Category Archives: astronomy

A recently-completed telescope

27 Saturday Feb 2016

Posted by in astronomy, Telescope Making

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Steve S recently finished a telescope with help from the DC-area amateur telescope making (ATM) workshop that I’ve been running at the Chevy Chase Community Center (CCCC) for several years (I took over from the late Jerry Schnall around the turn of the century) with help from several local ATMers and under the auspices of the National Capital Astronomers (NCA).

Steve had made the mirror quite a long time ago (not here in DC). The optics are quite good according to my tests, and if you look at the photos, I think you will agree that the body of the telescope looks excellent as well.

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As you can see, he used more-or-less dimensional wood rather than the more conventional plywood. Or should I say, clear pine that had been glued into boards at the lumber factory. He made the cradle with a bolt that allows one to loosen or tighten the grip on the tube so that one can rotate it or shift it forward or back to take care of any changes in balance.

It may not be obvious, but the wood is in fact coated with varnish.

The rocker box is held onto the azimuth bearing with sturdy wingnuts so that it can be more easily transported. The two circular sections of the azimuth bearing were table tops purchased at Lowe’s (IIRC).

 

Puzzlement when Trying to Figure a Convex Surface Through the Back

14 Saturday Nov 2015

Posted by in astronomy, flat, optical flat, Telescope Making

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Have you ever tried to make a convex optical surface?

If so, you know that it’s much more challenging than a concave one, since the rays of light do not come to a focus at all.

Some of us* at the Amateur Telescope Making workshop here in Washington DC have made several attempts at doing this, pretty much without success. I would like to show you some weird images that we got when we tried to ‘figure’ the convex surface by performing a Ronchi test from the back side, looking through what was supposed to be a flat.

What we find is that even though the glass itself is very clear and free of visible strain when seen by the naked eye or when using crossed polarized filters, it looks like we are looking through an extremely murky and totally un-annealed piece of ancient Venetian glass, causing all sorts of weird striations in what should otherwise be nice, smooth Ronchi lines.

These pictures go in order from outside the radius of curvature to inside the ROC.

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You might well think that the glass itself has lots of strain left in it, causing the very weird patterns that you see here. I can prove that this is not the case by showing you a short video that we made with crossed polarizing filters of the 5-inch diameter blank itself and two pieces of plastic (the protective covers for one of the filters). Judge for yourself.

This is not the first time that this strange phenomenon has occurred.

Any suggestions from those with actual experience would be extremely welcome.

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* Me, Nagesh K, and Oscar O.

Directions to Hopewell Observatory

25 Tuesday Aug 2015

Posted by in astronomy

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DIRECTIONS TO HOPEWELL OBSERVATORY:

Short version, if you have Waze, Google Maps, or some other GPS navigation system: make your goal to be 3804 Bull Run Mountain Road in The Plains, Virginia. That will get you to the gate mentioned in step 6, below. 

Long version:

(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, and a Walmart-anchored shopping center on the NW corner. 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 is beyond Mountain Rd.). 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 stone gate on the left, opposite the entrance. 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 can park here (but PLEASE don’t block the driveway around the towers!) and proceed the remaining few hundred feet to the observatory on foot, or…

(8) Take the grassy track around to the right of the station, and continue south, through (or around) a white metal bar gate. The few places among the trees near our operations building, the small house-like structure in the woods, are reserved for handicapped people, Observatory members, and those bringing telescopes. Please watch out for pedestrians, especially children! The observatory itself is in the clearing a short distance ahead.

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 if the traffic is light. (Otherwise, it can take much longer!) A map to the site follows. If you get lost, you can text me (Guy) at 202 dash 262 dash 4274.

map to hopewell oct 2019

Great Long Weekend of Observing Near Spruce Knob, WVa at 11th Almost Heaven Star Party

18 Tuesday Aug 2015

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I put all of my tickets (over 30!) into the raffle for a 100-degree-apparent-field-of-view eyepiece at AHSP but didn’t win it. I probably should have put a few tickets in some other raffles. They had a whole lot of different stuff being raffled off. The eyepiece I wanted was donated by Hands On Optics. At AHSP they give you ten tickets as part of your registration, and then you can buy more of them. Elizabeth Warner and her husband left the morning of the raffle (Sunday) and gave me theirs, which was very nice of them.

At Stellafane, they used to have just ONE humongous item in the raffle, like a full set of really expensive eyepieces from Al Nagler. So it used to be in fact all-or-nothing. Don’t know if it was like that this year?
I discovered that the things I really needed were:
* an inexpensive laser collimator so I can get collimated in a minute or two all by myself, accurately, instead of fumbling around for an hour and needing an assistant… (now on order)
* an inexpensive electronic timer controller for my Canon TSi so it doesn’t need any cables to a computer (also now on order)
* a way to get rid of dew. The last night was fantastic except for the dew, which even defeated the chemical hand warmer packets that I wrapped around my finder and Telrad. I bet it got to the secondary as well. I will study up on the physics of heat production by resistors or heating wire wrapped around those and devise something.
BTW, I had to use a borrowed hack saw and masking tape to cut each of my truss tubes by exactly an inch on the second day so that I could come to a focus with all my eyepieces. I used some local rocks to deburr the cuts.
They had some great presentations on astrophotography, including how to do it simply and effectively. I was much encouraged.

Charon (NOT Pluto) with a huge crater that may have bashed it out of round

14 Tuesday Jul 2015

Posted by in astronomy, astrophysics

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Here’s a very recent (7-12-2015) picture of Pluto Charon that shows a bright circular feature near 1 o’clock with a long white streak heading down and to the right for a very long way – possibly even as much as half the diameter of the entire planet. If you look near the top of the image, you can see that it’s partly in shadow, and the low angle of the light from the Sun exaggerates vertical elevation changes much as they do here on earth just after dawn and before sunset. So we can see that the upper portion of the surface of Charon Pluto appears to be very irregular and not precisely spherical.

pluto w large crater

Which should be no huge surprise, given how small Charon Pluto really is (only 1200 2300 km across, or about 750 1400 miles, which is much smaller than our own Moon (Luna or Selene), in fact less than the distance from my town (Washington DC) to Miami. In this image the ‘top’ of the planet looks almost like a somewhat-rounded 7-sided heptagon rather than a sphere.

It appears to me that the object (asteroid or comet or whatever) which smacked Charon Pluto and formed that large crater came not along a radius, but at some other angle — I’d have to do some experiments to see whether the object came, so to speak, from somewhere off to our right and from our back as we view the image, or from the exact opposite direction, from above and in front of us, perhaps a bit to our left. I just don’t know if the debris from such an impact would fly back in the direction from which the impactor came, or whether it would continue going forward in the direction of the impactor. It’s fun to do experiments with sandboxes and lofting various projectiles, but you never know how well your set up will match reality. Sand and water at room temperature probably don’t act the same way as the surface of Pluto (various types of frozen ices, at its insanely cold temperatures), being hit by something that vaporizes and melts solid rocks by the tremendous force of impact!

I got the image from here. And thought this was a picture of Pluto. But it’s not.