Hamilton Amateur Astronomers September 1997 Volume 4 Issue 10 Using Eyepiece & Photographic Nebular Filters Note: This article was obtained from the web and may be viewed at http://www.netcom.com/~regina-r/astro.html ebular filters -- whether for very inexpensive or oddball ones) have * Light Pollution Filters; visual use in conjunction appropriate and accurately cut threads * General Narrowband Nebular with an appropriate eyepiece, for eyepiece filters! DO NOT FORCE Filters; or for photography -- make handy the filters onto your ocular if in doubt! * Oxygen Nebular Line Filters; and accessories for the observer's toolkit. In The good-to-excellent quality range * Hydrogen-Beta Nebular Line this article, we discuss the advantages, 1.25" and 2.0" barrel eyepieces sold by Filters. and drawbacks, of each type. the above-mentioned companies, as Each will be discussed in turn, from Narrowband nebular type well as other fine astronomical information in our software program filters for improving contrast on certain specialty dealers, will provide the best EYEPIECE. The chart below of visible types of non-stellar deep-sky objects, results. l i g h t w a v e l e n g t h s and filter are discussed frequently in the NEBULAR FILTERS FOR DEEP- performance will help illustrate the newsgroup sci.astro.amateur and S K Y O B S E R V I N G & various nebular lines of deep-sky advertised in the catalogs of such PHOTOGRAPHY: objects that may be viewed or manufacturers as Lumicon and Orion photographed, and their transmission by T e l e s c o p e C e n t e r , p r o m i n e nt Four general types are of manufacturers / dealers for numerous greatest use to amateur observers: (Continued on page 5) models; and the largest amateur telescope makers often sell their own Nova East 97 "house brand" of eyepiece filters. We thought it might be useful to add our perspective on the use of filters, to n the Labour Day weekend I club gave very general, illustrated talks provide a middle - ground between the was fortunate to be on astronomy to the general public on unreservedly enthusiastic advertising vacationing on the east coast Friday and Saturday night. This was claims of retailers, and the conflicting and able to attend the Halifax RASC's followed by public viewing sessions at opinions of diverse amateur users. Star Party, Nova East, held at Fundy the observing site in one of the National Park. The party ran from campgrounds. These viewing sessions Like "high end" audiophile Friday to Monday, although I had to were very well attended with people of gear, eyepiece filters of each type and leave early Sunday evening to be able all ages going from scope to scope brand have their enthusiastic advocates, to drive home by Monday night. It was viewing the different objects. Groups as well as their firm denouncers. What a small party attended by about 50 of teenagers seemed especially is the general truth about them that few amateur astronomers, children and fascinated. They also hosted solar would really dispute? In trying to spouses. The site is a great place for a viewing sessions during the day. One answer this question, we offer the star party, with incredible dark skies person had a special filter to show solar following article, based on information and lots to do during the day. flares. When I looked there were two originally published in our software large flares visible, the first time I had programs REDSCOPE and EYEPIECE This star party was quite seen this other than in a photograph. 2.0. different from the others I have On Saturday the group held Warning: Not all eyepieces (especially attended this summer, with an emphasis their annual golf tournament at the on public education. Members of the (Continued on page 3) Editorial page 2 1998 RASC Calendars page 4 inside... Rob'serving Report page 2 Pacific Observatory page 5 Orbiting Gourmet page 4 A Delphinus Delight page 6 Sweatshirts & T-shirts page 4 For Sale page 6 Page 2 Editorial he end of the club year is suggestions on what it would take to get approaching and it is time to you out please pass on your comments start thinking about joining to any of the council members. the HAA council. It doesn't involve a lot of work and you can ask any council I don't especially like to split an member and they will tell you the same article between issues but it was vent Horizon is a publication thing - it is an enjoyable experience. All necessary with this month's article on of the Hamilton Amateur clubs need people to run things and all Using Eyepiece & Photographic Astronomers (HAA). club members have a responsibility to Nebular Filters. Thanks go to Steve help out where possible. It is also Waldee for allowing us to reprint his The HAA is an amateur important to get new people with fresh article. astronomy club dedicated to the ideas on the council. (Not that anyone promotion and enjoyment of astronomy on our council is "stale" yet.) A variety The "Expert" is taking a break for people of all ages and experience of positions are becoming available, so from answering questions this month. levels give it some thought. (Actually, the truth is that the questions that are still to be answered are tough The cost of the subscription is Summer will soon be over but not ones.) included in the $15 individual or $20 the observing. Getting dark earlier just family membership fee for the year. means that there is more time for Stewart Attlesey Event Horizon is published a minimum observing (and eating donuts and lying attlesey@interlog.com of 10 times a year. about what we saw afterwards). I keep wondering what is keeping most of you HAA Council from joining us at our observing Chair Doug Welch sessions. If you have any helpful Second Chair Grant Dixon Honorary Chair Jim Winger Secretary Patricia Baetsen Treasurer Barbara Wight ob'serving Education Dir. Grant Dixon Obs. Dir Rob Roy eport Editor Stewart Attlesey Recorder Tracy Webb Membership Dir Ann Tekatch Jupiter's Satellite Shadow Crossings Oct. 5 Europa 19:50---> 22:39 HAJA Coord Rosa Assalone Oct. 12 Europa 22:26--->01:15 Oct. 13 The first time is the start of the Oct. 20 Europa 01:01--->* Councillors shadow crossing (ingress) and the Oct. 20 Io *---> 20:04 Alan Shinn second is the end (egress). Only one of Oct. 27 Io 18:43EST--->20:59 Bill Tekatch the shadow's ingress and egress times Oct. 30 Europa *--->18:45 may be listed because of the time of Web Site evening twilight and Jupiter's setting For other events, such as eclipses, http://amateurastronomy.org/ time. Times are Eastern Daylight occultations and transits of satellites Savings up to Oct. 26. Thereafter, times search the table in the "RASC are back to Eastern Standard Time. Handbook" or "Sky and Telescope". At the beginning of October check JUST A REMINDER!!!!!! between 23:00 and 06:30 UT. At the Sep. 21 Callisto *---> 20:13 end of October between 23:00 and Sep. 21 Ganymede *---> 22:25 04:30 UT. Jupiter is setting about 1 !!! Double crossing visible from dusk to hour earlier every two weeks. To get 20:13 !!! your local EDT subtract 4 hours from !!!Callisto will also occult Europa this the UT shown for each event. After evening!!! Oct. 26 subtract 5 hours to get your local EST. Oct. 3 Io 00:57--->* Oct. 4 Io 19:26--->21:44 Monthly In-Sights Event Horizon - Hamilton Amateur Astronomers (Continued on page 3) Page 3 Nova East ... (Continued from page 1) prizes. The top prize was a copy of Fundy National Park Golf Course. I did The Sky software (which I did not Marg Walton not attend this, choosing instead to take win!). All in all it was a great party the kids and visit some of the other sites with lots of activities and a small group near the park, such as Hopewell Rocks, of friendly amateurs willing to share St. Mary's Shorebird Reserve, and an their party and their knowledge with a open quarry to do some rock hounding. very new amateur astronomer. The skies on Saturday looked doubtful for good observing later, but they did clear around 10pm and gave us 2 hours of observing before clouding over completely. Sunday's activity was a strenuous 9 km hike down into a river valley, rockhopping along the river to some beautiful clear potholes, just perfect for a swim, and then back out. Eleven of us participated in the activity, and all made it out in one piece. We were thankful to have a surgeon along, as the possibility for some broken bones seemed great! Four of us did get stung by some sort of weird, easily provoked forest bee. Just brushing by the foliage it was on seemed to enrage it and it attacked. The skies again looked iffy Rob'serving Report ... for observing, but we did manage to observe, despite being able to see only (Continued from page 2) ¼ to ½ the sky at any given time. Standard Time (UT-5hr=EST) There was a wide range of September scopes at the party. Dave Lane was * 16@dawn - Mercury at greatest * Mercury- best views in 3rd. week there with his 18" Dobsonian, there was western elongation, 18 deg. of Sept. Not visible most of Oct. a homebuilt 17.5" Dobsonian, and one * 18@07:05- Occultation of Saturn * Venus is low in the southwest person stayed up until 3am Friday by Moon (southern Ontario) evening twilight. Sets about 1.5 morning to finish his 15" Dobsonian in * 21- Double shadow transit on hours after sunset. time for the party. A visitor from Jupiter. * Mars is difficult to see in the Maine brought his son and his 6" * 22- Aldebaran 0.3 deg. south of evening twilight. Newtonian, but left his 18" Obsession Moon. * Jupiter is near the meridian in the at home. There was a 12" LX200 and * 22@19:56EDT- Vernal Equinox. mid -evening and sets after various smaller versions, many smaller midnight. refractors and reflectors and three October * Saturn rises at sunset and is visible 90mm Maksutov's, one was a Meade * 5- Crescent Moon near Venus and all night. Rings span 45" and are and one was a Questar. They were Mars. tilted 10 deg. to us. getting ready Sunday night to do a * 9@midnight- Saturn at opposition * Neptune & Uranus are a few direct comparison of the three, and nearest Earth. degrees west of Jupiter. unfortunately I had to leave before it * 15- Hunter's Full Moon. got dark. * 19- Moon occults Aldebaran in Rob Roy early morning. Observing Director The farewell dinner for * 21- Orionid Meteor Shower peaks royrg@mcmail.cis.mcmaster.ca everyone, included in our registration ~7pm. fee, was a corn and hot dog roast * 26- Venus and Mars only 2 deg. Sunday night. This was followed by apart. the door prize draw, with lots of great * 26@2am- Fall back to Eastern Event Horizon - Hamilton Amateur Astronomers Page 4 The Orbiting Gourmet (Part 3): Navel Gazing h, the humble orange. That straight out to the side and at eye level. of the head represents the day side of m o s t s u c c u l e n t o f At this point, he or she will see what the Earth and since most of us don't educational tools. people usually call a "half-moon" and have any eyes back there the orange astronomers call "first quarter". w i l l b e i m p o s s i b l e t o s e e . You people who have been Schoolteachers and people with young following this series of articles Next, the person holds the kids may be able to mysteriously sense probably think that this time, I've orange out in front with both hands. the orange without looking. completely flipped. But I'm serious! This is a full moon if the face of the orange is fully illuminated, or a lunar Depending on your knowledge When people hear that eclipse if the orange falls within the and the enthusiasm of your subject, you someone is involved with the HAA, shadow of the person's head. Held in can go far with this demonstration. Not they'll usually come out with the person's left hand, the orange enters only will it make the explanation something like "Y'know, I've always "last quarter", a phase that people don't unforgettable -- you can share the wondered...." or "This is probably a usually see because the moon is up orange afterwards. Try that with a plain dumb question, but..." I've always during the wee hours of the morning. old rubber ball ! found it a pleasant job to answer people's questions in a way that'll It's impossible for many Denise Kaisler satisfy them and bring them back for people to hold an orange (or anything kaisler@soback.kornet.nm.kr more. But how to do this?. else!), directly behind them at eye level. But this is the configuration for "new Enter: the orange. Sweet, moon". Explain that people rarely see a juicy, and useful for explaining new moon because it's only up during anything from gravitational lensing to the day. The illuminated back portion black holes. HAA Sweatshirts 1998 RASC Take the moon, for example. People often don't know why it changes shape over the course of a month. You & T-shirts Calendars can try explaining this using a pen and paper, but not everybody will get it. he good news is that you This is especially true of kids, who have e have received a sample haven't missed your a harder time making the leap from a 2- c o p y o f t h e R o y a l opportunity to get your very D picture to the 3-D reality. Astronomical Society of own official HAA-wear! Canada's 1998 Observer's Calendar and, once again, it's a beauty! What you do is this: Hand the The bad news is that's because I curious person an orange and put them haven't ordered them yet! These colour calendars show in a room with a single focused light breath-taking astrophotos taken by source -- a halogen flashlight, or one of Unfortunately, I didn't manage to Canadian astronomers. Also featured those desk lamps that uses incandescent get our order organized over the are details on Canadian star parties, the bulbs. If you're using the latter, get as summer . But, now daily phases of the moon and all bright a bulb as you can find. A normal that those lazy days of summer are past, significant astronomical events. 60 W bulb won't cut it. Explain that the I will be putting an order in to Otmar light represents the Sun, the orange Eigler and we will hopefully see HAA- Last year we quickly sold out represents the moon, and the person's wear in time for Christmas (if not of these calendars and had to place a head, well, that's the Earth (this should sooner). second order. At $7. each, they're sure be good for a joke or two, Grant). The to sell quickly again this year. To person's eyes are two people standing Stay tuned! reserve your copy, call or email me by on the night side of the Earth. September 30/97. Ann Tekatch Have your hapless subject Ann Tekatch stand facing away from the light, with 575-5433 the orange in the right hand, held tekatcba@mcmail.cis.mcmaster.ca Event Horizon - Hamilton Amateur Astronomers Page 5 Using Nebular Filters ... (Continued from page 1) seen, often with contrast enhancement u t t e r l y I N V I S I B L E o r b e i n g specific filters (which, simultaneously, as well. Sky fogging of photographic unmistakably VISIBLE, even with cut off unwanted light wavelengths.) exposures will be reduced, permitting scopes as small as 80mm aperture. Of exposures as much as three times longer course, the exit pupil should be in the than without an LPR filter: our DOS proper range for effective filter use, as freeware program EYEPIECE will shown by our program EYEPIECE. help you calculate the exposure times and sky fogging factor for appropriate OXYGEN NEBULA LINE FILTERS: Messier objects (see the end of this article for free download instructions.) A contrast enhancing deep-sky visual filter (currently made by GENERAL NARROWBAND Lumicon Company and Thousand Oaks NEBULA FILTERS: Optical), the oxygen line filter has its high transmission region tuned to pass One of the most versatile of the the light wavelengths radiated by contrast enhancing visual nebular doubly ionized oxygen near 500 BROADBAND LIGHT-POLLUTION- filters, a narrowband nebular line filter nanometers: the so-called "forbidden REDUCTION (LPR) FILTERS: has a narrower bandwidth than an LPR lines" of radiation that can occur in the filter. Typical light pollution filters will near vacuum of deep space but not This eyepiece or camera lens transmit all but a narrow band of under earthly conditions of higher filter has a relatively minor effect wavelengths that r educes light pollution pressure. The oxygen line filter on the bandwidth of visible light: it and skyglow, while the nebular line dramatically reduces skyglow, while enables enhanced results in viewing or filter blocks a broad band of transmitting wavelengths emitted by photographing images of celestial wavelengths while passing only a (Continued on page 7) objects whose faint light is obscured by narrow range, peaking sharply just the stray photons from street lamps and above 500 nanometers (in the bluish- from the dim but perceptible skyglow green wavelength range of light). caused by excited atoms in earth's The Pacific atmosphere. Those light wavelengths transmitted by the general nebular Observatory The typical broadband LPR filter are radiated by ionized oxygen filters have high transmission (which and atomic hydrogen, which fortunately should ideally achieve better than 90% happen to be in the blue-green light ur company, The Pacific efficiency) at all visual light region to which the dark adapted human Observatory, has just wavelengths except in a region centered retina is most sensitive. Some extended relocated to Ontario. We host around 560 nanometers, which contains nebulae, like the Veil in Cygnus, are astronomy speakers, host public the frequencies of the ye spread over such a wide area of the stargazing evenings and produce and llowish light of sodium- and mercury-vapor streetlights, eyepiece field that they are often show multimedia presentations. and airglow. Other wavelengths invisible to novice astronomers, or may We are bringing Terence radiated by oxygen and hydrogen are never seem to resemble in an eyepiece Dickenson to Brock University on little unaffected by an LPR filter, view -- even employing the largest of Saturday October 18, 1997 at 7:30 to and views of gaseous clouds like the scope apertures -- remarkable long- speak and show his astrophotography. Crab, Lagoon, and Orion Nebulae are e x p o s u r e o b s e r v a t o r y p h o t o s . Tickets are $8.50. For more somewhat enhanced in detail and However, a narrowband nebular line information we have 2 sites on the contrast; photos of these objects may be filter, even under moderately light internet (identical) detailing the event: recorded with longer exposures before polluted skies, will enhance images of the skyglow " washes out" the such nebulae with a clarity and contrast http://www.itcanada.com/~saturn background with stray light. not otherwise obtainable. A number of h t t p : / / w w w . v a x x i n e . c o m / different brands are available: if pacific_observatory S i n c e L P R f i l t e r i n g i s possible, obtain a filter with a high Carol Legate broadband and relatively gentle, the transmission factor in the bandpass John Nemy light of stars, clusters, and galaxies region (at least 90% is desirable). The Pacific Observatory which radiate a wide range of visible In heavily light polluted skies, (905) 892-4531 colors (and generally appear faint white the nebular line filter can make the or grey to the eye) will be quite clearly difference between a nebula being Event Horizon - Hamilton Amateur Astronomers Page 6 A Delphinus Delight ying high overhead and 75x) when the companion is placed Gamma Delphini should repay stretching southward during further away from the primary I see it you with its interesting colors during September evenings is the has a slight greenish emerald tint. Do this early Autumn season, so spend very distinct 'Summer Triangle' you notice this change in hues with some time and study this fine Delphinus marked by the three bright stars of your telescope, and if so at what delight Vega, Altair and Deneb. Altair is the powers? southernmost star of this triangle By Jeff Brydges representing Aquila the flying Eagle. If you scan to the northeast of Altair you'll see a faint diamond-shaped pattern of stars. This is the constellation of Delphinus the Dolphin. This diamond-shaped asterism is sometimes referred to as Job's Coffin, but there is some confusion as to the historical background of this name. The northeastern most star which marks the Dolphin's nose is one of the finest visual binaries visible in the early autumn. This star has the designation of Gamma Delphini, and it is easily resolved by low power telescopes. Gamma Delphini glows with the combined brightness of a 4th magnitude star. This binary system consists of two subgiant stars with spectra of G5 and F8. The individual magnitudes are 4.3 for the primary and 5.2 for its companion. The total luminosity of this system is about 30 suns. For Sale As far as sizes go, the primary is 4 times larger than our Sun and the entax SP Spotmatic with lockup, no battery - perfect for an companion is about 2.5 solar diameters. 50 mm - 1:1.4 lens astrophotographer Distance estimates place this pair over 28 mm - 1:3.5 lens $125 100 light years away. 200 mm - 1:4 lens, assorted hoods & Bellows with slide duplicator- also filters. perfect for an astrophotographer $ 400.00 $125 In a small telescope the two stars 6" f/8 Meade mirror appear to be separated by 9.6" at a P.A. Margaret Walton $120 of 268ø or almost due west of the margw@icom.ca primary. This duo was originally 905-627-7361 Or, make an offer on anything - as long discovered by F.G.W. Struve in 1830. as they go to good homes Since that time the two stars have been dmund Newtonian 4 1/4" closing on each other with a slight 5ø Reflector with 2 eyepieces John Gauvreau change in P.A. and a decreasing (10mm and 25mm Plossl) 24 - 122 Hatt St. separation. The most appealing $325 Dundas, Ontario feature of this pair is the fine colors 80mm finder scope - great spotting L9H 6Y4 these stars present. At low power 35x in scope, with 20mm eyepiece giving 11 627-7882 my 3" telescope I see a golden yellow power (twin to the finder on the 17" at pair. But at higher magnifications (50x- the Hamilton Centre's observatory) $150 Minolta 35mm SRT101 camera - mirror Event Horizon - Hamilton Amateur Astronomers Page 7 Using Nebular Filters ... (Continued from page 5) the low pressures of deep space). This ionized oxygen: planetary nebulae are filter has a very sharp high transmission particularly enhanced. response to the blue-green light of this specific frequency: the Beta line is the In addition, the oxygen line weaker line of atomic hydrogen, the filter provides the highest possible stronger being the h-Alpha or Hydrogen contrast enhancement for viewing many I line in the red color region, centered at types of large diffuse nebulae in sites 656.3 nanometers. Unfortunately, the that suffer from extreme light pollution. human eye can see very little of weak The oxygen line filter is, however, not red light, so the rich reddish hues of a designed for photographic use, since its hydrogen nebula radiating at 486.1 nm "filter factor" of attenuation will are largely undetected by eye through a Horsehead, Eyepiece Simulation, 17.5" Scope in increase exposure times beyond a telescope, though they register strongly Dark Sky, With Hydrogen-Beta Filter useful range, and will block on film. However, the weaker blue- wavelengths to which most film types greenish h-Beta line is much more objects the Cocoon Nebula (IC-5146) are sensitive. readily detected by eye: thus, for and the nebulosity of Campbell's example, the energy radiated by the Hydrogen Star (PK64+5.1, a planetary NARROWBAND HYDROGEN nebula IC-434, located behind the nebula surrounding star BD +30o 3639 BETA LINE NEBULAR FILTERS: Horsehead dark nebula, along our line at 19h 35m RA, +30o 31m DEC.) of sight, will show up to the eye (under The hydrogen-Beta filter the best viewing conditions) as a faint The h-Beta filter is NOT a (currently made by the Lumicon greyish smudge, with the Horsehead photographic filter: it is intended Company, as well as Thousand Oaks being a dark (or darker) spot against the strictly for visual observations at the Optical), is designed to enable the faint glow. This non-linear detection of eyepiece. visual astronomer to accomplish the color wavelengths by the dark adapted almost hitherto impossible task of human eye is called the "Purkinje" PHOTOGRAPHIC TESTS OF actually seeing the faint and elusive effect, after its discoverer, the 19th- FILTERS: Horsehead dark nebula near the star century Czech physiologist J. N. Zeta Orionis in the constellation Orion. Purkinje. To see the Horsehead, the Years ago, when one of this In years past, numerous experienced blue-green hydrogen-Beta wavelength website's authors (Waldee) was the observers (such as the late Walter Scott from IC-434 can be detected, as can the manager of a consumer science Houston) reported observations of the dark cloud of interstellar matter products dealership, we produced a Horsehead with small richfield arranged in front of it, if all "point of sale" display for the company, telescopes, but in this era of urban "competing" skyglow is reduced. The to try to illustrate the efficiency of sprawl and light pollution, the task is authors of this website have observed various forms of eyepiece nebular becoming difficult or even impossible. the Horsehead in Moonless, clear skies filters, by photographing a light The name "hydrogen-beta" of at least 5.8 to 6.0 limiting magnitude polluted region of sky where we refers to the Balmer Beta nebular (preferably darker), with this filter conducted the visual tests of filters that emission line of light wave energy at employed in scopes as small as 3 - 4 will be described below. The prints and 486.1 nanometers radiated by atomic inches in aperture, by following the negatives for this display were long ago hydrogen (excited atoms of hydrogen in recommendations of the program lost, so on the evening of 7-6-97, we EYEPIECE for exit pupil size in repeated the test and provide the results carefully selecting an eyepiece for f o r y o u r i n s p e c t i o n . M a n y appropriate magnification, when the astrophotographers have tested the object is nearest the meridian and above efficacy of filters with guided the rough air at the horizon. exposures in order to show the improvements and reduction of skyfogging (we especially recommend In addition to the Horsehead, the article Filters and Light Pollution on the hydrogen-Beta filter can also Chuck Vaughn's Astrophotography enhance the contrast of a few other Webpages ); but our own specific test extended objects like the California with a fixed camera tripod setup was Nebula in Perseus, faint "H-II" regions intended simply to show the reduction Horsehead, by Ryan Wood: 8" f5.2, Kodak in the arms of some bright spiral Ektapress 1600, 40', Lumicon DEEP-SKY[tm] galaxies like M33, or the Cygnus Filter. (Continued on page 8) Event Horizon - Hamilton Amateur Astronomers Page 8 Using Nebular Filters ... (Continued from page 7) Though we did not take special note of extraordinary contrast enhancement of light pollution. We constructed a with an LPR filter: but some small metal hood for the 50mm f1.7 improvement will be evident by eye. lens of our camera, that fitted closely The increased photographic exposure time is the best service provided by this type of filter, though for visual use, it can provide a slight contrast enhancement on some globular clusters, and on bluish reflection nebulae (such as the faint glow around some of the bright stellar members of M-45, the Pleiades, or part of M-20, the Trifid nebula.) 15-Minute Exposure at f/4, No Filter. them by eye while the picture was M-42, Ron Wood: 8" f5.2, Hypered Kodak being exposed, the camera unerringly Ektapress 1600; 30'; Lumicon DEEP-SKY[tm] captured numerous "UFOs": trails of Filter. airplanes taking off from a south Santa Clara county airport! All in all, it is over the lens, cutting off all light except hard to imagine that any decent deep- through a 27-mm aperture that was sky observing can be done at this fitted with threads for 1.25" eyepiece venue, but we manage to accomplish a filters. This changed the focal ratio of lot when fog comes in to blanket the the system to about f/4, still fast enough worst of the light pollution, by to attain skyfog limit in a few minutes observing away from the strongest with color-rich Kodak 400 print film. source of light, or by using filters on However, a vignetting of the negative extended nebulae. was caused by this adapter, so we have Using a standard "light cropped the scans of the photos to pollution rejection" filter [similar to a contain the exposed region of each Lumicon DEEP-SKY"[tm] or Orion frame, and just a bit of the dark region "SkyGlow"[tm]), which primarily around it. suppresses the yellowish wavelengths of sodium- vapor streetlights (plus Narrowband General Nebular Filter: 15-Minutes The exposure times were 15 some high atmospheric airglow), this 15 at f/4. minutes in each case. The site was one With the addition of a standard of the viewing venues we employ for visual narrowband nebular filter, astronomical observing, at over 3,000 primarily centered on hydrogen feet of elevation above sea level in the wavelengths (similar to a Lumicon mountains north of Santa Cruz, " U H C " [ t m ] o r a n O r i o n California. Lights at the horizon are "UltraBlock"[tm] model), we see a less- from the populous areas of Gilroy and strong transmission of reddish h-alpha Morgan Hill, and in the unfiltered wavelengths, combined with the picture are extraordinarily bright and greenish-blue light to which the dark intrusive in the long exposure! A adapted eye is most sensitive, resulting number of other "unidentified flying in a slightly less reddish cast than the objects" may be visible: more on these LPR Filter, 15-Minute Exposure at f/4. LPR filter picture above; note that the below. minute exposure captures a lot of star trails have nearly disappeared, In this exposure, the brilliance reddish radiation in the h-alpha range along with much of the nasty skyglow. of low- and high- pressure sodium from the city lights, but loses most of This type of filter is not intended for vapor streetlights is terribly evident. In the awful yellow pollution wavelengths. photography, but is designed to help addition, at the right of the horizon, a Sadly, however, the effect by eye is not obtain high contrast on emission trail is visible from the rising planet NEARLY so dramatic: in fact, it is nebulae such as M-8 (the Lagoon Jupiter, as are some fainter startrails. rather subtle, provided just the right exit Nebula) or M-17 (the Omega Nebula, pupil is chosen for the best effect. Do below), both in the constellation of not expect to view nebulae with (Continued on page 10) Event Horizon - Hamilton Amateur Astronomers Page 9 October Night Skies Event Horizon - Hamilton Amateur Astronomers Page 10 Using Nebular Filters ... (Continued from page 8) The Hydrogen-Beta filter [in Again, these tests above are Sagittarius. this case, a Lumicon "H-BETA"[tm] not indicative of the visual performance model] cuts off even more light, of the eyepiece filters, but instead a transmitting a very narrow region right demonstration of their general cutoff at 486.1 nanometers, the precise effects in reducing light pollution. The hydrogen- Beta wavelength. As you eye's sensitivity to faint light, and the can see in this photographic test film's response to visual wavelengths, exposure, very little light is recorded are strikingly different . from the streetlights at the horizon, though the trail of Jupiter is just visible M17 the Omega Nebula at the top right of the image. This EYEPIECE 2.5 Light Edition, the Note: we do not currently have the filter -- though NOT for photography -- author's DOS freeware program for server space to include the test photo is very efficient at eliminating almost calculating the appropriate exit pupil made through the oxygen line filter: all light pollution and skyglow, but for filter use, is available ONLY over however, it was similar to the hydrogen unfortunately works well visually for the Internet. Consult the "Download filter except for a slightly fainter only a few kinds of emission nebulae: Info & Sites" page at the WALDEE- registration of a somewhat more thus it should be a choice for the WOOD ASTRONOM ICAL SOFTWARE purplish color. dedicated amateur who has progressed website at: beyond the other types of filters, and http://www.netcom.com/~regina -r/ who believes that the study of such astro.html objects as the Horsehead and from which you may download the California Nebulae justify the cost. software from US or European servers. However, it does work as advertised, and permits one to see the faint nebulae, Yours, provided that the observing conditions Steve Waldee are propitious, and the telescope / eyepiece can provide the exit pupil necessary (shown in our software Next Month: This article will conclude program EYEPIECE and in the data with Visual tests of filters. sheets for the filter.) VISUAL TESTS OF FILT ERS: Hydrogen-Beta Nebular Filter: 15-Minutes at f/4. CALENDAR OF EVENTS Monday, September 15th, 7:00PM HAJA MEETING - McMaster Burke Science Building, room B148. Friday, September 19, 7:30 PM COUNCIL MEETING - At the home of Ann and Bill Tekatch. Call Doug at 525-9140 Extension 23186 if you are interested in attending. Saturday, September 20, 8:00 PM COSMOLOGY DISCUSSION GROUP - Room B148 (next to the Planetarium) Burke Science Building, McMaster University. Topic will be "Introduction to Cosmo logy". For more information contact Bill Tekatch at 575-5433 or tekatcba@mcmail.cis.mcmaster.ca September 26, 27 BINBROOK OBSERVING SESSIONS - Proposed observing nights. For confirmation or directions call Rob Roy (692-3245) or Ann Tekatch (575-5433) Thursday, October 2, 8:00 PM ROYAL ASTRONOMICAL SOCIETY OF CANADA Hamilton Centre - General Meeting - Spectator Building auditorium. Friday, October 3, 11:59 PM EVENT HORIZON DEADLINE - Please submit your articles and pictures to Stewart Attlesey, attlesey@interlog.com or modem (905)827-9105 or snail mail to 1317 Mapleridge Cres., Oakville, L6M 2G8 Friday, October 10, 7:30 PM HAA GENERAL MEETING - at the Spectator Building auditorium. Speaker to be announced. Parking lot observing, weather permitting. Monday, October 20th, 7:00PM HAJA MEETING - McMaster Burke Science Building, room B148. Event Horizon - Hamilton Amateur Astronomers