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San Diego Astronomy Association Celebrating Over 40 Years of Astronomical Outreach Offi ce (619) 645-8940 June 2006 Observatory (619) 766-9118 NASA’s Night Sky Network http://www.sdaa.org A Non-Profi t Educational Association Show Me the Planets P.O. Box 23215, San Diego, CA 92193-3215 by Mark Smith In this season of great planet watching, I thought it might be fun to explore some SDAA Business Meeting planets a little farther afi eld. It is not unusual to be asked about planets around other Next meeting will be held at: stars at a star party and it is nice to be able to talk about this subject in a way that Teledyne RD Instruments USA makes sense to the average person. After all, the most basic question that drives all 9855 Businesspark Avenue of astronomy is, “What’s out there?” and extrasolar planets are the “what” that most San Diego, CA, USA 92131-1101 captures the imagination of the average person. June 13th at 7:00 pm Unfortunately, talk about measuring the wobble of stars with Doppler shifts or looking for the drop in brightness due to a transiting planet does not mean much to Next Program Meeting the average person. Fortunately, you can explain, and even demonstrate, the most The Problem with Pluto important concepts of the search for extrasolar planets using nothing more than a by Dr. Gary Peterson three inch diameter foam squishy ball and a golf tee. If you add a small rubber ball June 21st at 7:00 pm glued to the fl at end of the golf tee, you are really set! Simply stick the golf tee about Mission Trails Regional Park a third of the way into the squishy ball and you are ready to begin. Visitor and Interpretive Center The best place to start is with the most basic property of gravity; it works both 1 Father Junipero Serra Trail ways. Yes, the Earth’s gravity pulls on us, but we pull back very slightly on the Earth. The Earth-Moon system provides an excellent illustration of how this works. The Earth pulls on the Moon and keeps it in orbit, but the pull of the Moon on the Earth CONTENTS causes all of the water to slosh around and causes our tides. Most people are familiar with this and that makes the next step easier. In an orbital system, all bodies revolve June 2006 Vol XLII, Issue 06 around the center of mass (barycenter) of the entire system. In the Earth-Moon sys- Published Monthly by the tem, this point is located approximately 1068 miles beneath the surface of the Earth San Diego Astronomy Association on the Moon side. Both the Earth and Moon revolve around this point. 75¢ /$8.00 year Now is the time to break out your squishy ball. Put it down on a fl at surface with Incorporated in California in 1963 the tee horizontal and give it a good spin. The tee causes the ball to wobble (the wobble is more pronounced if you glued the rubber ball onto the tee) just like the Night Sky Network .............................1 Earth-Moon system would appear to wobble around its barycenter. The same thing May Program Meeting...................................2 happens with the solar system, although the motion is much more complicated be- Treasurer’s Re rt..........................................3 po cause of the large number of bodies revolving around the sun. Since the Sun is much Not a Moment Wasted....................................4 more massive than anything else in the solar system, it is always near the solar system Outreach Outlook........................................5 barycenter (the exact location of which is not known). Still, the effect of the planets June Calendar ........................................6 revolving around the Sun could be detected by somebody in another star system and July Calendar ......................................7 fi nding that wobble is one of the main tools we use to fi nd planets around other stars. Sky Watch ....................................................8 Now, pick up your squishy ball and make the tee revolve around it in plane with Board Minutes.........................................9 your eyes. This very nicely illustrates a transiting planet. If you tilt the tee a bit off Program Meeting.......................................10 plane, the end of the tee will no longer transit and it is easy to see that the larger the Radio Astronomy......................................10 orbit, the less chance that we would be lucky enough to be in the exact plane neces- AISIG Gallery.............................................11 sary to catch a transit. However, if we are lucky enough to be in that plane, we can The Back Page...........................................12 gain more information about the planet’s size by looking to see how much of the star’s light it blocks during the transit. We can also learn something about the atmo- sphere of the planet by studying the change in spectra from the star during transits (easily explained at a star party by using a rainbow as an example). Continued on Page 2 San Diego Astronomy Association Continued from Page 1 Now comes the best part. Fourteen of the stars known Science and Engineering Fair, as well as a presentation from to have planets are visible to the naked eye. Three of them Jerry Hilburn on NASA’s New Horizons mission headed to (Gamma Cephei, Iota Draconis, and Epsilon Eridani) are mag- Pluto and beyond. nitude 3 stars and two more (Upsilon Andromedae and Tau Jen Lee, an 8th grader from Madison Middle School, shared Bootes) are magnitude 4 stars. See the table for a complete her project Asteroid Attack and explained how she used paint list. So, after the explanation on how we fi nd extrasolar plan- balls to simulate incoming asteroids and test the effect of their ets, you can point to one of these stars and let your guests ask angle of impact on ejecta height. Her conclusion: the steeper themselves what might be out there in these distant systems. the angle of impact, the higher the ejecta. This has obvious ap- The Night Sky Network is a program sponsored by NASA plication for any future science aimed at protecting Earth from to provide participating astronomy clubs with material use- asteroid impact. ful for explaining astronomical concepts and science. NASA Calvin Ritenour, an 8th grader from Marshall Middle School, funds the program based on the number of people it reaches compared the accuracy of stellar navigation using a sextant and the SDAA gets credit, and occasional goodies, when we to current GPS technology in his project Stars vs. Satellite use the material. If you fi nd this material useful and use any of – Which is Better? He ran his survey while on board the USS it at a star party, lecture, presentation, etc., please let me know Nimitz for its Tiger Cruise at the end of last year’s WestPac. and I’ll send the information on to NASA. Thank you to Scott Although dogged by cloudy weather during the cruise, he ob- Baker and Rich Strobel for enrolling us in this program. tained enough data to work with and found that there was little difference in the accuracy of the two approaches to navigation. May Program Meeting Conclusion – if GPS ever fails, you’d better know how to use a sextant! by Alice Harvey Jacob Rucker, a 10th grader at Canyon Crest Academy, At May’s meeting we were treated to presentations by three was our 1st place winner. This was actually Jacob’s third time of our four award winners from this year’s Greater San Diego presenting a project to the SDAA. Three years ago as a 7th 14 Naked Eye Stars with Planets Planet Mass Orbit Distance (au)/ Star Name Magnitude Orbit Period (days) (Jupiter=1) Eccentricity Gamma Cephei 3.2 1.8 2 / 0.2 913 Iota Draconis 3.3 8.7 1.3 / 0.7 551 0.9 0.6 / 0.9 2502 Epsilon Eridani 3.7 0.1 0.3 / 0.1 260 years 0.7 0.06 / 0.04 4.6 Upsilon Andromedae 4.1 2.1 0.8 / 0.2 242 4.6 2.5 / 0.4 1267 Tau Bootes 4.5 3.9 0.05 / 0.02 3.3 70 Virginis 5.0 6.6 0.4 / 0.4 117 HD 19994 5.1 2.0 1.3 / 0.2 454 2.4 2.1 / 0.1 1095 47 Ursae Majoris 5.1 0.8 3.7 / 0.1 2594 Rho Coronae Borealis 5.4 1.1 0.2 / 0.03 40 51 Pegasi 5.5 0.5 0.05 / 0.0 4.2 HD 89744 5.7 7.2 0.9 / 0.7 256 Gliese 777A 5.7 1.15 Unk Unk 0.8 0.1 / 0.3 14 HD 38529 5.9 11.3 3.5 / 0.3 2189 0.8 0.1 / 0.03 15 55 Cancri 6.0 0.2 0.2 / 0.3 44 4.0 5.9 / 0.2 2785 Page 2 SAN DIEGO ASTRONOMY ASSOCIATION NEWS AND NOTES, JUNE 2006 San Diego Astronomy Association grader, he did a project with his sister which was a prize winner Treasurer’s Report and was presented to the club. As an 8th grader, he started his by Lou N. Jackson current project – The Effects of Skyglow on Stellar Visibil- With the addition of our new members, we now have a total ity – and presented his fi rst year fi ndings at a program meeting. of 487 SDAA members. We added several new members last He is now in the third year of that project and has continued month: please welcome David Alvarez, Charles Betlach II, Mi- collecting data (now using digital imaging) to write a formula chael Ditges, Steve Hughes, Audrey Kane, Larry Marshall, Wil- that predicts the effect of distance from a major light source liam Porter, Diana Sanders, and Martin Villanueva.
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