Autumnal Equinox, 2006 Beginner's Corner: So what can I see with this thing? Part 2. BY PHIL HOYLE presented, I would say, might not be for the beginner; they would be more for the intermedi- In the last Horizon, I mentioned that if you ate or advanced observer. live under, or can travel to dark skies, that your If you're wondering what you can try to point biggest challenge will not be seeing objects in the your telescope to, the first place I would ask you sky, but knowing what to look for and how to to look is right here in your very own Horizon. find them. In this segment of the "Beginner's The "Dark Times Calendars", which debuted in Corner", I am going to cover how the beginner the winter edition, make an excellent first place can decide what to look for through a small tele- to look. I would note here that whenever a deep- scope or binoculars. However, the discussion space object is mentioned in the events section of will not necessarily be limited to what you can the calendars, that does not mean that object is see under dark skies. visible only on that specific day. It only means If you missed the June meeting, you missed a that the object will be at the given altitude above presentation that was on the same topic that I am the horizon at that specific time on that day. discussing here. It was an excellent presentation Take for example NGC 253, which is listed on by several people. However, some of the sources the line for the evening of September 4, and the morning of September 5. The same object will be visible later in the year, but earlier in the Inside Horizon evening (or morning, as the case may be). It will also be visible earlier in the year, but later in the Bright Stars of Summer . page 3 morning. The right ascension and declination of deep space objects don't change (except over a Dark Times . .page 5 period of thousands of years) so these numbers can be used to show you where they are in the Double Vision . .page 8 sky, or more specifically, on a sky map. Podcasts . .page 18 A second resource that you can use to decide what to look at is again right here in your Sidereal time . page 19 Horizon. Phil Creed's "Double Vision" is hope- fully the first in a series of articles that will be And More! designed around an observing season. This par- ticular article covers objects that can be seen in HORIZON 2 binoculars, but many of the objects are just as observable in a small telescope. There are also HORIZON is the quarterly newsletter of objects for beginner, intermediate and advanced The Wilderness Center Astronomy Club. observers. Editor: . Phil Hoyle Another tool in this Horizon is Ken Contributors: . .Phill Creed, Dave Gill, Schneller's table for "Sidereal Time for the . .Brian Gray, Ken Schneller Wilderness Center". Use this table in conjunc- Layout . John Waechter tion with a star atlas or star charting software to show you what part of the sky is up at the times WCAC Officers: listed in the chart. President: . Bill Castro If you are a beginner (or even an advanced Vice President: . Matt Hawrysko observer), I also highly recommend one or more Secretary: . John Waechter of the quality magazines published for our Treasurer: . Brian Gray hobby, such as Astronomy or Sky and Telescope. Planetarium Coordinator: . Dave Ross These magazines always have a sky map in the Observatory Coordinator: . .Brian Gray center of the publication and almost always have Inreach: . Dave Gill at least one article with a detailed observing list. Education Outreach: . John Waechter Some of these lists are not for the beginner, or WebMaster: . Bill Castro require a large scope or dark sky to see, so be WCAC Address: forewarned. Also, don't try to use the all-sky P.O. Box 202 map in the center of these magazines to find Wilmot, Ohio 44689-0202 deep space objects that might be labeled on Web Site: http://www.twcac.org them. For the most part, these all-sky maps are not detailed enough to match the position of the object on the map to its position in the sky; it's not that the objects are plotted in the wrong posi- http://www.stargazing.net/astropc/. But have a tion, there just aren't enough landmarks (or look around for yourself to decide what level of would that be skymarks) on these maps to get detail you want and how much you want to your telescope pointed in the right place. These spend. maps are extremely useful for letting you know Just remember one thing, when you are plan- which constellations and planets are visible in ning an observing session, the first place to look the sky on a given night. They are also extreme- is right here in your Horizon! ly valuable just to help you get familiar with the night sky. Some kind of atlas or sky guide is essential. This could take the form of a printed atlas or some kind of star charting software. My favorite hardcopy, since they were published, has been the Night Sky Observer's Guide by George Robert Kepple and Glen W. Sanner. My favorite star charting software (mainly due to the price: free!) is Cartes du Ciel. (That's French for Sky Charts.) If you want to check it out, go to HORIZON 3 The Bright Stars of Summer BY DAVE GILL Deneb (Alpha Cygni) Visual magnitude: +1.25 Each summer, we watch as the familiar asterism Absolute magnitude: -7.5 we call the "Summer Triangle" rises again from Distance: 1467 ly the horizon murk to its dominant position over- head. We point out the three stars, Vega, Deneb Spectral type: A2 Ia and Altair to visitors, and trace their parent con- stellations with our slicing green beams. Let's Altair (Alpha Aquilae) get to know them a little better - and appreciate Visual magnitude: +0.76 them. Absolute magnitude: +2.1 Let's start with the numbers (taken from The Distance: 17 ly Observers Handbook): Spectral type: A7 Vnm Vega (Alpha Lyrae) All three are bright; Vega is the brightest and Visual magnitude: +0.03 Deneb the faintest. All are white stars (spectral Absolute magnitude: +0.6 type A). Altair is the yellowest (coolest), with a Distance: 25 light years (ly) type of A7; Vega is the bluest (hottest) at A0. But Spectral type: A0 Va the interesting thing is the absolute magnitude. This mosaic of shots by British amateur Pete Lawrence captures the summer triangle region beautifully. HORIZON 4 Visual magnitude is what our eyes see. But the than a Milky Way disk star. Vega also sports a absolute magnitude reflects what the star would disk of cool dust that was discovered 20 years look like at a common distance of 10 parsecs (32 ago by the IRAS infrared satellite. It is believed light years). Now we see Deneb dominating the to extend about 70 AU from Vega and is analo- field at -7.5, a full eight magnitudes brighter than gous to the Kuiper belt in our solar system. Vega. That translates to about 1600 times There is also a hole in the center of the disk, brighter. At that distance, the Sun would be a 5th which may indicate planets. But by the time any magnitude star, just barely visible under TWC Earth-like planets could emerge from the early skies, and Deneb would far outshine Venus, cast bombardment of formation, Vega will be moving shadows and be easily seen in the daytime. Vega off the main sequence and become too unstable would be only slightly fainter than it is in our cur- to support life. rent sky. Altair would be about as bright as In looking toward Vega, you are also looking Polaris. to the general direction in which our Sun is mov- Altair is the 13th brightest star in our sky. It is ing through space. This is called the "apex of the a main sequence star, and since it is hotter than Sun's way". the Sun, it is also brighter, about 10.6 times Deneb is the superlative star in this group. brighter, with almost twice the mass of our Sun. But it is difficult to know how luminous it really It is also one of the closer stars to the Sun. It is is. Star distances are devilishly hard to measure. the second most luminous star within 20 light The most absolute method we have is by meas- years of the Sun; Sirius is the most luminous, uring the parallax of a star, the slight angular shift about 4 times more than Altair. Altair rotates rap- of the star with respect to distant background idly; its equatorial speed is over 100 times that of stars as the Earth orbits the Sun. Even the closest our Sun. It rotates in about 6.5 hours, compared stars have a parallax of less than an arc second to our Sun's 28 days. This rotation flattens the (1/3600 of a degree). Our most accurate meas- star; its polar diameter is about 14% less than its urements of Deneb's distance via parallax pegs it equatorial diameter. Although it looks constant at 3200 light years. The error band is from 2000 to us, Altair is a slightly variable star. It is called to 7000 light years. (So the 1476 ly quoted in the a Delta Scuti type star - varying by a few thou- numbers section may well be wrong.