As you might have gathered, the observations haven't been going brilliantly. No fault of ours, fortunately, except in the sense that Tim is trying to get the telescope to do things it's never done before and so it's uncharted waters, but it's still been a bit much for him. With sincere and fully merited respect to the crew of people who have managed to keep this beautiful and intricate piece of machinery working for several decades, it seems that a fair bit of kludging goes on here, and while that's an important and useful skill, it can make unpicking subsequent errors quite tricky. There's been a lot of work involved, is what I'm saying.
Though not for me, clearly: I'm still just doing my overnights, pretty well oblivious to everything else. This shift is my last, sadly, and I'll be on a plane back to Sydney around 5:00 p.m. tomorrow. I would love to come back someday, though it's extremely unlikely that I'll have the opportunity, so I'm trying to soak up as much of it as I can. Tonight's excitement was that I got to drive the dish manually, which is the thing I was most afraid of doing, even though the likelihood of my causing a disaster is pretty slim. Everything went fine, though, due in no small part to Tim's presence. We had to take manual control unexpectedly because...
Oh dear. I've painted myself into a corner here. I've been trying to avoid talking too much science, mostly because I'm not confident that I have a good enough grasp of the details to be able to communicate them accurately, let alone clearly. But to tell this story I have to acquaint you with some of the more basic operational stuff, so please bear with me and my dodgy metaphors:
So. In this photo, you can see the Dish and the Tower (the three-story lighthouse-looking building on top of which the Dish sits). The angle of this photo gives you a good idea of how the Dish moves: it can move in a circle around the Tower like a train on a small circular track (this is called movement in azimuth), and it can move up and down in an arc, as if the pointy bit that sticks up were drawing a rainbow across the sky (this is called movement in zenith).
With me so far? Good.
The hitch is that it can't move fully in either azimuth or zenith. In azimuth, it is limited by cables that can wrap around the base of the Dish, so you end up with only about 265˚ of movement in either direction. In zenith, it's limited in two ways: 1) you don't want to crash it into the ground, so you can only start observing at about 30˚ off the ground/horizon; and 2) the Dish can't do a complete arc and will stop at about 1.2˚ off full vertical. This gives you a range of a bit under 60˚ in zenith. (The only time it goes to full vertical is when it's being 'stowed' (stopped and locked in place), and you have to move it there under manual control - the computer doesn't do it.)
If you try to exceed any of the limits in either azimuth or zenith, alarms will go off and the Dish will shut down, and you'll have to move it manually back into an acceptable range. This is what happened tonight: the source we were tracking ended up directly above the Dish for about 10 minutes, and because the Dish can't go to full vertical, we got the alarms and hoo-ha. We waited until the source had moved back into an acceptable range, and then we went upstairs to the Old Control Room (that's the one you'd have seen them using in the movie) and I pressed the required buttons and tweaked the required dials to get it down to 2˚azimuth, at which point the computer could take over again and tracking could resume. It was awesome in the literal sense of the word: I couldn't (and still can't) take in that my hand was moving 1,000 tonnes of metal and cable and genius. I am quietly falling in love with this telescope.
Unfortunately I was unable to have one of the biggest-deal experiences of being here, namely riding and climbing the Dish. While I wasn't sure that I'd climb all the way up (the pointy bit at the top of the photo? Yeah, there.), I was very keen to ride it: what happens is, they tip it all the way down on one side (a bit more than it is in the photo), and you climb up onto a staircase and into a little caged platform thing. You then stay on that platform while the Dish is moved to full vertical for stowing, and once it's stowed you walk across the Dish and climb up to the top, if you want/need to. I wasn't sure if I'd be able to manage the climb - I'm fine with heights as long as I feel secure, but I wasn't sure how I'd go with the open air around me - but I was definitely keen to ride it up.
There was a great opportunity for me to do this first thing on Thursday morning, the first day of observing, because the Dish had to be stowed so that some work could be done to prepare for Tim's daytime observations. Unfortunately, after conversations with some of the Dish staff on Wednesday night, Tim had sussed that there were already problems presenting themselves and he had to make an early-morning phone call on Thursday to try to sort some things out. This made us a couple of minutes late getting down to the Dish, and they had gone ahead without us, and because they only allow you to climb when the telescope's not in operation, for obvious reasons, and there were no other down-times planned for the time I'd be here... yeah. No riding the Dish for me. My fervent hope is that I'll be able to come back at some point and I'll get to try it then, but for now I'll have to be happy just to have run it for three nights. Which isn't all that hard, really.
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