Gas Music from Jupiter

For the last few months I’ve been taken with what is becoming an unwieldy fascination.  It’s called radio astronomy. Turns out to be something that amateurs can actually take up.  There are a few websites devoted to the subject.  It’s not like antique cars or photography for which there are hordes of devotees and whole industries supplying equipment.  Oh no.  This field requires some freakish overlaps of interest- e.g., RF electronics and astronomy.

Lost in Space

For some years now I have been a volunteer at a local observatory. It is a very nice facility and it is operated by some gifted folk. We have a custom setup featuring an 18 inch Cassegrain in an automated dome.  Because of other obligations my participation waxes and wanes like the phases of Venus.  We volunteers give star talks to visitors who arrive in great squirming masses for a glimpse of the cosmos.  We give star talks because we often have to wait for the sky to darken or for the clouds to pass. When the sky opens up, we take a dozen visitors up into the dome and skate around the celestial sphere for the eye candy.

Being a chemist and not an astronomer, I have to avoid delving too deeply into the science during a star talk because, again, I’m not an astronomer.  But this business of being a chemist (an atom scientist) in an observatory has forced me to think about what it is that we’re really trying to do in introducing the public to astronomy. 

It is very easy to present astronomy as the science of telescopes and constellations.  After all, we navigate the skies by referencing the constellations and we look at the interesting objects through an impressively large, yet nimble, optical device.  People leave after an evening of viewing being greatly impressed with the telescope and the observatory.  You can’t help it.  It’s cool stuff.

But the telescopes and all the assorted apparatus are really not the focus of the activity. Astronomy is really about the stuff that is across the vast distance in deep space. How much stuff is out there? What is the stuff doing? And, what kind of stuff is it? They’re George Carlin questions. These are really the central questions of astronomy but we largely pass by the details of the stuff in favor of the show business aspect- the whizbang stuff that you need to keep everyones attention for 45 minutes.  But, the goal is to capture the fancy of K-12 students, so juicing up the show with some mind blowing stuff is OK.  It is fascinating to note that it is the adults that have the hardest time keeping on track.

Whizbang astronomy is necessary to keep the public coming in because most visitors do not have a physics background. To really appreciate the subtleties it helps to have some book learnin’.  Public outreach is not about true learning.  True learning requires struggle and most people are not inclined to struggle with a physics concept for very long. Public outreach is about info-tainment.  

This isn’t a condemnation or criticism. It just stems from the nature of population interest distributions and the bell curve.  I’d fall asleep at a car show or a botany conference.

So, the goal is to evaluate a modest radio telescope capability.  There are several parts of the spectrum that offer signals to detect that are within the realm of possibility for a hacker like myself.  One band is from 20 to 24 MHz. The other is the H(I) line at 1420 MHz, or 21 cm. The sun and Jupiter are active in the 20 MHz range. There is a program sponsored by NASA devoted to solar and Jovian radio observation called Radio Jove.  For a few hundred dollars it is possible to assemble a radio telescope- a receiver and a dipole antennna- to listen to 20 MHz signals eminating from Jupiter and Io.  Picking up 21 cm radiation will likely require a 3 meter dish in order to get enough decibels of signal gain going into the detector. Anyway, this antenna technology is part of my learning curve.

Introducing folks to radio astronomy will serve as a kind of counterpoint and will require that people venture away from the narrow optical band. It requires that we think about the observation of signals that have no visual counterpart and what clues it may afford regarding the condition of matter.

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About gaussling

Gaussling is a senior scientist in the chemical business. He occasionally breaks glassware and has been known to generate new forms of hazmats. Gaussling also digs aerospace, geology, and community theatre. View all posts by gaussling

6 responses to “Gas Music from Jupiter

  • Ψ*Ψ

    kinda off-topic but cool anyway: did you see the C&EN bit about C(6)H- ? (sorry, no super/subscripts :( )

  • gaussling

    Yeah, I glanced at it. Haven’t had time to read it. Given the low densities in the interstellar medium it is amazing that the atoms and ions have the chance to bump into each other. It would be interesting to find out what the prevalence of atomic carbon or oxygen is in some of these molecular clouds. Atomic hydrogen can be detected from the spin flip emission at 21 cm. It’s abundance is highest along the galactic plane.

  • Jordan

    Pretty cool. I was quite the amateur astronomer in my youth. How unwieldy is a radiotelescope desgined for 20MHz? And is “amateur radioastronomy” as susceptible to to urban EM pollution as amateur “telescopery” is?

  • gaussling

    The big problem with 20 MHz is the antenna. A dipole antenna for this band will be about 23 ft in length and will have to be at least 10 ft off the ground. The good news is that you just need some 75 ohm coax cable to run out to the antenna, which is just a heavy enough wirre to support it’s weight under wind loads. The difficulty with a 23 ft dipole antenna is that with the guy wires it starts to take up some space.

    There may be local RF interference. But there is software called Sky Pipe that is basically a data logger that will give a graph showing signal intensity over time. It is easy to spot the spurious signals.

    I have been hounding the folks at Radio Jove for more compact antenna configurations like a Yagi or helical antenna.

  • Jordan

    So the antenna is not “directional”? You just pick up whatever happens to be overhead at the time?

  • gaussling

    Directionality is measured as beamwidth. A wire diple antenna has very low directionality, or broad beamwidth. A dipole antenna is sensitive to signal from most directions in the sky. A Yagi antenna, which is what most TV antennae are, has beamwidth maximized in the direction of the director elements. I’ll see if I can find a graphic that I can post. It is useful to think of an antenna as a transducer.

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