Stars! A star is a large hot ball of plasma, which generates energy in its core by nuclear fusion.

Stars Generate Energy and Form New Elements! The gravitational pull in the center of the sun is strong enough to cause hydrogen to fuse to make helium. The reaction releases tremendous amounts of energy, which is the light that you see!

Stars Generate Energy and Form New Elements! In massive stars there is an ``onion skin'' of fusion shells with the outer layers dropping fuel to lower layers and heavier and heavier nuclei being cooked up as you move towards the center of the star.

Fusion!

Absolute and Apparent Magnitudes Absolute Magnitude is the measure of the amount of light a star gives off. (actual brightness of stars) Apparent Magnitude is the amount of light received by the Earth. (how bright stars appear) – If 2 stars are the same distance away, what might cause one of them to be brighter than the other?

Apparent and Absolute magnitude Orion

Hertzsprung-Russell diagram The relationships among a star’s color, temperature and brightness are shown in the Hertzsprung-Russell diagram. Main sequence stars run from the upper-left corner to the lower right corner. Stars in the upper left are hot, bright stars, and stars in the lower right are cool, faint stars. 1.What are the brightest and hottest stars? 2.Which stars are hot but not bright?

The Sun! A Very Typical Star! In comparison to all he stars in the Universe…. 1.The Sun is middle-aged 2.It is average brightness 3.It has an average temperature 4.It is average size Cool Fact! The Sun contains about 99.8% of all the mass in our solar system!

What about all the Other Stars that are not Main Sequence????? You will learn about the wide variety of stars tomorrow! You will also learn that stars CHANGE throughout the course of their life!