[meteorite-list] Trojan And Other Asteroids, Part One

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Sun Jun 26 03:12:27 2005
Message-ID: <42BE5538.1BE09134_at_bhil.com>

Hi, All,

    Having trouble posting. If this a dulpicate, delete. Sorry.

    The other web page in my first post about Earth Trojans:
    <http://www.astro.uwo.ca/~wiegert/etrojans/etrojans.html>
    Jerry, it has lots of animated GIF's, nifty diagrams, and
downloadable MPEG movies of the dynamics of the Trojan points,
along with an explanation that is almost as good as MexicoDoug's!
    You can't beat all those bright moving colors in an
explanation, I always say.

    And while we've been thrashing the topic of asteroid
3753 Cruithne, to which I will refer to as "Crazy Cruithne"
from now on, to death, the REALLY interesting thing to me I
found on that site (above) was a detection image of what may
turn out to be a true Earth Trojan! (You have to track one a
long time to be sure.)

    A real Earth Trojan. That would be wonderful if verified.

    They don't give the magnitude of the potential Trojan object, but
since they're using the big Canada-France-Hawaii telescope, I eyeball it
by comparison with fainter objects in the frame at perhaps magnitude 21
or so? That would make it about 300 to 600 meters, roughly. But I'm
guessing.

    They search 9 or 10 square degrees of sky (because of those loopy
"halo" orbits) and at this scale, that's a lot of territory to cover
searching by tiny, tiny patches. They don't say how much of that
territory they've covered, searching for an always moving target, and
don't say if they continue to search. If you've ever had the experience
of inadvertently "losing your way" while examining something under a
high power microscope, you know what I mean. "Where did it go?!!"

    I once had a "choice" summer job at my school, a temporary electron
microscope operator. If you think it's easy to "get lost" at 500X, try
50,000X! Incredibly frustrating when it occurs to you that it's like
searching a square kilometer area one or two square centimeters at a
time! Of course, my boss only did that a few times, and only to impress
on my youthful ego how little I really knew (very necessary), then set
me on simpler routine tasks at lower powers and gave the important jobs
to the "real" operators. Most of them didn't know an electron from a
Buick, but they could tickle those cranky old machines -- they had the
"feel." I didn't. I was a crackerjack calibrator, though. Picky,
picky, picky. Knowing how an electron thinks helps, too.

    Magnitude is a whacky unit of measure. When old Ptolemy made the
first star chart in all of history (that we know of), he naturally
wanted to indicate the relative brightness of the individual stars
compared to each other. It wouldn't be very useful to puts lots of
equally tiny dots all over the first skymap.

    But stars are points on the sky, no matter how bright, so you can't
make the brightest ones huge fat blobs. He knew of course that a dot
twice the size of another dot had PI times as much area and so could
indicate a star PI times as bright, but that was too big a step and
then the biggest dots weren't big enough.

    Close, but not quite right. You don't need to make a dot twice as
big for people to see easily and intuitively that one is bigger than
another. A 50% or so increase in diameter is enough for that. Besides,
PI was a mysterious thing to the Greeks, a religious mystery if you were
a Pythagorean, and IRRATIONAL. The Greeks just hated that.

    Ptolemy was estimating the stellar brightnesses by eyeballing and
comparing them. Great astronomer; no telescope. He knows he can reliably
group stars by brightness when one is about 2.5 times brighter or dimmer
than another, so he stages up the size of the dots to correspond to a
scale of "magnitude" in which each increase in one "magnitude" is a star
2.5 times brighter than a star with next smallest dot on The Great
Chart.

    In so doing, he invents the first logarithmic or power scale in
human history! I don't think he appreciated what he did or how useful
the notion of logarithmic scales could be. Of course, maybe he did, but
kept it his own little secret, as there are stories that other scholars
brought him hard messy numerical problems to which he would smilingly
hand back the answer to the next day. No problemo. Glad to help out,
Anaximos, old buddy. A good trick always helps your reputation as a
genius, you know...

    OK, he got that whole structure of the solar system thing wrong...
Hey! Nobody's perfect.

    The modern magnitude scale is based on powers of 2.512, a snap to
calculate with cheap modern calculators. In the "old days" there were
tables of magnitude to luminosity conversion in fine print by the 0.1
magnitude step, with little rows off to the side to interpolate the 0.01
steps, just like there were for regular logarithms. That was in the era
when a simple four function calculator like you can buy for 99 cents in
the Dollar Store or Target today cost $1500 straight from Remington
Rand! (And couldn't have done the job, anyway.)


Sterling K. Webb
----------------------------------------
Received on Sun 26 Jun 2005 03:11:52 AM PDT