By Danny, Tiffany, and Connor

 A “star” is a massive, luminous ball of plasma held together by gravity.  A star forms as a collapsing cloud of material composed mainly of hydrogen, along with helium and trace amounts of heavier elements.  Stars shine due to thermonuclear fusion. This is a process where hydrogen in the core of the star, releases energy that travels through the star and eventually radiates into space.

 Most stars are between 1 billion and 10 billion years old.  The more massive the star, the shorter its lifespan. This is because there is greater pressure in the star’s core.  Red Dwarfs can have a lifespan of up to hundreds of billions of years.

 Star Classification  classified by their spectra (elements that they absorb)  Temperature  There are 7 types  O, B, A, F, G, K & M  O & B stars are uncommon but bright  M stars are common but dim

The Hertzsprung -Russell (H-R) Diagram is a graph that plots stars color (spectral type or surface temperature) vs. its luminosity. On it, astronomers plot stars’ colors, temperature, luminosity and evolutionary stage

 This diagram shows 3 different types of stars  Main sequence stars  Super Giants/Giants  Dwarf stars

 Young stars  Fueled by nuclear fusion (converting hydrogen -> helium)  90% of stars are Main sequence stars  The hotter the brighter  Yellow dwarf & Red dwarf

A red giant is a relatively old star whose diameter is about 100 times bigger than it was originally. A blue giant is a huge, very hot, blue star. It is a post- main sequence star that burns helium. A supergiant is the largest known type of star; some are almost as large as our entire solar system.

 Small faint stars A white dwarf is a small, very dense, hot star that is made mostly of carbon. Their nuclear cores are depleted. They are about the size of the Earth and will eventually become a black dwarf

 A binary star is a system of two stars that rotate around a common center of mass (the barycenter). About half of all stars are in a group of at least two stars.

 The closest star to the earth is the sun.  The earth receives most of its energy from the sun.  The sun in our solar system is approximately 4.5 billion years old.

 "Stars." Imagine The Universe! Home Page. Web. 14 Mar  "Stars." Universe Today. Web. 14 Mar  "Stars, Constellations, Galaxies and Nebulae Facts." Kid's Cosmos-Science Resources for Teachers and Students. Web. 14 Mar