San Diego Astronomy Association Celebrating Over 40 Years of Astronomical Outreach
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San Diego Astronomy Association Celebrating Over 40 Years of Astronomical Outreach Office (619) 645-8940 October 2011 Observatory (619) 766-9118 http://www.sdaa.org October Program Meeting A Non-Profit Educational Association P.O. Box 23215, San Diego, CA 92193-3215 Date: October 19th Speaker: Prof. Alison Coil SDAA Business Meeting Topic: Lighting Up the Dark: How Galaxies Trace Dark Matter on Large Scales Next meeting will be held at: 3838 Camino del Rio North Measurements of the spatial distribution of galaxies on very large scales constrains Suite 300 both our understanding of cosmology as well as the physics of galaxy evolution. San Diego, CA 92108 October 11th at 7pm Dr. Coil has received her B.A. in astrophysics from Princeton University in 1997, Next Program Meeting her M.S. in astrophysics from the University of California October 19, 2011 at 7pm at Berkeley in 2001, and her Ph.D. in astrophysics from the Mission Trails Regional Park University of California at Berkeley in 2004. She has been Visitor and Interpretive Center a Hubble Postdoctoral Fellow at the University of Arizona 1 Father Junipero Serra Trail before joining the faculty at the University of California at San Diego in 2008. CONTENTS San Diego Astronomy Association (SDAA) sponsors speakers on a wide range of astronomy topics on the third October 2011, Vol XLIX, Issue 10 Wednesday of every month at the Mission Trails Regional Published Monthly by the Park Visitors Center. The Program meeting begins at 7:00 San Diego Astronomy Association PM. Each attendee receives one free door prize ticket. After $2.50 an issue/$30.00 year announcements and a small amount of business, the audi- Incorporated in California in 1963 ence is treated to the featured presentation. At the close of October Program Meeting...................1 the meeting the door prizes are presented. The event is open to the public. The Mission The Great Square...........................1 Trails Regional Park Visitors Center is at One Fr. Junipero Serra Trail, San Diego CA Jim Thommes’ Astronomical 92119. Call the park at 619-668-3281 for more information or visit http://www.mtrp.org. Discovery......................................................4 Please contact Bill Carlson ([email protected]) if you have an questions, com- Dark Clues to the Universe...................5 ments, or ideas for the Program Meetings. October Minutes............................6 October Calendar............................8 SDAA Contacts.......................9 ASIG Gallery..........................................10 The Great Square The Back Page...........................................12 As the Summer Triangle begins its fall to the sea, the Great Square of Pegasus climbs high in the east, heralding the change of season. The constellation of Pegasus, the Flying Horse doesn’t look much like a horse, but the Great Square asterism is readily identifiable and makes a good landmark for navigating the autumn sky. The Great Square is formed by four mag 2-3 stars, each about 12-15 degrees apart, making a giant square enclosing a relatively empty region of space. Although referred to Newsletter Deadline as the Great Square of Pegasus, the northeastern-most star in the asterism is α Androme- The deadline to submit articles dae (Alpheratz, aka Sirrah; mag 2.1), which is a tight binary of mags 2.2 and 4.4. The for publication is the other stars of the Great Square include β Pegasi (Sheat; mag 2.4) to the southeast, α PEG 15th of each month. (Markab; mag 2.5) to the southwest, and γ PEG (Algenib; mag 2.8) to the northwest. San Diego Astronomy Association Starting with the Great Square, the first deep sky object I ever star hopped to was M31 (mag 3.4), the great spiral galaxy in An- dromeda. M31 is a naked eye object under dark skies, and, at 2.3 million light years, arguably the most distant object visible without optical aid. I’ve never seen it naked eye in the city, but it’s visible with binoculars and is fairly easily found, beginning at α AND, the northeastern-most star of the Great Square. From α AND, head northeast about 7 degrees to the first bright star, δ AND (mag 3.3), and continue on that line another 7 degrees to the next bright star, β AND (mag 2). At β AND, make a right angle and head northwest about 4 degrees to mag 3.9 μ AND, and continue on that line another 3 degrees to mag 4.3 υ AND. In binoculars, M31 is visible as a small cloudy region a couple of degrees northeast of υ AND. The companion galaxies M32 (mag 8.2) and M110 (mag 8.9) become vis- ible through my reflector at 90x. Under a dark sky, you can these same stars to find the Triangulum galaxy (M33; mag 5.7). If you imagine the “right angle” formed by the line from α AND (point “A”) to β AND (point “B”), and the line from “B” to υ AND (point “C”), then rotate the right angle 180 degrees along the axis A-B, the point C will lie just a bit east of M33. M33 lies about 3 million light years away, and is the third larg- est member of the Local Group, after M31 and the Milky Way. But it has a very low surface brightness and is a challenge to find from the city. Moving on, if you again begin with the line A-B, and continue along that line northeast about 10 degrees, you’ll reach γ AND (Almach), a multiple star system comprising a mag 2.2 gold primary separated by about 10 arcsec from a blue companion that is a very tight double star (mags 5.0 and 6.8; 0.8 arcsec). The rest of the constellation Andromeda spans southeast of Almach as a band of stars. East/northeast of Andromeda, in the northern Milky Way, lies Perseus (“the Hero”). α Persei (Mirfak; mag 1.8), anchors the Alpha Persei Cluster (Melotte 20), which lies about 601 light years away. The Alpha Perseid Cluster seems to be a relatively underappreciated open cluster, probably because it covers a large field of view and is best seen through binoculars (or a wide fov refractor). The second brightest star in Perseus is Algol, the Demon Star (β PER), about 10 degrees to the south of Mirfak. Algol is an eclipsing variable star that comprises a tight triple star system. Algol generally appears mag 2.1, but every 2 days, 20 hours and 49 minutes, one of the com- panions eclipses the primary causing Algol to drop to mag 3.4 for about 10 hr. You can see an animation of Algol at Wikipedia.org. North of the Great Square lies Cassiopeia (“the Queen”), which at this time of year looks kind of like a “W” that’s being stretched a bit to the north. Due to the curve of the Earth, I sometimes get a bit tricked up about “east” and “west” when looking at rising constellations that lie at the more extreme declinations in the northern or southern sky because they seem to change orientation as they traverse the sky. Cassiopeia is a good example, where β CAS seems to be farthest east in the “W” as the constellation rises, but is, in fact, the westernmost star of the “W”. So, if you’re not sure, check out a star chart or look up the constellation at a site like Wikipedia. org or on Google sky, or wait until it reaches the meridian. From west to east, respectively, the three brightest stars of the “W” are β CAS, α CAS, and γ CAS; each is about mag 2.2, although γ CAS, the middle star of the “W”, can vary unpredictably by a magnitude or two. East of γ CAS in the “W” is δ CAS, and the easternmost (and northernmost) star of the “W” is ε CAS. If you imagine a line from δ CAS to ε CAS, then extend that line about the same distance, you come to naked eye iota CAS, a nice triple star system (mags 4.6, 6.9 and 8.4; 2.5 and 7 arcsecs). In my reflector, with an aperture cover, the closer component is nicely resolved at 220x. West of Cassiopeia is Cepheus (“the King”), a constellation that looks like a house, with the base of the “house” to the south and the high peaked roof pointing to the north. The base of the “house” includes α Cephei (mag 2.5) to the west, and zeta CEP (mag 3.8) and δ CEP (mag 4.1) to the east. δ CEP (mags 3.5-4.1) is a variable star and the prototype “Cepheid variable”, the “standard candle” stars that are used to determine the distances of galaxies from earth. δ CEP also is a double star, with a mag 6.1 companion (41 arcsec). Cepheus also contains the carbon star, Herschel’s Garnet Star (μ CEP; mag 4.1). Herschel’s Garnet Star is a naked eye star located just south of and about halfway along a line formed by α CEP and δ CEP, the base of the “house”. Its color isn’t particularly evident by eye, but the red color becomes apparent in binoculars and looks really nice through a telescope. Before leaving the north side of the Great Square, check out the Double Cluster (NGC 869 and 884; aka Caldwell 14). If you imagine a line from ε CAS, the easternmost star of the Cassiopeia “W”, to α PER, the Double Cluster lies about 1/3 of the way from ε CAS along and a bit south of this line.