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 D
Setup:
Recall reading assignment:
Chapter 2 (Discovering the Universe), pp. 24 – 52
Please take a moment to mute your cell phone!

2. Review questions coming …

3. This question counts double!
sec 10 9 11 12 14 13 8 6 1 2 3 5 4 7 15 26 25 27 28 30 29 16 24 18 17 23
Question 4 19 22 20 21
What is w Ceti?
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 dim star.
Next question coming …

4. This question counts double!
sec 10 9 11 12 14 13 8 6 1 2 3 5 4 7 15 26 25 27 28 30 29 16 24 18 17 23
Question 5 19 22 20 21
A star with 45mg would be …
A So bright that it is impossible.
B Outside the Galaxy.
C So large that it would cover half of the sky.
D Only visible in a large telescope because it would be too small.
E Impossibly dim.
Next question coming …

5. 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 6
Pluto is 15mg and asteroid Vesta is 7mg .
Which of the two is brighter and by how much?
A Pluto is 8 times brighter.
B Pluto is 8 times dimmer.
C Pluto is 1600 times brighter.
D Pluto is 1600 times dimmer.
E None of the above: magnitudes are size, not brightness.
Next question coming …

6. This question counts double!
sec 8 9 11 12 7 10 4 1 2 3 6 13 25 30 35 40 14 19 16 15 17 18 45 20 5
Question 7
Which of the following are real objects?
A Constellations: Yes, Star clusters: No, Galaxies: Yes.
B Constellations: Yes, Star clusters: Yes, Galaxies: Yes.
C Constellations: No, Star clusters: Yes, Galaxies: Yes.
D Constellations: Yes, Star clusters: Yes, Galaxies: Yes.
E Constellations: No, Star clusters: No , Galaxies: Yes.

7. Angular sizes How large is the Big Dipper? 250 apparent size
Stretch out your hand:
1 cm = 1o
25o
1o = 60 am (minute of arc)
1 am = 60 as (second of arc)
How large is the Moon?
1/2 0 apparent size
1/2o = 30 am = 1800 as
0.5o

8. Resolution Stars are points in all telescopes:
Resolution of the human eye is 1 am = 60 as
Smallest visible detail is as small as this.
Stars are points in
all telescopes:
Calculated size of a star:
~ as,
Resolution of best telescope:
~ 0.1 as.
Much more detail is visible
Resolution of a simple telescope is ~ 1 as

9. Alcor and Mizar The handle of the Big Dipper:
25 am
25 am
Mizar A & B
14 as
The handle of the Big Dipper:
the middle star is a double
How far apart are they?
25 am

10. Questions coming …

11. sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5
Question 8
How do stars look in the largest telescope of the world?
A They look like large disks and we can see a
lot of detail on them.
B They look like large disks but there is not much detail to see,
although telescopes would have been able the resolve the details.
C They look like tiny disks but few or no details can be
seen on them.
D They look like points (no details visible).
E They look like “star-shaped” objects with rays
emanating from them.
Next question coming …

12. 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 9
How large does the Moon appear in the sky?
A A few inches.
B A few thousand miles.
C A few arc seconds.
D A light year.
E A half a degree.
Next question coming …

13. Question 10
sec 10 11 9 13 14 8 12 6 2 1 3 4 15 5 7 16 26 25 27 28 30 29 17 24 19 18 23 20 22 21
How large is the Big Dipper?
A A few miles.
B A few light years.
C Five million light years.
D More than twenty degrees.
E A half a degree.
Next question coming …

14. 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 11
The two stars Alcor and Mizar are easily separated by the human eye.
This means that they must be farther apart than …
A a few degrees
B one arc minute.
C a few light years.
D a few million kilometers.
E a million light years.

15. Parallax How do we know the distance to the stars? Measure parallax:
(Closeby stars, for a start.)
Parallax
• Closeby stars seem to move on tiny circles, once a year
• Reflection of the motion of Earth around the Sun
• Most (far-away) stars move very little
Measure parallax:
the closer the star, the larger the circle
Parallax = 1 as ↔ distance 1 parsec (pc)
1 pc = 3.26 light years
Formula: distance[pc] = 1/parallax[as]
Practical limit - precision:
• Good telescope can measure where the middle
of the blurred image of a star is
with a precision of 1/1000 as
• Can use parallax method up to distances of pc
works only for the closest stars –
in the Solar Neighborhood.

16. Questions coming …

17. 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 12
What is parallax?
A Far away stars appear dimmer in the sky.
B Stars make one circle around the whole sky in one year.
C Stars move in tiny circles in the sky, once a year.
D The telescope must follow the star’s apparent daily motion.
Next question coming …

18. sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5
Question 13
How large an effect is parallax?
A Very large: stars move all the way around the sky
in a year.
B Large. You can see it by the naked eye without any difficulty.
C Tiny. We need a very precise telescope to detect the parallax
of stars.
D Extremely tiny. Not even the largest telescopes can see the
parallax of stars because stars are so far away.
Next question coming …

19. sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5
Question 14
Polaris, the North Star, has its parallax measured
as 0.01 arc seconds. How far is it?
A One parsec. (That would be ~ 3 light years.)
B A tenth of a parsec. (That would be ~ 1/3 of a light year.)
C A hundred parsecs. (That would be ~ 300 light years.)
D Ten parsecs. (That would be ~ 30 light years.)
E A thousand parsecs. (That would be ~ 3000 light years.)

20. 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)

21. 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

22. 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)

23. Questions coming …

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Question 15
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 …

25. 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 16
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 …

26. 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 17
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.