Perseid 2002 Results

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"Thank you so much for visiting our class on Friday! The kids loved it...they thought it was pretty cool to meet a "real" Astronomer! Thanks again, Janine"

The Perseids 2002 provided us with a comprehensive test run of radio and optical observing methods. Observations were carried out in a number of ways, including:

Visual observations
"Live" radio listening during visual observing sessions
Live monitoring of radio without visual correlation
Ongoing data collection before, during, and after the Perseids
Audio recording on VCR tapes
Casual monitoring of a second car radio 
Other people's observations

What follows is an edited version of our Education Development Coordinator's (Bruce McCurdy) report. The references to "Blackfoot" and other observers refers to optical viewing sessions held at the Blackfoot Staging Area well to the east outside the lights of Edmonton with members of the Edmonton Centre of the Royal Astronomical Society of Canada.

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The 2002 Perseids

By Bruce McCurdy

Visual observations

These observations were carried out on four different nights. I observed continuously from 1-4 a.m. the night before maximum (morning hours of August 12) at Blackfoot. Under good but not great skies (limiting magnitude ~6), I had hourly counts of 52, 43, and 51 Perseids, plus 10 meteors from other showers. I saw nothing brighter than mag -2, and nothing that left a persistent train of longer than 2 seconds. A good show, but not a great one. 

"Live" Radio

We used a good car radio in an open area (Blackfoot) and I was surprised with the number of hits (>100/hr.), which greatly exceeded my rates at home. This raises some questions about the sensitivity of my setup as well as the limitations of the urban environment. The good news is car radios do work, and work well, for this application, with nothing more sophisticated than normal car antennae. 

To a single observer facing south, roughly 25-30% of visual meteors had an audio counterpart, however many of the radio hits matched exclamations from observers facing other directions. The majority of these matches were brighter meteors, particularly those in the south, however this correlation was not 100% in that a couple of bright southern meteors were inaudible. 

Interestingly, when a visual train took a second or two to fade out, the audio would continue on for 5-10 seconds or even longer. Presumably this increased sensitivity would also explain the number of radio hits in which nobody saw anything, including the large majority of the underdense blips. The underdense events which did have a visual match were generally the fainter meteors; my *impression* was the rest were of 6th or 7th magnitude and therefore sub-visual. 

There were very few of the overdense extended signals which weren't picked up visually by anybody. One good one started at the exact moment I observed an extremely bright flash in the trees along the southern horizon; I suspect that would have been my best meteor of the night if the trees weren't in the way. That might explain the ones that got away. 

However, I was surprised to get the occasional match with meteors fairly low over the western horizon; my understanding was that this area should be outside the reflection path, but there were three or four of them that were exactly concurrent with a radio burst.

Live Monitoring at the Project's Radio Observatory

(These monitored sessions took place in Bruce's home radio observatory.) After returning home at 5 a.m. on the 12th, I listened with my son's new headphones for about an hour. While the number of good hits was fairly low at that time, there was a near constant babble of faint signals discernable in the static, lending a rich palette of colour to what I had previously heard as white noise. This did not translate at all well onto the VCR audio tapes, at least not through the small speaker on the 9-inch B&W TV I was using. I have also been monitoring on a routine basis during the hours I have spent at my workstation, and have heard many hits, all of which were duly recorded by SkyPipe.

Baseline Observing

Ongoing data collection using BSTRDS (Bruce's Steel Trap Radiometeor Detection System). I have been getting better results since pointing my antenna some 30 from due south, the recommended azimuthal offset for an antenna for a station at Calgary's distance, and have been monitoring more or less continuously. 

It definitely is worth the effort to examine the strip charts at "high power" by stretching the data out; I routinely set it at four minutes to the screen width, one minute per section which had the effect of narrowing the background noise and accentuating smaller spikes. Even so, pulling some of the smaller spikes from the ambient background noise is at least as much black art as science; if the line is "clean" I have greater confidence in tiny spikes, a judgment which has been borne out in the VCR tapes. 

There are some puzzling results, not the least of which is that peak activity seems to have occurred on August 9. Equally anomalous were the results of August 4, which were very low indeed. It strikes me that these may have been nights of outstanding and poor radio reception, rather than indicative of unusual peaks and valleys in the shower itself. 

The other puzzler was that peak rates seemed to occur between 1-5 a.m. -- similar to the visual peak times -- but did *not* pick up as the radiant neared the zenith ~6:30. This has me wondering if the angle of the radiant near the meridian v. the Calgary station due south, is unfavourable and leads to a lower number of detected meteors. 

Articles I've read on this subject in Sky & Telescope (August 1992, December 1997) recommend listening in a direction perpendicular to the radiant, however it is difficult to change one's station, antenna direction etc. in the middle of the night. 

Audio Recording

A VCR setup was used to accomplish this. I recorded Perseids from 2-10 a.m. from August 11-15. So far I have transcribed the first two nights, a painstaking process at 3 hours plus per tape. I verified to the audio, each and every spike recorded on SkyPipe, a total of 68 on August 11 and 100 on August 12. 

I am pleased to report the system is very reliable, as only two or three of these had no detectable audio counterpart; a few had static bursts of little or no signal, yet "sounded" consistent with meteors, and the large majority had a good solid matching signal. Roughly one third of all recorded meteors were of the overdense variety, with persistent trains that lasted from a few seconds to a few tens of seconds. 

Some of these picked up signals from stations further afield than Calgary, often a jumble of two, three or more signals within the same extended burst. One clear one didn't quite give a call signal, but identified the name of the show and gave the time as one hour later (CDT). I have recorded a series of good examples on our Greatest Hits video.

Casual Radio Monitoring

Independent monitoring using a modified car radio, which I have set up upstairs just inside a south-facing window. The good news is that I was able to do the modifications to run the radio with an AC adaptor, and I get a clear signal from local FM stations using a simple coat-hanger antenna. The bad news is that I have been unsuccessful to this point in getting good meteor data from distant stations. The strip charts nominally resemble the others, but the baseline of noise is much thicker. The few spikes recorded did not match up at all with the times of the "good" data, and no spikes bore the characteristic signature of an overdense event. Obviously I need a better antenna -- a car antenna does suggest itself.

Other People's Observations

Finally, I did extensive reading of results from *all* around the world as reported to the meterobs news group. The consensus was this year's Perseids were fair at best, although many people were too hampered by poor conditions to form an opinion about the shower itself as opposed to their own disappointing experience. 

One interesting observation was by Pierre Martin of Ottawa, who reported a burst of activity just after 0700 UT on August 12. My own experience was I had my best 10-minute bin of the night from 0710-0720, recording 18 meteors visually and 36 on "live" radio. Furthermore, the hour from 0700-0800 had the highest SkyPipe count of the month, with 26 hits. So there seems to be some correlation between visual observations at different sites with radio observations, an exciting prospect.

 

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We gratefully acknowledge the financial support of the 

Edmonton Centre of the Royal Astronomical Society of Canada, Department of Physics (University of Alberta)

and the

Natural Sciences and Engineering Research Council of Canada

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