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There are several allocations for radio astronomy across different bands that correspond with spectral lines for various elements and chemicals.

See the list of allocations here: http://www.naic.edu/~rfiuser/s...

I thought that the telescope at Arecibo, Puerto Rico was the US's biggest telescope. Did Puerto Rico vote for independence while we weren't looking?

... this really does sound like a case of paranoid schizophrenia. The business with the photo of the lighting transformer pretty much proves it. :(

Frankly, he'd have been better off being clubbed by mobsters and stuffed into the trunk of a car. I hope they find him before he does serious harm to himself or anyone else.

Well it might not be. I recently came home from a hacker conference where we discussed the relative merits of using puts("Hello Word!!!\n"); against printf ("Hello World!!!\n"); and how both are open to attacks from malware juggernauts. Upon returning home I noticed THIS installed on my roof. It's damn lucky I have a keen eye for subtle details or I could have been another victim of malware overlords bugging my house. These people have power beyond your understanding.

A biggie was the radar return of the distance to Venus, which instantly corrected our measurements of the Earth-Sun distance, which then instantly changed the size of the Universe.

You could just look at http://www.naic.edu/~nolan/radar/AUSAC.html. Some big stuff there. Rotation rates of Mercury (which was in error) and Venus, for instance. Radar maps of the topography of Venus. All cheaply done. All this for twenty minutes in Iraq.

That's not true. The community of radio astronomers recognize Arecibo as a "jewel" of a telescope. It is being used to conduct three very important Galactic surveys and has very broad international support. NSF decided to cut funding to a minimum as they saw their overall budget being reduced.

Also, I'm not convinced that a public outcry on /. would "lead to more money coming into their field". At any rate, the strict money saving no longer seems to be necessary as the NSF budget has been increased. For more info, and to read what a selection of radio astronomers think of Arecibo : http://www.naic.edu/aorss/cornell_daily_sun.html

# The first planets outside the solar system were discovered around Pulsar B1257+12, a rapidly rotating pulsar with three Earth-like planets in orbit. ( early 1990s )

# One of its first accomplishments: Establishing the rotating rate of Mercury, which turned out to be 59 days rather than the previously estimated 88 days ( 1965 ).

# Detailed maps of the distribution of galaxies in the universe ( late 1980s ).

# The first pulsar in a binary system was discovered ( 1974 ), leading to important confirmation of Einstein's theory of general relativity and a Nobel Prize for astronomers Russell Hulse and Joseph Taylor ( 1993 ).

# Investigations of ice craters at the polar regions of the planet Mercury with the radar system ( 1990s ) and similar investigation of the lunar poles for evidence of ice ( 1997 ).

# Provided much of our pre-Magellan mission knowledge of the surface of Venus via 1.5 km resolution imagery of the surface through the planet's cloud cover using the radar system.

# The observatory has made major contributions to our understanding of the chemistry and dynamics of the Earth's upper atmosphere and ionosphere.

# Discovery of two classes of pulsars: millisecond pulsars, which rotate several hundred times per second, and slower-rotating pulsars, which rotate about once per second. The slow-rotating pulsars speed through space, while millisecond pulsars move slowly through space.

Closing down Arecibo would be like closing down the Fermi Lab particle accelerator to Particle Physics. Its A MASSIVE asset to the Radio Astronomy field, and this short sidedness to get a few measly million (when compared to the countless millions allocated to other projects) is Absurd

It's not the world's largest telescope. There are plenty of telescopes that are larger than this. The James Clerk Maxwell Telescope is about 5 meters in diameter larger. Arecibo is about 295 meters larger.

And then you've got the array telescopes like VLA and VLBA, if you wanted to get pedantic about effective telescope size.

http://www.naic.edu/public/about/photos/hires/aovi ews.html

While you are right that most radio telescopes do not transmit, there are some that most certainly do. The world's largest radio telescope, Arecibo, houses 2 very powerful radar transmitters -- one of which is capable of a megawatt of transmission power! It uses these (either by itself or with other huge telescopes like the GBT receiving) for making radar measurements of planets, moons, asteroids, comets etc.

You can read more about it here:
http://www.naic.edu/~pradar/pradar.htm

And yes, IAARA.

The world's largest single-piece telescope is the Arecibo one. The world largest composite telescope is the VLBI project which is larger than the earth itself (I work very near one of the sites). The world's largest composite low-frequency radio telescope array will be ready in 3 years in (mostly) the Netherlands.

See also www.jive.nl (the dutch VLBI section), www.lofar.nl (low-frequency radio telescope array) and http://www.naic.edu/ (Arecibo).

At 305 meters (1000 feet) in diameter, the radio telescope at Aricebo is still the world's largest (* with a single main surface).

(I wonder what the largest antenna array amounts to, area-wise?)

I also wonder if Aricebo couldn't be fitted out for optical imagery somehow. I expect that having a light-reflective surface could cause problems during certain times of the day (like perhaps melting part of the overhead structure when the sun hits it right). But perhaps they could engineer tiles that flip over, providing a light-reflective surface during the night, and a not-so-shiny surface for daytime use?

Aricebo info: http://www.naic.edu/public/the_telescope.htm

(Also seems like it would make a great sporting arena; perhaps in the post-apocalyptic era...)

There are multiple sites around the world like this. HAARP is based in Alaska. The other sites are in Norway, Russia, and, once it is reconstructed, there will be one at Arecibo. (The other one was on the other side of Puetro Rico but was destroyed by a hurricane in the mid '90s). UCLA also has a site near Fairbanks. I personally have been to both HIPAS and HAARP.

A dish is a telescope. Ever see a picture of Aricebo?

Check it! Just a big version of what you got on your house.

Mostly right except for

train the receiver in that direction again when they have time

The receiver is actually fixed and just gathers what passes in front of it as the earth turns (you insensitive clod)

I'm heavily involved in a 5-6 year project to use the Arecibo telescope to search for new pulsars. The project uses a new 7-beam receiver system, each of which takes data from up to 1024 nearby frequency channels. The data is 16-bit sampled over 15000 times per second from each frequency channel. We need the time and frequency resolution to find exotic millisecond pulsars.

Over the couse of the survey we expect to take about 1 PB of data. We're still trying to figure out exactly how we will process and store it all.

For more info, you can poke around here.

Go see the radio telescope at Arecibo, Puerto Rico.

To clarify:

Antenna beam width is inversely proportional to apeture size. Building several small antennas and hooking them together as an array (like the VLA and VLBA do) increases the apparent apeture size (although it has a very bad fill factor!), reducing the beamwidth of the composite antenna.

Furthermore, increasing the apeture size also increases sensitivity by increasing the total received power. If an antenna with an effective apeture of one square meter receives a signal of -100 dBm, using an antenna with an effective apeture of two square meters would double (+3 dB) the received power (to -97 dBm), all else being equal. Likewise a four-square-meter apeture would provide 6dB of gain relative to the 1 square-meter antenna.

Finally, it's easier and less expensive to build and use multiple smaller antennas than one big honkin' antenna. The dishes of the VLA are steerable; they can see more of the sky. Arecibo is not nearly as flexible.

USAF Museum in Dayton Ohio.

Arecibo observatory in Puerto Rico.

I just got back from Puerto Rico. One of my "must see"'s was the Arecibo Observatory

I hate to nitpick, but Arecibo is not a volcanic caldera, in spite of what the tabloid press might report. In fact, it is a large limestone sinkhole in the karst terrain of Puerto Rico: check out this link for more info. (I promise its not a goatse.cx link.)

One of the cuter stories is that when they were searching for the perfect site on Puerto Rico, they took a dime and slid it around on a contour map of the island - and where it fit nicely inside the contours, there the dish went... Its amazing to look at, and I recommend a visit if you vacation in PR.

OTOH, your other point is completely correct - Arecibo only sees a limited range of the sky, and cannot view anything south of a certain declination (14? I forget). Not being able to see the Gal;actic center is particularly galling! That's why the new GBT (100m, unlike 305m at Arecibo, but the GBT is fully steerable) is so exciting.

The submission has one detail wrong - the neutron star is orbiting the other star in only 11 minutes. The situation is the same as the Earth going around the sun (the definition of a year) in only 11 minutes.

Neutron stars actually spin much faster than that. The neutron star B1937+21, discovered in 1982 rotates in 1.6 milliseconds (625 full spins per second). Rapidly spinning neutron stars are also called pulsars, because of the radio pulses they emit. One of the first pulsars discovered was the neutron star in the middle of the Crab Nebula, which rotates 33 times per second.

Obligatory links:
Jodrell Bank
Parkes
Arecibo

1) The sticks on the picture look like VHF omnidirectional antennae. Also, you only need large antennae when the satellite is far away, like geostationary orbit. On the Low Earth Orbit (~800km), all that is needed is a very small transmitter, comparable to a mobile phone in terms of power; well, at least for low bandwidth connections. There are quite a few tiny satellites like that in orbit right now. They are being used radio hams , scientific experiments, etc...

Another part of the answer is that dishes can only reasonably be used at microwave frequencies (above 1GHz), otherwise they would be too large

2) With omnidirectional antennae, there is no need for attitude control, see above.

It looks like the NAIC which runs the Arecibo observatory received approximately 10 million dollars in grants this fiscal year. These grants helped fund not only this research, but research by more than 150 scientists who use the observatory each year. So if you assume that each scientist uses the same portion of resources, as a first approximation, this project cost about $67,000. Now compare that to NASA satellite missions which typically cost several hundred million dollars, and I think that this research has been very cost effective.

I would also keep in mind that much of that money goes to the staff which keeps the observatory, and other facilities operational. I count about 147 people on the directory, though I admit some are listed twice, this includes a scientific staff of about 24 research scientists, but most of the staff is made up of mechanics, electical workers, cooks, janitors, security, and staff for the visitor's center. So though it's true that many people are starving in the world, this observatory is giving people jobs so they can put food on the table.

So maybe it's better to view astronomical observatories in this way: We learn about the composition, physical processes, and origins of the Universe around us, and at the same time provide jobs for a lot of people.

Much of the current data was picked up during the Arecibo upgrade, where the telescope was essentially out of commission and staring up at the sky.Since the earth rotates, the sky over the telescope changes, so just grabbing all the signal ("drift scans") still provided useful data.

Arecibo is huge - 305m in diameter, almost exactly a kilometer around (makes a good jogging track!): that's too large to steer. So it was designed as a spherical dish section, not parabolic like a sattelite dish: a parabola sees perfectly in one pointing direction, but a spherical dish can see fuzzily in any direction.

During the upgrade, the old line feed has been augmented by a Gregorian reflector, which allows perfect focus from a spherical dish. But the line feed still exists, as you can see from the pictures. So now, while the Gregorian takes astronomy data, the old line feed can continue looking off in some other (random) part of the sky, and take useful search data! And if the piggyback project is still running, the SETI people also get first dibs on all our data to search for their signals.

With additional tests for pulsations, one wonders how many of our pulsars the SETI people will rediscover. Useful check on their processing quality, I'm sure...

Arecibo's neat - consider visiting if you ever get a chance. Takes your breath away to realize the size of it all!

Much of the current data was picked up during the Arecibo upgrade, where the telescope was essentially out of commission and staring up at the sky.Since the earth rotates, the sky over the telescope changes, so just grabbing all the signal ("drift scans") still provided useful data.

Arecibo is huge - 305m in diameter, almost exactly a kilometer around (makes a good jogging track!): that's too large to steer. So it was designed as a spherical dish section, not parabolic like a sattelite dish: a parabola sees perfectly in one pointing direction, but a spherical dish can see fuzzily in any direction.

During the upgrade, the old line feed has been augmented by a Gregorian reflector, which allows perfect focus from a spherical dish. But the line feed still exists, as you can see from the pictures. So now, while the Gregorian takes astronomy data, the old line feed can continue looking off in some other (random) part of the sky, and take useful search data! And if the piggyback project is still running, the SETI people also get first dibs on all our data to search for their signals.

With additional tests for pulsations, one wonders how many of our pulsars the SETI people will rediscover. Useful check on their processing quality, I'm sure...

Arecibo's neat - consider visiting if you ever get a chance. Takes your breath away to realize the size of it all!