1. “Beyond the solar system where no man
has gone before.”

2. Characteristics of Stars A great deal is known about our universe.
Stars and “empty” space radiate energy in all
directions.
Learning about star characteristics and the
universe is dependent on interpreting the
radiated energy.
Star Color and Temperature

3. Star Color and Temperature
Yellow
Blue
RED
2,500
6,000
30,000 K
Cool stars
Hot stars
Long wavelengths
Short wavelengths
R O Y G B I V

4. I the stars. How is the color of a star related to
Discuss with a friend:
How is the color of a star related to
the temperature of the star?
2. How EM waves related to the
temperature of the star?
I will get an A on my exams and quizzes.

5. Light Year How far is far? – Astronomical distances
Interstellar space is measured using the
light year.
Light Year
the distance that light travels in one year
light travels 186,000 mi/sec (WOW!)
Light travels 6 trillion miles in one year.
One would have to travel the speed of light
for one year to go 6 trillion miles.
Nothing in the universe is faster than light...
except students when a class has just ended.

6. How far is far? – distance across a galaxy
100,000 light years across
6 trillion miles X 100,000

7. Measuring the Brightness of a Star
Stellar Brightness
Magnitude – the brightness of a star
Magnitude is measured using (-) and (+) numbers
the more (-) the number, the brighter
the more (+), the dimmer the star
Apparent Magnitude
A star’s brightness as it appears from earth
factors controlling apparent magnitude
how big the star
how hot the star
how far away the star
Which is brighter: star or star ?

8. Absolute Magnitude Example: -26.7 +5 32.6 ly
measures the “actual” brightness
Two stars with the same absolute magnitude
will not be the same apparent magnitude.
WHY?
compare absolute brightness
Use a standard distance of 32.6 light years
away from earth.
Example:
Apparent Magnitude
Absolute Magnitude
-26.7 +5
bright
dim
Earth
32.6 ly

9. So, rank stars from biggest to smallest.
Distance, Apparent Magnitude, and Absolute
Magnitude of Some Stars
32.6 ly
View from Earth
Star
Name
Distance
Light Years
Apparent
Magnitude
Absolute
Magnitude
Sun NA
-26.7
5.0
4.27
Alpha Centauri
0.0
4.4
Sirius
8.70
-1.4
1.5
-0.1
Arcturus 36
-0.3
Betelgeuse
520
.08
-5.5
1.3
-6.9
Deneb
1600
So, rank stars from biggest to smallest.

10. The brighter, the bigger the star
Brightness scale – Using Absolute Magnitude
Deneb
Betelgeuse
Arcturus
Sirius
Centauri
Sun -7 -5 -3 -1 1 3 5 7 9
Bright
Dim
The brighter, the bigger the star

11. I the stars. 3. Describe the difference between
Discuss with a friend:
3. Describe the difference between
absolute and apparent magnitude.
4. How is a light year defined?
5. How fast does light travel?
I will get an A on my exams and quizzes.

12. Super Giants and Red Giants
How are stars classified? – The Hertzsprung-Russell
Diagram (HR-diagram)
-10
Very Bright -5
Super Giants and Red Giants
Absolute Magnitude
Main Sequence +5
+10
White Dwarfs
Very Dim
+20
20,000
14,000
10,000
7,000
5,000
3,000
Surface Temperature (K)

13. HR-Diagram O B A F G K M Cool, bright Hot, dim Spectral Class
The Hotter, the Brighter
The Cooler, the Dimmer
Hot, dim
20,000
14,000
10,000
7000
5000
3000
Surface Temperature (K)

14. Oh, Be A Fine Guy (or Gal), Kiss Me
Spectral Class Divisions
O B A F G K M
Oh, Be A Fine Guy (or Gal), Kiss Me
Hottest
Coolest
Sub-divisions
O0O1O2O3…O9 B0B1B2B3…B9A0………
What spectral class is our sun?
G2 (5,5050 C, 9,9410 F) G2

15. I the stars. 6. What is the HR-diagram?
7. How is the HR-diagram used to
classify stars?
8. How is the spectral class used to
9. What are specific differences between
main sequence, red giants, and
white dwarf type stars?

16. HR-Diagram Stellar Evolution Surface Temperature (K) Variable
Star Stage
Red Giant
Stage
Dust and
gasses
Protostar
Planetary
Nebula
Stage
Main Sequence
Star
Black
Hole Stage
White Dwarf
20,000
14,000
10,000
7,000
5,000
3,000
Surface Temperature (K)

17. Are we running out of gas?
As you can see, the sun begins
as a nebula, spends much of its
life as a main sequence star,
becomes a red giant, planetary
nebula, white dwarf, and finally
a black hole and dies.
So, what phase is our sun?
Are we running out of gas?

18. Final Exam according to Syllabus Each student gets
Final Exam –Option-1
Final Exam according to
Syllabus
Each student gets
there own set of
three questions
Final Exam – Option-2
May 9, Wednesday-MS2
8:00 am – 9:50 am
50% on Exams 1 & 2
50% on:
The Atmosphere
Global Winds
The Solar System
Beyond the solar system
NO ESSAY QUESTION