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Date: March 6, 2010

Title: What To Do in Case of a Total Solar Eclipse and an Overcast Sky: Mexico City 1991

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Podcaster: Edgardo Molina

Description: Ever felt sorry for traveling far away chasing a total solar eclipse, just to find out that during the partial and totality phases the sky is overcast? Solar Radio Astronomy to the rescue. Witness the event within the invisible radio frequency spectrum in the high frequency bands. If you know how to pack a telescope you certainly will be able to pack a portable pocket size antenna, an H.F. radio and a netbook with all the required software to do something uncommon for the traditional eclipse chasers, when conditions are against you during the eclipse event.

Organization: Pleiades. Research and Astronomical Studies A.C. www.pleiades.org.mx (web site soon to be presented also in English)

Bio: Edgardo Molina. B.S. in Mechanical Engineering from the Anahuac University in Mexico City. Post graduate studies in IT Engineering and a Masters Degree in IT Engineering. Working for IPTEL, an IT firm delivering solutions to enterprises since 1998. Space exploration enthusiast who participated in several Mexican space related activities. Licensed amateur radio operator with call sign XE1XUS. Amateur astronomer since childhood and actual founder and president of the Pleiades. Research and Astronomical Studies A.C. in Mexico City, Mexico. Avid visual observer and astrophotography fan. Public reach through education in exact sciences, engineering and astronomy. Lectures and teaching in several universities since 1993.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by orbitalmaneuvers.com. Check out the site for the soon to be published sci-fi thriller by RC Davison, “Orbital Maneuvers”. The novel follows a space shuttle crew’s struggle for survival after being stranded in orbit by a devastating asteroid impact on the United States. Shuttle commander, Susan Corin must not only contend with the aftermath of the disaster, and a damaged shuttle, but must deal with a crew member whose homicidal actions have put the rest of the crew in grave danger. At the website you can read the first 3 chapters of the book, read background information about the space shuttle, the International Space Station, asteroid impacts and more, as well as sign up to be notified when the book is published. Thanks to 365 Days of Astronomy for bringing this wonderful source of information about space and astronomy to the public.

Transcript:

Hello, My name is Edgardo Molina from Pleiades. Research and Astronomical Studies in Mexico City, Mexico. I am your host today for this episode of 365 days of astronomy.

Have you ever wondered how you can possibly enjoy a total solar eclipse with an cloudy sky? Well, considering that solar eclipse chasers worldwide rely on fine weather to do their trick, I can no longer trust Mother Nature.

Now a little background on our main subject. Winding time back to 1991, location Mexico City, the highlands to the west. I was sadly looking at the weather forecast for july 11th. The forecast showed a dull gray overcast sky. Even with the possibility of light rain just in time for the total phase of the solar eclipse that took place then.

As an avid amateur astronomer I had a couple of small refractor scopes and their respective filters and projection screens just in case the weatherman could be wrong! Then I started thinking: How about experiencing the eclipse in a totally different way? Let´s say, moving the tuning knob on the electromagnetic spectrum and switching to the radio frequency domain? As it is well known, our Sun is a magnificent source of electromagnetic radiation. If I could record the decrement of that radiation due to the Moon eclipsing the solar disc, how would that show in an x-y graph?

Now let´s get to work. Considering the fact that I have been an radio amateur operator for most of my life, I had a decent collection of radio equipment and antennas that could eventually allow me to receive some of the electromagnetic radiation coming from the Sun. I did a lot of research on the subject: Solar Radio Astronomy. In a time where no Internet was available to the general public. How different such a project could be nowadays with all the information at our fingertips. Well, public and university libraries were the sources for my initial research. I also happened to have several issues of the Scientific American magazine, which by the time it contained the now defunct (and of course much missed) section named “The Amateur Scientist” that clearly showed a way to achieve some basic solar radioastronomy using a very elemental electronic circuit and an x-y plotter, plus a shortwave receiver and a tricky to construct wire antenna. That was almost everything from the technical and practical point of view that was required for me to do the experiment. That magazine article sparked the idea when I was unable to find more sources for amateuristic research. Finally I was just armed with the idea, my amateur radio station XE1XUS. and a worn scientific magazine.

I did not matter to me at the time, that the weather could show it´s bitter face. I felt a passion to do something no one was able to do before (at least in an amateur way). Nowadays I haven´t heard of not too many solar eclipse chasers who do this kind of observations. All of them focus in the photographic experience and little research on other wavelenghts is done. All of the eclipse chasers that I know, cry in desperation due to a cloudy sky the same day the eclipse is taking place. In my case I could easily pick up a comfortable spot anywhere in the totality path and still could presence the magnificent event in another part of the spectrum.

First of all I took a trip to Mexico City´s República del Salvador street just downtown, where around a hundred specialized electronic mimics of a Radio Shack store are located. I was able to buy the electronic components with little effort and resources. Got also a decent soldering station and the required tools to mount everything neatly in a project box.

Then there was the task to obtain an X-Y plotter. For those of you listening, who were born by the mid 90´s, we are talking about the prehistoric time of personal computers. Few or none programs were written at that time to graph variables in real time, without specialized analogue to digital converters. Sound cards on the other hand, that could eventually do the job, were also non existent.

I had the chance to do my major in Mechanical Engineering at the Anahuac University in the outskirts of Mexico City, there I saw one fine example, unfortunately out of order. I was authorized to take it home and use it on the experiment on the condition of returning it in a full working state plus safe and sound. I was able to do some clockwork on the stepper motors, I had to adapt a fine point stylus for it to start recording because of the lack of spare parts. Got some rolls of graph paper and that was it.

The radio part was an easy one. The Sun is so close to us as compared to other radio sources in space and it has strong radio activity showing on the shortwave bands. High Frequency to get it closer to a decent definition. As an amateur radio operator I realized that I could use the 15m band, corresponding to a frequency in the 21Mhz range. There was a single requirement from my radio astronomy sources that pointed out the importance of working on amplitude modulation or any of its products (namely Upper Side or Lower Side bands) for the radio solar emissions to be properly received. No problem on that due to the use of a High Frequency radio for amateur communications. The Automatic Gain Control found on most shortwave receivers was not something to be present during the experiment. The radio I was considering also provided the means to adjust it to cero to avoid this effect.

Finally an antenna was to be chossen. Since the solar emissions were strong and at the main phases of the eclipse the source of them would be nearly at the zenith, I seriously considered the plain old dipole antenna. In a horizontal layout it would provide me with a radiation pattern with a lobe pointing straight up where the Sun and the Moon would be offering their show. The orientation of the main axis of the dipole antenna pointed North-South, so no tracking or adjusting to it would be necessary. The antenna was connected directly through a coaxial feedline without any impedance matching network, due to the fact that we would not be using it for transmission, only to receive the solar radio emissions. It proved fine during the tests.

I hooked everything together, first the dipole antenna to the radio, then the audio output of the radio (namely speaker output) was connected to the electronic circuit that provided several functions between the radio and the X-Y plotter. Those were grossly named: pass band filtering, ac to dc conversion and signal level control. Then came the X-Y plotter, I would synchronize the paper roll for the graph using the time signal provided by another short wave radio tuned to the WWV station in Fort Collins Colorado, USA. Remember that it was 1991 and the only GPS receivers available for decent time synchronization, were only available to the military and some fancy high tech civilian labs or corporations. Anyway, the WWV time signal and manual coordination with the plotter was ok for starting the recording drum. I manually marked the graph paper and turned on the plotter recording drum while listening to the WWV time signal, just minutes before totality. Then adjusted the volume on the radio and the signal on the electronic circuit between it and the plotter. I started recording a spiky graph acording to the background noise variations produced by the Sun and received on the 15m band.

What I was expecting at that time was to notice how the graph amplitude on the plotter would be diminishing as the Moon covered the Sun disc. The Moon would act as a radio emission obstruction and the background noise would definitely decrease during totality. As the partial phases of the eclipse were passing by, the clouds would not move from their position above most of Mexico´s territory. It is important to point out that July is just the middle of our rainny season so if everything stayed that way, I could be experiencing the solar eclipse in a different way and the only one to positively assure that witnessed it despite the cloudy sky. Things got worse just minutes away from totality when it started to rain lightly. My telescopes were safely recovered from their positions and the only optics playing a role were those from my brother´s photographic camera silently waiting for a hole in the clouds to allow us to record a picture of the totality phase. As we approached totality the clouds kindly dissipated and for the fortune of a few visual observers totality would be the show of the century. My graph showed a decrease in amplitude for every spike of radio background noise on the 21Mhz band, I was excited, then “Totality!”, someone yelled outloud while I was running in and out of my radio station to witness both in the radio and visual parts of the spectrum.

Totality was the most memorable event for everybody that day looking through a very small hole through the clouds, this eclipse was the longest one for it´s respective Saros cycle. Photos were taken by my brother using a telephoto lens and the proper filters during each phase. After the whole show ended I forgot that my radio astronomy setup was silently working for me. What a pleasant surprise to see the graph. It clearly behaved like I had anticipated. It showed no background noise during totality, just a flat line like the ones nobody want in a medical monitor. Three events were just barely recorded due to the amplitude of the curve drawing the graph, diamond ring at the beginning of totality, Bailys pearls in the middle of totality and diamond ring at the end of the event. Then the amplitude of the background noise started climbing again as the background noise on my speaker monitor also marked the end of the radio emission silence provided by an interfering Moon during totality.

This experiment was encouraged by me to be done by around 20 other amateur radio stations along the path of totality in the Mexican territory. All of them were successful reproducing my setup. Most of them did not have the chance of a clear view of the show due to the bad weather, but we all felt proud to have witnessed a solar eclipse in a totally different way.

Nowadays with the advent of portable computers, real time signal recording software and ultra portable radios, I am excited again up to the point of planning a trip to Australia during the total eclipse taking place on 2012. I will of course be guided by one of our members at Pleiades. Ruben Ruiz, who is the only Mexican eclipse chaser with several successful chases under his belt.

Ruben, if you are listening, you better start pulling out the old soldering iron and doing your homework on solar radio astronomy. It will certainly be a doubtful weather Down Under!

For the 365 days of astronomy podcast this is Edgardo Molina from Pleiades. Research and Astronomical Studies in Mexico City, Mexico. Our astronomy group can be contacted at www.pleiades.org.mx where our email contact address is waiting for your kind comments and feedback. Thank you for listening.

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