1. Characteristics of Stars
Section 27.1

2. Definition of a star
It’s a body of gases that gives off lots of energy in the form of light and heat
They vary in size and mass, some are smaller that 20 km in diameter or up to a 1000 times the size of our sun!

3. Variations in composition and temperature
Using a spectrometer, scientists can determine what type of gases compose a star
Every chemical element has a characteristic spectrum

5. Temperature The temperature of a star is indicated by its color
The red ones are the coolest and the blues are the hottest
Most Temps range between 2800°C to 24,000°C.

6. Star Temperatures

7. Motion
Actual motion can only be measured by high powered telescopes since stars are so far away
Apparent motion of stars is what we see and is only due to the motion of the earth

9. Actual Motion of Stars
They rotate on an axis, they revolve around other stars, and they move towards or away from earth
Don’t forget the red shift

10. Distance to the Stars
It’s measured in light years- the distance that light travels in one year ( about 9.5 trillion km)
Light from the sun takes about 8 minutes to reach earth

11. Parallax
Scientists can use this to measures stars within 1000 light years of accuracy by measuring the angle between a stars’ apparent position over a period of 6 months
The closer the star, the larger the angle

12. Stellar Magnitudes
The visibility of a star depends on its brightness and distance from earth
Over 3 billion stars can be seen through a telescope, but only 6000 can be seen with the naked eye
The 2 scales that scientists use to measure brightness are apparent magnitude and absolute magnitude

13. Apparent Magnitude The brightness of a star as is appears from earth
The most powerful telescopes can detect stars with an apparent magnitude of about 29
Those stars are 1.5 billion times fainter than those seem with a naked eye

14. Apparent magnitude

15. Absolute Magnitude
How bright a star would be if it were 32.6 light years away
Scientists use this distance because it’s equal to one parsec

16. Classification of stars
Main-sequence stars- stars that are visible in the night sky, this includes the sun
Super giants – are bright because they have so much surface area to project light
White dwarfs- these stars are hot and dim because of their size