Because of the current high winds, the DC Rec & Parks department has closed all recreation center classes, so no telescope making class tonight.
Back again on Tuesday.
Because of the current high winds, the DC Rec & Parks department has closed all recreation center classes, so no telescope making class tonight.
Back again on Tuesday.
I just finished a 6″ f/8 Dobsonian telescope as a gift for my great-nephews, one of whom I discovered is VERY interested in astronomy and happens to live in a place with pretty dark skies – about the middle of Maryland’s Eastern Shore. The mirror is excellent, and the mechanical parts all work very well — in my opinion. Let’s see what the recipients think.
I finally succeeded in putting in the mirror yesterday afternoon in a very stiff and cold wind right outside my house, estimating where the mirror should go by aiming at a distant chimney. This takes patience because it’s trial-and-error, no matter how much you calculate beforehand!
Later that evening, after the nearly-full Blue Moon came over the trees at DC’s Chevy Chase Community Center where we have our telescope-making classes, fellow ATMer and all-around interesting person Jim Kaiser helped me collimate it by pointing the scope at the illuminated curtains in the windows of the CCCC. We then verified that the Moon actually did come to a focus with the eyepiece nearly all the way screwed in. If you want to focus on closer things than the Moon or galaxies, you need to screw the eyepiece out towards you, the observer in the cheap but effective helical focuser that was lying around the shop.
This scope incorporates a couple of innovations by me, and a bit of artistic whimsy.
First small innovation: I made the secondary diagonal mirror holder so that no tools are needed at all: you just rotate the part holding the elliptical mirror and turn a little thumbscrew to collimate it quickly and easily, while you watch. Here is a sketch of how I made it.
Second innovation can be seen near my right hand (to your left) atop the cradle: two 1/4″-20 machine screws with simple homemade knobs on top, going through threaded inserts (T-nuts would work too), which push against a piece of lumber in the shape of prism with an isosceles right triangle at each end. I call this the tube brake, which can be applied or released quite easily, whenever needed. Small springs (almost impossible to see in this photo) pull this brake up against the corner of the tube, while the machine screws press it down. If you want to change the position of the eyepiece because a taller or shorter person has arrived, no problem. A few CCW turns of the wooden knobs releases the brake, you rotate the tube to the desired position, and then you lock it down again with a few clockwise turns. If you add or remove a heavy eyepiece or a finder or whatever, same procedure, except this time you can slide the scope up and down inside the cradle.
The artistic whimsy is partly seen in a photo Jim took of me after we got it collimated but before we rushed back inside: lots of colors, thanks to several tons of paint cans salvaged by fellow ATMer Bill Rohrer from being thrown away by a third party who lost his warehouse lease, and also because smurf blue is the favorite color of one of the boys. The altitude bearing is made out of the Corian countertop that my wife and I got rid of a few months ago when we had our kitchen remodeled. (30 years ago we did it ourselves, mostly. This time we hired professionals. They are SOO much faster and better at this than us!)
So that my young relatives can keep this thing looking good, they also get four or five quart or pint cans of paint – the ones I used on the scope. Free, of course. The more we
get rid of put to use, the better. They can repaint anything that gets scratched, you see?
You can also see some wood-cutting fun above and below. This retired geometry teacher had a lot of fun figuring out how to lay out and cut out stars with 5, 6, and 7 points, as well as a crescent moon and a representation of Saturn seen with its rings edge-on. I guess you could show Saturn’s rings a 30 to 45 degrees to the viewer, if you instead carved it out of solid wood or did wood burning, but I just had a hand-held jigsaw and a Dremel knockoff. And plus, this is supposed to be a scope that is USED rather than just admired for its artsy parts.
I designed what I wanted onto two sheets of paper and then taped them to the plywood. This worked, but it wasn’t the most wonderful plywood, so on many of the pull strokes, the wood splintered a bit. So that side got to face inside.. Painting all those little nooks and crannies was tough!
(The purpose of the cut-outs was simply to make the telescope lighter. It’s got a very heavy and sturdy base. Each square inch of plywood removed saves about 7 grams. Also, more holes means more hand-holds!)
I have tested three different Newtonian mirrors from 12″ to 16″ diameter over the past few years that were labeled as being by Meade. One had been refigured by someone else before I tested it.
Each of the mirrors initially looked nice and smooth, and the Ronchigrams looked pretty close to the theoretically-perfect image generated by RonWin or similar software.
However, when I did a zonal test, in every single case, the mirror turned out to be seriously under-corrected, in some cases by about 50%. In other words, if a perfect mirror should have the outer zone (say the outer inch) to “null out” at 0.236″ from the location where the central zone nulls out, then the mirrors I tested might null out at only 0.118″ instead.
I took care to repeat the measurements several times in each of these cases, and in one case the owner also took a set of readings; his and mine agreed pretty closely.
I don’t know if it’s my skills at reading Foucault/Couder shadow zones that are suspect, or if I’m correct. Anybody else have similar or opposite stories or experiences?
This weekend, I’m hosting a small workshop at the Community Museum in Gaithersburg, MD, where interested persons from 8 to 88 years of age can make their own telescope in an hour or two. We will be using surplus but high-quality achromatic primary doublet lenses as well as inexpensive eyepieces, along with PVC tubing and some really cool tripods to hold it steady. We will some basic optics experiments to help explain how these gizmos work, and will have spray paint and colored tape to decorate the tubes.
If you are interested, here is the necessary information:
You will also see how various types of telescopes such as reflectors, refractors, and catadioptrics are put together and operate, using actual examples, including the type made and used by Galileo around 1609.
$30 City of Gaithersburg residents/$35 non-residents. Space is limited to 15 so pre-registration is required. To register go to RecXpress at https://online.activenetwork.com/gaithersburg/Start/Start.asp. It’s activity #49690.
For more information or if you have trouble registering call the museum at 301-258-6160 or email@example.com
The answer is, of course, no. Though they do bear some resemblance to the amazing astronomy graphics you come across these days at websites like Astronomy Picture of the Day, or graphs that astronomers show to their peers, these are merely wonderful doodles made by a fellow-volunteer at the registration desk at last week’s American Astronomical Society at the Gaylord convention center at the National Harbor in Oxon Hill, MD. Sorry, I have forgotten his name and I also didn’t get permission to post. (He was an undergrad or grad student but I forget where.) So I definitely need to pay him royalties if he ever tracks me down.
(He won’t get very rich though: even 12% or 37.5% or 99.99% of zero income from this blog is still zero…)
All of us volunteers and paid staff were very impressed by his doodles.
I’m sure that the reaction of a group of Freudian psychoanalysts would have been quite different.
I was inspired to try making some Astronomical cutouts in the side panels of a 6″ f/8 Dob I’m making for my Great-nephews. The tube is smurf blue, as requested. I’ve never tried cutting out decorative holes in plywood before, so don’t laugh too much.
Three highlights of my visit in late
🏵the weekly Friday-night telescope-mirror-Making workshop there …
🏵visiting some of their big, ancient refractors, one of which is the smaller cousin of the 26″ refractor at the USNO in DC …
🏵viewing some of their collection of old & modern donated telescopes, which they are endeavoring to put into service again and into the hands of interested observers …
I’ll post pix in a bit
Anybody interested in the night sky, including members of local astronomy clubs like NCA and NOVAC, are invited to the Fall 2018 astronomical open house and star party at Hopewell Observatory on the night of December 1 (Saturday evening and on into Sunday morning). Feel free to pass this invitation to friends, neighbors, and family and anybody else you care to notify.
We are located about 30 miles west of the Beltway on Bull Run Mountain – a ridge that overlooks Haymarket VA from an elevation of 1100 feet, near the intersection of I-66 and US-15. Detailed directions are below.
Assuming good weather, you’ll get to see planets, star clusters and nebulae and the Milky Way itself, as well as many other galaxies. If you like, you can bring a picnic dinner and a blanket or folding chairs, and/or your own telescope, if you own one and feel like carrying it. We have outside 120VAC power, if you need it for your telescope drive, but you will need your own extension cord and plug strip. If you want to camp out or otherwise stay until dawn, feel free!
If it gets cold, our Operations Building, about 40 meters north of the Observatory itself, is heated, and we will have the makings for tea, cocoa, and coffee.
Warning: While we do have bottled drinking water and electricity and we do have hand sanitizer, we do not have running water; and, our “toilet” is an outhouse of the composting variety. At this time of year, there are almost no insects of any kind, although it’s always wise to be safe and check yourself for ticks after you get home.
The road up here is partly paved, and partly gravel or dirt. It’s suitable for any car except those with really low clearance, so leave your fancy sports car (if any) at home. Consider car-pooling, because we don’t have huge parking lots. We will have signs up at various places along the way to help guide you, and will try to have parking spaces denoted.
Two of our telescope mounts are permanently installed in the observatory under a roll-off roof. We have others that we roll out onto the grass in our roughly one-seventh-acre field. We have two 14-inch scopes (one hand-made Dob and one Celestron SCT), and a 10” f/9 reflecting scope also made by hand. We are about to install a brand-new Astro-Physics GoTo computerized mount in addition to our sturdy, highly accurate, but 1970s Ealing mount. The entire observatory was hand-built, and is maintained, by the labor of its founders and current members.
The drive is about an hour from DC. After parking at a cell-phone tower installation, you will need to hike south about 130 yards to our observatory. Physically handicapped people, and any telescopes, can be dropped off at the observatory itself, and then the vehicle will need to go back to park near that tower. To look through some of the various telescopes you will need to climb some stairs or ladders, so keep that in mind when making your plans.
It’s not the inky-scary dark of the Chilean Atacama or the Rockies, but Hopewell Observatory is mostly surrounded by nature preserves maintained by the Bull Run Mountain Conservancy and other such agencies. Also, our Prince William and Fauquier neighbors and officials have done a pretty good job of insisting on smart lighting in the new developments around Haymarket and Gainesville, which benefits everybody. So, while there is a pretty bright eastern horizon because of DC and its VA suburbs, we can still see the Milky Way whenever it’s clear and moonless.
The easiest planet to find will be Mars, and with our telescopes you may be able to see polar caps and dark regions. Saturn will set fairly early (6:43 pm), Uranus and Neptune will be findable, Venus will rise a bit before 4 am, and the moon will rise after 2 in the morning.
We should also be able to track down and examine many, many deep-sky objects.
You can find detailed directions and a map to the observatory below:
[Note: if you have a GPS navigation app, then you can simply ask it to take you to 3804 Bull Run Mountain Road, The Plains, VA. That will get you very close to step 6, below.]
(1) From the Beltway, take I-66 west about 25 miles to US 15 (Exit 40) at Haymarket. At the light at the end of the ramp, turn left/south onto US 15. (Exit is at approximately latitude 38°49’00″N, longitude 77°38’15″W.)
(2) Go 0.25 mi; at the second light turn right/west onto VA Rt. 55. There is a Sheetz gas station & convenience store at this intersection, along with a CVS, a McDonald’s, a Food Lion, and a Walmart-anchored shopping center on the NW corner that includes a number of fast- and slow-food restaurants, including a Starbucks.. This is a good place to stop for restrooms or supplies.
(3) After 0.7 mi on Va 55, turn right (north) onto Antioch Rd., Rt. 681. You will pass entrances for Boy Scouts’ Camp Snyder and the Winery at La Grange. (38°49’12″N, 77°39’29″W)
(4) Follow Antioch Rd. to its end (3.2 mi), then turn left (west) onto Waterfall Rd. (Rt. 601), which will become Hopewell Rd. (38°51’32″N, 77°41’10″W)
(5) After 1.0 mi, bear right onto Bull Run Mountain Rd., Rt. 629. This will be the third road on the right, after Mountain Rd. and Donna Marie Ct. (38°52’00″N, 77°42’08″W) Please note that Google Earth and Google Maps show a non-existent road, actually a power line, in between Donna Marie Ct. and Bull Run Mtn. Rd.
(6) In 0.9 mi, enter the driveway on the right, with the orange pipe gate. There is a locked stone and metal gate on the left, opposite our entrance, labeled 3804 Bull Run Mountain Road. Don’t take that road – it goes to an FAA radar dome. Instead, go to the right (east). We’ll have some signs up. This is a very sharp right hand turn. (38°52’36″N, 77°41’55″W)
(7) Follow the narrow paved road up the ridge to the cell phone tower station. You should park around the tower (any side is fine) or in the grassy area before the wooden sawhorse barrier. Then you should walk the remaining hundred meters to the observatory on foot. Be sure NOT to block the right-of-way for automobiles.
(8) If you are dropping off a scope or a handicapped person, move the wooden barrier out of the way temporarily, and drive along the grassy track to the right of the station, into the woods, continuing south, through (or around) a white metal bar gate. The few parking places among the trees near our operations cabin, the small house-like structure in the woods, are reserved for Observatory members. If you are dropping off a handicapped person or a telescope, please do so and then drive your car back and park near the cell phone tower.
Please watch out for pedestrians, especially children! The observatory itself is in the clearing a short distance ahead. We do not have streetlights, and there will not be any Moon to light your way, so a flashlight is a good idea. In the operations cabin we have a supply of red translucent plastic film and tape and rubber bands so that you can filter out everything but red wavelengths on your flashlight. This will help preserve everybody’s night vision. In the cabin we also have a visitor sign-in book; a supply of hot water; the makings of hot cocoa, tea, and instant coffee; hand sanitizer; as well as paper towels, plastic cups and spoons.
The location of the observatory is approximately latitude 38°52’12″N, longitude 77°41’54″W. The drive takes about 45 minutes from the Beltway. A map to the site follows. If you get lost, you can call me on my cell phone at 202 dash 262 dash 4274.
Last weekend I practiced doing some astro-imaging during a beautiful night that featured a nearly full moon night, up at Hopewell Observatory. I was particularly concerned with getting decent ‘flat’, ‘dark’ and ‘bias’ subframes, which are shots where you take images of what appears to be nothing at all. However, using those apparently ‘nothing’ subframes, you can subtract out noise and unwanted internal signals, in order to get decent images. I was using a Celestron 14-inch Schmidt-Cassegrain telescope on an ancient Ealing mount whose drive has some problems; as a result my ‘light’ sub-frames could only be 2 minutes long. I am also using a second-hand Canon EOS Xsi 450D DSLR camera that has had the infrared-rejection filter removed.
I did the stacking and registering and removal of noise using a program called Deep Sky Stacker, with no further processing. One day I will learn how to adjust colors with something like Pixinsight to make it look more beautiful I was fairly pleased with the results, which you can see here: