1. Properties of Stars

2. Star Color – the color of a star is a clue to its temperature a.The coolest stars are red b.The medium stars are yellow c.The hottest stars are blue

3. Star Characteristics The color of the star can be a clue to its temperature. – The hotter the star the shorter the wavelength the star emits.

4. Measuring Distance to Stars Parallax – using the location of a star at two different times to calculate its distance from Earth – The nearest stars have the largest parallax (seem to move the most) and the farthest stars have the smallest parallax (seem to move the least)

5. The closer the star the more it “moves” in the sky!

6. Measuring Distance to Stars Light-year – the distance light travels in one year (9.5 trillion kilometers) We use this when determining astronomical distances since miles and kilometers would be way too small of a number The next closest star after our sun, Proxima Centauri, is 4.3 light years away from our sun

7. Stellar Brightness Apparent magnitude – measure of how bright a star appears from Earth This varies due to the star’s temperature, size, and distance away from Earth Absolute magnitude – measure of how bright a star actually is To get a stars absolute magnitude, astronomers have to compare all stars at an equivalent distance

8. These three stars can have the same absolute magnitude when their sizes, temperatures, and distances from Earth are taken into account

9. Comparison of Apparent Magnitude and Absolute Magnitude of Stars NameDistance (light years) Apparent Magnitude* Absolute Magnitude* SunN/A-26.75.0 Alpha Centauri4.270.04.4 Sirius8.70-1.41.5 Arcturus36-0.1-0.3 Betelgeuse5200.8-5.5 Deneb16001.3-6.9 The more negative, the brighter and the more positive, the dimmer Astronomers estimate that there are 200-400 billion stars in our Milky Way Galaxy, but we can only see about 2,500 visible to the naked eye on Earth

11. Life Cycle of a Star 1. Stars begin as large clouds of gas and dust called nebula 2. The nebula then contracts and shrinks and its temperature increases – This process may take ~ 1 million years 3. Now the star is a protostar – still developing, large, red object – It can’t be classified as a star yet because it does not undergo fusion

13. 1.A star becomes a main-sequence star when fusion begins – Stars at this stage have a delicate balance between gravity pushing inward and the gas pressure pushing outward Stable, main-sequence stars have varying lifespans: – Large, blue stars may only last a few million years – Small, red stars may last hundreds of billions of years

15. As a star begins the end of its lifecycle it will become a red giant – Red giants are red in color because they are cooler – Red giants are HUGE in size compared to when they were a main-sequence star

16. When a small to medium sized star dies it becomes a white dwarf – White dwarf – a small, cool star near the end of its life When a large star dies it becomes a supernova – Supernova – an exploding star – When the largest stars explode, they can form black holes

17. Hertzsprung-Russell Diagram H-R Diagram – shows the relationship between the absolute magnitude and temperature of stars