Amateur Radio Astronomy

I have heard the planet Jupiter. Sometimes it sounds like waves breaking on a beach; sometimes like “pebbles hitting a tin roof,” as Dale Hooper puts it.

“Popcorn,” was the sound assessment of Dave Bernson, president of the Salt Lake Astronomical Society, and Hooper agreed — it did sound like kernels popping.

Hooper, a software engineer who works for Utah State University’s Space Dynamics Laboratory and lives in Hyde Park, Cache County, spoke last week about his experiences exploring the galaxy through a different form of astronomy than the usual telescope-peeping. He is an amateur radio astronomer who has built an observatory in his backyard. During the meeting of the Salt Lake Astronomical Society he told of his adventures in the field.

[Dale Hooper tells members of the Salt Lake Astronomical Society about his radio astronomy adventures. Photo by Cory Bauman]

From his sometimes-stifling control room —- if he turned on an air conditioner it would create radio interference in the sensitive equipment —- Hooper detects radio waves emanating from our galactic center, Jupiter’s vast electromagnetic circuit, even the spinning pulsar star remnant within the Crab Nebula. With successive scans of the Milky Way’s reaches he is building up a map of the bright radio sources in the galaxy.

[Hooper’s control room. Photo courtesy Dale Hooper]

“Visual light is just part of the electromagnetic spectrum,” he said. Optics focus only on “small window” of the spectrum. According to a NASA educational site, electromagnetic radiation forms streams of energy, from radio to microwaves, light (infrared, visible and ultraviolet), X-rays and cosmic rays.
Everything that moves gives off some form of electromagnetism, maybe excepting isolated black holes.

With the right gear, amateurs can pick up some of the signals.

For Hooper, the spark was a Sky & Telescope Magazine series of articles, starting in May 1978, about building one’s own radio telescope. Components were hard to find and enthusiasts had to assemble many parts that are available off the shelf today.

But, he said, he knew as soon as he read the articles that it was only a matter of time before he built an observatory — time “and, of course, money.”

He said two sources of electromagnetic emissions detectable by radio astronomers are:

*** Synchrotron radiation, which does not radiate from a heat source. It is the release of “charged particles accelerated in a magnetic field.”

A prominent synchrotron source not far from Earth (that is, close on cosmic scales) is the Crab Nebula, more than 6,000 light-years away, the remains of a star that went supernova. Chinese astronomers observed the star’s violent demise in the year 1054, when the light of the explosion hit Earth.

The spinning pulsar star that remains “is apparently pumping enormous amounts of energy into the nebula in the form of high-energy particles and magnetic fields,” according to NASA. “As particles stream out from the pulsar and spiral around magnetic field lines, they produce a distinctive kind of radiation known as synchrotron radiation.”

Radio astronomers can chart this type of radiation in the pulsar, Jupiter’s system or when a black hole speeds up particles, Hooper said.

*** Thermal radiation, which can come from cold, dark dust clouds or from atoms and molecules.

When he was building a radio telescope, Hooper found a ten-foot satellite dish that the owner no longer needed. “I gave him 100 bucks for it and hauled it away.” As satellite receivers have grown smaller, some old-fashioned big dishes are still available for free, or commercial outlets will sell one for about $750, he added.

[Hooper’s radio astronomy dish, modified from a satellite dish. Photo courtesy of Dale Hooper]

Removing the dish’s C-band electronics, he installed a specialty feed horn and choke. The feed horn captures signals bouncing off the dish while the choke “blocks out stray interference.” He aligned the dish north and south on its supports and began making “drift scans” of objects that moved in front of it.

[View of a profile of a deep-space radio source, courtesy of Dale Hooper]

A radio source from deep space takes 16 minutes to move across his field of view. As it moves, the signal’s intensity varies. Plotted on a graph, the changes show the radio profile of the object. With enough passes, an image builds up showing how the target’s radio brightness differs from one region to another. It’s a type of map.

Compared with when he began, he said, “this … is really a good time in amateur radio astronomy, because there is a lot of support.” The Society of Amateur Radio Astronomers, the SETI League, GNU Radio and others provide help over the Internet, and specialty hardware is available.

Originally he used an ICOM shortwave radio receiver, but he has upgraded to a “research-grade, rack-mountable, total power receiver.” It is much more sensitive.

“Something that’s really nice about radio astronomy, especially when you have skies like you’ve had this year, is that you can observe when it’s cloudy. In fact, you can observe during the daytime.”

He displayed charts he has made of the intensity and direction of radio waves coming from the North America Nebula, 1,500 light-years away; the Crab Nebula, 6,300 light-years; and the Swan Nebula, 6,000 light-years distant. One light-year is nearly 5.9 trillion miles.

“Radio Jove,” a radio available as a kit or fully assembled, is handy to listen in on Jupiter’s radio activities or solar flares. The antenna is as simple as wires strung in the backyard with a cable between.

Gravity from the king of planets impacts the small satellite Io so forcefully that this moon is continuously erupting with volcanoes. Volcanic particles spewing into space react with Jupiter’s magnetic field and “the particles get ionized.” Charged particles whip around the magnetosphere and set up an electrical circuit that put out radio waves detectable on Earth. “The Jupiter-Io system has been called the largest DC circuit in the solar system,” he said.

The circuit rotates with the planet, creating a large X-ray source near Jupiter’s north magnetic pole. It’s as if Jupiter were a “very slow-moving pulsar.”

The group listened, delighted, as Hooper played recordings of the sounds of solar flares and two different types of radio eruptions from Jupiter. The L-Bursts sound like waves; the S-Bursts, like pebbles or popcorn.

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