October 2005 - Utah-Astronomy - mailman.xmission.com

List down?
by Patrick Wiggins 19 Oct '05

19 Oct '05

Testing to see if the list is working. I tried posting to the list a few minutes ago but my post did not seem to post. Plus, when I go to the list's web page (http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy) and use the link at "To see the collection of prior postings to the list, visit the Utah-Astronomy Archives" I get a "Not Found The requested URL /lurker/list/utah-astronomy.en.html was not found on this server." error message. Ideas? Patrick

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Test #1, please ignore
by Patrick Wiggins 19 Oct '05

19 Oct '05

I'm having trouble with some of my posts to Utah Astronomy. This is a test message. Please excuse and ignore it. But then the subject line says "Please Ignore" so why are you reading this anyway? :-) Test #1: Addressed manually

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Re: [Utah-astronomy] Totally Off Topic Harry Potter
by Patrick Wiggins 19 Oct '05

19 Oct '05

Cynthia Blue wrote: > Just a quick note, as I know there are a few HP nuts on this list. =) Oh, there for a moment I thought you were referring to Hansen Planetarium nuts. :-) > Fandango now has tickets on sale to Goblet of Fire, it says November 17th at 12:01 am. But I think that is actually on friday morning. Yes, that should be 12:01 a.m. on Friday the 18th. > Patrick, I bought yours so don't go buy another! ;) Thank you! So, Cynthia, tell us all, have you got your robes and wand yet? Finite Incantatem! Patrick

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Reminder: Cassini lecture tonight at the Salt Palace 7-8:30
by Richard Tenney 18 Oct '05

18 Oct '05

I would like to cordially invite members of the Utah Valley Astronomical Association [and SLAS] to attend a Public Forum entitled ÂSaturn & Its Moons: A Ring-Side View from Cassini-HuygensÂ which will be presented free of charge at the Salt Palace Convention Center in conjunction with the 117th Annual Meeting of the Geological Society of America. On Monday evening, 17 October, 2005, from 7:00Â8:30 p.m., a panel of top mission scientists will present a non-technical overview of the latest scientific findings from this international mission of science and exploration. See spectacular new images from space, learn about leading-edge research, and ask questions of mission specialists, including: Torrence Johnson and Rosaly Lopes from NASAÂs Jet Propulsion Laboratory, Carolyn Porco from the Space Science Institute, and Laurence Soderblom from the U.S. Geological Survey. Hosted by the GSA Planetary Division, this program is open to the public and is sponsored by Subaru of American, Inc. For more information visit http://www.geosociety.org/meetings/2005/PublicForum.htm Please help us spread the word! This is a unique opportunity for space-lovers young and old. Questions are encouraged! Best regards, Christa Stratton Marketing Manager Geological Society of America 3300 Penrose Place Boulder, CO 80301 (303) 357-1093 (303) 357-1070 (fax) cstratton(a)geosociety.org __________________________________ Yahoo! Music Unlimited Access over 1 million songs. Try it free. http://music.yahoo.com/unlimited/

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Re: Partial Lunar Eclipse Monday morning
by Chuck Hards 17 Oct '05

17 Oct '05

Excellent partial eclipse under perfectly transparent skies. Shadow moving-off the lunar face as I write this post. Penumbral shading quite apparent. The moon was actually rather higher than I expected, not down in the muck at all. Thanks for the notice, Kurt! > From: Canopus56 <canopus56(a)yahoo.com> > Although it looks like it will be clouded out, there > will be a partial eclipse of the Moon on 10/17/2005 > 12:03:21 UTC (Monday morning 10/17/2005 at 6:03 AM > MST) visible low on the western horizon. __________________________________ Yahoo! Music Unlimited Access over 1 million songs. Try it free. http://music.yahoo.com/unlimited/

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Re: Green Lasers
by Chuck Hards 17 Oct '05

17 Oct '05

I'd welcome any suggestions as to what a consumer can in fact look for, as a guide to laser brightness, if duty cycle and listed output are not good enough indicators for a common pointer. We're not talking about lab lasers where precise regulation is sometimes required, after all. Also, what is the typical manufacturing variation between identical units? The consumer needs a reasonably accurate guideline in the absence of hands-on testing before purchasing. Most of these are purchased via mail-order, sight unseen. What's left to judge a purchase by then, testimonials? > From: Ivo Stutznegger <ics_ute(a)yahoo.com> > However an indication that the laser operates at > less > than 100% duty cycle doesnÂt necessarily mean that > it > is dimmer. __________________________________ Yahoo! Music Unlimited Access over 1 million songs. Try it free. http://music.yahoo.com/unlimited/

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Re: Green lasers
by Chuck Hards 17 Oct '05

17 Oct '05

Are these for real? The outputs listed are just amazing for battery-powered, diode lasers. More typical of "outdoor laser show" gas lasers. Yes, they should certainly be bright enough- even for a full-moon pointer! ;) Anybody have one? > From: Patrick Wiggins <paw(a)trilobyte.net> > Think these would be bright enough? > > http://starphaser.com/products.htm __________________________________ Start your day with Yahoo! - Make it your home page! http://www.yahoo.com/r/hs

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Re: Green lasers
by Chuck Hards 17 Oct '05

17 Oct '05

Respectfully, I built my first lasers in the mid-seventies in high school, back in the olden days. A dye laser (rhodamine, IIRC, from Scientific American plans), nitrogen gas laser, and a He-Ne gas laser for which I destroyed literally hundreds of pounds of glass tubing while learning to make apparati. As I recall, that one never did work right! But I do appreciate all the nuances, Ivo. One needn't know all the ins-and-outs of lasers in order to make an informed purchase. For the vast majority of what is currently marketed and legal in the US as pointer-style lasers, duty cycle is indeed a reasonably accurate predictor of intensity at a given output rating- yes you are right that there are reasons for operating the module at less than 100% duty cycle- -BUT- it certainly appears to be the primary reason why some "5mw" lasers are significantly brighter than other "5mw" lasers, all other things being equal. I plan to purchase a true 5mw, 100% duty-cycle unit, and will gladly make it available for side-by-side comparisons. Want to design the experiment, Ivo? > From: Ivo Stutznegger <ics_ute(a)yahoo.com> > I would definitely agree with the first statement of > your first post on this thread. -ÂI've discovered > that powerrating is not in itself a foolproof > indicator of brightness.Â > > However an indication that the laser operates at > less > than 100% duty cycle doesnÂt necessarily mean that > it > is dimmer. There is a very good reason to operate a > portable battery powered laser at less than 100% > duty > cycle. __________________________________ Yahoo! Music Unlimited Access over 1 million songs. Try it free. http://music.yahoo.com/unlimited/

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How the ancients used eclipses to measure the position of stars
by Canopus56 16 Oct '05

16 Oct '05

The following is a post I did in a usenet group about how Hipparchus used eclipses to measure the ecliptic longitude of stars. Thought is might make some interesting reading - Canopus56(Kurt) ========================= mack wrote: > If I put a bit of time into it, I can by looking at > the fuzzy terminator against blue sky just after > sunset, differentiate a full moon from a moon 24 > hours away from a full moon, but that's about as > good as I can get. Presumably the Greeks > had much better accuracy than that. How did they > do it? <snip> > Presumably any of these measurements would be > confounded by parallax? Evan's _The History and Practice of Ancient Astronomy_ also contains an example of how Hipparchus might have used eclipses to measure the solar (ecliptic) longitude of Spica. Evans at 256-259. Once the solar longitude is found, transformation into right ascension is a straight-forward application of a spherical right triangle. The technique Evans used to demonstrate how the ancients estimated the solar longitude of Spica might be applied to the partial lunar eclipse set for Monday morning - Oct. 17 at 12:03 UTC to determine the solar longitude and right ascension of alf Psc. The following are some instructions. Materials: Graph paper, protractor with weight on a string to measure angles (or a sextant), a drafting compass and a metric ruler (to measure scales). 1) On the graph paper, draw a degree grid for your western horizon about 20 deg by 20 deg. 2) As the maximum eclipse approaches, with the protractor or sextant, measure and mark the relative alt and az of: a) sigma Aries b) omicron Psc You can use any fixed point on the horizon or due west. Hipparchus would have had his catalogue noting the ecliptic latitudes of some bright stars along the ecliptic. The ecliptic latitudes for the two stars above are: Obj Ecliptic latitude sigma Aries -01d17m39.1s or about -1.294167 decimal degrees omicron Psc -01d37m12.9 or about -1.62 decimal degrees and for checking purposes (not used in computations) - Obj Ecliptic longitude sigma Aries 44d 56m 38.6s omicron Psc 27d 44m 35.3s c) To define the ecliptic, draw a circle around sigma Aries and omi Psc with a radius equal to the absolute value of their ecliptic latitudes. A tangent line along the top of the two circles will define the ecliptic. The Moon will be about 0.7 degrees above this line at the maximum eclipse. You can confirm the obliquity of the ecliptic at your geographic position by downloading an Excel spreadsheet from: http://www.jqjacobs.net/astro/arc_form.html For example, at my op the angle between the horizon and the ecliptic at the time of maximum eclipse will be about 42.3 degrees. d) At the point of maximum eclipse - 1) measure the alt and az of the Moon and plot it on the graph paper. 2) the zenithal distance of the Moon. 3) for reference purposes, also measure the angular distance between the Moon and omi Psc, the Moon and alp Psc, and omi Psc and alp Psc. e) Now adjust the plotted position of the Moon for geocentric parallax using the equation: P = arcsin ( ( r * sin z ) / d ) where: r = radius of the Earth d = geocentric earth moon distance (center of earth to Moon) where - r/d = approx. 1/57 z = Moon's zenithal distance f) Apply the parallax in azimuth on your chart and replot the Moon higher. g) On the chart, construct a perpendicular line through the center of the Moon to the ecliptic (using the drafting compass). For geometric construction hints see - http://whistleralley.com/construction/c3.htm in http://whistleralley.com/construction/reference.htm h) On the chart, construct a perpendicular line through the center of alpha Psc to the ecliptic (using the drafting compass). i) Measure the degrees of longitude between the Moon and alpha Psc on the ecliptic line. Hipparchus was believed to have constructed a table of solar ecliptic longitudes although his tables have not been passed down. That is he knew how to compute the mean and apparent solar longitude based on his prior estimation of the tropical year at 365 1/4 days. See Evans _History_ at 226-231 re: solar longitude tables. j) At the moment of maximum eclipse on 10/17/2005, the Sun's position - which is 180 degrees from the Moon will be - JD Ecliptic long RA/Dec 2453661.062315 +204Âº16'33" +13h29m55s -09Âº24'47" per http://www.gcstudio.com/cgi-bin/sunpage and the RA and Dec per the Minor Planet Center will be - Date__(UT)__HR:MN R.A._(ICRF/J2000.0)_DEC R.A.__(a-apparent)__DEC 2005-Oct-17 12:03 m 13 29 25.49 -09 21 51.6 13 29 42.07 -09 23 33.0 Note that if the Sun is 180 degrees away, the ecliptic longitude of the Moon should be about - 24d 16m 33s = +204d 16m 33s - 180d 0m 0s and that's about 3 degrees away from the ecliptic longitude of omi Psc at - 27d 44m 35.3s which looks about right on the chart I plotted for the eclipse from Cartes du Ciel. k) On your graph paper-chart, measure the ecliptic longitude between alpha Psc and the Moon along the ecliptic line. Add this to the ecliptic longitude of the Moon. This gives the result, the ecliptic longitude of alpha Psc. In conclusion, this is one probable method by which an ancient like Hipparchus would have used the Moon and eclipses to determine a low precision ecliptic longitude position of a star. In this example, I have not adjusted for precession from 2000 or for atmospheric refraction. Hipparchus discovered precession, but atmospheric refraction was first published by Ptolemy in the second century C.E. and after Hipparchus. Regards - Canopus56 __________________________________ Yahoo! Music Unlimited Access over 1 million songs. Try it free. http://music.yahoo.com/unlimited/

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Re: Green lasers
by Chuck Hards 16 Oct '05

16 Oct '05

Well, it looks like for a hand-held "pointer" type laser, 5mw is the legal limit in the USA. So, to get the brightest possible unit, you would want one that is: A. Actually optimized to put out a true 5mw. Many sold as 5mw are actually under that figure, typically between 3mw and 5mw. The term "5mw" can be used as a marketing tool by some sellers. The honest ones will list a true output, within a reasonable margin. -AND- B. Continuous-duty cycle. As discussed yesterday, some of the lower-priced green lasers use a 50% duty cycle, and are noticeably dimmer than the continous-duty type. After all, they are only "on" half the time. If all one wants is just a 'green laser' with a reasonably visible beam, then let lowest price dictate the purchase (the venerable 5-D-cell flashlight still works great for a fraction of the cost). If one is after best laser visibility for one's money, then let price be just one of several criteria. I'm still shopping for a street-legal unit...but also having a friend living in Korea do some looking-around for one of those 100mw babies! ;) __________________________________ Yahoo! Music Unlimited Access over 1 million songs. Try it free. http://music.yahoo.com/unlimited/

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