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Chasing RFI Waves – Part Six

Here is part six of my non-fiction work about the National Radio Astronomy Observatory in Green Bank, West Virginia. You can also read parts one, two, three, four, five and seven.

Tidbits

The NRAO site is around 2,700 acres. It runs along the crest of the adjoining mountains. One big current problem, that will only get bigger in time, are wireless routers folks are starting to use in their homes. Mr. Sizemore has actually gone out and identified every wireless router in the area. At the time of writing there were 45 such routers.

The NRQZ (National Radio Quiet Zone) gives the NRAO the right to file comments to the federal frequency regulation bodies (FCC and NTIA) for permanent, fixed, licensed radio transmitters wishing to be installed in the NRQZ. The NRAO does not have any “power” to regulate radio use. However, the FCC and NTIA “determine”, in most cases, that it is in the public interest to uphold the NRQZ protection requests. However, there is a West Virginia state law that provides protection within a 10 mile radius of a radio telescope from any source, licensed or unlicensed, that causes interference. A wireless router, like a garage door opener, is an unlicensed device and thus falls under the state law.

Still, each case of interference has to be treated individually, and it is in everyone’s interest that it’s resolved it in a friendly way, for the sake of community relations. At the time of writing, Mr. Sizemore was working with the NRAO lawyers and local legislators to see how the problem of wireless routers could be addressed. They’re a real problem when it comes to interference, and they’re unlike past problems, where faulty equipment was to blame, which could be fixed or replaced. Well-functioning routers will emit interference and cause significant problems to NRAO’s daily work.

Of the 45 routers mentioned above, 26 were provided by the local telecommunications company to their customers free of charge, with the contract, so they could be removed by the telecommunications company itself. The rest were privately owned, and NRAO was naturally pursuing a voluntary removal approach with the router owners.

In the office space above the control rooms are the offices of the scientists and staff at NRAO. It’s a long hallway, part of the new construction, cleanly carpeted. The walls are filled with research posters.

Mr. Sizemore and I stopped to talk about one of the posters. Before, folks thought of the galaxy as a fairly uniform soup of fog. With the GBT (Green Bank Telescope), Jay Lockman, one of the senior scientists at NRAO, was able to discern that this fog was more like clouds. To the layperson, this may not seem like a lot, but to astronomy, that’s a big piece of the puzzle. Now they can try to figure out how the clouds work, what they’re made of, how they move, etc. This discovery could not have been made until the GBT was online.

As we continue to walk, one side of the hallway draws particular attention. Framed photos of the various Jansky lecturers are mounted there. Every year one is chosen, and he gives a lecture on a subject of his choosing. A lot of them are Nobel prize winners. Grobe Rieber was one, of course. Frank Drake (the Drake equation) is also one. Arno Penzius and Bob Wilson are also on the wall. They are Nobel Prize winners for their early work on background microwave radiation. They are the two scientists that discovered background radiation.

There’s an interesting story behind their work. In October of 2005, Mr. Sizemore met the technician who did the hands-on work for their experiments. The man and his wife visited NRAO one day, and Mr. Sizemore showed them around. The man acknowledged that he was scared for his life at times, as he worked with them. They had no sense of the practical or common sense, and would often ask him to do very dangerous experiments. Penzius, for example, could not figure out how to unbuckle his seatbelt. The technician had to do that for him. He couldn’t figure out how it worked, and yet he won a Nobel prize for theoretical work in physics!

Mr. Sizemore showed me his old office, the Quiet Zone office. That’s where the administrative work for the NRQZ is done. He used to be responsible for that, but he’s thankfully gotten help in that area in late 2005, when NRAO hired an NRQZ Administrator and let him focus more on chasing down interference. While he was in that office, he conducted more than 10,000 propagation studies. Paulette Woody, the new NRQZ Administrator, started on the 17th of October, 2005.

As we drove on the NRAO campus, Wesley stopped to show me his “hiding place” – his monitoring station, where he does his RFI hunt-work. It’s a big trailer that can be hauled from place to place, but has been made stationary and hooked up to power lines. Here he monitors the gross violations of the Quiet Zone and also looks at the local environment – powerline noise, illegal use of radios, etc. For example, at the time of my visit there, the amateur radio bands were being used improperly by a group of people and the signal was strong enough to overload the 140-foot telescope, so it became a serious problem. Wesley told me that it will likely be taken care of long before I write up about it, and the likely action taken will be that he calls the FCC in, to enforce the rules in place. After 20 years on the job, Wesley has built up a network of contacts he can call upon when he needs help. One of those contacts is the man in charge of the Enforcement Bureau at the FCC, whom Wesley knew when he was still a satellite technician.

Depending on the sorts of studies performed, the data collected by NRAO in a single day can get to be as much as 50 GB (nowadays it’s probably more than that). The data is usually written to LaCie portable drives and either handed out or shipped out to scientists responsible for the studies. The data isn’t archived locally. It’s recorded for the individual astronomers. Once it’s shipped out, it’s someone else’s data and they are responsible for it. If they lose the drive containing the data, they need to re-run the study. NRAO simply doesn’t have the money or the staff to act as a data warehouse for the data. Astronomers, like most scientists, also guard their data quite jealously and consider it proprietary until they decide whether they can publish it.

The sewer system on site is unique. Because NRAO has to worry about interference, they didn’t want any pumps on-site. What happens is that waste fluids from the sewer system flow into a series of sediment ponds that are built on a gentle slope. They are gravity-fed and include absolutely no motors. NRAO actually won an award for this design. As the water flows through the ground from pond to pond and through vegetation, it gets purified and is ready to be discharged into the adjoining streams of water.

The telescopes and their research

Mr. Sizemore had a story to tell about the motors that run the individual plates of the GBT. NRAO ordered a few samples, saw they worked alright, then ordered a whole batch, about 1,500 or so. When they started to do live testing, the motors ran out after a few days. They opened one up to see why and discovered that the carbon brushes were completely burned out. They’d disintegrated. Upon contacting the manufacturer, they found out that he’d switched the type of carbon brush from the harder ones they specified to softer brushes, which were a few cents cheaper per brush. They were basically cheating NRAO. NRAO’s Business Office sent back all the motors and had the brushes replaced. Add to this experience countless similar others over the years and one can see why they’re wary when dealing with contractors and manufacturers.

There are other radio telescopes on the NRAO Campus, all of which are involved in ongoing research. For example, the 45-foot dish is doing a project on solar radio burst spectrometry. They’re looking at the Sun and measuring the bursts of radio noise from it (solar flares and the like).

They also have calibrators, which are rock-solid sources of radio waves. They always emit at the same frequency and strength. Researchers point their equipment at them to see if their equipment is reading correctly and make any needed adjustments.

One of the telescopes on site is used as a teaching instrument. NRAO being involved in both research and educational efforts, brings groups of school-age children on-site to teach them about radio astronomy. The telescope is not a fancy, cryogenically cooled machine, but a simple wire-mesh dish with simple control and monitoring gear that the kids can play with. It’s fully functional though and it does pick up many radio waves. It’s sufficient to teach radio astronomy and galactic coordinate systems and such.

The fastest telescope at NRAO is a 20-meter dish which will go from horizon to horizon in 90 seconds. It’s not being used at the moment. In the past, the most popular program at NRAO was universal time and polar motion.

Time is not a naturally occurring thing. It’s a man-made contrivance. Time is nothing more than your position relative to something else at a given instance. We keep time by the rotation of the earth on its axis, and the rotation around the sun. Einstein said time is all relative depending on your motion and such. In order to keep accurate time, not only do we have to know the rotation of the Earth on its axis and around the Sun, but we have to know the wobble. Because the Earth is a spinning body, just like a spinning top, it tends to wobble.

There’s a plaque next to the telescope, with a plot of the position of the North pole of the Earth over 5 years. You’ll see that it wonders around, it doesn’t stay in one place. In order to have accurate time, we must know what that wobble is. How do you do that? There are quasars. They are quasi-stellar objects. We think they’re the black holes at the centers of galaxies. They’re very far out there, and they’re very strong, so they can act as a point source. Even though the distance to them is enormous and they’re moving relative to us, because of that distance to them, their movement is insignificant compared to the movement of the Earth itself. When we look at those quasars and we see any apparent shift in their position, we can determine what the Earth’s wobble is. That’s a use of radioastronomy that most people can grasp: timekeeping.

Source: NASA, Hubble Telescope

NRAO used to conduct regular time studies. Wesley actually started out at NRAO as an interferometer operator. The program running on the interferometer at that time was the universal time and polar motion. They fed that data into the master clock of the Naval Observatory. If you’ll remember, at the end of 2005, there was some discussion in the news because a leap second would need to be added to clocks. Wesley would take out leap seconds from atomic clocks. It would be done over time, with microsecond increments. NRAO was a major contributor to time-keeping for the US.

We can use those same quasars to monitor tectonic plate movement, geodesic work. This is also documented on a plaque there. There are several major tectonic plates on the Earth’s crust. If you put a radiotelescope on one plate and one on another plate, then look at a quasar, any apparent shift in their position will be due to the movement of the crustal plates. That means we can use radio astronomy for geodesic-type work.

The Howard E. Tatel Telescope was also the first telescope involved in the search for extra-terrestrial intelligence. Dr. Frank Drake, working on Project Osma, used it for his studies. That sort of work isn’t done by NRAO anymore. It’s not part of their primary mission. Now this sort of work is done through private organizations like the SETI (Search for Extra-Terrestrial Intelligence) Institute in California. You, dear readers, can participate in the study if you want, by downloading an application that will let your computer crunch through the data gathered from space in the search for signs of ET intelligence. The processing power of your computer will only be harnessed when your screensaver is active. This is a good example of distributive computing, where the power of many varied computers is put to work on a single task.

The HET Telescope is not being used currently. It’s part of a three-element interferometer. The second element is another 85-foot dish on the NRAO site, and that’s now used to do pulsar studies.

What are pulsar studies? Well, it starts with the sun, which is supposedly a fairly old star. It is hypothesized that in a number of significant years in the future (we’re talking billions), the physical nature, the make-up of the sun will start to change. It will collapse and throw off its outer shell, being left with a big hot center called a white dwarf. Now, if you have a star that is several times larger than the sun, like 6-8 times, when it’s in its death throes and its gravitation collapses, it blows off the outer shell, the nucleus will collapse to a very dense neutron star. A typical neutron star is several miles in diameter.

If we were to compare what’s going to happen to the Sun in Earth-terms, It’s like collapsing our planet to the size of a golf ball. A teaspoon of that sort of matter will weigh hundreds of thousands of tons. It would have an enormous magnetic field, so the only radiation that will escape from that neutron star will be through the poles of the magnetic field. Since the rotational axis and the magnetic poles do not have to align, the star could be spinning on its axis and the magnetic fields could be perpendicular to that axis, so that it will act as a sort of magnetic lighthouse. Every time it will sweeps its magnetic pole in the direction of the Earth, we will get a pulse of energy, hence the word pulsar.

Source: NASA, Hubble Telescope

Why are pulsars interesting? Because the spin of certain pulsars is as accurate as we can time it with an atomic clock. What’s a second? 1/60th of a minute? No! It’s over 9 billion vibrations of a Cesium electron at a certain pressure and temperature. That’s the official definition. The pulsars that NRAO looks at spin at millisecond time intervals. A big research topic now is using the timing of pulsars to prove gravitational waves.

There are certain time standards kept in cities throughout the world, such as Paris, Moscow, DC, but they are susceptible to destruction from natural or terrorist events. With pulsars, we have out of this world time standards that cannot be destroyed. They also serve as perfect navigational beacons, if we will ever do space travel.

The question that’s been asked in the past is, why don’t pulsars slow down? Well, they exist in binary pairs, two of them orbiting each other. Our Sun is an oddity, because it’s alone out there. There can also be trinary star systems, but gravity usually kicks the third star out. You know what they say, three’s a crowd… So, these pulsars are in binary orbit with other stars like red giants, white dwarfs, or other some such thing. They feed off the energy of their companion, and they don’t slow down, they stay in a constant rotation, or at least as constant as we can time it.

There are platforms out in the field at NRAO. They’re actually crossed dipoles. One of the big questions in astronomy is reionization. The dominant theory of the creation of the universe is the Big Bang. When it occurred, that primordial soup was extremely hot, so everything was fragmented into elemental particles, such as quarks, muons, etc. As things cooled down, particles came together and created molecules, then stars, etc. When the stars started to fire up and generate ultraviolet light, they re-fragmented some of the elemental hydrogen left over from the big bang that had not yet coalesced. That hydrogen was re-fragmented to its elemental particles, and sometime later, it re-congealed. NRAO is looking at that reionization process. They’re looking at this cycle of heating and cooling that takes places as the universe expands. Don Backer, one of the astronomers at NRAO, is looking at that extremely red-shifted signal (meaning very big waves) to see if he can determine when the heating/cooling cycles occurred. The signal is somewhere between 125-226 MHz. They’re not sure where that signal is and what frequency they’ll find it at, so they’re hunting background radiation at the moment, trying to discern a “flashlight in a floodlight”. When they do find it, it’ll be interesting.

The powerlines

One of the things you’ll notice at NRAO is that there are no powerlines on-site. All of the power cables are underground. There’s a main cable that feeds the site, which NRAO runs through a generator where the power is conditioned, mostly in its frequency. The cables that run to each building are all buried. It’s easy to understand why. They don’t want any arcing of power lines above ground.

A couple of years back, one of their lines went dead and they started digging around, looking for the cause. It turned out to be a black snake which had crawled across two contact points and shorted itself and the lines. He was still there, unable to move, because he’d been fried!

And that’s the end of part six. You can also read parts one, two, three, four, five and seven.

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Places

The historic Seneca Schoolhouse in Maryland

If you should drive into the Maryland countryside, along River Road, the Potomac River and the C&O Canal, past farms and mansions, you’ll find a lone building made of red sandstone, standing in a meadow. This sign will be next to it.

The building is the one-room Seneca Schoolhouse, the only school in the area during the later part of the 19th century, after the Civil War. The schoolhouse was established by a local farmer and miller by the name of Upton Darby, who generously provided the land, stone and wood for the building. Local families contributed money or skills for its construction.

I love the cozy little building. It’s wonderful architecture. I love the door knob especially, though I doubt it’s the original one, as it says “City of New York” on it…

There’s more information at the schoolhouse museum’s website, including visiting and contact info. When we stopped to see it, the light may have been perfect but nobody was around to show us inside, so all we could do was to walk around.

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Places

The Old Stone House in Georgetown, DC

I’ve been in love with early American stone architecture since college. One of the reasons I chose to go to my alma matter, Middlebury College, was its wonderful stone architecture. I find such buildings to be as natural and organic as possible. Stone, wood and glass are to me the best-suited, most recyclable, most natural and best looking building materials one can use.

The Old Stone House is well known in Georgetown and is visited by many tourists and locals alike. It is the oldest standing building in DC, because it was built in 1765. A cabinetmaker by the name of Christopher Layman built it and lived in it. After his death it passed through the hands of various owners, until it was bought by the National Park Service in 1953 (almost two hundred years after its construction) and restored to what is believed to be its initial condition.

The house itself is fairly simple and fairly small. The interiors are spartan, as is the case with most early American architecture. But the exterior looks great and the gardens are lovely. I heard stories that the gardens were turned into a parking lot in the 20th century, because the house was a used cars lot, and that the NPS did quite a bit of work to get it back to its initial state. Kudos to them.

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Places

Chasing RFI Waves – Part Five

Here is part five of my non-fiction work about the National Radio Astronomy Observatory in Green Bank, West Virginia. You can also read parts one, two, three, four, six and seven.

Senator Robert Byrd

Senator Byrd (1917-2010) was a consummate politician. He was from a very poor state – West Virginia. He served in the Senate for over 50 years. He was the longest-serving senator and the longest-serving member in the history of the United States Congress. While in office, he used his seniority to help his home state. As such, there are a lot things in West Virginia named after him. He was directly responsible for obtaining the funding for the GBT.

The actual shovel used during the groundbreaking ceremony for the GBT by Senator Byrd is encased in a display box in one of the NRAO lobbies. If you happen to see it and notice it’s a bit short and also very shiny, here’s why: Senator Byrd used a normal, brand new shovel at the ceremony; afterwards, NRAO chromed it and also had the handle shortened, so it could fit in the display case.

I’ll let Mr. Sizemore tell what happened at the ceremony, as it portrays Senator Byrd quite nicely:

“Senator Byrd went up to the podium and gave his dedicatory speech. He is a very good speaker. He frequently cites the Bible during his speeches. While you sit there, wondering where he’s going with all the stuff he talks about, he draws it all together in the end and it starts making sense to you. The National Science Foundation dignitaries were gathered there, as well as some of the local politicians, and also all of the NRAO big wigs.

A public reception was held at the site after the ceremony, where the local population was invited. All of the suits gathered quickly around the Senator at the reception, trying their best to hobnob. The Senator’s reaction was priceless. He laid his hand on the NRAO Director’s shoulder, and said, “George, take all these people away and leave me alone!” He would not let any politician or dignitary come within 20 feet of him the rest of the day. He stood in the sun, on the pavement, for 2 hours, and shook hands with every local person that was there. Meanwhile the suits went over to a table set up for them and pouted. Well, as the reception drew to a close, Senator Byrd pulled out his fiddle and played with one of the NRAO employees, then stood up and left.

The night before, he stayed at one of the local hotels. The old gentleman got up at 5 in the morning, and went down and had breakfast with the kitchen staff. Now, can you imagine whose votes he got? “Hey, mom, guess who I had breakfast with this morning!” He got their votes, and their families and friends’ votes! The man is a consummate politician!”

The total funding for the telescope came to 75 million. Fifty-five million went to the contractor for building it to the NRAO specs, and NRAO got the rest of the money to build the receivers, monitors, and other equipment that went along with it. After the telescope was built, NRAO needed to go into binding arbitration because the contractor wanted more money – 20 million more to be exact. In the end, they got almost 4 million – not their ridiculous figure – thanks to the arbitrator.

Here’s Mr. Sizemore’s take on basic research and general politics:

“The main problem with basic research, not just radio astronomy but physics, chemistry, mathematics, is the mindset of society. People want immediate gratification. They’re not willing to put in the long-term effort required for projects on which the return is 20, 30 or even 40 years. We are very short-sighted. We can’t see past the next election.”

The GBT Control Room

The whole room is enclosed in copper sheeting and copper fabric – the walls, ceiling, floors and even windows have copper over them. The room is what they call a Faraday Cage. It attenuates signals inside by 60 dB at 1 GHz. That’s not sound waves, it’s radio waves. You can also measure radio waves in decibels.

The windows have a thin brass wire lattice, so light can penetrate. Here we get into some more murky ground. To most radio waves, the lattice wire is a solid wall. The smaller the wavelength, the more likely it is that the radio signal will pass through. As computer processors increase in power, the wavelength of their radio signals gets smaller, since the frequency of the processors increases. That means that soon enough the wire lattice for the windows won’t suffice anymore to block out the radio waves generated by next-generation computers.

Even the door is made of copper and has a brass doorstep, on which Mr. Sizemore cautioned me not to step – apparently they need a tight seal and brass is pliable. Stepping on it would dent it. There are also copper “fingers” between the door and the doorstep. They need good contact between the two, and denting or dirt from your soles will prevent it — that’s another reason why it’s best to step over it as you enter or exit the room.

The reason for this is that the equipment generates radio interference. Since there’s a direct line of sight from the control room to the GBT, the only way to minimize that is to make the room into a Faraday Cage.

Here’s a tale of woe about the windows. The contractor “screwed up the execution of the design in any way possible”. One of the main problems was the use of copper fabric on the walls. They applied it to the wall with a water-based adhesive. Now the fabric is slowly turning green. The copper is turning into copper oxide, which is not as conductive and is also poisonous. Around the windows, they don’t have that problem, they have another, which is worse.

The contractor put copper and zinc together in the framing. The metal parts were zinc-plated. When you put those two elements together and add a little moisture from the sweating of the windows, you get a battery! The windows immediately corroded. You couldn’t just plug your Walkman into the windows and run it off the electricity generated, but they did have a lot of corrosion, so that was a major problem that needed to be taken care of immediately. In Wesley’s words, “watch contractors, they’ll mess it up in any way possible.”

Nathan, one of the technicians, and Mr. Sizemore had to re-do all of the windows. They had to take all of the windows apart down to the metal and send all of the framing off to have it nickel-plated. They also replaced the copper fabric on the walls around the windows with nickel fabric. If you put nickel and copper together, the electrolytic action isn’t as bad and it doesn’t corrode.

When they were refitting the windows in the GBT control room to do away with the “battery effect”, they had to do a lot of banging. As they started away in the morning, they banged at the frames for about a half hour or so, until Phil Jewell, the Deputy NRAO Director, whose office was directly underneath, walked in to see what was going on, with a confused look on his face. Nathan couldn’t resist: “Hey Phil, did we wake ya?” he spouted, a huge grin spreading across his face. Wesley was quiet as a mouse, not knowing how Phil would react to Nathan. Thankfully, Mr. Jewell just grinned and walked away.

They still had a problem with the sweating on the windows, which they needed to alleviate, since they were still made of metal that could corrode over time, though at a much slower rate than before. Some of the scientists on-site got together and offered a bunch of “solutions”. One of them was to put Plexiglas over the windows to keep air circulation to a minimum. But then another decided to drill holes in the Plexiglass to keep the air circulating through, since the sweating still occurred. They then used a fan to blow air over the windows to cut down on the circulation. Not very practical!

The final solution was offered by one of the technicians, who happened to live in a mobile home. For those of you who haven’t had this experience – including me – windows sweat a lot in mobile homes. He went to the general store in town and got a little window kit from 3M. It’s film that is applied to the windows and shrunk with a blowdryer. After the fix was proven, the 3M film was replaced with plexiglass with a resealable access hole to allow desiccant packs to be inserted between the window and plexiglass covers.

Each window now has a round hole at the bottom that is used to exchange the dessicant packs once in a while, and also a moisture indicator that points out the approximate time when the packs need to be changed.

Sometimes it’s a little hard to see the forest for the trees. It helps to stop over-analyzing things sometimes. It certainly becomes less of a headache when the problem is far less complex than originally thought!

In the Control Room, the GBT operator constantly monitors the equipment from the Control Console. The operator is responsible for two main things: the safe operation of the telescope, and the implementation of the different observing programs that various astronomers use. The observation is done in various modes. Normally most astronomers come and “babysit” their programs to make sure they’re getting the data they need, although the trend nowadays is to observe more and more by remote access. The advantage with being there is they can change their program on the fly if adjustments need to be made. Other programs are run over and over, so there’s no need for the astronomer to be there. NRAO operators record the data and ship it off to the astronomers.

In some cases, people that do research there win the Nobel Prize. In other cases, there are people who look at their data then chuck it to the circular file and try again. Some of the research pans out and some of it doesn’t. NRAO is a basic research institute and that means a lot of effort is put in to look at things that only matter down the road.

In the computer control room, separated from the main area by a glass wall, the collective whir of each of the computers adds up to a somewhat deafening noise. The interesting thing about NRAO is that it has a good mix of both old and new technology. Nowhere is this more apparent than in this room. Most of the equipment in there is one of a kind. The pictures here are worth a thousand words. The synthesizer filters, the front panels, the painting of these panels, is all done in-house.

All of the fiber lines from the GBT come right into the equipment room, where the optical signal is converted back into a radio signal.

The spectral processor is another big piece they have in the room. Wesley told me to think of it as nothing more than a big radio. It takes the radio signals it receives and splits them into 1,024 different channels. Then if they have interference on one channel, they can drop it and still reclaim part of the data, provided the interfering signal is not strong enough to overload the first amplifier. The newer spectral process has over 250,000 channels and the technology gets better with each year.

If the signal is strong enough to overload the cryogenic amplifier, and drives it into a non-linear portion of its amplification, then everything in the entire band is lost. The data has to be collected again once the interference is done away with. If the interference is there but not strong enough to overload the first amplifier, then they may be able to drop that interference provided it doesn’t occur precisely on the astronomical signal you’re looking at: same frequency/wavelength. That’s what the spectral processor is good at.

Inside the spectral processor you’ll find another oddity that’s part of that mix of unique, old and new equipment. The circuit boards aren’t printed (they don’t have the circuits embedded into them) but they are wire-wrapped. The cards have little posts sticking out of them, and wires are run from post to post to post. It’s very old technology, but it works great. It’s something NRAO has a lot of experience with, it’s very robust, and it’s cheap to do one card that way. If they were going to do dozens of cards, they would ship them out and have them done as printed circuits.

They also have equipment manufactured by other organizations. For example, they have a CalTech Pulsar machine. They get very picky about the equipment brought on-site. They have to be careful that it doesn’t interfere with the other equipment there, and especially not with the telescopes.

NRAO operates frequency and time standards on the site. Because of the sensitivity of their work, they have to have very accurate frequency standards. They operate a hydrogen maser, a machine that gives them very accurate 5 MHz readings that are piped all over the site. Everything then gets slaved to that signal.

They also operate an atomic clock on site that gives a very accurate time standard. The clock may go away in the future, since a time signal just as accurate can be obtained from the GPS satellites.

Here Mr. Sizemore pointed out a common point of confusion for many people. Stores sometimes sell atomic clocks or watches. They aren’t atomic clocks as scientists define them. A real atomic clock has a Cesium atom movement in it. The movement of those atoms is used to drive it. The clocks one can buy at Radio Shack or Sharper Image are normal digital clocks with a radio receiver built-in that can tune into the time signal transmitted by our government and set itself. Not quite the same thing.

One of their research efforts involves trying to excise interference from the astronomical data, provided, of course, that the amplifier isn’t overloaded. They are looking at a real-time solution, one that would involve an antenna that receives and records only the interference, and the normal dish would record all of the signals. The two recordings would then be spliced together and the interference would be excised. It sounds simple, but it gets more complicated in practice. At any rate, one of the NRAO scientists is working on that very project.

And that’s the end of part five. You can also read parts one, two, three, four, six and seven.

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Places

Fall colors in Rock Creek Park

These are photos from a wonderful walk we took in Rock Creek Park (on the Maryland side) in the fall of 2006. It was a beautiful autumn day, the light was wonderful, and the fall foliage was a delightful sight.

This is the oldest tree in Maryland. It’s an oak that dates back to even before the time of the American Revolution. Even though there’s a plaque next to it explaining this, it seems to be a well-kept secret, because in all the years we lived in the DC area, we lived near this tree and we seldom saw people stopping by it.

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