1. Constellations An group of stars the ancients originally named after mythical characters

2. Measuring the Stars Parallax Apparent shift in position of a star relative to other stars caused by the motion of the observer. The larger the effect of parallax the closer the star is. Parallax is used to estimate distances to nearby stars.

3. Parallax

4. Original Photo Photo taken 6 months later

5. Measuring the Stars Light-year The distance light travels in 1 year Speed = 3 × 10 8 m/s (300,000,000 m/s) Parsec Equal to 3.26 light years The distance at which an object has a parallax of one arc second.

6. Magnitude The brightness of a star The lower the magnitude, the brighter the object Each lower magnitude is 2.5 brighter than the next Magnitude 1 star is brighter than a magnitude 2 star Can have a zero magnitude and negative magnitude Examples A magnitude 1 star is 2.5 times brighter than a magnitude 2 star A magnitude 2 star is 2.5 times brighter than a magnitude 3 star

7. How many times brighter is a magnitude 1 star compared to a magnitude 3 star? How many times brighter is a magnitude 1 star compared to a magnitude 4 star?

8. How many times brighter is a magnitude 1 star compared to a magnitude 3 star? 2.5*2.5 = 6.25 How many times brighter is a magnitude 1 star compared to a magnitude 4 star? 2.5*2.5*2.5 = 15.6

9. Apparent magnitude How bright a star appears to be as observed from Earth. Depends on distance Absolute magnitude The brightness an object would have if it were placed at a distance of 10 parsecs (32.6 light years) from Earth. Does not depend on distance

11. Luminosity The amount of energy that a light source emits per second Does not depend on distance Depends on temperature & size Varies from (.0001 to 1 millions) times brighter than the sun

12. Luminosity For an analogy with which you are familiar, consider again the headlights of a car. When the car is far away, even if its high beams are on, the lights will not appear too bright. However, when the car passes you within 10 feet, its lights may appear blindingly bright. To think of this another way, given two light sources with the same luminosity, the closer light source will appear brighter. However, not all light bulbs are the same luminosity. If you put an automobile headlight 10 feet away and a flashlight 10 feet away, the flashlight will appear fainter because its luminosity is smaller

13. MASS of a STAR Mass of a star determines Temperature & Size Temperature & size determines L uminosity Greater original mass of star  shorter life span

14. More massive a star  greater gravity pressing inward Greater gravity  requires greater density inside the star in order to balance its own gravity. Greater density  higher temperature in the core Higher temperature  faster the rate of nuclear fusion Faster the rate of nuclear fusion  larger energy output Larger energy output  greater luminosity

15. Greater luminosity  More rapidly it burns hydrogen fuel  Shorter lifespan of the star Greater original mass of star  shorter life span

18. Alpha Centauri 4.3 light years away is the closest star to our solar system