting you did over spring break?

How do we classify stars?

What is a star? A large ball of gas held together by gravity with a core so hot that nuclear fusion occurs. Nuclear Fusion – process that occurs when the nuclei of several atoms combine into one larger nucleus. This releases a great amount of energy that fuels stars.

How do we classify stars? Stars have different spectra and different colors depending on their surface temperatures. Size: Super Giant - Largest Red Giant Main Sequence White Dwarf Neutron Star - Smallest Temperature: Hot = Red/Orange Hotter = White Hottest = Blue/White Most massive stars are usually the hottest and are blue-white. The smallest stars tend to be cooler and red.

Hertzsprung-Russell Diagram This graph plots luminosity of stars versus the temperature of stars. The y-axis represents luminosity while the x-axis represents the temperature. It is used to categorize stars. Most stars exist along the Main sequence, while some are exceptions.

What does luminosity mean? The true brightness of an object. (Absolute Magnitude) This depends on the star’s temperature and size, not it’s distance from Earth.

What is apparent magnitude? The measure of how bright an object appears from Earth. (Apparent Magnitude) * The fainter an object in the sky appears, the greater its apparent magnitude measure. *

How do stars form? Nebula – a cloud of gas and dust. Stars form deep within cold, dense, and dark clouds of gas and dust. Gravity causes the densest particles to collapse and form a protostar. Eventually, the energy produced by the protostar heats the gas and dust surrounding them to create a star.

Death of Stars White Dwarf Supernova A hot, dense, slowly cooling sphere of carbon. *After helium is gone from core, the cast of gases exposing just the core* An enormous explosion that destroys a star. *Stars with more than 10 times the mass of the sun*

Death of Stars Black Hole An object whose gravity is so great that no light can escape Gravity is so strong that the matter crushes (death of star)

Life Cycle: Protostar Main Sequence - fusing hydrogen to helium Red Giant – energy in the core causes the outer layers to expand Red Supergiant – not all stars have enough mass to reach this stage. Death: White Dwarf Supernova – explosion leaving behind neutron star Black Hole

Classifying Stars Video https://www.youtube.com/watch?v=ld75W1dz-h0

Questions For Students What is a star? List at least 2 ways stars are classified. Where do most stars exist on the H-R diagram? Define Luminosity. Define Apparent Magnitude. What do stars form from? Name one way a star can die. List the steps of a star’s life cycle.