Star MapsandConstellations

Dr. Bill Pezzaglia

Very Short Lab Version

Updated:2012Sep26

Star Maps & Constellations

A. Constellations and Star Names

B. Coordinates and Star Maps

C. Magnitudes and Brightness of Stars

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Star Maps & Constellations3

A. Constellations & Star Names

1. A constellation Story

2. Constellations

3. Star Names

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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

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North Star

2. Constellations: Most maps today don’t showthe animals, they only show dots and lines.

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The bright reddish star Arcturus, means "guardian of the bears".

Can you find Bootes? 7

Can you find Ursa Major (Big Bear, aka Big Dipper?) 8

Constellations around the North Pole9

Constellations around the North Pole10

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

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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

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Note: this asterism dominates the winter sky in the south

A.3a Star NamesMost 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.

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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.

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A.3b The Greek Alphabet 15

B. Celestial Cartography

1. The Celestial Sphere

2. Coordinates

3. Map Projections

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Fig 1-1, p.20

B.1a The sky looks like a big ball called “Firmament” 17

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

B.2b Celestial Coordinates

i. Declination is the name of celestial latitude

ii. Right Ascensionis the name of celestial longitude (and we measure it in hours).

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B.2c. What are the coordinates of Rigel?

•Note: North is “up”•Dec= -10 deg•RA = 5h 10 min

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B.3a Mercator Projection Map 21

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 22

N

E

Things at top and bottom are S – T – R – E – T – C – H – E - D

Hours RA 18 12 6 3 1 0

B.3c Mercator Map of Sky 23

N

E

30

60

Deg

rees

Dec

lina

tion

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

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B.3f Polar Map 25

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 26

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 27

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

C.3b Gemini 28Mag2

Mag3

Mag4

Mag6

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

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