Download Star Maps and Constellations

Star Maps
and
Constellations
Dr. Bill
Pezzaglia
Updated:
2009Sep13
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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. The Story of Two Bears
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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.
Ref: http://www.nmm.ac.uk/server/show/conWebDoc.4006
When Zeus’s wife Hera found out about this, she became
very jealous and angry…
Ref: http://www.nmm.ac.uk/server/show/conWebDoc.4006
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Using her magic powers Hera turned pretty
Kallisto into a great clumsy bear.
Ref: http://www.nmm.ac.uk/server/show/conWebDoc.4006
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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.
Ref: http://www.nmm.ac.uk/server/show/conWebDoc.4006
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A long time after these events, Kallisto’s son Arktos was out hunting in the
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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…
Ref: http://www.nmm.ac.uk/server/show/conWebDoc.4006
Zeus was greatly alarmed at this turn of events. He appeared
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instantly and turned Arktos into a bear as well to stop him from
killing Kallisto.
Ref: http://www.nmm.ac.uk/server/show/conWebDoc.4006
Now both mother and son were bears and could be
happily reunited at last.
Ref: http://www.nmm.ac.uk/server/show/conWebDoc.4006
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To protect both bears from Hera’s jealous anger, Zeus 12
decided to throw them by their tails far up into the sky.
Ref: http://www.nmm.ac.uk/server/show/conWebDoc.4006
It also stretched their tails which as you can see are very long unlike 13
normal bears' tails!
Ref: http://www.nmm.ac.uk/server/show/conWebDoc.4006
Bootes, the Heardsman, with his hunting dogs (Canes Venatici)
chases the bears around in circles, i.e. keeps them at the North pole
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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 is
dominating our
southern sky
right now!
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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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A.3c Flamsteed Number Notation:
•Lacaille extended Bayer's notation by using lower
case (and some upper case) Latin letters.
•John Flamsteed (1646-1719)
First Royal Astronomer of England
•Assigned stars “numbers”, starting with
1 in the west, and working eastward.
•Hence Vega is
–
–
a-Lyrae in Bayer
3-Lyrae in Flamsteed!
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A.3c Conflicting Notations
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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.
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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.1c Ancient Observatories
•Have gigantic protractors to measure angles
•This one is at the ancient observatory of Beijing
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B.1c The Beijing Observatory (1231 Kublai Khan)
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B.1c The Beijing Observatory (1231 Kublai Khan)
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B.2a Geographic Coordinates
Review Latitude and Longitude
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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
12
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.3e Ortographic Map
Can only get a portion of sky on one map,
but has much less distortion!
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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.2a Herschel Extends the Table
William Herschel (1738-1822)
extended the scale in both directions
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C.2b Herschel-Pogson Relation
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Herschel’s measurements suggested a 1st magnitude star is 100x
more luminous that a 6th magnitude one. Norman Pogson (1854)
showed that this is because the eye’s response to light is logarithmic
rather than linear.
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C.3a Number of Stars by Magnitude
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•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
Mag
6432
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References (updated 09Aug)
On Constellations
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•
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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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