August 2008 - Utah-Astronomy - mailman.xmission.com

Binoviewer with fixed focal length Newtonian
by Canopus56 20 Aug '08

20 Aug '08

After last night's SLAS meeting, a question came up from a club member about getting a binoviewer to work with a fixed objective focal length - limited backfocus Newtonian. The following are my reply notes, which may be useful to other club members that own binoviewers. =================== I. Short answer: With respect to your question on getting your binoviewer to work with a fixed objective focal length 10" Newtonian, the short answer appears to be that you will need to use a 2x shorty barlow to project the prime focal plane to the focal plane of the binoviewer. Looking at the Orion and TeleVue binoviewers, both either sell a corrector lens or a recommend the use of a shorty barlow to project the prime focal plane into a range that the binoviewer requires. TeleVue Binoviewer Page "Bino Vue comes standard with the Flat Coupler and 2x Amplifier installed on the body. This permits the Bino Vue to be used in all telescopes with just a moderate focuser intravel requirement." http://televue.com/engine/page.asp?ID=70 Orion Binoviewer Page "Includes thread-on 2x Barlow lens so you can choose two levels of magnification . . . Reflectors and short-focal length refractors may require the short 2x barlow lens" http://www.telescope.com/control/product/~category_id=101607clearance/~prod… Use of a negative barlow to reposition the prime focal plane will increase magnification between 2x to 3x. So you will want to use the highest focal length set of eyepieces that you have, e.g. two 32mm fl eyepieces, to get a true-field-of-view that is equivalent to that seen using a 10mm or 15mm eyepiece. I reocmmend first doing an initial focus test on a daylight terresterial target like a distant mountain top using a single 32mm e.p. Do two tests: 1) The 2x barlow using the barlow body (3x-4x mag); and, 2) Unscrewing the negative barlow lens off the bottom of the 2x shorty barlow and rethreading the barlow lens directly on the bottom of your binoviewer (2x-3x mag). Another option, if you own one, is a TeleVue variable positive relay lens - brandnamed the TeleVue Powermate. Put the TeleVue Powermate in the optical path. That will let you raise the primary focal plane to enough back focus so the binoviewer will work. http://www.televue.com/engine/page.asp?ID=42 II. Long answer: The length of the optical path of a typical binoviewer is about 5 to 5 1/4 inches or around 150mm. Since the distance between the telescope tube and prime focus on a 10 inch Newt is around 140 mm, there is no way to get the binoviewer to focus. This is particularly true where a rack and pinion focuser is about 90mm to 100mm about the level of the telescope tube. To compensate for this physical limitation, the primary focal plane of the objective is projected, or moved, to a new location further out-focus of the telescope tube. This effectively increases the backfocus of the telescope. One reason amateurs prefer variable objective focal length telescopes like SCTs is you do have sufficent backfocus to do pretty much anything. Unlike a fixed objective flocal length Netwonian telescope, you do not have to mess with negative or positive projection of the primary focal plane to a new location. Positive or negative projection effectively gives you more backfocus at the expense of increased magntification. Since the objective len's primary focus is fixed, the primary focal plane has to be projected to another location. If you use a negative lens (a barlow) to project (or move) the primary focal plane to a new location, the technique is called negative projection. If you use a positive lens, the technique is called positive projection. Attached (omitted in in this newsgroup post version) find an optical layout diagram with image math notes for negative projection with the binoviewer and three pages on negative projection image math from Edmund's publication 9078 "Photography with your Telescope". We can discuss those at some point in the future if you are interested in further study on negative projection. Clear Skies, Kurt

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Tunguska on Mars / SLAS meeting / Grins
by Patrick Wiggins 18 Aug '08

18 Aug '08

NASA just released an image from Mars Odyssey which makes a good analogy of the Tunguska event on Mars (shock wave damage but no big crater): http://themis.asu.edu/zoom-20080813a A reminder that SLAS will be holding it's regular monthly general meeting tomorrow (Tuesday) evening. U of U Physics' Dr. Dave Keida will present an update on the U's two new observatories. http://slas.us/displayevent.asp?EventID=1193 And, totally off topic but if you're looking for a few grins: Why I didn't make the olympics! http://www.youtube.com/watch?v=pfwM1DWGmsc Cheers, patrick

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Launch on schedule (Look out Kwaj!)
by Patrick Wiggins 18 Aug '08

18 Aug '08

Brian Webb with the Launch Alert listserve advises: "Tomorrow morning's launch of a Minuteman III ICBM from Vandenberg AFB remains on schedule. Barring any problems, liftoff is slated to occur at 01:01 PDT, the start of a six-hour launch window." patrick

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Re: [Utah-astronomy] Obs Notes: Venus and Mercury at sunset 8-17 to 8-23
by Canopus56 18 Aug '08

18 Aug '08

Watched Venus and Mercury on night of 8-17. Mercury not visible to naked-eye or in 10x50 binos. Mercury was visible about 1.1 degs from Venus in small refractor at 25x beginning at 8:44pm MDT, or about 22 minutes after local sunset. ZLM 12.7 MPSAS. At sunset tonight Mecury should be closer to Venus. - Kurt

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PST-Calcium note - dark cloth cover note
by Canopus56 17 Aug '08

17 Aug '08

While observing our quiet Sun today, I pulled out the PST-Calcium today for some practice. Although the PST-K image is notoriously dim, I noticed that by using dark light pollution blocking cloth and a separate terry cloth towel, the image was quite passable. Although the solar disk is currently blank, the PST-K looks like it is going to be really fun as solar max approaches. - Kurt P.S. - Two decent sized proms and one small prom seen in PST-Ha.

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Obs Notes: Venus and Mercury at sunset 8-17 to 8-23
by Canopus56 17 Aug '08

17 Aug '08

On 8/17 through 8/23 at sunset, Venus (-3.9) and Mercury (-1.1) will be visible within a 1.2 deg eyepiece view. Venus and Mercury will be at approx. 275 az alt 8 at 8:20pm MDT each night. Venus becomes naked eye visible at around 8:35pm, allowing for easy target acquistion. On 8/16/2008 2:20UT (8:20 MDT), I watched Venus and Mercury (Saturn was not visible) with 10x50 binos and a smaller 70mm refractor for the purpose of getting a feel for the visibility of this wide conjunction. The following are my notes on visibility as Venus set between 8:20pm MDT and 9:00pm MDT: 8:20 MDT - Venus visible telescopically at approx. 7 degs alt; 275 az. Venus phase easily seen in refractor at low power. Sky Quality Meter ZLM 8.7 MPSAS (-5.5 mags). (The sky was much brighter near the horizon.) Unable to detect Saturn or Mercury. 8:35 MDT - Venus visible the naked eye. Sky Quality Meter ZLM 9.5 MPSAS (-4.2 mags). Mercury not detectable visually or telescopically. 8:56 MDT - Mercury first detected telescopically about 1.5 degs from Venus - but only 2 degs above the horizon. Mercury was only visible for a couple a minutes before being obstructed by a horizon object. Sky Quality Meter ZLM 13.1 MPSAS (-0.6 mags). Zero magnitude stars just coming out within 25 degs zenithal distance. ~9:05 MDT - Venus sets. Saturn (1.1) was not detectable at any time. For this evening (8/17 to 8-23), Mercury should be much easier to detect telescopically in the same AFOV as Venus, earlier in twilight and at a higher initial altitude. - Kurt

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Misc Ealing experiment images from 2008-08-17
by Canopus56 17 Aug '08

17 Aug '08

Jupiter - bad - Ealing test 2008-08-17 06:48UT http://gallery.utahastronomy.com/main.php?g2_itemId=11701 Bright crater image test - Manilius - 2008-08-17 07:00UT http://gallery.utahastronomy.com/main.php?g2_itemId=11703 Manilius - Geologic Lunar Map http://gallery.utahastronomy.com/main.php?g2_itemId=11705 - Kurt

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Re: [Utah-astronomy] Aug 16 Lunar Eclipse webcast 1_30 MDT
by Canopus56 16 Aug '08

16 Aug '08

Greatest eclipse point at 21:10 UT (3:10pm MDT). View still good at 4:00pm MDT. Probably will still be okay to 5pm MDT. Three camera live summary view from Netherlands, Norway, Canary Islands http://www.xs4all.nl/~carlkop/eclipsmaan2008/english.html NASA Eclipse page summary http://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2008Aug16P.GIF - Kurt

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Aug 16 Lunar Eclipse webcast 1_30 MDT
by Canopus56 15 Aug '08

15 Aug '08

Spaceweather.com is listing a number of webcast links for tomorrow's eclipse that begins around 1:30 MDT. http://spaceweather.com/ The eclipse track is across western Europe and Russia and will not be visible from North America. After the SLAS sun party tomorrow, you'll have just enough time to get to an internet connection and watch the eclipse. - Kurt

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Obs Rep Io Eclipse Reappear 8-14-2008
by Canopus56 15 Aug '08

15 Aug '08

Observed an occasional eclipse reappear event (EcR) for the Jovian Moon Io at 2008-08-14 at 4:52:55 UTC (2008-08-14 10:52:55 MDT) from SLC, Utah (111 W, 40N). A small 70mm refractor on an alt-az mount was used. This is an EcR event listed for 4:54 UT on p. 218 of the 2008 RASC Observers Guide. A watch time offset was calibrated to a NIST WWV shortwave signal. Events were: ~4:52:30 Io first visible as faint averted image object emerging from Jupiter's shadow about 15 arcsecs for Jupiter's disk and 15 arcsecs to the southwest of Europa. 04:52:55 Io visible with direct vision. ~4:53:15 Io magnitude change ends; fully visible. This was an enjoyable supplement to watching planet and shadow transits. It added to my sense of the majesty of the Jovian system as a celestial object in motion. At 12:40am MDT, Europa began a transit of Jupiter's disk. The next EcR event for the US Intermountain West is 2008-08-17 06:09 UTC (2008-08-17 12:09am MDT) and involves Europa. This 8-17 EcR event will be visually more dramatic and more photogenic for time series imaging. Three of the Galiean moons will lined up "minnow" style on the east side of the Jovian disks. The GSR will transit at 10:55pm MDT on 8-16 (2008-08-17 4:55 UT). Then at 12:09 am MDT (6:09 UT), the fourth Jovian moon Europa will "wink" on about 15 arcsecs to the east of the 45 arcsec dia. Jupiter disk. Details on other EcR events visible from the Intermountain West and Pacific zones through Nov. 1, 2008 can be found at my note page at: http://members.csolutions.net/fisherka/astronote/tours/JMEcl2008/JupEclSP.h… - Kurt

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