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(meteorobs) RE: Important new Leonid obs. info.; Linearids; Binary Kleopatra
I thought the discussion of sonic booms might be of interest.
As I understand the issue the booms if they happen, are
usually reflected by the tropopause where the stratosphere
begins. If someone were above that and not on a noisy
airplane I would think one could hear/record them with
amplification.
----------
From: Joan and David Dunham
Sent: Saturday, November 13, 1999 9:57 PM
To: webmaster@lunar-occultations.com
Subject: Important new Leonid obs. info.; Linearids; Binary Kleopatra
More on observing the Leonids, and Linearids; Binary Kleopatra:
_________________________
DON'T USE EXTENDED PLAY; don't aim cameras low
Peter Gural writes:
"Do NOT use extended play when recording meteors as this does
degrade the imagery with added noise.
Also I would not aim cameras below 45 degrees elevation due to
extinction. Best angle in elevation is 60 degrees but folks can go
higher. Also best in terms of highest probability of catching a
meteor is 60 off the radiant but these are only guidelines and dont
have to be that close (say +- 20 degrees)."
_________________________
Determining Limiting magnitude for lunar observations; focal reducers
Jeff Lackmeyer asked:
>I have some questions about the lunar video. I know I need to do a
limiting magnitude determination of the video system. I haven't
done one before, but I think I know how to do one in principal.
Since the moon will be in Aquarius, I figure that I need to print
out some of AAVSO's Aquarius charts from the web, scan stars in
those areas, and identify the dimmest star visible on tape.
My answer: But going away from the Moon will defeat the process,
since lunar glare reduces sensitivity. Rather than scanning
selected stars away from the Moon, it would be better to try to
image the brightest stars that will be occulted, or just scan ahead
of (the dark side, which will be advancing) the Moon to see if you
see any stars. I'm copying this to Rob Robinson; maybe he can put
some multisite predictions on the web for some of the 7th and 8th
mag. stars that will be occultated like he has done now for psi 1
Aqr. So far, I have just addressed the occultations on the evening
of the 17th, but we should look at those on the evening of the 16th
as well. I notice an error in my Nov. 9th message; the first star
listed for Washington should have been identified as SAO 146509.
>For this application, how precise does the determination
>need to be, i.e. what is the desired precision, +/- 0.5 or
>more precise?
I would think to about half a mag. would be fine.
>Does it need to be determined in real time, or can the
>limiting magnitude tape be reviewed later?
It should be done the night of the observation and near
the Moon, as mentioned above. Of course, any haze or thin
clouds will also affect what you can see.
>Since
>the moon will be much lower in the sky at the end of a recording, is there a
>need to do the determination both at the beginning and end of the recording
>period?
Yes, that would be useful, if there are suitable stars occulted
both early and late.
>does it really need to be done both nights?
Yes, because the lunar glare will be a little greater on the
17th than on the 16th, and sky transparency might differ, too.
>While the video system may not be able to pick it up, there will be
some earth light on the dark side. This may reduce the magnitude of
the detectable flashes.
That won't be a strong effect, the Earthshine will be quite faint.
>Also there is the effect, that when a very dim star is video taped,
it my look steady when played back at normal speed, but may show a
great deal of flicker when stepped frame by frame. The flashes may
last only a fraction of a second, and may sometimes get lost due to
this flicker.
Hopefully, some will be bright enough to see the structure of their
decay in brightess by single-framing.
>I also have a question regarding the use of a focal reducer in this
application. My understanding is that in theory, the F ratio used
has no effect on the limiting magnitude of a point source. In
practice, the focal reducer adds more air to glass surfaces with a
slight loss of definition and probably limiting magnitude as well.
Is the slightly lower limiting magnitude worth the gain of FOV that
the focal reducer would provide?
Certainly. Also, you will probably GAIN in limiting mag. with the
focal reducer because in practice, stars (and meteor flashes) are not
point sources; they are smeared into seeing disks. By using a focal
reducer, the finite size of the seeing disk is concentrated on fewer
pixels of your camera's CCD, providing more light for each pixel and
a gain in sensitivity. This more than offsets the loss due to more
glass surfaces, etc. So focal reducers are a win-win situation.
David
_________________________
Obtaining the PC23C camera:
One observer asked:
> ("...with the sensitive PC23C camera costing only $79,...)
> Could you give me any more specifics on this, ie: manufacturer or a
>web site where I can look this up?
See http://www.supercircuits.com for ordering and some technical
info. about the PC23C. See also the item about video setup tips by
Scott Degenhardt and others (tells accessories needed to use with
the camera, etc.) at http://www.lunar-occultations.com/iota
_________________________
Leonids silent? 1966 veteran Richard Nolthenius writes:
FWIW, I saw the storm of '66 from the Mojave Desert, with rates of
many many meteors / second, including a number of bolides comparable
to large phase moons - and not a single sonic boom. I'd be really
suprised to "hear" of any this time around. Don't sacrifice too much
to aim for sonic booms, is my advice.
I'll be video recording with our PC23C from Fremont Peak.
_________________________
A few meteors from the LINEAR (Comet C/1999 J3) radiant were seen,
but no storm:
__________
I would like to report an observation of the Linearids meteors.
On the night of Nov 10-11, I went to Chews Ridge, CA to attempt
observing any activity from this new shower. I observed from 7:30pm
-11:15pm PT. The sky conditions were mostly clear, but some high
cloudiness occaisonally so the ZLM varied from 5.5 to 6.2. Just
after I arrived at the location, I saw a mag 2.0 Linearid at 7:45pm
or 03:45Z, which is about 16hr before the published closest approach
time. The meteor was moderate speed, about 20 deg path length,
passing "upward" in the NW near the constellation Cygnus. The path
traced backwards almost exactly to the bowl of the big dipper.
I did not observe any other Linearids in the remaining 3 hours or
so. I did observe several Taurids, though.
Sincerely,
Mike Linnolt
6033 Geary Blvd. #318
San Francisco, CA 94121
__________
Mike,
Thanks for your Linearid report. You asked:
>Have you heard of any other observers report any Linearids?
There is a claim of one bright possible Linearid seen
from central Arizona, I think also the evening of the 16th. D. Dunham
__________
I observed from ~21:30 to 22:30 on 11-9 and saw one mag. 0 meteor
that would trace back to the bowl of Ursa Major. This was from a
limiting mag. sky of ~ 3.
On 11-10 from 20:30 to 23:00 I observed about 3 potential Linear
meteors and about 6 Taurids. This was from a sky of limiting mag 5
with milky way visible overhead. Limiting mag ~ 2.5 at 20 degrees
from horizon.
11-9 observation was from Lincolnton, NC. 11-10 observing was from
western Lincoln Co. This is NW of Charlotte in the transition from
Piedmont to foothills region.
-Brian Hissom dbhissom@abtsdot net
Catawba Valley Astronomy Club
__________
As a warm-up for the Leonids next week, I got out this morning
(0400-0500 CST). Except for haze that blocked out about 10 degrees
above the horizon, the sky was very dark and clear. Limiting mag.
about +6. Observing location: +33.6690 -94.1755, 2.5 miles west of
Ashdown, southwest Arkansas. Counted a total of three very faint
meteors coming from the predicted radiant in the bowl of the Big
Dipper. Walter Webb, Red River Astronomy Club.
_________________________
Binary Asteroid (216) Kleopatra
IAU Circular 7308 issued today reports that images of Kleopatra
taken with the European Southern Observatory's 3.6m telescope with
an adaptive optics system on October 25 shows a bifurcated shape or
a nearly-contact binary system for Kleopatra. Images and more
information is at http://sc6.sc.eso.org/~fmarchis/Science/Kleopatra
Earlier Arecibo radar observations indicated that Kleopatra was
probably bifurcated. On 1991 January 19, an occultation by
Kleopatra was timed from 9 stations. Analysis of the timings showed
that Kleopatra was unusually elongated, about 60 km wide by 240 km
long; the results are shown on p. 73 of the January 1992 issue of
Sky and Telescope, and also at http://www.anomalies.com/iotaweb
(Under "About IOTA - Official FAQ", 1st item there, "What is an
example of the result of an event?"). It was fortunate that at the
time, Kleopatra was near a maximum of its light curve, indicating
that it would be broadside to us. The opposite was the case (near
minimum light, end pointed nearly towards the Earth) during the only
other well-observed Kleopatra occultation, on 1980 October 10.
_________________________
David Dunham, IOTA, 1999 November 13
Joan and David Dunham
7006 Megan Lane
Greenbelt, MD 20770
(301) 474-4722
dunham@erols.com
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