2. Origins of Constellations
Ancient constellations:
Constellation names we use derive from ancient Mesopotamia (modern day Iraq)
Others were added by the Babylonians, Egyptians, and Greeks.
“Modern” constellations
40 more were added by 1600s
IAU officially defined 88 constellation boundaries in 1928
EVERY culture around the world has their own constellations
Asterisms – named groups of stars that are NOT constellations ex: Big Dipper, Great Square
Stars that make up constellations are all different distances from our Earth and Sun.

3. Star Names
The "common" names derive from ancient Arabic, and often have meanings
EX:
Rigel = leg
Betelgeuse = armpit of the giant
Deneb = tail
Altair = bird

4. Star Names
in 1603, the first "modern" naming system was developed by Johann Bayer, using:
the Greek alphabet for the brightness of the star
the Latin name of the constellation
EX: the brightest star in Orion (Betelguese) is also called a Orionis, the 2nd brightest, is called b Orionis
one problem with this system is that some stars vary their brightness - Betelgeuse is NOT always brighter than Rigel!
There are over 10 different systems that are/have been used for naming stars

5. The Many Names of Betelgeuse
Alpha Orionis
58 Ori
HR 2061
HD 39801
SAO BD
HIP 27989
H 6
ADS4506
WDS
TYC

6. Star Brightnesses - the Magnitude Scale
Introduced by Hipparchos ( BC)
Divided the stars into 6 classes
brightest stars were 1st magnitude
faintest stars were 6th magnitude (unaided eye)
larger the magnitude, the fainter the star!
Today it is similar, but more mathematical, logarithmic scale
1st magnitude stars are 100 x brighter than 6th magnitude stars
1 magnitude difference = x difference in brightness, so
A 1st mag star is 2.5 times brighter than a 2nd mag star, and a 1st mag star is 2.5 times 2.5 times brighter than a 3rd mag star

7. Star Brightnesses - the Magnitude Scale
formalizing the mathematics has produced stars with negative magnitudes (Sirius = -1.42)
Magnitude scale has been extended to all astronomical objects

8. Scientific Models
way of representing an object, process, or behavior, to make it more understandable
Can be:
a physical object (globe)
a mathematical formula
(F = ma)
a conceptual idea
Doesn’t have to be correct in order to be useful!

9. Celestial Sphere Model of Universe
Earth-center (geocentric)
Stars orbit the earth, attached to a huge sphere
Pivots above the N and S poles (NCP & SCP)
Half way between, above Earth’s equator is the:
Celestial Equator
divides the northern sky from the southern sky
Passes through East and West points
Fully developed by about 200 B.C.
Believed to be true until around 1550

10. Rotation vs Revolution
Rotation is:
Spinning
Earth rotates once every:
Revolution
Orbiting
Earth revolves around the Sun once every:

11. Sun’s Apparent Motion
Sun appears to slowly move Eastward along the ecliptic
Over one year, it traces out the ecliptic
Plane of Earth’s orbit around the Sun
Plane of the solar system

12. Sun’s Apparent Motion Planets also move Eastward along the ecliptic
12 constellations the ecliptic passes through are the zodiac