CL - Stars (remote)[40]-1 (1)

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Apr 30, 2024

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Computer Lab Stars (Virtual Lab Remote Edition) Star Data Launch the Voyager 4 program from csub.apporto.com. Single-click on any bright star to bring up its Info Panel. The Info Panel information has the following meanings: Under the General tab: Name: The star's Arabic name and other common names. The star's Bayer name is a Greek letter followed by the constellation. The Greek letter Alpha usually indicates the brightest star in the constellation, Beta would be the second brightest, and so on. The Flamsteed Number of the star, for example "58 Ori" would mean this is the 58 th star (counting west to east) in the Orion constellation. The Harvard Revised (HR) number of the star in the Yale Catalog. The Smithsonian Astrophysical Observatory (SAO) Catalog number. The star's number in the Henry Draper (HD) Catalog of spectral types. Plus, additional catalog numbers for the star. Type: Such as Star, Double Star, Moon, Variable Star, Constellation, Galaxy, etc. Magnitude: The apparent magnitude of the star, lower values mean brighter looking stars. Right Ascension: The star's right ascension. The year following the R.A. value is what year this position was calculated for, the value changes year to year due to precession and proper motion. Declination: The star's declination. Distance: The distance to the star in parsecs and light-years. Size: Stars will have no angular size listed because they appear as just a dot in the sky, objects like planets and nebulae which have visible extent will have sizes. Azimuth: The azimuth of the star in the sky for the current viewing location and time. Altitude: The altitude of the star in the sky for the current viewing location and time. Under the Visibility tab: Name: [Same as above.] Rise: Time and azimuth that the star rises. Transit: Time and altitude when the star crosses the meridian. Set: Time and azimuth that the star sets. Midnight Transit: Time of year when the star is visible all night. Solar Conjunction: Time of year when the star is near the Sun – it is not visible at all at night. In Constellation: The constellation in which the star resides. Stars – 1
Under the Physical tab: Name: [Same as above.] Spectral Type: The spectral class of the star (following the OBAFGKM system) followed by the luminosity class of the star (a roman numeral between I and VII). Color Index: Exactly how this is calculated is not important. Hot, blue stars will have a color index that is negative, white or yellow stars near zero, and cooler red stars will have positive values. Proper Motion: The Proper Motion of the star, the rate at which it appears to move across the celestial sphere, because of its actual motion through space (or the combination of its movement and our Sun's movement). This gives the rate at which both the Right Ascension and Declination of the star change with time in arc seconds per year. Radial Velocity: The Radial Velocity of the star, how fast it is moving towards or away from the Earth and Sun. Positive values are stars moving away. Absolute Mag.: The absolute magnitude of the star which is the apparent magnitude the star would have if viewed from a distance of 10 parsecs. The absolute magnitude is a way of stating the star's luminosity, how much total light it emits. Temperature: The star's surface temperature in Kelvin. Questions: [Selected answers are given at the end of these instructions.] 1. For the star you chose, what is its: (a) common name? Sirius (b) type? Double Star (c) distance away in light years? 8.601 ly (d) transit time today? 5:40 PM (e) spectral type? A1Vm (f) direction of motion, towards us or away? [Hint: See the Radial Velocity entry above.] Away Stars – 2
(g) absolute magnitude? 1.45 Magnitudes The Voyager 4 program doesn't list the star's luminosity in watts nor does it list the brightness we see in W/m 2 . Voyager uses an older system, the magnitude system. The star's brightness is indicated by the "Magnitude:" value under the General tab. The magnitude system dates back to Hipparchus who called the brightest stars magnitude 1, next brightest magnitude 2, down to the dimmest stars visible with the naked-eye, magnitude 6. The magnitude system is still in use today but in a slightly modified form. Using telescopes, we can see stars dimmer than were visible to Hipparchus, these have magnitudes like 7, 8, 9, etc. Note that dimmer objects have higher magnitude values. Because we can measure the apparent brightness very accurately, we now allow magnitudes in-between whole numbers, there are stars with magnitudes like 4.76 and 0.79. Very bright objects will have magnitudes with negative numbers, the magnitude of the Sun is -26.7. Use the Voyager 4 program to look up the magnitude of each of the following objects. You can use menu choices under the Center menu to find all of these objects. Also fill in the distances for the Moon (in km) and planets (in AU). Object Magnitude Distance Object Magnitude Distance Moon -11.8 4000214 km Sirius -1.44 8.6 LY Sun -26.7 1 AU Betelgeuse 0.56 428 LY Venus -3.9 1.68210 AU Polaris 2.00 431 LY Mars 1.1 2.00992 AU Orio n Nebula 4.00 1761 LY Pluto 14.5 34.97701 AU Andromed a Galaxy 3.50 3.13 MLY Questions: 2. Which is brighter today, Venus or Sirius? Sirius is brighter 3. Would you expect the Moon's magnitude to vary from day to day? Why? A lot or a little? Yes, the Moon's magnitude does vary from day to day, but the variation is relatively small. 4. Can Pluto be seen with the naked eye? No These values are all apparent magnitudes, how bright they look, not how bright they really are (their luminosity). The Andromeda Galaxy has the highest luminosity of all the objects in this list, it puts out enough light that it can be seen with the naked-eye on Earth Stars – 3
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despite being over two million light-years away. No surprise it's so luminous, the Andromeda Galaxy is the combined light of a trillion stars! Of the objects in the above list, Pluto has the lowest luminosity. That’s because (1) it emits no light on its own, (2) it is very far from the Sun, and (3) its small size means it reflects little of the feeble sunlight reaching its vicinity. Inverse-Square Law The magnitude system indicates how bright objects appear to us. A lower magnitude means brighter. In particular, every 5 steps of magnitude represent a factor of 100 in brightness. So a star with magnitude -1 appears 100 times brighter to us than a star of magnitude +4. How bright the star appears to us is determined by how much total light it emits and how far away from us it is. The effect of distance on how bright the object looks is described by the inverse-square law. It says that if we move n times further away from an object that object should appear n 2 times dimmer. Let’s check this using the Sun. Select the Window/Location Panel menu and click on the Solar System tab. Drag the Distance slider to 1 AU, you can just leave the Longitude and Latitude values as they are. Select the Center/Planets/Sun menu and record the magnitude value of the Sun under the General tab) in the top line of the table below. Sun: Distance Magnitude 1 AU -26.72 10 AU -21.72 100 AU -16.72 You should've got -26.72 for the Sun's magnitude, this is the brightness of the Sun as seen from Earth since the Earth is usually about 1 AU from the Sun. change the Distance slider in the Location Panel to 10 AU. Record the new magnitude and repeat for a distance of 100 AU. 10 AU is 10x further from the Sun than 1 AU, so by the inverse-square law the Sun should appear 10 2 = 100 times dimmer. But 100 times dimmer on the magnitude scale means 5 steps higher, so the Sun’s magnitude at 10 AU should be -26.72 + 5 = -21.72 . Was it? It’s another factor of 10 in distance from 10 AU to 100 AU, so that should be five more steps of magnitude to -16.7. Question: 5. What would the magnitude of the Sun be if viewed from a distance of 1,000,000 AU? [You can’t set this on Voyager, so you need to work out the answer mathematically. That’s six factors of 10 (10 6 ) further than the 1 AU distance so six factors of 100 in decreased brightness which is six steps of 5 higher on the magnitude scale: -26.72 + 5 + 5 + … + 5 = ?] 3.28 magnitude Stars – 4
6. The star Altair is about 1,000,000 AU (=15.8 LY) from the Sun. Would you be able to see the Sun with the naked eye from Altair? It's unlikely that the Sun would be visible with the naked eye from Altair. Again, the further away from an object you are, the dimmer it will appear; but the variation follows a well-understood law, the inverse-square law. If you know how much total light a star emits (its luminosity) and how much light actually reaches us here on Earth (the magnitude), you can calculate how far away the star is. The mathematics is complex, but the concept is simple. Well, there is one complicating factor; interstellar (between stars) dust can absorb some starlight causing dimming (“extinction”) separate from the inverse-square law. Planetary Magnitudes Select the Earth tab in the Location Panel, this should put you back on Earth viewing from Bakersfield. Select the Tools/Planet Report… menu and then select the "Apparent Magnitudes" option from the pop-up menu (probably after moving or hiding other windows). Click the check boxes so that all the planets are selected (you can't select the Earth because we are viewing from Earth and it doesn't appear in the sky), then click "Update". The chart shows the magnitudes of these planets month-by-month for a year, you can click on “Next Interval” and “Last Interval” to change years (that may be necessary to see some of the features described below). The white curve for Venus is almost always the highest, this means Venus is almost always the brightest planet in our sky. Why Venus? For a few reasons; Venus is close to the Earth, Venus is close to the Sun, and Venus is surrounded by clouds which reflect most of the sunlight hitting them Questions: 7. Mars is always closer to us than Jupiter, why is Jupiter usually brighter in our sky? Jupiter's larger size and its relatively consistent distance from Earth result in its generally brighter appearance compared to Mars in our sky. 8. Mercury's brightness (the brown line) rises and drops more than any other planet. What is happening when it drops so low? When Mercury's brightness drops significantly, it is typically due to its position near inferior conjunction The main factors determining what magnitude a planet will appear to have are • how close it is to the Sun (inverse-square law) • how close it is to the Earth (inverse-square law) Stars – 5
• the size of the planet (bigger reflects more light) • phase as seen from Earth (how much of reflected light heads our way) • albedo of planet (‘albedo’ measures how reflective the body is) Magnitudes from Jupiter Close the Planet Report window. Click on the Solar System tab in the Location Panel, select Jupiter from the pop-up window, and drag the distance slider down to zero. We are now viewing from Jupiter's location. Select the Tools/Planet Report… menu again. These lines now represent the varying brightness of planets as seen from Jupiter. Sadly, Voyager won't let us turn on the plot for Earth (a bug in the program); from Jupiter, Earth's brightness plot would be similar to that of Venus. 9. Which planet generally appears brightest in Jupiter's sky? Click the "Next Interval" button a few times to make sure of your answer. Venus Star Colors Select the File/Open Settings… menu, find the "110 Settings" folder, and open the Settings File called "Enhanced Colors". The program is now displaying the stars with larger dots and with brighter colors. Click on a bright star that appears blue in color to get its Info Panel. Check the "Spectral Type" under the Physical tab for your star, it should be either type O or B (if not, try clicking on another blue star). The spectral class follows the OBAFGKM system, for example B8 or K3. The luminosity class (listed immediately following the spectral class) is a Roman numeral with the following meanings: I (Ia and Ib) Supergiant stars II, III, IV Giant stars (mostly Red Giants and Yellow Giants) V, VI Main Sequence Stars VII White Dwarf Example: If the star’s “Spectral Type” says “G2V”, that means the star has spectral class G2 and luminosity class V. In the following table, record the spectral class (like M1 or G5), luminosity class (I, II, … , or VII), distance (in light years), magnitude, absolute magnitude ("Absolute Mag."), and temperature for 12 stars. Remember, 'magnitude' measures the star's brightness in our sky while 'absolute magnitude ' measures its luminosity (and that lower values mean more light). Stars 1 and 2 on the list must be O or B types. Types 3 and 4 must be type A (they will appear white or blue-white on screen). Stars 5 and 6 type F (white), 7 and 8 type G (yellow), 9 and 10 type K (orange), and 11 and 12 type M (red). Stars – 6
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If you are having difficulties finding stars of the right type (color), here is a trick that you can use. Select the Display/Stars… menu and click on “Filter Stars by Spectral Type” and select only the star type you want to find. After you click OK the displayed stars will all be just that selected type. Number Type Spectral Class Luminosi ty Class Distance (LY) Magnitud e Absolute Magnitud e Temp. (°K) 1 O or B B3 IV 627.7 ly 4.73 -1.69 16400 °K 2 O or B B9 III 634.5 ly 3.25 -3.20 11600 °K 3 A A0 Va 25.297 ly 0.02 0.57 10000 °K 4 A A7 V 16.773 ly 0.93 2.37 7400 °K 5 F F3 IV 50.14 ly 3.36 2.43 7000 °K 6 F F2 V 169.70 ly 4.76 1.18 6600 °K 7 G G8 IV 44.71 ly 3.72 3.04 5000 °K 8 G G9 III 108.68 ly 3.57 0.96 4700 °K 9 K K3 II 460.7 ly 2.71 -3.04 3200 °K 10 K K3 III 174.23 ly 3.84 0.20 3800 °K 11 M M2 II 448.0 ly 3.82 -1.87 3800 °K 12 M M0 III 1128.6 ly 7.26 -0.44 2500 °K Questions: (give the star's Number from above to answer most questions) 10. Which star is furthest away? 12 11. Which star is closest? 4 12. Which star appears brightest in the sky? [Hint: Magnitude measures Apparent Brightness] 3 13. Which star appears dimmest in the sky? 12 14. Which star is the most luminous? [Hint: Don’t decide this based on Luminosity Class] 1 15. Which star is the least luminous? 11 Stars – 7
16. Which star is hottest? 1 17. Which star is coolest? 12 18. Of the 12 stars, Supergiant 1 Giant 4 how many were Main Sequence 4 White Dwarf 0 19. (a) Will the closest star always be the brightest? No, a far-away star can appear brighter if it has high enough luminosity. (b) Was it in your case? yes 20. (a) Will the brightest star always be the most luminous? No, the most luminous may be too far away to appear brightest. (b) Was it in your case? Yes 21. (a) Will the most luminous star always be the hottest? No, the hottest star may be small and hence not as luminous. (b) Was it in your case? Yes 22. (a) Will the hottest star always be type O or B? Yes, the OBAFGKM system does rank stars from hottest to coldest. (b) Was it in your case? Yes 23. (a) Will the most luminous star always be a giant or supergiant? Usually, giant and supergiant stars are so much larger than main sequence stars that they almost always have greater luminosities. (b) Was it in your case? Yes Stars – 8
24. If two stars have the same magnitude – that is they appear equally bright in the sky – but one is much closer to us, which star is actually brighter (which star has the higher luminosity or lower absolute magnitude, emits more light)? The star that is farther away is actually brighter. 25. If two stars have the same absolute magnitude (the same luminosity), but one is hot (blue) and the other is cool (red), which has the larger size? Red star Star Clusters If you were previously filtering stars by type, turn that off. Select the Center/Common Asterisms/Pleiades menu. An asterism is a group of stars that form a recognized pattern, but which is not one of the official 88 constellations (an asterism might be a subset of stars within a constellation or might be stars that connect across two or more constellations). Zoom to 3°. The Pleiades is a star cluster, click the “Show” button in the Info Panel and you’ll see the seven brightest stars of the cluster highlighted. The Pleiades is also known as The Seven Sisters. We will assume that every star currently displayed is part of the Pleiades cluster. Close the Info Panel. You are going to count the number of stars of each spectral type in the region shown on screen and fill in the following table. In principle, you can tell the spectral class of each star just by its color displayed on screen. In practice that just isn't going to work. Select the Display/Stars… menu. Click on the check box next to "Filter Stars by Spectral Type", you can now control which types of stars are displayed. Turn off all but types O and B, click OK, then count the stars on screen and enter the total in the table. I expect you will count between ten and twenty O and B stars; if not, you likely don’t have the correct settings (Did you zoom to 3°? Are you still operating off of the Enhanced Colors settings file?). Next turn on only type A and count. And so on. If you are having trouble counting the stars left on screen you can turn on the grid option by clicking on the Grid button ( ) along the right edge of the window. Count all the stars on the screen, not just those that you think are part of the cluster. You will repeat this for a second star cluster shortly to fill in the rest of the table. Pleiades (3°) Hyades (4°) Spectral Type Number Seen Percentage (%) Number Seen Percentage (%) O, B 14 15.56% 1 1.41% A 34 37.78% 11 15.49% F 20 22.22% 19 26.76% G 14 15.56% 16 22.54% K 8 8.89% 24 33.80% M 0 0% 0 0% Stars – 9
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Total 90 100% 71 100% Calculate the total number of stars of all types and enter that at the bottom of the table. The percentages are calculated as follows: divide the number seen by the total and multiply by 100%. For example, if you had 5 G-type stars in a cluster with 68 stars total, that would be = 7.4 % As a double-check, if you’ve calculated all the percentages correctly, they should add up to 100%. Select the Center/Common Asterisms/Hyades menu, Zoom to 4°, and close the Info Panel. Again count the stars of each spectral type, you should probably start with class M stars because those are probably the only ones you're currently displaying! Make sure to turn off the "Filter Stars by Spectral Types" option when finished. H-R Diagrams The Pleiades is a young cluster, it has many blue stars. The Hyades is an older cluster, most of the blue stars are gone (they have gone supernova or evolved into red giants or white dwarfs). The fraction of blue stars seen in a cluster can be used to date how old the cluster is. A more precise way of determining a cluster's age is to make an H-R Diagram using the stars of the cluster. Select the Tools/Star Survey… menu. Select "Color-Magnitude Diagram" (which is another name for an H-R Diagram) in the upper-left pop-up menu. This shows a standard H-R diagram but with all the low luminosity stars missing. All those red dwarfs and white dwarfs are missing because this diagram is plotting "Naked Eye Stars" and the dwarf stars are too dim to be seen with the naked eye from Earth. Select "Stars within 20 Parsecs" in the upper-center pop-up menu. These are our neighbor stars, a typical group of stars. Now dwarf stars are much more common. There should still be even more dwarf stars in this chart because there are lots of dwarf stars within 20 parsecs (65 light years) of Earth that haven't been discovered yet. In an H-R Diagram for a specific star cluster, there are usually stars missing from the upper end of the main sequence, stars that have become red giants (or gone supernova). Where the main sequence ends (called the turnoff point because the line of stars going up the main sequence often seems to turn off towards the red giant area) can be used to estimate the cluster's age. Select "Sky Chart Region" from the upper-center menu. You should now see an H-R diagram using mostly stars in the Hyades cluster. Star Masses Accurate masses can be determined whenever we can measure the orbit of one object around another (earlier in the semester we used the orbits of Jupiter's moons to determine the Stars – 10
mass of Jupiter). We can use stars in binary systems (two stars orbiting each other) to determine the masses of the stars. The mathematical formula is Newton's version of Kepler's third law, D 3 = ( M 1 + M 2 ) P 2 or ( M 1 + M 2 ) = D 3 / P 2 where M 1 and M 2 are the masses of the stars in solar masses, D is the distance between the stars in AU, and P is the period of the orbit in years. The formula only determines the total mass of the two stars, further information about the orbits is needed to figure out how much of the total mass belongs to each star. Our nearest stellar neighbor is Alpha Centauri which is actually a double star. Open the Settings File "Alpha Centauri" and read the provided Info. Hold down the zoom "+" button until you see α 1 Cen (Rigil Kentaurus) and α 2 Cen (Tollman) separated by one or two inches. Start the animation. 26. What causes α 2 Cen to speed up and slow down? The gravity from α1 Cen, it is following an elliptical orbit and obeying Kepler's 2nd Law. Again, careful observations of double star systems allow calculation of the masses of the stars. Now open the file "Zeta Cancri" and read the provided Info. Zoom in using the + button or by selecting 30" from the zoom pop-up menu. Start the animation. Q. Why doesn't ζ 2 Cnc move? A. It does move, all three stars orbit each other around a common central point. It doesn't move on screen because we have it locked at the center but we can change that. Change the menu at the bottom of the screen from Equatorial to Galactic. Click on the nearby button to unlock Zeta2 Cancri and then animate. 27. Which of the three stars has the most mass? That would be the one that moves the least, ζ1 Cnc. Now open the Settings File "Double Double", again read the Info then zoom in until you see all four stars distinctly. Animate. The two pairs are about a sixth of a light-year apart and the pairs take hundreds of thousands of years to orbit each other. The Nearest Stars Ask any child why some stars appear brighter than others and they might answer because some are closer to us than others. That is certainly true for the Sun, it appears far brighter to us than any other star because it is much closer to us. But for most stars, the closer means brighter rule does not work very well. Stars – 11
Our nearest neighbor stars can be displayed on the Voyager 4 screen. Select the Tools/Solar Neighborhood… menu, select the "Star Names" option. This is a three-dimensional view of the stars, move the scroll bars to rotate the view. You can also click on stars to get information on the star and its location. Here is a list of our nearest stellar neighbors. Use the table to answer the questions that follow. There are 31 stars listed in the table, to calculate a percentage, divide the number by 31 and multiply by 100. Distance Spectral Luminosity Abs. Star Name (ly) Type Class Mag. Sun - G2 V 4.85 Proxima Centauri 4.24 M5.5 V 15.5 Alpha Centauri A 4.36 G2 V 4.38 Alpha Centauri B 4.36 K1 V 5.71 Barnard's Star 5.96 M4 V 13.2 Wolf 359 7.86 M6 V 16.6 Lalande 21185 8.31 M2 V 10.4 Sirius A 8.66 A1 V 1.42 Sirius B 8.66 A2 VII (wd) 11.3 Luyten 726-8 A 8.79 M5.5 V 15.4 Luyten 726-8 B 8.79 M6 V 15.8 Ross 154 9.70 M3.5 V 13.1 Ross 248 10.3 M5.5 V 14.8 Epsilon Eridani 10.4 K2 V 6.19 Lacaille 9352 10.7 M0.5 V 9.75 Ross 128 11.0 M4 V 13.5 EZ Aquarii A 11.1 M5 V 15.3 EZ Aquarii B 11.1 M? V 15.6 EZ Aquarii C 11.1 M? V 17.4 61 Cygni A 11.4 K5 V 7.49 61 Cygni B 11.4 K7 V 8.31 Procyon A 11.4 F5 V 2.66 Procyon B 11.4 A? VII (wd) 13.0 Struve 2398 A 11.5 M3 V 11.2 Struve 2398 B 11.5 M3.5 V 12.0 Groombridge 34 A 11.6 M1.5 V 10.3 Groombridge 34 B 11.6 M3.5 V 13.3 DX Cancri 11.7 M6.5 V 17.0 Tau Ceti 11.8 G8.5 V 5.68 Epsilon Indi 11.9 K5 V 6.89 Gliese 1061 12.0 M5.5 V 15.3 Questions: Stars – 12
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28. What percentage of the stars are part of a multiple star system (a star is part of a multiple star system if it has an A, B, or C following its name, treat Proxima Centauri as if its name was Alpha Centauri C). 18/31 = 58% 29. What percentage of the stars are: (a) Type O: 0% (b) Type B: 0% (c) Type A: 9.68% (d) Type F: 3.23% (e) Type G: 9.68% (f) Type K: 16.13% (g) Type M: 61.29% (h) Giant or Supergiant: 3.23% (i) Main Sequence: 93.55% (j) Dwarf (white dwarf): 6.45% 30. What percentage are more luminous than our Sun (have a lower Abs. Mag.)? 16.13% The Brightest Stars: Bayer Common Spectral Luminosity Distance Lum. Name Name Type Class (ly) (L sun ) α Cma Sirius A1 V 8.6 25 α Car Canopus A9 I or II 310 13,500 α Cen Alpha Centauri G2 V 4.4 2 α Boo Arcturus K2 III 37 170 α Lyr Vega A0 V 25 50 α Aur Capella G8 III 43 150 β Ori Rigel B8 I 860 120,000 α Cmi Procyon F5 V 11.4 8 α Ori Betelgeuse M2 I 640 60,000 α Eri Archernar B3 V 144 3000 β Cen Hadar B1 III 390 42,000 α Aql Altair A7 V 17 11 α Cru Acrux B0.5 IV 320 25,000 α Tau Aldebaran K5 III 65 520 Stars – 13
α Sco Antares M1.5 I 600 75,000 α Vir Spica B1 IV 260 20,500 β Gem Pollux K0 III 34 43 α PsA Fomalhaut A3 V 25 17 α Cyg Deneb A2 I 2600 200,000 β Cru Mimosa B0.5 IV 350 34,000 Questions: The above list contains 20 stars, calculate the percentages by dividing the number fitting the category by 20 and then multiplying by 100%. 31. What percentage are: (a) Type O 0% (b) Type B 30% (c) Type A 25% (d) Type F 5% (e) Type G 10% (f) Type K 15% (g) Type M 10% 32. What percentage are: (a) Giant or Supergiant: 25% [These have Luminosity Class I, II, III, or IV.] (b) Main Sequence: 50% (c) Dwarf: 25% 33. What percentage were also on the Nearest Stars list? 0% (None of the stars on the list have distances less than 12 light-years.) That is, what percentage of stars on this list have distances less than 12 light-years? 34. What percentage are more luminous than our Sun (have a Lum. greater than 1)? 100% 35. Are any of the main-sequence stars on the list type K or M? No 36. Looking at the list, are there any stars closer than 50 ly that are more than 100 times the luminosity of the Sun? Yes, two, name them: Alpha Centauri A, Alpha Centauri B Answers to Questions: 1. Answers vary 2. Whichever has the lower magnitude, probably Venus. 3. Yes, because of phases, a lot. The changing distance between the Earth and Moon contributes only a small variation. Stars – 14
4. Answer hidden 5. Answer hidden 6. Answer hidden 7. Answer hidden 8. The dips occur, surprisingly, when Mercury is closest to us! That's when we see just its dark side. 9. Answer hidden 10 & 11. Look at Distance. 12 & 13. Look at Magnitude (lowest or most negative is brightest). 14 & 15. Look at Absolute Magnitude (lower or more negative is more luminous). 16 & 17. Look at Temperature. 18. Check their Luminosity Class (I supergiant; II, III, IV giant; V, VI main sequence; VII white dwarf). 19. (a) No, a far-away star can appear brighter if it has high enough luminosity. 20. (a) No, the most luminous may be too far away to appear brightest. 21. (a) No, the hottest star may be small and hence not as luminous. 22. (a) Yes, the OBAFGKM system does rank stars from hottest to coldest. 23. (a) Usually, giant and supergiant stars are so much larger than main sequence stars that they almost always have greater luminosities. 24. Answer hidden 25. Answer hidden 26. The gravity from α 1 Cen, it is following an elliptical orbit and obeying Kepler's 2 nd Law. 27. That would be the one that moves the least, ζ 1 Cnc. 28. 18/31 = 58% 29. Answer hidden 30. Answer hidden 31. (a) 0% (b) 30% (c), (d), (e), (f), (g) Answer hidden 32. Answer hidden 33. Answer hidden 34. 100% 35. No 36. Answer hidden Stars – 15
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