The Perseids are generally the strongest meteor shower of the year. And the Bridgeport / Mono Lake area has some of the most spectacular geology in the country. We made the most of both opportunities. Our group convened at Honeymoon Flat Campground. Here's the topo map and coordinates. We got sites with great views of the sky, and a shady spot for our kitchen setup. Because this class sat square on the final exam period for the second Cabrillo summer session, our student turnout was lower than usual, and didn't have the 18-22 year old contingent. Now, this was the first bit of teaching for me on my new left hip, as I was on and off crutches throughout the weekend. Made for a challenge, but we did a great deal of field work and everyone felt they got their money's worth for sure.
Friday night we did our first Perseids counts. I handed out forms for logging the meteor type (Perseid, Delta Aquariid, Capricornid, or sporadic) and counts, in bins of 15 minutes each. We got in several counts, and one meteor in particular deserves special praise...
The Aug 11,
2007 Fireball (at 12:05am PDT). By all accounts, this one meteor made
the whole trip worthwhile for everyone. It was the most spectacular fireball
I've ever seen - a brilliant, slow, fireball as bright as the quarter moon,
of magnitude -9 I estimate which took almost 6 seconds to cross half the sky
(~90 degrees). It moved from Ursa Minor due south and slightly downward, in
the northern and western sky, ending in Corona Borealis or very close to it,
about 20 degrees above the horizon. This was within a few minutes of midnight.
The meteor shed orange fragments in all directions, glowing green and then purple
and then red towards the flame-out. It was not a Perseid, but instead a sporadic.
It was easily bright enough to have left some fragments hitting the ground.
It looked like it simply slowed down enough to stop glowing, rather than actually
burning completely up. It left no persistent train such as Perseids do, nor
did it have a terminal explosion. It showed strong color changes from bright
green then to red and then dull red before ending. Here is a page which shows
of this fireball, seen in the Sacramento Valley area. This account
from a Mother
Lode newspaper article, says the fireball made a loud explosion
noise, indicating that it indeed made it to the lower atmosphere and probably
did leave meteorites somewhere. This was about 120 miles or so west/northwest
from us in Bridgeport (here's our
position and coordinates) , which makes perfect sense if you consider
meteor trails are typically 30-40 miles in elevation. I've filed a report on
this event with the American Meteor
Society. In September, Jeff Jolin reported to me that he heard
no sounds, unlike the newspaper report of sonic booms, and he was in Auburn
and saw the meteor. I had the strong impression of hearing the meteor hissing
through the air. That makes no sense in terms of a sizzling meteor obviously
- but talking about this with NASA meteor expert Peter Jenniskens he said it's
not so crazy ... "The hissing you heard while seeing the meteor has been
reported by others. It could be VLF radio emissions in the audible frequency
range that are transformed into audible sounds by objects in your environment
(glasses, tooth fillings, paper, vegetation). Still a controversial issue because
of lack of good coincidence detections. Lightening all over the globe also creates
VLF/ELF signals." Since the VLF/ELF signals travel at the speed of light
and not the speed of sound (at this speed the sounds would take 10 minutes or
so to arrive), you would hear them as you saw the meteor.
Saturday morning I got up early and worked on preparing the traditional French Crepes breakfast, and savored by all. First stop on Saturday's planetary science field work was at Mill Creek/Cemetary Road next to Mono Lake. Here, the Black Point volcanic eruption 13,000 years ago was the setting. Just a few months ago, it was announced that a massive comet impact had likely hit North America 12,900 years ago. Researchers have found a dark layer of carbon spherules, microdiamonds, and soot from the holcaust that followed at several sites around North America. 12,900 years is an eyeblink geologically, and so if this layer were to be visible, it would have to be in a depositional environment. The concurrent Black Point volcanic eruption here made for a convenient time marker to search for this layer. Was the comet impact just before, or just after the Black Point eruption? Not sure anyone knows. The tortured dark volcanic ash deposits behind Yaron above right are due to the Black Point eruption, so searching for the comet impact layer might be expected immediately above or below this thick, severely bent band. This time was also the end of the last Ice Age, and Mono Lake was much deeper and covered this location, so that ash deposition layers are the main feature (below about a foot of topsoil).
Yaron and I collect samples from these layers, for later examination in the microscope at the Cabrillo geology lab.
Next we hike the half mile from Mill Creek to Wilson Creek, closer to Black Point itself and hopefully with a longer sequence of deposits for us to search. We all got enthusiastically into the search for comet fragments and vaporized Clovis culture Native Americans, mammoths, and saber-toothed tigers! But alas, none of the dark-ish layers we found looked promising in terms of their apparent composition or position in the layering.
Michelle, Carla and I search the ash deposits in the upper sequence of the wall of Wilson Creek, but found no dark layers.
Saturday night, as we set up for meteor shower observations, I prepared the Megrez refractor + ST2000XCM CCD camera to demonstrate the art and science of astrophotography. I settled on the Andromeda Galaxy as the subject matter - bright, with plenty of varying contrast so that a relatively short set of exposures would do a great job. The galaxy was only about 20 degrees up and atmospheric reddening required some color balancing. I wrote a computer program to take the raw Perseid meteor shower counts from the class, and from myself, and standarize them to the zenithal hourly rate. This was the first formal counts for the class, and there's definitely an art and skill to being an effective observer. Especially challenging after a hard day in the August sun driving and geologizing at locations over 6,000 ft elevation. In fact, the final count on Saturday night had to be 86'ed - it was obviously affected by repeated nodding off by everyone. Friday night was good, Saturday night was much better, and the peak of the shower actually was predicted for early Sunday evening after the class ended. There were two very bright Perseids worth noting, one slightly dimmer than Venus, and one as bright or a bit brighter (magnitude -4) which was very low in the west, just skimming the Sierra. This was near midnight.
Click on the Excel plot to get a clearer view. Each point is the ZHR corresponding to a 15 minute count. The purple points are the numerical average for the ~7 class members participating in each count. My own counts are higher, but then I've had a lot more experience in the art of observation, and were about what was tentatively predicted.
The Andromeda Galaxy - 6x5min stack in Registax 3 with the Megrez Flourite triplet APO and ST2000XCM CCD camera on the GM8 mount. "sRGB + gamma" single-shot color processed in CCDOPS ver 5, Photoshop CS2: levels, AstroTools: 2x 'make stars smaller', 'space noise reduction', 'local contrast enhance', color balance (towards blue), unsharp mask.
Sunday morning, I rose early and snapped the title shot at top - the Sierra crest above Twin Lakes, from camp. After cooking a breakfast of eggs and hash browns, the plan for today was a lecture on glaciation at Twin Lakes, then a trip to Travertine Hot Springs for a final lecture on hot spring formation, springs on Mars, and calcium carbonate precipitation.
After a short soak for some of us, we said our goodbye's and I distributed the take-home final exam. Thank you all for helping making this yet another memorable experience! And thanks for being willing to work especially hard on this particular Astro 28. And a special thanks to Chris Angelos - president of the Santa Cruz Astronomy Club, for his help in all aspects of the trip, including helpful explanations around the telescopes. And to new Astro 28'r Michael Kran, an extremely enthusiastic amateur astronomer with many connections to Bay Area astronomy clubs, for his help with the solar viewing, and interesting topics of geological and astronomical conversation with the class.
Next trip - to Mono Hot Springs with the Astro 28W class in mid September. Come join us!
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