Download The Sky

Constellations
•  Human Eye/brain is
very good at seeing
patterns in random dots
•  “The stars are a given.
Constellations are what
we draw.” (R. Solnit)
•  We use Latinized Greek
names
Asterisms
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Asterisms are obvious patterns
Big Dipper = Plough = Great Bear = Arktos (in Greek)
Which is where our word arctic comes from
Stars are various distances from us
Ancient Chinese Star Map, 7 Century
•  Dunhuang chart is oldest star chart
•  Contains 1345 stars in 257 constellations
Origin of Our
Constellations
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Ancients named 48 constellations
But not in a patch of southern sky
Which can not be seen from
A latitude of ~36°N =Sumeria?
And a time of ~2800BC
New Constellations Added
•  New constellations when sailors went to south hemisphere
•  Hevelius 1690 and Rost 1723
Names of Stars
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Al-Sufi 964AD: based on Ptolemy’s Almagest
We use mostly Arabic names for the brightest stars
Vega, Altair, Deneb, Algol, Betelgeuse, Mizar
Modern star designations: HD 209458B;
RXJ114722+345612
•  Names not for sale
Bayer 1654
•  Denoted stars with Greek letters in order of brightness
within constellation
•  αβγδε ζηθικλµνξοπρστυφχψω Andromeda
Kugel Globe
~200BC
•  May be the oldest celestial
globe still in existence
•  Depicts same constellations
•  Celestial Equator= projection
of Earth’s equator
•  Ecliptic= path of sun thru sky
•  Intersection = Vernal Equinox
=“Mile Zero” in the sky
Constellation is
Area of Sky
•  International Astronomical
Union Set Boundaries in
1928
•  Right Ascension
(longitude)
•  Declination (latitude)
Scientific
Method
•  Observation, Model,
Prediction
•  Good Theory: Testable
& Simple=Occam’s
razor
Observations
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Stars rise in the East and set in West every day
Circumpolar stars never set
And altitude of Pole=Latitude
So different latitudes / different circumpolar stars
Theory/Model:
Celestial Sphere
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Zenith /Nadir – Horizon
Meridian: am + pm
North & South Celestial Poles = rotation axis
Celestial Sphere surrounds Earth contains the stars
Rotates carrying stars around once per day (rise,set)
Simple & Testable-every day
Polaris is:
a.  the brightest star in Constellation Ursa
Minor so it is also called α Ursa Minor
b.  seen in the Zenith when standing on the
North Pole
c.  appearing nearly still as the Earth rotates
d.  circled by the Circumpolar stars as seen
from Victoria
e.  all of the above
Cassiopeia 1776
•  Note Right Ascension (longitude) & Declination (latitude)
Cassiopeia – Hevelius 1611-87
•  Beautiful charts but …
First Printed Star Charts
•  Perseus in 1482 woodcut
•  Star positions not very precise
but figures provided base for
later star maps
•  48 ancient constellations with
•  Latinized Greek names