Transcript Star Maps and Constellations

Star Maps
and
Constellations
Dr. Bill
Pezzaglia
Very Short Lab Version
Updated:
2012Sep26
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Star Maps & Constellations
A. Constellations and Star Names
B. Coordinates and Star Maps
C. Magnitudes and Brightness of Stars
Star Maps & Constellations
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A. Constellations & Star Names
1. A constellation Story
2. Constellations
3. Star Names
1. Story of the Bears: Bootes, the Heardsman, with his hunting dogs (Canes Venatici)
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chases the bears (Ursa Major, Ursa Minor) around in circles, i.e. keeps them at the North pole
North Star
2. Constellations: Most maps today don’t show
the animals, they only show dots and lines.
The bright reddish star Arcturus, means "guardian of the bears".
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Can you find Bootes?
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Can you find Ursa Major (Big Bear, aka Big Dipper?)
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Constellations around the North Pole
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Constellations around the North Pole
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In 1928 the IAU (International Astronomical Union) divided the
sky into 88 constellations, each star belongs to exactly one constellation.
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
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A.3a Star Names
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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.
A.3b Bayer Notation:
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•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.
A.3b The Greek Alphabet
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B. Celestial Cartography
1. The Celestial Sphere
2. Coordinates
3. Map Projections
B.1a The sky looks like a big ball called “Firmament”
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Fig 1-1, p.20
B.1b Angular Size
•All the stars look the same distance away
•We measure the angle between stars
•Your finger at arms length is about 1 degree wide
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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).
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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
How to “project” a round ball onto flap map? Mercator Map is
made by project a ball onto a cylinder (problems at the poles!)
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B.3b Mercator Map of Earth
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Things at top and bottom are S – T – R – E – T – C – H – E - D
N
E
B.3c Mercator Map of Sky
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N
60
Degrees Declination
30
E
Hours RA 18
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6
3
1 0
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
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.
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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!
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C. Magnitudes and Brightness
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1.Magnitude Scale:
Hipparchus of Rhodes (160127 B.C) assigns “magnitudes”
to stars to represent brightness.
The eye can see down to 6th
magnitude
C.3b
Gemini
Mag
6432
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References (updated 09Aug)
On Constellations
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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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