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DaveO
2003-May-25, 11:15 PM
Hello!
Like I said; this is a Dumb Question.
I just finished watching 'Goldeneye' for the 417th time; and something's been bugging me about the Arecibo observatory they use as a set in the film.
I know absolutely nothing about the observatory other than a) it's bloody huge, and b) it's had Famke Jenssen, Isabella Scorupco and Jodie Foster running around it from time to time; so overall it's a pretty spectacular place.
My question concerns that triangular thingamadoohickey hanging over the dish - what I'm assuming is the observatory's reciever proper. The triangular thingamadoohickey hangs over the dish; along with another semicircular whatsit suspended under the triangular thingamadoohickey on a circular track. Clearly; the semicircular whatsit is designed to rotate on the track. This is shown in the film; but I'm not entirely sure that's real or a special effect.
Since the observatory can only see in one direction - a visual cone straight up - and since rotating the reciever wouldn't change that - it'd simply show straight up at a different angle - my question is:
a) What exactly is the rotating semicircular whatsit?
b) Why does the semicircular whatsit rotate? In other words; what advantage does a rotating semicircular whatsit have over an average, gardern-variety stationary semicircular whatsit have? (I thought about compensating for the Earth's rotation; but a simple and cheap computer program ought to be able to deal with that much better than a complex and costly rotating semicircular whatsit.)
c) Unrelated question: that little control room at the apex of the triangular thingamadoohickey must be to hold equipment required for the reciever. Since the dish reflects all recieved energy directly at the reciever; is there any danger to a human operator in that control room?
d) Totally unrelated question: Neat looking site or not; why does some godforsaken place way out in the middle of Puerto Rico get all the real gorgeous babes running around it?
:) :)
Note - any unscientific terminology in this post is entirely intentional. ;)
Thanx!

ToSeek
2003-May-26, 12:27 AM
How about if you read the links below and come back with the questions they don't answer?

About the observatory (http://www.naic.edu/about/ao/telefact.htm)

More technical than the above (http://www2.naic.edu/~astro/guide/node2.html)

From space.com (http://www.space.com/scienceastronomy/astronomy/arecibo_profile_000508.html)

Photos (http://www.bitshift.org/pictures.shtml)

Well, I'll take a shot, anyway:

a, b: The observatory can be aimed to a limited extent by moving the focus. The focus is the "gregorian focus", which is the sort of geodesic-looking thing hanging down from the suspended track.

c: The control room isn't at or near the focus; it's on a hill next to the observatory. In any case, I don't think there'd be enough energy to be dangerous, but I could be wrong.

d: Because astronomy is SEXY!

Comixx
2003-May-26, 02:44 AM
I was watching some Steven Segal movie...the badguy was some super-genius programmer (arent they all) who designed defense satellites (typical)...which he then takes control of, and with other badguys, tries to blackmail the US military into giving him money(ah, originality...or not).

The funniest thing about this movie was the bad-guy was at Arecibo, which is the dish he used to transmit and take over his satellite, and also command his satellite to change orbit over several hundred meters within seconds...amazing dish, to be a radio telescope and a satellite transmitter capable of overpowering scrambled military narrow-beam microwave transmissions.

Hale_Bopp
2003-May-26, 04:45 AM
I believe it was Carl Sagan in Cosmos who made the statement that all of the energy every captured by all of the world's radio telescope is less than that of a single falling snowflake.

From that statement, I would say that even Arecibo's dish focusing all the radio waves it collects would present no danger to a human at the focus.

Rob

Kaptain K
2003-May-26, 09:26 AM
Except when it is being used as an interplanetary radar. I don't think you want to be anywhere near it when it transmits a multi-megawatt pulse at Venus, an asteroid, or other object. :o

DaveO
2003-May-26, 10:36 AM
Lol - OK; thanks for the link ToSeek; I should have done that first; except my browser's a bit squirrely at the moment. (I get one web-page and 20 popups every time I click - pain in the arse; I tell you.)
OK; let's see if I've got this straight - and this time; I'm not going to use semi-amusing terms. :o
OK; the triangular platform is just that: A platform upon which the actual reciever is mounted. The semicircular track holds and moves the focus - the geodesic mounted underneath. The reason it has to do this (And this is where it gets hazy for me; let's see if I've got it straight), is that the dish isn't a parabola; which would send any incoming signal to a central reciever, but circular; which doesn't. So; the track rotates and moves the geodesic to the spot where the particular radio signals are focussed; and collects them. OK; I think that's right. Thanx!
(BTW - I'm aware the little control room at the apex isn't the control room for the dish itself; I just assume it's a maintenance and monitoring spot...or something like that.) Thanx again!

ToSeek
2003-May-26, 02:44 PM
OK; the triangular platform is just that: A platform upon which the actual reciever is mounted. The semicircular track holds and moves the focus - the geodesic mounted underneath. The reason it has to do this (And this is where it gets hazy for me; let's see if I've got it straight), is that the dish isn't a parabola; which would send any incoming signal to a central reciever, but circular; which doesn't. So; the track rotates and moves the geodesic to the spot where the particular radio signals are focussed; and collects them. OK; I think that's right. Thanx!


I think that's part of the truth, but not the whole truth. The rest of it is that it is possible to aim the telescope to a limited extent, not by moving the reflector itself (obviously) but by moving the focus. So you're not limited to targetting just directly overhead.

Argos
2003-May-26, 03:15 PM
Except when it is being used as an interplanetary radar. I don't think you want to be anywhere near it when it transmits a multi-megawatt pulse at Venus, an asteroid, or other object. :o

Like these folks?

http://www.geocities.com/Area51/Dimension/5189/extracom.htm

tracer
2003-May-26, 04:08 PM
Like these folks?

http://www.geocities.com/Area51/Dimension/5189/extracom.htm
Hoo boy. Dig this passage from the 2nd paragraph:

"We assume that the planet Earth is in peril and we need help. We think that the acquaintance of our drama - human degradation, political abuses, nuclear weaponry, environmental threats - by the neighbors and the resultant experience exchange increases our chances of being successful in the solution of some of those problems."

So their main reason for wanting to send messages is to beg the aliens to "save us from ourselves." :roll:

Glom
2003-May-26, 07:31 PM
The one thing I can't figure out is why they need a dish the size of Arecibo to simply contact a satellite.