Stars
Constellations
 A group
of stars
that appears to
form a pattern
in the sky
Virgo
AQUARIUS
Constellations total of 88
different
constellations can
be seen in the N
and S hemispheres
 As you move
north you can see
more stars.

Andromeda
Aries
Constellations Ursa
Major
- (Big Bear)
is the most
famous
constellation
Constellations The
Big
Dipper is part
of Ursa Major
Constellations Two
Polaris
stars of
Ursa Major
are used to
find the North
star- Polaris?1&2 (pole star)
Constellations-

Polaris is part of Ursa
Minor (the little
dipper)
Ursa Minor
Constellations


As the earth rotates on
its axis the
constellations move.
They rotate around
Polaris counter
clockwise.
The earth’s axis points
toward the N. Star
Pg. 617 (fig. 28.2)
Orion in
Winter
Constellations

Some constellations
can only be seen
during specific
seasons
This is due to earth’s
rotation around sun
and tilt of the earth
Lyra in
summer
?3,4&5
Circumpolar Rotation around Polaris
What happens as you travel North?
 The
number of circumpolar stars
visible, increases as the observer
moves North
Can you tell what
constellations
these are?
?6
Ursa Major
?7
Lyra
?8
Orion
Aquarius
Gemini
Stars- How far to a star?


Closest Star = Sun
93,000,000 miles
= 1 astronomical unit
Next closest star
 Proxima Centauri
 25 trillion miles
 2.5 x 10 13
 4.2 light years
Light year



Distance that light
travels in one year
5,900,000,000,000
miles
Polaris- 680 LY
Betelgeuse (red
supergiant ) is 490 LY
?9
Properties of Stars
 Our
Sun-
Diameter 855600 miles
 110x earth
 Density
 1.4 x density H20
 Mass
 300,000x earth

How does our sun compare?



Diameter average
Density mid to high
Mass Other stars range
from 1/100th to 50x
our sun
How do we size up?
Wow! Jupiter is BIG
Our sun is REALLY BIG!
Guess Not!
We are REALLY SMALL!
I feel so insignificant!
Color?
Depends on surface
temperature
cool
Hot- ~30,000 ° C
Medium- our sun (5500°C)
Green
stars
look
white
to us!
Classification of stars
?10 & 11
Composition of Stars
How can we tell?
You know this!
Spectroscopy!
Our sun Hydrogen (70%)
 Helium (28%)
 No 2 stars have the
same spectra (like a
fingerprint)

-Brightness
Apparent Magnitude how bright a star
appears to earth
observer.
 Depends on
 Distance from us
 what is between us
 true brightness
Brightness-

Luminosity True brightness
 Depends on…(2 things)
1. Size -if same size,
blue is more
luminous
2. Temp.- if same
temp., bigger is
more luminous
Absolute MagnitudeRigel- foot of Orion
40,000 suns
“Blue Super Giant”




How stars would appear
if they were all the same
distance from earth.
All stars place 32.6 LY
from the sun
Our sun abs. Mag = 4.8
Negative is brighter
?12