Dialing in a radio eclipse

By Phil Plait | February 18, 2011 7:00 am

On January 4, 2011, the Moon passed directly in front of the Sun, treating much of Europe, north Africa and western Asia to a total solar eclipse. I saw lots of really interesting pictures from the event, but this has to win for what must be the oddest image:

[Click to penumbranate.]

This was the view using LOFAR, or the LOw Frequency ARray, a radio telescope in the Netherlands. It’s designed to sense radio waves from space in the range of 10 – 250 Megahertz (which encompasses FM radio and TV broadcast signals, interestingly). Lots of astronomical objects emit at this energy. The Sun is not a terribly luminous source, but it happens to be pretty close by, making it bright.

The images show the partial eclipse at 140 MHz, starting at the upper left as the Moon was already leaving the Sun’s disk. By the last image (lower right) it was all over. I had to laugh: it was cloudy in the Netherlands that day and people missed seeing the eclipse themselves, but clouds are transparent to radio waves. In fact, radio astronomers can, in many cases, observe astronomical objects even during the daytime, rain or shine — for a class in grad school, we observed the Sun when there was snow on the radio dish!

I remember, around that same time, staying up all night at the observatory (and sleeping during the day) for two weeks in a row for my Masters Degree. At about the halfway point I was reconsidering my choice of doing optical astronomy. Of course, now we have robotic observatories which observe for you, and deliver the data via email or FTP. It’s a far more genteel way of doing science.

Image credit: ASTRON. Tip o’ the welder’s mask to Cecileavdm via Noisy Astronomer.

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (17)

Links to this Post

  1. Ook LOFAR zag de zonsverduistering van 4 januari | Astroblogs | February 18, 2011
  1. Of course, now we have robotic observatories which observe for you, and deliver the data via email or FTP.

    “When I was your age, we had to trudge through the snow (uphill, both ways) , and sit for hours in the freezing cold, staring into a little eyepiece, just to get a good view of the night sky!”

  2. Jake C

    How is a low freq array looking at 10 – 250 MHz? 10 – 250 KHz, I could see, but 10 – 250 MHz is the VHF band, which is where FM and TV sit. The LOFAR wikipedia entry says it measures 30 – 1.3m , which matches up with 10- 230 MHz, but I don’t see how they call that “Low Frequency”. Just seems odd.

  3. Skip

    Erm no totallity for this one, so plenty of places got a paritial eclipse.

  4. Michel

    Leave it to us dutchies to beat weather and water.
    [/gloat]

  5. TMB

    My wife can’t stay awake at night. She ended up going into radio astronomy, and thought “Alright, now I can observe in the day instead.” Of course, she forgot that it means that you observe day *and* night, so it’s even more exhausting. ;-)

  6. Luke H

    That’s an amazing resolution for 2 meter wavelength. Like Ellie said in Contact: “I need a bigger antenna”!

  7. Pete Jackson

    Phil, you really dig up good stuff! It would be great to see one day what happens if a central or deep partial eclipse is experienced at the observatory. It would be nice if your friends at ASTRON could digitize the circle outlining the moon’s visual position into the pics.

    @2Jake: While the frequencies are considered low in radio astronomy terms, you are right in that they are not ‘low’ by the standards of radio broadcasting, where 30-300 MHz (typical TV and FM band) are considered “Very High Frequencies”, 3-30 MHz (short wave) are “High Frequencies, 300 kHz-3 MHz (medium wave, where AM is) are “Medium Frequencies”, and 30-300 KHz are “Low Frequencies”. In radio astronomy, 10 MHz is as low as you can usually go from the ground because of ionospheric reflection and absorption.

  8. Gary Ansorge

    7. Pete

    ,,,and then there are the UHF(Ultra high frequencies) bands, extending into the Giga hertz range.

    When making such designations, it’s all relative. In the “good old days”, as in the first 50 years of radio(beginning a little over a century ago), the kilohertz range was all we could generate. Now we do terahertz. So soon you young whipper snappers forget. It’s a good thing you have us old farts around to remind you, this isn’t the way it has always been.

    When my great grand mother was a kid(late 1800s) she was shooting at”them gol darned Injuns”.
    She lived to see Sputnik. I was born smack dab in the middle of WWII. Things have changed a bit during my life time but I STILL can’t buy a ticket to visit the moon.

    Come on kids. Speed it up,,,

    Gary 7

  9. Garrett

    Same question as Jake C, why do they call it low frequency? Is it some sort of artistic license, because HFFAR or VHFFAR didn’t look good? Or maybe they’re just ignoring ITU convention and calling it “low” relative to the higher frequencies of microwaves and optical frequencies?

  10. Matt B.

    Radio band designations are not relative, Gary: http://en.wikipedia.org/wiki/Radio_spectrum.

  11. Mr. D

    The reason this is “low frequency” for astronomers is because the usual, run of the mill, radio astronomy band is the L band at 1.4 GHz, where the hydrogen 21 cm line is. Everything below is low frequency, above is high.

  12. Jamey

    @Garrett – remember, these are the same people who think in terms of three elements – Hydrogen, Helium, and “metals”. For astronomical purposes, it *is* low frequency.

  13. George Martin

    @8 Gary says:
    In the “good old days”, as in the first 50 years of radio(beginning a little over a century ago), the kilohertz range was all we could generate.

    Did you really mean kilohertz? Even if you start counting the first fifty years from Heinrich Hertz, people, including ham radio operators, were using 10s of MHz routinely long before that first fifty expired. Related to the above, Jansky’s observations were around 20 MHz. and he was looking for interference to AT&T’s trans Atlantic radio telephone communications.

    George

  14. Messier Tidy Upper

    Interesting and one of the most different views of an eclipse I’ve ever seen. Thanks. :-)

    @5.TMB :

    My wife can’t stay awake at night. She ended up going into radio astronomy, and thought “Alright, now I can observe in the day instead.” Of course, she forgot that it means that you observe day *and* night, so it’s even more exhausting.

    If she only wanted to observe in the daytime then she might’ve done best to specialise in the field of solar astronomy! ;-)

  15. Mike Saunders

    You can still design circuits with lumped elements at 250MHz, as a mmWave guy that’s pretty freakin’ low (almost DC!)

  16. Jarno

    I live in the Netherlands and I’m a high school chemistry teacher. My classroom has a view out to the east from where my students and I could see the eclipse in all it’s majestic beauty. Turns out the city where I work was the only place in the Netherlands where the eclipse was not obscured by clouds!

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