1. 30.1 notes Characteristics of Stars
Std 1d: Know the evidence indicating that the planets are much closer to Earth than the stars are.
Std 2d: Know that stars differ in their life cycles and that visual, radio, and x-ray telescopes may be used to collect data that reveal those differences
Objective 1: Describe how astronomers determine the composition and temperature of stars
Objective 2: Describe one way astronomers measure the distance to stars
Objective 3: Explain the difference between absolute magnitude and apparent magnitude

2. Characteristics of Stars
Star – a large celestial body that is composed of gas and that emits light
The energy comes from nuclear fusion
Stars vary in color (ex. Reddish, blue-white, yellow)

3. Analyzing Starlight
Astronomers learn about stars by analyzing the light they release
Dark-line spectra shows the star’s composition and temperature
Used to determine the elements
Dark-line spectra - bands of color crossed by dark lines where color is diminished

4. The Composition of stars
Stars most common element is hydrogen.
Second is helium
Carbon, oxygen and nitrogen are in small amounts

5. The Temperature of Stars
Temperature is indicated by color
Hottest are blue stars = 35,000 ⁰C
Coolest are red stars = 3,000 ⁰C
Yellow stars are about 5,500 ⁰C

6. Objective 1: Determining the composition and temperature of stars
What are the 2 most common elements to make up stars?
Hydrogen and Helium
What color are the hottest stars?
blue
What color are the coolest stars?
Red
What is used to determine a stars composition and temperature?
Dark-line spectra

7. The sizes and masses of stars
Stars vary in size and mass
Dwarf stars can be as big as Earth
The sun is a medium-sized star
Giant stars have a diameters 1,000x the diameter of the sun
Most stars visible from Earth are medium-sized stars, similar to our sun

8. Stellar motion
Apparent motion is motion visible to the unaided eye. It is caused by the movement of Earth.
Earth’s rotation and revolution causes the stars to move in the night’s sky

9. Actual motion- most stars have several types of actual motion
they rotate on their axis
they may revolve around another star
they either move away or towards our solar system

10. The Doppler Effect
Doppler effect – an observed change in the frequency of a wave when the source or observer is moving
Stars moving towards our solar system = blue shift
Star moving away = red shift
Distant galaxies have red-shifted spectra
What does galaxies having a red shift mean?
The universe is expanding (galaxies are moving away)

11. Distances to stars
Distance between Earth and stars are measured in light years
Light year - the distance light travels in one year or 9.46 trillion km in one year
The sun is 8 light minutes from Earth

12. Nearest star to Earth
Proxima Centauri = 4.2 light years away
Parallax - an apparent shift in the position of an object when viewed from different locations. The larger the shift the closer the object (sun)
Used to determine the distance of the star (if close)

13. Objective 2: Describe one way astronomers measure the distance to stars
What color are galaxies that are moving away?
Red shift
What does a red shift in galaxy color suggest?
The universe is expanding
How doe astronomers measure the distance of close stars?
Parallax

15. Stellar brightness Visibility of a star depends on: Brightness
Distance from Earth
Apparent magnitude- the brightness of a star as it appears on Earth (lower # = brighter star)
Absolute magnitude- the brightness that a star would have at a distance of 32.6 light-years from Earth

16. Objective 3:Difference between absolute and apparent magnitude
What 2 things effect the visibility of a star?
Distance and brightness
What is the brightness of the star 32.6 light-years from Earth?
Absolute magnitude
What is the brightness of a star seen from Earth?
Apparent magnitude
What does a lower apparent number mean?
The brighter the star