1. Measuring Distances in Space Astronomical Units, Light Years, Parsecs

2. Measuring distances in space The universe is enormous! Units of measurement on Earth are too small Other units are used instead

3. Astronomical Units Used for measuring distances in the solar system Symbol: AU The distance between the SUN and the EARTH is 15 million km (15,000,000). 15 million km = 1 AU

4. Distance to Other Planets Sun-Mercury = 0.39 AU Sun-Venus = 0.72 AU Sun to Mars = 1.52 AU Sun to Jupiter = 5.20 AU Sun to Saturn = 9.54 AU Sun to Uranus = 19.18 AU Sun to Neptune = 30.06 AJ Sun to Pluto = 39.53 AU

5. Light Years For objects that are VERY far away like stars, astronomers use light years to measure distance. Definition: The distance light travels in one year = 9,460,000,000,000 km (nearly 9.5 trillion km) Light travels 300,000 km/sec The closest star to earth (excluding the sun) is 4.22 light years away (Alpha Centauri)

6. Light Years If you could drive nonstop to the sun at 60 mph, it would take 180 years. Light makes the same trip in eight minutes. So the sun is about eight light-minutes away.

7. Distances in Light Years Sirius-brightest star in the sky: 8.6 light years Rigel-brightest star in Orion: 777 light years Center of the Milky Way galaxy: 27,700 ly Furthest galaxy seen in the universe: 15 Bill ly Sun to Pluto is 13 light hours (0.0015 light years)

8. Parsecs & Parallax Parsec = 3.26 light years Parsec = “Parallax of one arc second”

9. Parallax Definition: difference in the apparent position of an object viewed along two different lines of sightapparent position Used to determine the distance to celestial objects

10. Parallax

11. Units What unit would you use to measure the distance between: Jupiter – Saturn? Earth – Rigel? Edge of the Milky Way – Center of MW? Sun-Edge of the solar system?