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 (Email) 2. Image Proc. Lab turned in: Feb. 21 Please take a moment to mute your cell phone!

Review questions coming …

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 …

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 …

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.

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

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

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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 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 …

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 …

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.

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? 

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

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)

Questions 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 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 …

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 …

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.