1. Astronomical Distances

2. Stars that seem to be close may actually be very far away from each other.

3. The universe is immense in size Astronomers use units and methods of measuring that we are not used to on Earth

4. Parallax is used to measure the distance to nearby stars Parallax: when objects appear to move or shift due to earth’s orbit ★ This method uses trigonometry ★ nearby stars = 300 light years or less

5. Parallax Jan. June draw this

6. Inverse square law of light is used for distant stars the intensity of light falls off as the square of the distance from the source

7. Light year is a unit of distance, NOT time Light Year: the distance light travels in one year (9.5 trillion km!!!) ★ Kilometers are too small to use in astronomy ★ one light-year is equal to 9,500,000,000,000 kilometers.

8. Light Year

9. Parsec is used to measure greater distances between stars and galaxies 1 parsec = 3.26 light years

10. Astronomical Units (AUs) measure distances between planets (our solar system) AU is the average distance between the Earth and Sun (1 AU) ★ 1 AU is about 150 million km

11. ★ Mercury is the closest at 0.39 AUs while Neptune is the farthest at 30.06 AUs

12. 1 AU Sun E draw this

13. 60 second summary

14. Review#1 What is parallax used for? to measure a star’s temperature to measure a star’s distance from Earth to measure a star’s mass to measure a star’s magnitude

15. ๏ parallax measures a star’s distance from earth

16. Review#2 What does a light year measure? temperature time distance magnitude

17. ๏ distance

18. Reviw#3 An AU is used for distances between... stars galaxies solar systems planets

19. ๏ planets

20. Review#4 Which measurement is used for distant stars? AU parallax inverse square law of light light year

21. ๏ inverse square law of light