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2 Astronomy deals with large numbers! Distance between Earth and Sun (Astronomical Unit, AU) Nearest star - Proxima Centauri - ~4.2 light years away = 271,000 AU’s = kilometers »ROUND-OFF! Kilometers Diameter of the Milky Way is ~100,000 light years kilometers 9,007,199,254,740,992 or 2 52

3 Cosmic Voyage While you are watching The Cosmic Voyage, please write down any questions or comments on a sheet of paper, along with your name AND section, and hand it in as you leave at the end of class. We can then take care of any concerns on a personal level. Thanks!

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7 Our Cosmic Address Earth Solar system Orion arm Milky Way Local Group of Galaxies Local Supercluster of Galaxies Universe

8 ….where astronomy begins.

9 Every star that you see in the sky is part of our galaxy, the Milky Way. Every single star. We can see 3 galaxies naked eye: Andromeda (M31), Large Magellanic Cloud (south of equator) and Small Magellanic Cloud (south of equator).

10  Contrast the old definition of constellation with the astronomers’ definition of constellation  State why we see different constellations during different times of the year.  Summarize what is meant by the “Celestial Sphere” and why the concept is useful.  Relate the celestial coordinate system to the latitude and longitude system on Earth, stating similarities and differences.

11 A specific, delineated region of the sky, stars and objects placed within official borders set in  Contrast the old definition of constellation with the astronomers’ definition of constellation Constellations for astronomers

12 We see different constellations throughout the year. We can see Pegasus now, but not Orion. In January, we’ll be able to see Orion, but not Scorpio. Why? What is happening? What is involved?  State why we see different constellations during different times of the year.

13  Motions in the Sky The Reason for Seasonal Constellations  State why we see different constellations during different times of the year.

14  State why we see different constellations during different times of the year.

15 Watching the Sun move against the background stars.

16 The Celestial Sphere Summarize what is meant by the “Celestial Sphere” and why the concept is useful.

17  Summarize what is meant by the “Celestial Sphere” and why the concept is useful.

18 Latitude Longitude  Relate the celestial coordinate system to the latitude and longitude system on Earth, stating similarities and differences. Review of the terrestrial coordinates

19 a projection of the Earth’s coordinate system onto the sky, with differences: Sky Latitude Declination (  ) Sky Longitude Right Ascension (  ) measured in angle (degrees, arcmin, arcsec) measured in time (hours, min, sec)  Relate the celestial coordinate system to the latitude and longitude system on Earth, stating similarities and differences. Celestial coordinates (equatorial)

20  Relate the celestial coordinate system to the latitude and longitude system on Earth, stating similarities and differences.

21 Pratice with celestial coordinates A B C

22 Contrast the old definition of constellation with the astronomers’ definition of constellation

23 You purchase a registered star for $100 (hey, it comes with a certificate!). The coordinates are: RA: 00 hr 10 min 05 sec and Dec: +29 o 55’ 53”

24 Notes APOD