1. Distances in Space This Mini Lesson Will Cover: What units do astronomers use to measure vast distances in space?

2. Day 1: Units of Measure in Space “Are we there yet” Go to the following link and check out how vast space really is. Plug in the typical speed of a car (70 mph) or NASA’s fastest space probe, Voyager I, (39,000 mph) and see how long it would take to get to some objects in deep. http://janus.astro.umd.edu/astro/distance/

3. Day 1: continued Obviously, distances in space are large. The Sun is 93 million miles from earth and the nearest star after that is 23 trillion miles and it only gets worse. What units do astronomers use to measure vast distances in space besides miles and kilometers?

4. Day Uno: 1) Astronomical Unit (AU) = the average distance from the Earth to the Sun. a) About 93 million miles or 150 million kilometers b) Used for measurements in our Solar System. c) The Earth is one AU from the Sun. 2) Light Year (ly) = the distance that light travels in a vacuum in one year. (HUGE) a) About 9.5 trillion km or 5.7 trillion miles b) Used to measure the distance between stars and galaxies. c) Proxima Centauri, the next closest star after the Sun, is 4.2 ly away. It takes light 4.2 years to travel that distance. d) ** Remember, Light-year is a distance, not a unit of time.

5. Day 1: How are distance measured in space. 1) Giant Meter Sticks (Just Kidding) 2) Parallax – shifting of the apparent position of a nearby star as Earth orbits the Sun. What’s that. Hold up a finger in front of you. Close one eye and then the other. See the shift. Astronomers can determine the distance to nearby stars by measuring that shift. Doesn’t work for far away objects.

6. Day 1: cont… 3) Cepheid Variables are stars that get brighter and fainter in a regular pattern. They are used to determine longer distances. (this is all you need to know.) The longer the period between two bright maximums the greater the stars absolute magnitude. The apparent magnitude can then be calculated which will give you the distance.

7. Day 2: Problems Use what you learned yesterday to answer the following questions. 1. You want to record the distance to the Andromeda Galaxy. What unit of measure should you use? 2. Pluto is 39 times farther from the Sun than the Earth. How many astronomical units is Pluto from the Sun? 3. Earth is 149.6 million km from the Sun. If Saturn is 1,434 million km from the Sun. How many astronomical units is Saturn from the Sun? 4. Sunlight reaches Earth in 8.33 min. How long, in minutes, would it take sunlight to reach Pluto?

8. Day Dos: Answers 1. light-year 2. 39 AU 3. 1,434 million km / 149.6 million km = 9.5 AU 4. (39 AU x 8.33 min) / 60 min = 5.4 hours

9. Day 3: Problems 1) The distance between Polaris and Earth is 431 ly. If light travels at 3.0 x 10 8 m/s in space how far is Polaris from the Earth in km? 3) What are two methods of determining stellar distances. 2) Explain why looking at distance objects in space is like looking back in time?

10. Day 3: Answers 1. 431 ly(3.0 x 10 8 m/s) / (3.16 x 10 7 s /year) = 4.1 x 10 18 m * Don’t to forget to figure out how many seconds are in a year. 2. Parallax and Cepheid Variable periods 3. Answers can vary. Light takes time to travel through space. The light that hits your eye may have travelled for thousand, millions or billions of years. Therefore you are witnessing events that have already happened. Astronomers try to appear farther into the universe because they can see events that happened when the universe was first forming.