1. First Slide
2. How to operate the telescope simulator
| To change to the next slide, click on the next link in the frame to the left. | |
| Some of the detailed photos may take a moment to load-- please wait. |
| If you have any problems in understanding the material, please contact the AAVSO (aavso@aavso.org). | |
| And now, let’s begin! |
4. Welcome to the AAVSO telescope simulator!
| Today, you will learn how to perform a valuable scientific measurement--star brightness. | |
| You’ll also learn how much fun it can be to do real science from your own backyard. | |
| This learning experience was designed to take 15 minutes but may be affected by the speed of your Internet connection and current Web conditions. | |
| In addition to estimating brightness, you’ll learn how to find variable stars with AAVSO charts. |
| We’ll also cover how scientific data can be useful even when it contains “noise”. | |
| You’ll learn that your observations can be very valuable, even while you’re learning to make better and better estimates. |
| In order to make your
brightness estimate
later, you will need to
have the star chart for W
Cygni in front of you.
Click on the image to
the right, then click on the chart again to select the chart frame, now print out a
copy of this chart.
OR, for a higher resolution W Cyg chart click here and then right click to save the image onto your computer, open it in an image program and print (the chart should resize to fit the page). |
| The sky is full of wonderful things to see. | |
| But, just looking at its beauty often doesn’t provide answers to the riddles of the universe. |
9. Astronomy theories need data!
| Most of the discoveries astronomers have made about the universe needed light measurements to confirm or suggest theories. | |
10. Data is information from instruments
| There are all kinds of instruments astronomers use to make measurements of star brightness. | |
| We call these measurements photometric data. | |
| Photometric means light-measuring. |
11. Your eyes are your instruments
| You are going to use your own eyes and a special technique for making photometric measurements. | |
| The technique is called: Interpolation of Magnitude. | |
| Interpolation is a word scientists use when a measurement is estimated between two known values. | |
| People interpolate all the time! |
13. Interpolation
| Your car’s gas gauge needle is half way between empty and 1/4 tank. | |
| You interpolate you have 1/8 of a tank left--time to get gas! |
14. Interpolating star magnitude
| Making a brightness estimate is easy in theory but requires some practice. | |
| We call the measurement of brightness the star’s magnitude. | |
15. Interpolation of magnitude
| We estimate the brightness of the variable star by using at least two stars of known brightness; one brighter than the variable, one fainter. |
16. Interpolation of magnitude
| Just like the gas tank example, if a star’s brightness seemed about half way between two stars that were known to be magnitudes 5.0 and 6.0, what is the magnitude of the variable star? |
17. Interpolation of magnitude
| That’s right -- half way between 6.0 and 5.0 is | |
18. How to find a variable star
| The AAVSO makes thousands of star charts (sky maps, like road maps) used to find and estimate the magnitude of variable stars. | |
| Because all AAVSO observers use the same charts, our results can be very good, and can be compared with each other’s. |
19. How to find a variable star
| If you do not have the W Cyg chart in front of you, please click on the image and print one out now. This chart is for W Cygni, a star you can find with binoculars from your own yard. | |
| But first let’s try a simple lesson in interpolation and using star charts. | |
20. Variable and comparison stars
21. Decimal points can be confusing
22. A big magnitude number is faint, a big dot is bright!
23. Making your first estimate
24. Making your first estimate
25. Making your first estimate
26. Making your first estimate
27. Making your first estimate
28. Making your first estimate
30. Interpolation is an educated guess
32. Making your first estimate
| But, whatever your estimate, congratulations on your first variable star observation! | |
| Write your result down on a piece of paper. | |
33. Why do we call it an estimate?
| Different people will make different estimates of brightness using this method. We all see the world differently. | |
| Yet, all the estimates are “right”! There is no one correct answer. | |
| All scientific measurements have variation. We call it error or noise. |
34. I thought scientists only used exact numbers!
| Well, a number can never be too exact in science, especially astronomy. But, all measurements are really estimates to a certain precision. The trick is understanding what that precision is. |
| The graph on the right is a portion of the AAVSO data that show the change in brightness over time of a star called SS Cygni. | |
| We call this a light curve. | |
| SS Cygni is located in the constellation of Cygnus the Swan. |
| SS Cygni brightens dramatically every few months. | |
| Each dot represents a measurement made by an AAVSO observer somewhere in the world. We have records on some stars back to 1911! | |
| You can make measurements like these too! | |
| The magnitude is plotted on the Y axis (up and down) | |
| The day and time of the observation is plotted on the X axis (left and right) | |
| You can see the noise in the data. | |
| Note that the curve is not a nice straight line. | |
| Rather, it is a wide band of individual observations. | |
| Astronomers and physicists can use even noisy data to learn many things about how stars work. | |
| With practice, AAVSO visual observers can estimate brightness to a precision near 0.1 magnitude. |
40. There is no perfect estimate
| Your observations are estimates because everyone gets a little different result. | |
| You don’t have to be perfect--just do the best job you can. | |
| Practice will help a lot! |
42. More practice
43. How did it go?
44. W Cygni
| We are now going to make two estimates of a semi- regular star called W Cygni (W Cyg). You should have its chart in front of you. | |
| Advance one slide and it will be the next picture. |
45. Slide 45
46. You’re kidding!
| OK, there are lots of stars in the picture... | |
| You will need to learn to “star hop” to the star you want. But it’s easy. | |
| Here’s how! | |
| Take a look at the AAVSO W Cyg (size aa) chart. | |
| Hold it so that it is tilted about 45 degrees clockwise (to the right). It will better match the picture if tilted a little. |
| The way a group of stars looks in a telescope can vary because of the type of telescope, how you look into it, and the season or time of night. |
| Learning how to match the telescope view to the chart is something you’ll learn when actually observing. | |
| But, back to our estimate! |
| Find the following things on your chart in this order: | |
| 1) M39 (star cluster) | |
| 2) Comp star 53 and a line of stars pointing from it to the south | |
| 3) Rho (pronounced “row”) Cyg, a Greek letter that looks like a “p” | |
| 4) W Cyg | |
51. Slide 51
| This is how you star hop--from the easiest thing to see to the variable star. | |
| Now, let’s try it on the photo! | |
| We’ll go full screen and I’ll show you the landmarks we just found on our chart. | |
53. Slide 53
54. Slide 54
55. Slide 55
56. Slide 56
57. How did you do?
| Were you able to do it? | |
| If not, or if you had a lot of trouble finding things, do not be discouraged and try let’s try it again. |
58. Slide 58
59. Slide 59
60. Slide 60
61. How did you do?
| Is it getting easier to make the estimates? | |
| Did you have less trouble finding W Cyg and the comparison stars? | |
| Practice really helps, doesn’t it! | |
62. Is that your final answer…?
| On the right is a section of the light curve of W Cyg from the AAVSO data base. | |
| The two dates on which you made estimates are shown with dashed lines. |
63. Is that your final answer…?
| On April 28 the observations were between about 6.3 and 5.7 magnitude. | |
| On July 19, the observations were between about 7.3 and 6.4 magnitude. |
64. Is that your final answer…?
| How did you do compared to other AAVSO observers? | |
| If one or more of your estimates are outside of the band of results, why? | |
65. If your results were different from AAVSO observers’...
| Practice helps. Some AAVSO observers have made thousands of measurements. | |
| You were looking at a computer, not the sky. | |
| You are still learning! |
66. You are teaching your eyes to see the world differently!
| Many new observers need time before they can see fine differences in brightness. This takes practice but is a skill that can help you enjoy all the beauty in the night sky. |
| I bet you did pretty well! |
| You learned how to find variable and comparison stars using AAVSO charts and a technique called star hopping. |
| You then learned how to estimate the brightness of a star using a technique called interpolation of magnitude. |
| You learned that your data is valuable even as you are perfecting your technique because everybody gives their best estimate and astronomers really use even noisy data. |
| Variable star observing can be rewarding and fun! | |
| Contact the AAVSO for more information. (helplearning@aavso.org) | |
72. Variable star observing is fun!
| The changing night sky is something that can fascinate you for years to come. | |
| You can expand into new and exciting measurement technologies such as CCD photometry or analyze your data and other people’s just like scientists do! |
73. Help Professional Astronomers
| AAVSO members participate with NASA an other professional astronomers in their research. | |
| One day, the Hubble Space Telescope may even move to look at a star because of your observations! |
74. The AAVSO can help you grow as a variable star observer
| AAVSO offers a number of free services, including charts, from its web site--www.aavso.org | |
| AAVSO membership provides a number of other benefits: |
75. Mentor Program
| Member benefits include a mentor program to team you up with an experienced variable star observer in your area. You can learn a lot in just one night! |
76. Publications, meetings, and more!
| AAVSO also offers a newsletter, twice-yearly meetings, a Journal, an internet discussion group, special project groups, and many more ways to increase your enjoyment of astronomy. |
77. Thank you for learning how to estimate brightness!
78. Estimating star magnitude: First steps in variable star astronomy
| Adapted from Hands-On Astrophysics: Variable Stars in Science, Math, and Computer Education by Janet A. Mattei et al, 1997 | |
| PowerPoint Presentation developed by | |
| Chuck Pullen, AAVSO | |
79. Credits and Acknowledgements
| Janet A. Mattei, Director, AAVSO | |
| Kerriann Malatesta, Technical Assistant AAVSO | |
| Lew Cook, AAVSO | |
| Lance Shaw, AAVSO | |
| Dan Kaiser, AAVSO | |
| Victor, Nancy, and Kyle Jewhurst | |
| Christine Miller, California State University Sacramento | |
| And all those who helped test the early versions of this presentation! |
| Return to the AAVSO home page. |