Star Maps and Constellations Dr. Bill Pezzaglia Updated: 2009Sep13

Star Maps & Constellations A.Constellations and Star Names B.Coordinates and Star Maps C.Magnitudes and Brightness of Stars 2

Star Maps & Constellations 3

A. Constellations & Star Names 1.A constellation Story 2.Constellations 3.Star Names 4

1. The Story of Two Bears 5 Ref: Zeus, father of all the Greek gods, became interested in a mortal maiden called Kallisto. He began to spend a lot of time with her.

When Zeus’s wife Hera found out about this, she became very jealous and angry… 6 Ref:

Using her magic powers Hera turned pretty Kallisto into a great clumsy bear. 7 Ref:

Now poor Kallisto was doomed to wander forever in the forest in this unnatural form. Zeus was very unhappy with this, but he could not do anything about it without upsetting his wife. 8 Ref:

A long time after these events, Kallisto’s son Arktos was out hunting in the forest when he spotted a bear and was about to shoot it. What he didn't realise was that this bear was actually his mother in enchanted form… 9 Ref:

Zeus was greatly alarmed at this turn of events. He appeared instantly and turned Arktos into a bear as well to stop him from killing Kallisto. 10 Ref:

Now both mother and son were bears and could be happily reunited at last. 11 Ref:

To protect both bears from Hera’s jealous anger, Zeus decided to throw them by their tails far up into the sky. 12 Ref:

It also stretched their tails which as you can see are very long unlike normal bears' tails! 13 Ref:

Bootes, the Heardsman, with his hunting dogs (Canes Venatici) chases the bears around in circles, i.e. keeps them at the North pole 14

2. Constellations: Most maps today don’t show the animals, they only show dots and lines. 15 The bright reddish star Arcturus, means "guardian of the bears".

Can you find Bootes? 16

Can you find Ursa Major (Big Bear, aka Big Dipper?) 17

Constellations around the North Pole 18

Constellations around the North Pole 19

In 1928 the IAU (International Astronomical Union) divided the sky into 88 constellations, each star belongs to exactly one constellation. 20

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 21 Note: this asterism is dominating our southern sky right now!

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. 22

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. 23

A.3b The Greek Alphabet 24

A.3c Flamsteed Number Notation: Lacaille extended Bayer's notation by using lower case (and some upper case) Latin letters. John Flamsteed ( ) First Royal Astronomer of England Assigned stars “numbers”, starting with 1 in the west, and working eastward. Hence Vega is –  -Lyrae in Bayer –3-Lyrae in Flamsteed! 25

Portion of Norton's Star Atlas showing both Bayer and Flamsteed notations. Note "q" Herculis is an example of Lacille's notation. R, S, T, U and V Coronae Borealis are Argelander's Variable Star notation. A.3c Conflicting Notations 26

B. Celestial Cartography 1.The Celestial Sphere 2.Coordinates 3.Map Projections 27

Fig 1-1, p.20 B.1a The sky looks like a big ball called “Firmament” 28

B.1b Angular Size 29 All the stars look the same distance away We measure the angle between stars Your finger at arms length is about 1 degree wide

B.1c Ancient Observatories 30 Have gigantic protractors to measure angles This one is at the ancient observatory of Beijing

B.1c The Beijing Observatory (1231 Kublai Khan) 31

B.1c The Beijing Observatory (1231 Kublai Khan) 32

B.2a Geographic Coordinates Review Latitude and Longitude 33

B.2b Celestial Coordinates i.Declination is the name of celestial latitude ii.Right Ascension is the name of celestial longitude (and we measure it in hours). 34

B.2c. What are the coordinates of Rigel? Note: North is “up” Dec= -10 deg RA = 5h 10 min 35

B.3a Mercator Projection Map 36 How to “project” a round ball onto flap map? Mercator Map is made by project a ball onto a cylinder (problems at the poles!)

B.3b Mercator Map of Earth 37 N E Things at top and bottom are S – T – R – E – T – C – H – E - D

Hours RA B.3c Mercator Map of Sky 38 N E Degrees Declination

B.3d Which Way is East? Because you are looking up rather than down, East and West are reversed on star maps! 39

B.3e Ortographic Map 40 Can only get a portion of sky on one map, but has much less distortion!

B.3f Polar Map 41 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.

B.3g Your Starwheel 42 Your starwheel (aka “Astrolabe” aka Planisphere) has a polar map in it. The rivet in the center is the North Star!

C. Magnitudes and Brightness 43 1.Magnitude Scale: Hipparchus of Rhodes ( B.C) assigns “magnitudes” to stars to represent brightness. The eye can see down to 6 th magnitude

C.2a Herschel Extends the Table 44 William Herschel ( ) extended the scale in both directions

C.2b Herschel-Pogson Relation 45 Herschel’s measurements suggested a 1 st magnitude star is 100x more luminous that a 6 th magnitude one. Norman Pogson (1854) showed that this is because the eye’s response to light is logarithmic rather than linear. 22.5

C.3a Number of Stars by Magnitude 46 There are only about 15 bright (first magnitude and brighter) stars There are only about 8000 stars visible to naked eye There are much more stars with higher magnitude!

C.3b Gemini 47 Mag 2 Mag 3 Mag 4 Mag 6

References (updated 09Aug) On Constellations