Dear Friends,
Be Well.
David
By Breanna Draxler |
February 6, 2013 8:09 am
Spectrograph of the February 2 solar flare. Image
courtesy of Richard Flagg, Windward Community College Radio Observatory.
We’re not supposed to look at the sun, but no one said
anything about listening. If you, like amateur astronomer Thomas Ashcraft, had
your radio tuned to the right frequency last Saturday evening, you would have
heard the garbled effects of a solar flare drowning out radio waves here on Earth after it
erupted on the surface of the sun. For those of you who still want to listen
after the fact, you’re in luck:
Thomas Ashcraft is an independent, self-taught radio astronomer
who operates his own Heliotown Observatory in north central New Mexico. Using optical
telescopes and radio instruments, Ashcraft keeps an eye (and an ear) on the
Sun, Jupiter, meteoric fireballs and transient luminous events called red
sprites. He recorded the sound of the solar flare this weekend and shared his
methodology and thoughts with DISCOVER writer Breanna Draxler via
e-mail.
DISCOVER: What exactly are we hearing on this
recording?
Ashcraft: We are hearing a solar Type III radio burst
that was generated by a solar flare as recorded at 28 MHz and 21 MHz. Although
the flare was relatively small, this particular radio burst was quite strong.
Type III solar radio emissions are produced by electrons accelerated to high
energies by solar flares. As the electrons stream outward from the sun, they
excite plasma oscillations in the sun’s atmosphere. The plasma oscillations in
turn generate radio emissions that sweep out into space.
On one stereo channel there was a voice transmission
in progress, likely a ham radio operator, and as the solar radio wave passed
through the voice gets thoroughly overpowered and then returns as the blast
passes through. Type III solar bursts are also called “fast drift bursts”
because they drift down in frequency. It is a little hard to hear in this
recording but the burst actually hits one channel at 28 MHz first and then can
be heard at 21 MHz a second later on the other stereo channel. Listen
close to hear this.
What kind of equipment do you use to record the
activity of a solar flare?
I have a complex array of instruments and observe at
multiple frequencies. This particular solar burst was recorded using two simple
shortwave radios connected to a three element yagi antenna. The Sun radiates
across the full spectrum but, serendipitously, it can be very strong and hot at
common shortwave radio frequencies. I audio record into a digital recorder.
Was the flare on February 2 a big one, relatively
speaking?
The flare at 1954 UT on February 2, 2013 was
relatively small in x-ray output. It was measured at C 2.9. Stronger flares go
way higher into M classification and occasional very powerful flares achieve X
classification. But interestingly, some X-class flares produce minimal
receivable radio bursts whereas some smaller flares can send forth a strong
electron blast.
How does it compare to the superflares of 1960 and
1859?
This flare was generated by a small sunspot group so
there was less physical area of magnetic entanglement. Superflares are
generated by very very large sunspots so they pack more force due to sunspot
size across and below the sun’s surface.
What kind of damage could a major flare do to our
electronic-dependent society today?
Well, that is a complex question. Modern satellites
are prepared for strong flares to a great degree. Occasionally a satellite is
knocked out by a strong flare but not often, at least so far. I have
experienced the strongest solar flares of the past two decades and I don’t
think the modern power grid sputtered appreciably up to an X 28 flare, which
was the largest flare in recorded history. Modern society cannot afford to have
business transactions interrupted so they work hard to safeguard their
equipment as best they can.
What can we expect in terms of solar flares as the sun
enters a new solar cycle this year?
The sun is well into its solar cycle at this point,
nearing maximum actually, and it has been a relatively weak solar cycle in
terms of strong flares. It is baffling to solar scientists. So, it is somewhat
hard to predict what is coming. But, I would bet, and as an astronomer myself,
hope, that there will be some large sunspot groups within the next year or two
based on my own experience of the past three solar cycles. Large sunspots
and hot radio emissions make for great fun.
For all the details on superflares and their future
threats, check out DISCOVER’s Beware:
Superflare.
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