[Prev][Next][Index][Thread]
(meteorobs) 1950's Harvard meteors. Motion Detection
Re Marco Langbroek's note on Harvard Survey meteors.
Sorry: I meant to use the fact of the potential IRAS-Iraki-Alcock 1953/4
meteors as an indication of possible longevity for the shower. I had no
intent of suggesting 'more strong' then. I had intended to note that there
was the possibility of a serious sampling based selection effect due to the
surveys being few and far between... ...I must have forgot.
Marco's hit the nail on the head re the video survey need.
It's a shame that the moon was pretty good for such a survey this year: ie
opportunity missed. Most of the photo and vid groups are no doubt putting
all their efforts into the difficult task of catching eta Aquariids from
northern climes. I'm not sure that's going to allow much field of view
overlap with the eta Lyrids, but I've no idea of the details of such things.
I'd found no meteors with IRAS-Iraki-Alcock orbital connection in either
the DMS photo or video orbit databases, nor in the Japanese MSSWG dataset,
with the latter seemingly an all year round survey, whilst the former
appears to be more shower campaign orientated [ie not likely to pick up eta
Lyrids by accident].
MOTION DETECTION
Right where to start, and how not to go on too long! Okay...
Field of view tests: I have one once a year cos of the slightest of indents
in my right retina [ie, to make sure it's a normal blip and not increasing
in extent]. It is a peripheal vision test designed to map the outline of
the retina. It's nothing to do with motion detection. "Ah, but..." you
say "why do they flash lights in the middle of the eye if they're testing
the edge?": ANSWER :- to map the blindspot and/or test for any incipient
maculation.
It is of course possible that RMcN & ML have had other tests which just
sound like mine but are not the same.
MOTION DETECTION per se:- okay, you have a white screen with parallel
black lines on it. It & yourself are moved far enough apart so that you
can't resolve the lines anymore, and you just see a greyish screen [given
sufficiently thick lines]. At this point the lines are somehow set moving.
Do you think you'd notice this? Very probably. Motion detection is at a
higher resolution than vision. You'd also notice it more when it started
and when it stopped than when it was in motion.
Motion detection is more a brain thing than an eyeball thing [yes, I do
know the retina is a sticky out bit of brain...] You don't "see" it at the
lowest level, you "detect" it. If you notice summat move out of the corner
of your eye, you look around _quick_ to see what it is: you wouldn't bother
if you already knew.
If the Rob McNaught who wrote is the legendary Rob McNaught from Australia,
you've probably had more of a chance to use a blink comparator than the
rest of us. If so, I'm sure you note no difference in your ability to use
one. Possibly the faintest things aren't as easy as they once were, but in
meteor work that'd show up as a change in your magnitude distributions over
time [though varying moon, weather & meteor shower structure don't help
such investigations].
The above is also a bit pattern based though. If you want a test to see
how your personal motion detection capabilities are over time, I'd suggest
that simple "personal equation" would suffice. Visual occultation
detection is going to be slightly akin to meteor watching. You're waiting
for something you know is going to happen, but not entirely sure when or if
[asteroid occultation better example than lunar here]. When it happens you
log it. Occultation people need to allow for their personal equations to
correct the logged time.
Personally, I reckon your personal equation is not going to be much
different than it ever was. However, this is no good for testing between
people, because it is a _personal_ detection test, not an intercomparison
of relative detection abilities between folk.
ASTIGMATISM: Mike Linnolt says he has astigmatism. I know a couple of folk
with this. The brain can allow for astigmatism, so that optical correction
is not always necessary. Except for the fact that there is then a terrible
price to pay, as this extra effort can cause people to have terrible near
migraine level headaches at the back of the head [the poor old visual
cortex gets overloaded].
Peripheral vision and averted vision aren't necessarily the same, some may
be surprised to learn, basically because the rods ['night vision' bits]
are mapped at varying concentrations upon the retina. If you're not
correcting for the astigmatism maybes the collection of rods just off eye
centre is not getting as much use as in non-astigmatic folk, and you're not
getting as faint. I dunno...
I _did_ know someone who swapped from spectacles to contact lenses and
gained almost a magnitude or more [in a kind of "where did all those stars
come from!?" sort of way], so I _wouldn't_ try using spectacles if I was you!
Personally I'd say what is really happening between Norman MacLeod and Mike
Linnolt is one has greater visual acuity, whilst the other has greater
peripheral vision... ...relatively speaking. Motion detection irrelevant.
OF COURSE, this is reckoning everything else as equal, vis a vis observing
sites etc. You can be stuck at an observing site with next to no field of
view and still very see faint stars overhead if seeing/light pollution allows.
As for a test of field of view... ...I dunno. I've just stuck my arms out
sideways as far they go, trying my best to keep a straight line through
them via my torso, and then raised my thumbs and tried my best to look
straight ahead. I can just "see" a hint of my right thumb, but not my left
one unless I bring my left arm forward a bit. There's crude and
unscientific for you, but if one can see neither whilst the other can see
both, it's a measure. And of course, if you can see the back of your
hands, you're probably a rabbit...
In closing, I'm not great authority on these things, it's just bits and
bats I've picked up over the years, everyone use their own experience to
weigh up the above. I'm pretty certain motion detection is to a far higher
resolution than "seeing" vision. It's more "hard wired" as well, so
reaction time is quicker [ie you detect it, you don't "think" about it: if
you catch a high altitude plane's strobe at the very periphery of vision
you'll detect it before you'll identify it as a non-meteor (this is
probably experience dependant though)].
Anyway, how "exact" are the corrections used to transform results from
differing observing circumstances to a common ground? Is it a "science" or
a "state of the art" thing? ie, is it really "twice" as many, and should it
really only be "20%" more likelihood? Shave one, raise the other, & the
discrepancy fades. [Swap homes for a month!]
Peripheral vision and averted vision are not necessarily the same: it is
not necessarily the case that someone who sees faint light has as wide a
field of view as someone who does not, although obviously all combinations
of ability are possible.
Cheers
John
John Greaves
UK
To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html