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The Denver Observer December 2017

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The Denver Observer December 2017 The Denver DECEMBER 2017 OBSERVER Messier 76, the Little Dumbbell Nebula, one of the deep-sky objects featured in this month’s “Skies.” Image © Joe Gafford. DECEMBER SKIES by Zachary Singer The Solar System of view in your ’scope will include the Moon’s Sky Calendar 3 Full Moon December will be a decent month for eastern section and the star, with plenty of 10 Last-Quarter Moon planetary events; though some planets are room. 17 New Moon slipping from view, others will take their I recommend you observe early—it 26 First-Quarter Moon place. We also have an occultation of Alde- should be a beautiful view, with the star a baran; as seen from Denver, the Moon will bright spark near the Moon’s edge, and over pass in front of the star at approximately the following minutes (they’ll go fast, just like In the Observer 4:06 PM, on the 30th. At that point, with the recent solar eclipse did), you can see the Moon move in its orbit around us, using the sunset still more than half an hour away, the President’s Message . .2 star won’t be visible to the naked eye, but it star for a benchmark. (Before 4:00 PM, look Society Directory. 2 should be in a telescope if you know where for Aldebaran outside the square, but along to look: Imagine a square drawn just large the diagonal from the Moon’s center to that Schedule of Events . 2 enough to touch the edges of the Moon, and lower-left edge.) About Denver Astronomical Society . 3 with the square’s bottom parallel to our local Aldebaran will reappear at about 5:00:27, Astro Update . 4 horizon. At about 4:00 PM, a few minutes give or take several seconds, for observers before the actual event, you’ll find Aldebaran close to the DTC area. Look for it along the DAS News . 5 at the lower-left (“easternmost,” relative to our Moon’s western edge, at about the “2 o’ clock sky), corner of that box—a half-degree field position” on the Moon’s disk—or imagining The Observer is available in color PDF format from the DAS Continued on Page 3 website: http://www.denverastro.org/das/denver-observer/ THE DENVER OBSERVER DECEMBER 2017 Society Directory PRESIDENT’S MESSAGE by Ron Hranac DAS Executive Board Astronomy Lingo President: Ron Hranac Amateur astronomy has its own, somewhat stars that form patterns, but are not officially [email protected] unique vocabulary. That’s fine if you’ve been constellations, such as the Teapot in Sagit- Vice President: in the hobby for a while, but if you’re new tarius or the Big Dipper in Ursa Major). Lindsey Shaw [email protected] to amateur astronomy or are simply curious Most amateur astronomers use a tele- about it, astronomy’s everyday lingo may as scope, which is an instrument with lenses or Secretary: Ed Ladner well be Latin. Here’s a look at some of the es- mirrors, or a combination of lenses and mir- [email protected] sentials. rors to make distant objects appear as if they Treasurer: What better place to start than with than are closer, bigger, and brighter. There are three Michael Nowak [email protected] the phrase amateur astronomy? According to general types of telescopes: refractor, reflector, Executive Board Members: my copy of Webster’s New World Dictionary, and catadioptric (or compound optic). Brent Blake Zach Gilbert “amateur” means “one who does something The name refractor comes from the Julie Candia Ed Scholes for pleasure, not for pay; nonprofessional.” In telescope’s basic design, which includes an Jack Eastman Sorin Joe Gafford Dan Wray particular, amateur is derived from the Latin objective (main) lens at the front end of the Past President, Ron Pearson amare, which means “to love.” That same dic- tube that refracts (bends) the incoming light President Emeritus, Larry Brooks tionary defines “astronomy” as the science of toward the focus point at the back of the Committees the stars and other heavenly bodies, their mo- tube where the eyepiece is located. The Alvan Van Nattan-Hansen Scholarship Fund: tion, position, size, etc. The word astronomy Clark-Saegmuller 20-inch telescope in DU’s Jeff Tropeano (Chair) is from the Greek ἀστρονομία, for “law of the historic Chamberlin Observatory is a refrac- PO Box 100621 Denver, CO. 80250-0621 s t ar s .” tor. EGK Dark Site Committee: Naked-eye observing of the sky is an easy As you’d expect, a reflectoruses mirrors, Darrell Dodge, Interim Chair way to simply enjoy what’s up there. It’s also instead of a lens, to form an image. (What [email protected] a good way to learn some of the modern is commonly called a Dobsonian or Dob IDA Representative: Dr. Robert Stencel constellations (88 recognizable star-patterns, telescope is actually a reflector ’scope on a [email protected] with boundaries defined by the International Dobsonian mount.) Light enters the front of Volunteers or Appointed Astronomical Union; examples include Orion the telescope’s tube and travels to rear. There, Representatives and Ursa Major) and asterisms (groups of the light is reflected by what is called the ALCor: Darrell Dodge 303 932-1309 Continued on Page 3 Newsletter Editor: DAS SCHEDULE Zachary Singer 303 718-4188 [email protected] Newsletter Proofreaders: December 2017 Darrell Dodge, Ron Hranac 3 DAS Holiday Party—Embassy Suites Tech Center—Starts at 6:00 PM. The speaker Website: will be Karly M. Pitman, Ph.D., Executive Director of the Space Science Institute. Darrell Dodge 8 E-Board Meeting—At DU’s Historic Chamberlin Observatory, 7:30 PM. [email protected] All members welcome. IT Coordinator: 16 Dark Sky Weekend—EGK Dark Site & Brooks Observatory Ken Sturrock [email protected] 30 Open House—DU’s Historic Chamberlin Observatory—Starts at 4:30 PM External Outreach Coordinator: (January 2018) Julie (July) Candia [email protected] 5 DAS General Meeting—DU’s Olin Hall, Rm. 105—Starts at 7:30 PM Public Night Coordinator: 12 E-Board Meeting—At DU’s Historic Chamberlin Observatory, 7:30 PM. Hugh Davidson 303 679-0629 All members welcome. Librarian: Eileen Barela Telescope Loan Program: During Open House, volunteer members of the DAS Public Nights feature a presentation on astronomical Ed Scholes bring their telescopes to the Chamberlin Observa- subjects and a small-group observing session on the [email protected] tory’s front (south) lawn, so the public can enjoy historic 20-inch telescope (weather permitting), at Cham- views of the stars and planets, try out different berlin Observatory on Tuesday and Thursday evenings DAS Information Line: telescope designs, and get advice from DAS mem- (except holidays), beginning at the following times: (303) 871-5172 bers. The Observatory is open, too (costs listed DAS Correspondence: below), and its historic 20-inch telescope is open March 10 - September 30 at 8:30 PM Denver Astronomical Society for observing with no reservations necessary. October 1 - March 9 at 7:30 PM P.O. Box 102738 Denver, Colorado 80250 Open House costs (non-members): If the skies are clear, Public Night costs (non-members): $4/adult, [email protected] $2/person ($5/family), $1/person in inclement weather. $3/child and students with ID. DAS mem- DU students with ID, and DAS members free. New-Member Ambassador: bers and DU students with ID: free. Digby Kirby Members of the public (non-DAS/DU, as above), please [email protected] make reservations via our website (970) 301-2287 (www .denverastro .org) or call (303) 871-5172. http://www.denverastro.org The Denver Astronomical Society One Mile Nearer the Stars - 2 - ∞ THE DENVER OBSERVER DECEMBER 2017 President’s Message Continued from Page 2 primary mirror back toward the front of the tube where a smaller In simple terms, the distance the light travels through a tele- secondary mirror reflects the light out the side of the tube to the scope from the objective lens (or the primary mirror) to the focus focus point and eyepiece. In some reflectors, the secondary sends point, where the eyepiece is located, is called the focal length. The the light back towards the main mirror, in a similar manner to the longer the focal length, the greater the magnification when using third type of ’scope. a given eyepiece. (Magnification is calculated by dividing the tele- A catadioptric telescope uses a combination of lenses and scope’s focal length by the eyepiece’s focal length.) mirrors. Light enters the front of the tube and passes through a How much magnification is enough? It depends; too much, and lens (called a corrector or meniscus) to the primary mirror at the the image becomes dim and fuzzy. A good rule of thumb is to use rear of the tube. The primary reflects the light back to the second- no more than 25x per inch of telescope aperture: For a 6-inch, 25 ary, which is mounted on the rear of the corrector. The secondary times 6 equals 150 power; for a 10-inch, 25 x 10 equals 250 power. mirror reflects the light back once more toward the primary, where Dim deep-sky objects often benefit from usinglower power than a hole in the primary’s center lets the light pass through to the this and tight double stars may need more. eyepiece. It may sound complex, but this back-and-forth light-path A telescope’s focal length divided by its aperture is the focal results in a much more compact design. The popular Schmidt- ratio, or f-number.
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