Stars form from clouds of dust and gas called nebulae. Gravity causes the gas and dust to collapse into a dense protostar at the center. When the protostar becomes hot and dense enough, nuclear fusion occurs, releasing energy and causing the star to shine. A star's lifespan depends on its mass - lower mass stars last for billions of years, while higher mass stars only last millions of years before ending their lives in supernova explosions. Scientists classify stars based on their temperature and the elements they absorb, with classifications ranging from hottest O-type stars to coolest M-type stars.

1. Classifying Stars A brief overview of how stars are formed and how to classify them By: Erica Oberholtzer ED 205-08 Enter

2. Click the links below to navigate How a star is formed The mass of a star Life cycle of a star Stellar classification Types of stars- Part I Types of stars- Part II Hertzsprung-Russell Diagram A look at the H-R diagram Extra practice About the author Resources Quit

3. How is a Star Formed? Stars begin their lives as nebula Gravity then pulls together dust and gas from the nebula to form a protostar These clouds of dust and hydrogen gas then collapse under their own gravity The center of this cloud then becomes very hot and nuclear fusion occurs. This process releases so much energy that the star then shines with its own light. Quit

4. Stars are Different Sizes Stars have a life cycle that depends on the initial mass of the star. The more mass a star has, the faster it will burn. Low mass stars, or small stars, survive for billions of years. These small stars die quietly, and in their place, a small white dwarf is left behind. High mass stars, or large stars, survive for a few million years. These large stars die in supernova explosions, and in their place, a black hole is left behind . Quit

5. Summary: Life Cycle of a Star Quit Click on the picture above to watch a video from the history channel on the life cycle of a star!

6. What is Stellar Classification? The classification of stars is based on the elements they absorb and their temperature, and are listed from hottest to coldest Quit Class Temperature Conventional Color Mass (The Sun=1) Radius (The Sun=1) Luminosity (The Sun=1) O 30,100–60,000 K blue 60 M ☉ 15 R ☉ 1,400,000 L ☉ B 10,100–30,000 K blue white 18 M ☉ 7 R ☉ 20,000 L ☉ A 7,600–10,000 K white 3.1 M ☉ 2.1 R ☉ 80 L ☉ F 6,100–7,500 K yellowish white 1.7 M ☉ 1.3 R ☉ 6 L ☉ G 5,100–6,000 K yellow 1.1 M ☉ 1.1 R ☉ 1.2 L ☉ K 3,600–5,000 K orange 0.8 M ☉ 0.9 R ☉ 0.4 L ☉ M 2,000–3,500 K red 0.3 M ☉ 0.4 R ☉ 0.04 L ☉

7. Types of Stars Type O Stars in Orion’s Belt Type B stars in the Pleiades open star cluster  Quit

8. Types of Stars (continued) Above: Type A Star- Vega Below: Type A Star-Sirius Type F Star- Procyon Type G Star- The Sun Type K Star- Arcturus Type M Star- Betelgeuse Quit

9. The Hertzsprung-Russell Diagram The H-R Diagram shows the relationship between absolute magnitude, luminosity, classification, and effective temperatures of stars. It is a graph that plots star color versus its luminosity. The H-R Diagram can be used to define different types of stars. It can also be used by scientists to measure how far away a star cluster is from the Earth . Quit

10. A Look at the H-R Diagram Quit

11. Star Cut-Outs For extra practice, print this slide, color the stars the appropriate color and cut out. Then, put the stars in order from coldest to hottest Betelgeuse 3,100 C 0.04 L Aldebaran 5,000 C 0.4 L The Sun 5,400 C 1.2 L Polaris 6,100 C 6 L Vega 10,000 C 80 L Spica 31,000 C 1,400,000 L Regulus 20,000 C 20,000 L Quit

12. About the Author Erica Oberholtzer is 24 years old, and is currently at Grand Valley State University as an integrated science major; actively pursuing her bachelors degree. Hoping to be an elementary or middle school teacher one day, she spends her time finding out more about the science world, and hopes to incorporate all aspects of it into her classroom one day. Any questions or comments, please click the link below: Quit

13. Resources Life Cycle Video: Teacher Tube Images: Wikipedia- Nebulas Deep Space Photos Star Field Observatory Hubble Information Center H-R Diagram Quit