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Posts Made By: Joseph Babendreier

April 15, 2012 06:05 AM Forum: Comets

2012 DA14

Posted By Joseph Babendreier


I copied this from the NASA site tracking near earth objects:

Discovered by the LaSagra observatory in southern Spain, the small asteroid 2012 DA14 will pass within about 3.5 Earth radii of the Earth's surface on February 15, 2013. Although its size is not well determined, this near-Earth asteroid is thought to be about 45 meters in diameter. Asteroid 2012 DA14 will pass inside the geosynchronous satellite ring, located about 35,800 km above the equator. Its orbit about the sun can bring it no closer to the Earth's surface than 3.2 Earth radii on February 15, 2013. On this date, the asteroid will travel rapidly from the southern evening sky into the northern morning sky with its closest Earth approach occurring about 19:26 UTC when it will achieve a magnitude of less than seven, which is somewhat fainter than naked eye visibility. About 4 minutes after its Earth close approach, there is a good chance it will pass into the Earth's shadow for about 18 minutes or so before reappearing from the eclipse. When traveling rapidly into the northern morning sky, 2012 DA14 will quickly fade in brightness.

May 6, 2012 12:53 PM Forum: Telescope Making

grinding a mirror // my first attempt

Posted By Joseph Babendreier

Thanks to the kindness of one of the Astromart old-timers--and his unflagging encouragement--I'm jumping into the mirror grinding adventure.

If this works, I'll be truly amazed.

I guess for some of you, it's the sort of thing you do with your eyes closed and your hands tied behind your back. But for the first-timer, it looks like a daunting task.

I got some books (four of them at this point) so I've got more information/advice than I can cope with.

I'll let you know how it goes.

Clears,
Joe

May 21, 2012 05:56 AM Forum: My group wants a donation or deal for our cause

anybody got extra #80 grit for some rough grinding

Posted By Joseph Babendreier

One of the Astromart members sent me a DIY "CARE package" to grind a 12 blank. It included everything, as far as I can tell, except #80 grit for the rough grinding. (Not that I have any experience grinding... but I am about to get some.)

Before buying some grit new from some dealer, I was wondering if any of you folk might have a bag of the stuff just lying around, which you're never gonna use anyway.

Clears,
Joe

PS As you can see from my profile, I'm a chaplain in a boys school. I've introduced lots of the boys to stargazing.

May 28, 2012 04:29 AM Forum: Telescope Making

1.25" Ronchi tester -- the EASY-tester

Posted By Joseph Babendreier

A friend of mine told me about this tester for primary mirrors:

http://schmidling.com/ez-testr.htm

Looks interesting.

Anybody ever use one of these?

Clears,
Joe

June 6, 2012 05:45 AM Forum: After Dark

If you missed the Venus transit…

Posted By Joseph Babendreier

Living in Kenya, I was working with a narrow window to begin with, using a sun funnel.

I got a brief glimpse, but it was mostly cloudy.

In case something similar happened to you, remember the story of Guillaume de Gentil, as recounted in Coming of Age in the Milky Way. He left France to go to India to record the transit of Venus due to occur in 1761. Despite leaving a year ahead of time, he was still at sea on the day of the transit. He decided to stay on, since Venus was due to pass across the face of the sun 1769. When the day arrived, he was fully prepared. He had everything ready to record the event as accurately as scientific instruments would allow in those days. Just as the transit was about to begin, in an otherwise clear sky, a lone cloud passed in front of the sun and somehow managed to remain there for the entire three hours of the transit. Things didn’t work out any better when he returned home to France. In his absence, his relatives had convinced the courts to declare him dead and taken possession of all his goods.

Some people have all the luck.

Clears,
Joe

June 25, 2012 06:13 AM Forum: Telescope Making

Querry on grinding a 12.5" mirror

Posted By Joseph Babendreier

Update on progress:

I have almost reached the sagitta of 3mm using #100 grit. There is no noticeable astigmatism, at least not by rough measure. I say this because I can slide a series of drill bits in various directions under a straight edge and each size pushes out the same distance no matter which direction I choose. So, I feel that things are going pretty well.

BTW, I made a new tool using small pieces of 4mm glass. This works quite well. The grinding proceeds very smoothly.

The one thing that I'm not sure of this: there's still a 5mm ring all around the edge where no grinding (or at least very little) has taken place and so the edge is still flat. Otherwise, there seems to be a nice smooth curve from center out towards the edge.

Is this the normal thing?

Clears,
Joe

July 4, 2012 03:24 PM Forum: Eyepieces

Zhummell 3mm EP

Posted By Joseph Babendreier

I got a 3mm EP (basically a Xmas gift). It's a Zhummell. Seems to be pretty good quality from the look of the EP externally.

I've tried it a few times mostly on planets, with no success.

I guess it's just too much power for my 10" Dob, with a FL = 1118mm (making the mag close to 400X).

I read somewhere that you could go up to 50 times the diameter of the mirror.

Last night I tried it on the full moon. All I could see was a very fuzzy view (e.g., a crater) and then the edge of the moon quickly floating out of the FOV. I tried getting the focus as perfect as possible, but nothing seemed to improve the view.

Any comments?

Clears,
Joe

July 25, 2012 06:18 AM Forum: Telescope Making

foucault tester

Posted By Joseph Babendreier

I built a Foucault tester. Photos attached.

Is the telescope viewer supposed to be focused on the mirror that is being tested? Or on infinity?

From the picture, is there any way if you can tell me whether the slit for the light source is narrow enough?

I'm asking because I don't see any patterns like the ones in the book when testing a parabolic mirror. So, I must be doing something wrong.

Clears,
Joe

PS For the record: I can see the mirror darken when moving the knife edge into the field of view.

July 28, 2012 03:40 AM Forum: Meteorites & Meteors

odd crater on Mars just discovered

Posted By Joseph Babendreier

There's an image posted lately on the NASA APOD website you may want to look at. It shows a crater on Mars discovered by the MRO:

http://apod.nasa.gov/apod/ap120718.html

This crater is very odd. No debris around the crater and there's a hole at the bottom of the crater.

Clears,
Joe

August 6, 2012 02:47 PM Forum: Telescope Making

question on adding turpentine to pitch

Posted By Joseph Babendreier

I getting ready to make a pitch lap for a 12.5 inch mirror.

I have some pitch from a batch made for ATM use several years ago. The label says Gugulz (made in Switzerland) and looks like pitch alright. It's #73.

I read somewhere that one should add a bit of turpentine before heating.

Can I use "white spirit" paint thinner? (I have industrial quantities of that stuff lying around.)

Can I use mineral turpentine? (Dirt cheap and available.)

In Kenya (where I live) nobody sells wood turpentine.

Clears,
Joe