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!

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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 …

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 …

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 …

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.

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

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: ~ 0.001 as, Resolution of best telescope: ~ 0.1 as. Much more detail is visible Resolution of a simple telescope is ~ 1 as

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

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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 …

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 …

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 …

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.

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 2-300 pc works only for the closest stars – in the Solar Neighborhood.

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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 …

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 …

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.)

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)

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

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 = - 4.4 mg (close to us) Crucis m=1.6mg, distance=27 pc => absolute M=-0.6mg distance modulus = 2.2 mg (not that close) Centauri m=2.6mg, distance=120 pc => absolute M=-2.8mg: bright star looking faint; distance modulus = 5.4 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 = 13.6 mg (very far from us, halfway to the center of the Galaxy)

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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 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 …

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 …

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.