The View Up Here

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A Day In The Life

Posted by Tom Benedict on 28/08/2012

People sometimes ask me, “What kind of work do you actually do at a telescope? Isn’t it just looking up at the stars?”

The answer is “Yes and no.” We do have people here who look at the stars. Or rather, we have observers who operate our facility to take data for astronomers around the world. But most of our staff is tasked with keeping the place running. That’s where my job fits in. When people ask what our job description is, I like to say that it reads: “To do anything and everything necessary to collect science-quality photons every single night of the year.” Mostly, that’s keeping things in good shape and making sure everything runs smoothly at night. But sometimes it means taking on project work.

So what’s a typical work day like? Well… There isn’t one. Every day is different. Some projects we get are big, and span several years. Others are small projects and may only span a few days or a few hours. Here’s a recent example of a small project that is only taking a couple of days of actual work:

Recently, the need came up to measure the width of the slit on our dome. The “slit” is the opening in the dome that the telescope looks out through.

CFHT and the Mauna Kea Atmospheric Monitor

This is a photograph of our facility showing the shutter in the closed position. (Unfortunately I still haven’t made any photos of our telescope with the slit open. Note to self…) The big white panels are the shutter, which covers the slit through which the telescope looks. At night the shutter rolls back like a giant garage door.

To measure the open part of the slit, we stuck two Leica Disto laser measuring units back-to-back and attached them to the shutter. As the shutter opened, we triggered the units to take measurements off to either side. Add the two measurements up, and voila! You have the width of the shutter at that point along the track.

Aaaah! But the shutter has a back side, too, that it slides down as the shutter opens:


Measuring this was a little trickier…

It started about a week ago. One of my co-workers and I climbed to the top of the building to test-fit the Leica Disto unit. Unfortuantely we couldn’t put it smack dab in the middle of the shutter the way we did on the lower edge. But we were able to position it off to one side.

Dual Disto Rail - Installed

Because each Disto will measure over a hundred feet with millimeter accuracy, this still works. We should still be able to add up the two numbers and get the width of the slit. Unfortunately the chunk of metal I mounted the Disto unit on wasn’t entirely flat. One laser beam intersects the arch girder on its thin edge. But the other laser beam was so skewed, it actually hit the enclosure on the far end. I needed to get several degrees of tilt to make everything line up correctly.

So that’s what I did today. I tore the thing down and muddled through a way to get more adjustments out of the mount. Here’s what I came up with:

Dual Disto Rail - Overview

This is an overview of the Disto rail mount. The two Leica Distos are mounted back-to-back on a rail. The rail keeps them pointing in opposite directions, and offers some protection from knocks, dings, and other things that go bump in the night. The rail is in turn mounted at 90 degrees to a second rail along which the first rail can slide. This offers some lateral adjustment in case the Distos need to be offset from the base. The second rail is then mounted in the roll/pitch/yaw platform.

Dual Disto Rail - Roll Pitch Yaw

(I dare you to find an uglier collection of nuts and bolts!) It’s a mish-mash of metric (M6 set screws) and SAE (#10-24, #12-32, and 1/4″-20 for the roll and yaw adjustments). This is one stark reality about working at a place like this: Unless you have time to plan a thing, it is, by default, a scrap box project. I started designing in SAE, intending to use 1/4″-20 for everything. Then I found out our 1/4″-20 screw selection had been ravaged. So I grabbed some #12-32 screws. Lo and behold, I couldn’t get both lengths I was after. Rather than chop screws, I grabbed the next size down and found some the right length. Then I found out we didn’t even have SAE set screws. So I had to use metric.


So it’s a frankenbeast. But it works! I adjusted the two M6 set screws to take out residual roll (I got it to better than 0.002″ across that whole bar!) Now the 1/4″-20 hex head bolt at the back lets you tip the laser beams by several degrees.

I’m slated to go up tomorrow to test-fit this thing again and see if I can bullseye the two laser spots on the edges of the arch girders. If I can, we’re in business for taking these measurements. And if not? I’ve got a machine shop and a scrap box waiting for me on ground floor.

– Tom

P.S. In case you’re wondering how the thing actually attaches to the shutter, that base is essentially a giant fridge magnet. On the bottom are three neodymium magnets I stripped out of some dead hard drives. See? Scrap box project!

P.P.S. So what’s the view like when you’re standing on top of a telescope dome? In a word: Outstanding.

A Day In The Life

4 Responses to “A Day In The Life”

  1. This was really cool, thanks, Tom!

    • Tom Benedict said

      Glad you liked it!

      I’m working on another post for a longer project I’ve been working on. Hope to have that one in the next couple of months. (There’s still a good bit of work still to do.)

  2. Yaniv said


    • Tom Benedict said

      Heh! I’m not sure you’d be envious of the conditions today. 25kts, sub-zero temperatures. I need to go back up to test the new mount, but I really REALLY don’t want to do it in those conditions.

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