Saturday, 15 May 2010

Odd one out

One point for spotting the odd one out.

Two points for naming the array.

Ten points for explaining why the dishes were unusually close to each other on 10th May 2010 HST.

100 points for explaining the reason for doing this.


Keera Ann Fox said...

The odd one out is actually the drill sergeant barking orders to the others, and they are standing close together because they were ordered to.

The name of the array is Harry McCorckle's Motley Crew of Dishware.

And the bottom photo is an illustration of the difference between northernmost declination (the girl in red) and out-of-bounds declination (the girl on the roof).

All of this took place on May 10 in order to wave bye-bye to Gordon Brown as he finally throws in the towel.

Keera Ann Fox said...

OK, so that's not a girl on the roof. Stoopid hoodie. But I stand by everything else I said. More or less.

Anonymous said...

I'll take the geeky starter for 10: for an interferometer baseline length D, the angular resolution goes as 1/D but the sensitivity goes as 1/(D squared). Thus, they sometimes set up in a very compact configuration to go after the very faint sources that they can't get at higher resolutions. If I recall correctly, in the ultra-compact configuration of this particular array, the TCS has to be clever enough to slew the dishes in the correct sequence to avoid them actually clipping each other as they rotate. I'm not sure if this is implemented in software or wetware. :-)

Maybe that's the observer stood on the car roof to watch them slew and radio the telescope operator if they're going to collide. :-)

Tom said...

Keera - all the points go to you for making me laugh!

Anon - I can't award you the 100 points but you win a 100 point bonus for pretty much getting it spot on with the reason for the array being so small. This is stuff I remember learning as an undergraduate - UV coverage and all that, but yes, you bring them close together to increase sensitivity if you don't need the resolution.

I don't know anything about the Smithsonian Submillimeter Array TCS. I didn't think the dishes got close enough to interfere with each other. If they can that's interesting. I'll ask around.

Thank you!


Keera Ann Fox said...

Happy to have made you laugh! :-D

One question (well, lots, including will there be a translation of Anon's answer, but I'll start with one): Why did this happen on May 10?

Beep said...

I just did not understand this post, but the comments have helped. I'm glad there are witty people like Keera in the world to bring light and laughter to others. Now I just have to grow a brain and study what Aaron said.

Tom said...

Keera - the only reason I mentioned the date was because I hoped someone from the SMA might tell me what they were looking at - if anything. They'd need a date and time for that. Nothing more significant than that!

Beep - I'll try and keep this as short and understandable as possible.

The bigger the telescope (larger diameter) the better the resolution. That means it can see more small detail as well as collecting more light so can see fainter things.

There's a way to cheat and that's by using two smaller telescopes, placing them some distance apart and then combining their signals. Place them 200 yards apart you end up with the same resolution a telescope with a 200 yard mirror/lense/dish has. You lose a lot of sensitivity though as you only have the light collecting power of the two small telescopes and not a huge 200 yard diameter mirror.

The physics is complicated but well understood and not something I could go into in a comment!

If there's something very large you want to look at (like the Galactic Centre for instance) then you can often drop the resolution requirement and instead try to improve sensitivity. Now it gets really complicated because even though you still only have two small telescopes you use the Earth's rotation to improve the coverage of the part of the sky you're looking at (look up UV-plane coverage if you really want!).

My guess is the SMA was setting up to look at the Galactic plane, which is really quite big!


Beep said...

Some people do call me "Beep." I guess it's catching on.

Thank you for these comments. I learned a lot.