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Locating things in the Sky Instead of using metres or even kilometers, we use the Astronomical Unit (AU), the Parsec (pc) and the light year (ly). Questions: 1. How many AU is Jupiter from the Earth? 2. How many parsecs is it to the edge of the solar system? 3. How far is a light year in AU and pc? We also have a need for a different co-ordinate system in astronomy to describe where things are in the sky... We use a system called Right Ascention (RA) and Declination (dec). RA is like longitute and describes how far round an object is, and declination is like latitude and describes how far up or down an object is. We can use these measurements to determine the location of all things in the sky. Example: Use sky globe to find the coordinates of the galaxy 'Andromeda'. Now find a pretty picture of Andromeda using Google Sky, and it's coordinates in RA and dec. Exercise: Repeat the above example for 5 important objects in the night sky. For each record the co-ordinates, date of observation, and any other information you can find out about it which you think is relevant. Why do you think each is considered important in astronomy? Object RA Dec Date of observation Information about the object (e.g.: how big is it, what is it made of, how far away is it, why is it considered important in Astronomy?) Extension Tasks: Try and find a bright star (magnitude 3 or above), find out its name, which constellation it is in, what is it's age, chemical composition, distance from Earth, etc. Now do the same thing for a prominent galaxy. What is the difference between a constellation and a galaxy? Aren't they both collections of stars? Why do the stars look different when we use the infra-red or microwave functions in Google Sky?