Star Maps and Constellations Dr. Bill Pezzaglia

1. Star MapsandConstellationsDr. Bill Pezzaglia Very Short Lab Version Updated:2012Sep26

2. 2 Star Maps & Constellations • Constellations and Star Names • Coordinates and Star Maps • Magnitudes and Brightness of Stars

3. 3 Star Maps & Constellations

4. 4 A. Constellations & Star Names • A constellation Story • Constellations • Star Names

5. 1. Story of the Bears: Bootes, the Heardsman, with his hunting dogs (Canes Venatici)chases the bears (Ursa Major, Ursa Minor) around in circles, i.e. keeps them at the North pole 5 North Star

6. 2. Constellations: Most maps today don’t showthe animals, they only show dots and lines. 6 The bright reddish star Arcturus, means "guardian of the bears".

7. Can you find Bootes? 7

8. Can you findUrsa Major(Big Bear, aka Big Dipper?) 8

9. Constellations around the North Pole 9

10. Constellations around the North Pole 10

11. In 1928 the IAU (International Astronomical Union) divided thesky into 88 constellations, each star belongs to exactly one constellation. 11

12. 12 A.2c Asterisms • The “Winter Hexagon” is not a constellation • Its an “Asterism”, a grouping of stars • An asterism might contain several constellations,or just a piece of a constellation Note: this asterism dominates the winter sky in the south

13. 13 A.3a Star Names Most of the bright star have individual names. The names are often related to the part of the "picture". • Alhena in Gemini means "mark", pertaining to a mark on the foot of Gemini twin Pollux. • Betelgeuse (Orion) means “shoulder” (well ….) • Deneb (in Cygnus the Swan) means "tail". • Denebola is "tail of the Lion" (Leo) • Deneb Algedi is "tail of the sea goat" Capricornus, • Denebokab is "Tail of the Eagle" Aquila.

14. 14 A.3b Bayer Notation: • Bayer in 1601 designated a star in a constellation by a lower case Greek letter followed by the genitive form of the constellation. In general the letters are assigned in order of brightness beginning with Alpha • For example, Alpha Centauri (abbreviated α-Cen) is the brightest star in the constellation Centaurus, while Beta Centauri or "β-Cen" is the second brightest. • However, in some cases (n.b. Ursa Major), Bayer named the stars not in order of brightness, but in order of location.

15. 15 A.3b The Greek Alphabet

16. 16 B. Celestial Cartography • The Celestial Sphere • Coordinates • Map Projections

17. B.1a The sky looks like a big ball called “Firmament” 17 Fig 1-1, p.20

18. B.1b Angular Size 18 • All the stars look the same distance away • We measure the angle between stars • Your finger at arms length is about 1 degree wide

19. 19 B.2b Celestial Coordinates • Declinationis the name of celestial latitude • Right Ascensionis the name of celestial longitude (and we measure it in hours).

20. 20 B.2c. What are the coordinates of Rigel? • Note: North is “up” • Dec= -10 deg • RA = 5h 10 min

21. 21 B.3a Mercator Projection Map How to “project” a round ball onto flap map? Mercator Map is made by project a ball onto a cylinder (problems at the poles!)

22. 22 Things at top and bottom are S – T – R – E – T – C – H – E - D B.3b Mercator Map of Earth N E

23. 23 Hours RA 18 12 6 3 1 0 B.3c Mercator Map of Sky 60 N 30 E Degrees Declination

24. 24 B.3d Which Way is East? Because you are looking up rather than down, East and West are reversed on star maps!

25. 25 B.3f Polar Map This is an orthographic map with the North Star in the center. It has must less distortion, but you can only get half the sky on it. Need a second one for South Polar region.

26. 26 B.3g Your Starwheel Your starwheel (aka “Astrolabe” aka Planisphere) has a polar map in it. The rivet in the center is the North Star!

27. 27 C. Magnitudes and Brightness • Magnitude Scale: Hipparchus of Rhodes (160-127 B.C) assigns “magnitudes” to stars to represent brightness. The eye can see down to 6th magnitude

28. Mag 2 Mag 3 Mag 4 Mag 6 28 C.3b Gemini

29. 29 References (updated 09Aug) On Constellations • http://chandra.harvard.edu/photo/constellations/index.html • http://www.seds.org/Maps/Const/constS.html • http://www.lindahall.org/services/digital/ebooks/semler/semler32_33.shtml • http://www.astromax.org/con-page.htm