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My Backyard Observatory A roll-off-roof shed, a 10-inch Newtonian, and a retired physicist who should be asleep The Shed  |  The Pier  |  The Telescope  |  Fall 1999 Observing Log  |  Dew  |  Light Pollution  |  For Beginners

Hello, and welcome. My name is Alan Petrov. I taught physics for thirty-one years, mostly to undergraduates who would rather have been elsewhere, and retired in 1997. I had promised myself an observatory when I retired, and my wife, who is a patient woman, held me to it. The shed went up in the summer of 1998, the telescope moved in that September, and I have spent more clear nights out there since than I care to admit to my doctor. I put this page together for two kinds of people: those who are thinking of building a small observatory and want to know what actually worked, and those who are just starting out in astronomy and want honest advice from somebody who has made most of the mistakes already. I have tried to be precise where precision matters (measurements, dates, what you can really expect to see) and to leave out anything I am not sure of. If you find an error, please write to me; I would rather be corrected than be wrong on the Internet. A word on location: I live at roughly 42 degrees north latitude in a suburb with more streetlights than I would like. Everything below is from that spot, so if you are further south, some of my "low in the south" objects will be comfortably higher for you.

The Shed Why a roll-off roof? A dome looks the part, but for a single telescope in a backyard a roll-off roof is simpler, cheaper, and better in one important way: when the roof is off, the whole sky is open and the shed cools to the outside air temperature quickly, which matters more for image quality than most beginners realize. A warm telescope in a warm box gives you wobbly planets. The disadvantages are wind, and the fact that the neighbors can see you in your bathrobe. Size. 8 feet by 10 feet, outside dimensions. That is enough for the telescope on its pier, a small table, a stool and one visitor. It is not enough for two visitors. I built the walls only 5 feet high so that the telescope, which is on a pier in the middle, can see down to about 20 degrees above the horizon on all sides. Higher walls would block the low south, where Sagittarius and the summer Milky Way live, and I wanted those. Construction, in order: Four concrete deck piers at the corners, with 4x4 posts and a 2x6 floor frame, 16 inches on center. Plywood floor. The floor does NOT touch the telescope pier (see below). 2x4 stud walls, sheathed in plywood, T1-11 siding on the outside. Painted a dull gray so it doesn't glow under the moon. The roof is a flat, very slightly pitched frame of 2x6 rafters on 24-inch centers, plywood, and rolled roofing. It is a separate unit that simply sits on the walls. The track: two lengths of 2-inch steel angle iron, bolted to the top plate of the two long walls, running the length of the shed and continuing out past the north end onto an extension frame. The rollers: ordinary garage-door rollers, the 2-inch nylon kind with ball bearings, eight of them, bolted to the underside of the roof frame through steel brackets. They ride in the angle iron the same way they ride in a garage-door track. The whole roof, which I estimate at about 350 pounds, rolls off to the north with one hand. The extension frame: two 4x4 posts set in concrete about 9 feet north of the shed, with a 2x6 beam across and the angle iron continuing onto it. When the roof is rolled off, it sits entirely on the extension, clear of the sky. Stops at both ends of the track so the roof cannot roll off the end, and two hasps with padlocks that hold the roof down when closed. Wind is the enemy of a roll-off roof, and I have had gusts here of 60 miles an hour. Weather sealing. The roof overhangs the walls by 3 inches on all sides and there is a strip of rubber garage-door bottom seal along the top of each wall that the roof presses against. Rain has come in exactly once, in a sideways storm in April, and it was a cupful. What I would do differently. Make it 10 by 12. Put the door on the south wall, not the east, so that it doesn't face the neighbors' porch light. And put the electrical outlet higher; I trip over the cord in the dark about once a month. Cost. Lumber, roofing, hardware and concrete came to a bit under $1,400 in 1998. The electrician who ran a buried line from the garage charged another $300. I did all the carpentry myself with a friend's help on the roof frame, which is a two-person job whatever anybody tells you.

The Pier The single most important part of the whole project, and the part people skimp on. A telescope at 200 power magnifies vibration 200 times as well. If the mount is on the floor, every step you take shows up in the eyepiece. Mine is a column of concrete poured into a 12-inch cardboard form tube, 4 feet into the ground (below the frost line here, which is what matters; find out yours) and 42 inches above the floor. It sits in a hole I dug and filled with a footing of concrete about 24 inches square before setting the tube on top. Four 1/2-inch J-bolts were set in the wet concrete at the top, matched to a steel plate that the equatorial mount bolts to. The floor of the shed has a hole cut around the pier with about an inch of clearance all around, so the floor and the pier never touch. You can jump up and down next to the telescope and the star in the eyepiece does not move. It took two weekends and about eleven bags of concrete mix, and I would not change a thing.

The Telescope A 10-inch f/6 Newtonian reflector: a parabolic primary mirror 10 inches across with a focal length of 60 inches (1524 mm). The mirror and diagonal were bought; the tube is a length of cardboard concrete-form tube, painted, with a plywood mirror cell and a commercial focuser. I built it in 1995 and it lived on a wheeled Dobsonian base in the garage until the shed was ready. Now it rides on a German equatorial mount with a clock drive, bolted to the pier, which means that once an object is centered the mount follows it across the sky and I can actually sit and look instead of nudging every twenty seconds. Eyepieces. Three, plus a 2x Barlow lens. Magnification is the telescope's focal length divided by the eyepiece's: 32 mm Plössl 48x finding things, big clusters, M31 12 mm Plössl 127x globular clusters, planetary nebulae, most nights on the planets 7 mm orthoscopic 218x planets and double stars on steady nights only 7 mm + Barlow 435x perhaps three nights a year, and mostly to remind myself why not A useful rule: the highest magnification worth using is about 50 times the aperture in inches, and only when the air is steady. For my 10 inches that is 500x on paper. In practice, on an ordinary suburban night, 127x to 218x is where the planets look best. The air, not the telescope, is nearly always the limit. Finder. A 9x50 straight-through finder, and a simple 1x reflex sight beside it. The reflex sight is the best twenty dollars I have spent on this hobby. Collimation, which means lining up the mirrors, needs checking every few weeks. If your Newtonian shows stars as little comets on one side of the field, that is the problem, not your eyes.

Observing Log: Fall 1999 Copied from the notebook that lives in the shed. "Seeing" is steadiness of the air (I rate it I to V, with I best, following the old Antoniadi scale); "transparency" is how clear and dark the sky is. All times are local daylight time. The sky this season, in brief: the Summer Triangle (Vega, Deneb, Altair) is overhead at dusk; Sagittarius and the heart of the Milky Way are low in the southwest and sinking a little earlier each week; Pegasus and Andromeda are rising in the east; and the two great planets, Jupiter and Saturn, are rising in the east in the mid evening and are well up by midnight. Both are on their way to opposition (Jupiter in late October, Saturn in early November), which means they are nearly as big and bright as they get. This is a very good autumn for planets. Venus, meanwhile, has swung around into the morning sky and is blazing in the east before dawn. Thursday-Friday, August 12-13. Perseid meteor shower, no telescope. New Moon was the 11th, so the sky was as dark as this yard gets. Lay on a lawn chair from 11:30 pm to 2:30 am and counted 61 meteors, most of them in the last hour as Perseus climbed. Several bright ones with lingering trains. My wife came out for twenty minutes, saw four, and pronounced it "nice." High praise. Saturday, August 14. Seeing III, transparency fair. Waxing crescent Moon set early. Toured the summer objects before they are gone for the year: M22 (globular cluster in Sagittarius) resolved to the core at 127x even at its low altitude; M8, the Lagoon Nebula, with the UHC filter, showing the dark lane; M11, the Wild Duck Cluster in Scutum, which is one of the finest sights in any telescope, a dense fan of faint stars with one bright one at the edge. Finished on Albireo, the double star at the head of Cygnus: one gold star, one blue, and no photograph does it justice. Saturday, September 4. Seeing II, transparency good, no Moon in the evening. The best night of the season so far. M13, the great globular cluster in Hercules, high in the west: at 127x it was a swarm of individual stars right across the face, with the dark "propeller" lanes just visible with averted vision. M57, the Ring Nebula, a tiny gray smoke ring at 218x. M27, the Dumbbell, in Vulpecula, large and obvious with the filter. Then waited for Jupiter, which cleared the neighbor's roof about 11 pm. All four Galilean moons strung out on one side. The two main cloud belts plain, with detail in the north belt at 218x once it rose higher. Saturn up by 12:30 am; rings wide open this year, Cassini's division clear all the way around at 218x, and Titan off to one side. Closed the roof at 1:45 am. Saturday, September 11. Seeing III, transparency very good after a cold front. Two days past New Moon. The autumn objects. M31, the Andromeda Galaxy, at 48x: the bright core and a long hazy oval stretching most of the way across the field, with M32 a small round smudge just beside it and M110, fainter, on the other side. It is over two million light years away and it is the farthest thing most people will ever see with their own eye. In binoculars from the dark end of the yard it was plain to the naked eye as a faint patch. The Double Cluster in Perseus (NGC 869 and NGC 884) at 48x, both clusters fitting in one field: hundreds of stars, several of them a distinct orange. This is the object I show visitors first, every time. Also picked up Uranus in Capricornus at 218x, a small but definite greenish disk, not a point like a star. It is easy in the finder if you have a chart. Sunday, September 12. Seeing II. Went out at 11:30 pm just for Jupiter. The Great Red Spot was on the Earth-facing side (it is more of a pale salmon than red these days) and I watched it cross the middle of the disk over about an hour. Io's shadow was on the planet as a tiny black dot, which always looks like a flaw in the eyepiece until you realize what it is. These are the nights the pier pays for itself. Saturday, September 18. First quarter Moon, so no deep sky. Spent the evening on the Moon itself along the terminator (the line between day and night, where the shadows are longest): the crater chain of Ptolemaeus, Alphonsus and Arzachel, and the Straight Wall just past them, a thin dark line at 218x. The Moon is the one object that is at its best from a suburban backyard and I have never understood people who look at it once and never again. Thursday, September 23. Autumnal equinox today. Clouded out. Sat in the shed with the roof closed and a cup of tea and cleaned eyepieces. This is also part of the hobby. Saturday, September 25. Full Moon, the Harvest Moon, rising huge and orange in the east at sunset. Not a night for faint things, so I put the low-power eyepiece in and let the neighbors' grandchildren look at the Moon and then at Jupiter and its moons when it rose. One of them asked if the little dots were "Jupiter's planets." Close enough. The first question a child asks at the eyepiece is always better than the lecture I had planned. Coming up in October: New Moon on the 9th, so the weekend of the 8th-10th is the one to plan around. Jupiter reaches opposition on the 23rd and will be visible all night. I will add entries as the weather allows.

Dew On a clear, still night, anything pointed at the sky radiates its heat away and gets colder than the air around it, and water condenses on it. In an open-roof observatory this is the nightly enemy. A Newtonian's primary mirror, down at the bottom of the tube, is fairly safe; the small secondary mirror, the finder's objective, and every eyepiece are not. What works for me, in order of usefulness: Dew shields. A tube of closed-cell foam camping mat, cut and taped to extend a few inches past the front of the finder. The same on the front of the main tube. The shield slows the radiation to the sky. Cost: a few dollars. Heat. A homemade dew heater: a strip of resistance wire wrapped in cloth tape around the secondary mirror holder and the finder objective, run from a 12-volt battery through a small resistor so it is barely warm to the touch. You want a degree or two above the air, no more. Keep spare eyepieces in your coat pocket, not on the table. A fogged eyepiece cleared by body heat is ready again in five minutes. A 12-volt hair dryer of the kind sold for cars, for emergencies. Never wipe a dewed optical surface; you will scratch it. Warm it and let it clear.

Light Pollution On a good night from my yard I can just see stars of about magnitude 5.5 with the naked eye. From a truly dark site that figure would be 6.5 or better, and the difference is not one magnitude; it is the difference between a gray sky and a black one with the Milky Way casting a shadow. I am not going to pretend a suburban observatory is a dark site. But a great deal can be done. Talk to your neighbors. Kindly. The house to my east had a dusk-to-dawn floodlight on the garage. I brought the family out to look at Saturn, explained the problem, and offered to pay for a shield for the fixture. They put it on themselves the next weekend and now it lights their driveway instead of my shed. Most people have simply never thought about it. Build low walls, sit low. The 5-foot walls block every streetlight on the block from where I sit at the eyepiece. The sky is still brighter than I would like, but at least there is no glare in my eye. Filters. A UHC ("ultra high contrast") nebula filter screws into the eyepiece and passes only the colors that emission nebulae glow in, cutting most of the sky glow. On M8, M27, M57 and the Veil it is the difference between "I think so" and "there it is." It does nothing for galaxies, clusters or planets; those need a dark sky, or patience. Choose your objects. Planets, the Moon, double stars, globular and open clusters and the brighter planetary nebulae are all fine from the suburbs. Faint galaxies are not. Save those for the once-a-year trip to the mountains. Dark adaptation. Your eyes take twenty to thirty minutes to reach full sensitivity and one glance at a white light undoes it. Use a dim red flashlight only, and cover the shed's outlet lamp with red film.

Advice to Beginners I get letters from people who want to know what telescope to buy. My answer disappoints them, so I will give it here with the reasons. 1. Buy binoculars first. An ordinary 7x50 or 10x50 pair, which you may already own. With those, a planisphere (a rotating star wheel that shows the sky for any date and hour) and a good beginner's star atlas from the library, spend a season learning the constellations and finding the bright deep-sky objects: M31, the Double Cluster, M13, the Pleiades, the Orion Nebula in winter. The Milky Way in 10x50s from a dark site is a better sight than most objects in most telescopes. If after a season you still want a telescope, you will know the sky well enough to use one, which is the part most first telescopes never get past. 2. Aperture, not magnification. A telescope's important number is the diameter of its main lens or mirror, because that sets how much light it gathers and how much detail it can show. Any telescope sold on the strength of "600 POWER!" printed on the box should be left in the box. Magnification is just the eyepiece, and above about 50 per inch of aperture it only makes a bigger blur. 3. The best first telescope for most people is a 6- or 8-inch Newtonian on a simple Dobsonian mount: a plywood box that swivels and tilts. It gives more aperture per dollar than anything else, it has nothing to go wrong, and it is what I would buy today if I were starting over. You do not need a computer on it. You need a chart and a little patience. 4. Steady mount over everything. A wobbly mount ruins a fine telescope; a rock-steady one flatters a modest one. 5. Find your local astronomy club. Go to a public star party. Look through six different telescopes in one night and ask their owners what they would do differently. Every one of them will tell you, at length, and it will be worth it. 6. Have modest expectations of the eyepiece and large ones of the sky. Galaxies do not look like the photographs. They are gray smudges; the color in the pictures comes from long exposures on film. But they are the real thing, the light that left them before there were people, landing in your own eye. Once that idea takes hold, the gray smudge is enough.

Neighbors in the Cape Canaveral neighborhood Skywatch: Satellites You Can See - Priya's page on spotting satellites and the Mir station with the naked eye. I have started checking it before each session; a bright pass across the field is a fine surprise, and it is nice to know what it was. Shuttle Launch Viewing Guide - a Titusville resident who has watched launches since 1981. Steve's Model Rocketry Page - for the daytime. The Paper Airplane Laboratory - a father and daughter doing real experiments with a tape measure and a stopwatch. This is how physicists are made. Mr. Delgado's 7th Grade Science - a science teacher's page; I wish I had had him. Back to Cape Canaveral

Visitors since October 1998: Questions, corrections, and reports of your own clear nights are welcome: [email protected] Last updated: September 26, 1999. Next update after the October new Moon, weather permitting. © 1998-1999 Alan Petrov. Clear skies.