Photographing GTC’s tertiary mirror


Yesterday the maintenance team took the tertiary mirror out of the huge GranTeCan telescope, and I was invited to take photos.
The light path on a KECK telescope
The light path on a KECK telescope

(Starlight hits the huge primary mirror first, then bounces up to the smaller secondary mirror at the top of the telescope, then back down into a tube called the baffle to the flat tertiary at 45º, which sends it to the scientific instruments at the sides. The tertiary is elliptical, and measures about 100 x 50 cm.  I don’t know what it cost, but I’d take a wild guess at 300,000€.)

It meant a special trip up the mountain, but I got to climb all over the huge telescope almost like it was a jungle gym – on the walkway around the primary, taking photos through the broken Cassegrain focii, while the engineers fitted a special frame onto the mirror ready to lift it out with the crane (they’d already taken the top half of the baffle off.) Then I went up to the first balcony and Nasmyth again while the mirror lifted through the air. Then I took close up photos on the dome floor while they put it onto a different frame for moving it along the floor, and removed the crane frame. And I followed it through to the realuminizing area.
We stopped for lunch, then I took a few pictures of the mirror being cleaned and put into the special vacuum tank where the thin layer aluminium will be replaced.

Running up and down stairs was more exercise than you might think, since the Nasmyth platforms are two stories up, and the Roque is high enough that there’s only 75% of the usual amount of oxygen. By the time I left, I was tired.

I went home via the water mine (to collect spring water), the cash point and the supermarket, getting more and more tired. I was 2/3 of the way around the supermarket when I realised that I had someone else’s handbag in my trolley. It took about 30 seconds to realise that I’d left my own trolley and walked off with someone else’s. They were very nice about it, but I was still embarrassed. And when I got to the till, I found I didn’t have my handbag. Luckily I hadn’t abandoned it in the supermarket –  it was still in the car.

After that, I pretty much gave up on the rest of the day and sat down with a large G&T.

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