1. Prepare your scantron:
Use
a pencil,
not a pen!
Fill in your name and fill the bubbles under
your name.
LAST NAME FIRST, First name second
Put your 4-digit code instead of “IDENTIFICATION NUMBER”.
--- (The last 4 digits of your OleMiss ID.)
Question # 1: answer A
Question # 2: answer A
Question # 3: answer E
Setup:
Note extra credit deadlines:
Signup: Feb. 6 ( )
2. Image Proc. Lab turned in: Feb. 21
Please take a moment to mute your cell phone!

2. Review questions coming …

3. This question counts double!
sec 8 9 11 7 10 4 1 2 3 13 6 12 25 30 35 40 14 19 16 15 17 18 45 20 5
Question 4
Which constellation is farthest?
A The Big Dipper is closer than Cancer because
the Big Dipper looks larger in the sky.
B Cancer is farther because
its stars look dimmer in the sky.
C All constellations are at the same distance (one
astronomical unit).
D This question is nonsense because constellations
are not real objects.
E This question is nonsense because the distance to constellations
changes as Earth revolves around the Sun.
Next question coming …

4. This question counts double!
sec 10 9 11 13 14 8 12 6 2 1 3 4 15 5 7 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22
Question 5
Judging by the name, what is t Ursae Maioris?
A The name of a bright star.
B The name of a planet.
C The name of a constellation.
D A galaxy.
E The name of a not very bright star.
Next question coming …

5. This question counts double!
sec 8 9 10 11 7 4 1 2 3 12 6 13 25 30 35 40 14 19 16 15 17 18 45 20 5
All individual stars visible in a telescope are …
A outside the Galaxy.
B inside the Galaxy, but not necessarily
in the Solar Neighborhood.
C inside the Galaxy, and mostly in the Solar Neighborhood.
D 50% inside the Galaxy, 50% outside.
E nowhere close to the Galaxy, which is much farther away
from us than the individual stars in the sky are.

6. Understand brightness of stars: the magnitude scale
(Hipparchos ~ 170 BC)
An m = 10mg, star,
need
an amateur telescope
to see it
The Andromeda Galaxy
m = 3mg in total
An m = 17mg, star,
need
a professional telescope
to see it
Magnitudes mean brightness:
• The larger the number, the fainter the object
• One magnitude difference means a lot dimmer (2.5 times)
A fifth magnitude star: m = 5mg,,
just visible to the naked eye
A third magnitude star: m = 3mg
A second magnitude star: m = 2mg __ I
A first magnitude star: m = 1mg
m = 2.5 × lg I
Vega

7. Example: stars in the Big Dipper
4.0 mg
1.9 mg
2.2 mg
3.3 mg
5.6 mg

8. Questions coming …

9. sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22
Question 7
The magnitude of a star tells us …
A How far the star us from us.
B How bright the star appears in the sky.
C How bright the star is in reality.
D How large the star appears in the sky.
E How large the star is in reality.
Next question coming …

10. sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22
Question 8
Which one is brighter, a 1mg star or a 5mg star,
and how much?
A The magnitude of a star does not refer to
brightness at all, it refers to size.
B The 1mg star is much brighter.
C The 1mg star is a little brighter.
D The 1mg star is much fainter.
E The 1mg star is a little fainter.
Next question coming …

11. sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21
Question 9
Do you need a telescope to see Pluto whose
brightness is a 15mg?
A No, it can be seen by the naked eye.
B Yes, but even binoculars will suffice.
C Yes, a small amateur telescope is needed.
D A fairly large amateur telescope or a small
professional telescope is needed.
E Pluto is only observable in the largest professional
telescopes in the world.

12. Exercises on magnitudes 1
This is how Orion looks to a naked-eye
observer in complete darkness.
Exercises on magnitudes 1 
 Orionis: 0.5 mg
Orionis is one of the brightest stars in the sky.
How bright do you think it is?
How bright do you think Orionis is?
 Orionis : 2.0 mg 
 Orionis : 4.3 mg
How bright do you think Orionis is? 

13. Exercises on magnitudes 2
Capella is 0 mg.
How bright do you think the following are?
Exercises on magnitudes 2
2 mg
Pleiades
1 mg
International
Space Station
Aldebaran
1 mg
- 4 mg
Venus
- 2 mg
Jupiter

14. Apparent and absolute brightness
Recall:
A parsec (pc) is a unit of distance, 3.26 light years.
Why this unit?
Because the orbit of Earth looks 1 arc sec radius from the distance of 1 pc.
How bright it looks
(m)
How bright it really is
(M)
Solar neighborhood (~100 pc)
A star’s absolute magnitude is
how bright it would look
from 10 pc (32 light years) away.
The Sun: M = 5mg
(an average star)

15. Distance makes stars dimmer
The rule: 2.5 times as far away, looks 2mg dimmer
Distance makes stars dimmer
Star A and star B have the same absolute magnitude M = 5mg
Star B is 10 pc away: apparent magnitude m = 5mg
Star A is 25 pc away: apparent magnitude m = 7mg
Reality:
Looks like: B
10 pc B
25 pc A A

16. Distance modulus The distance modulus m - M = 5  lg d - 5
Relation: M (abs. magn.), m (appt. magn.), d (distance in pc)
Meaning of relation: the farther a star, the fainter it looks
m - M = 5  lg d - 5
The name of “m - M” is: the “distance modulus”
How to use this?
Centauri m=1.3mg, distance=1.3 pc => absolute M=5.7mg : a faint star looking bright;
distance modulus = mg (close to us)
Crucis m=1.6mg, distance=27 pc => absolute M=-0.6mg
distance modulus = mg (not that close)
Centauri m=2.6mg, distance=120 pc => absolute M=-2.8mg: bright star looking faint;
distance modulus = mg (far from us - still in the solar neighborhood)
Centauri m=3.5mg, distance=5200 pc => absolute M=-17.1mg: whole star cluster looking faint;
distance modulus = mg (very far from us, halfway to the center of the Galaxy)

17. Questions coming …

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Question 10
How bright would the Sun look in the sky
from a distance of 10 parsec?
A -12mg (as bright as the full Moon).
B 1mg (as bright as the brightest stars in the sky).
C 5mg (barely visible to the naked eye).
D 15mg (very faint).
E Invisible: we cannot see that far.
Next question coming …

19. sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22
Question 11
Which of the following data of Sirius cannot be directly
measured from Earth, only calculated?
A Its apparent brightness, which is m =  1.5mg.
B Its absolute brightness, which is M = + 1.5mg.
C Its speed of motion in the sky.
D The color of its light.
Next question coming …

20. sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21
Question 12
Polaris, the North Star, is m = 2mg, not particularly
bright. Its absolute magnitude is M = - 4mg.
If you imagine Polaris placed where the Sun is now,
would it look brighter, or fainter than the Sun?
A Ten thousand times brighter.
B Somewhat brighter.
C About the same.
D Somewhat fainter.
E Ten thousand times fainter.