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(meteorobs) Possible lunar impacts recorded in Calif. May 7-9, & some seen from Texas; May 17th occ'n, Mex. & Cuba, by another dogbone asteroid?; GPS, etc.
More information is given below about the following topics:
1. Possible eta Aquarid lunar impacts have been videorecorded by Frank Anet
in California, and others seen from Texas; confirmation is sought.
2. Preliminary update for the occultation of 7.2-mag. SAO 210027 by the
M-class
asteroid 382 Dodona shows only a small shift north from the nominal
path the night of May 16-17, putting the likely path across central
Cuba and central Mexico (including the northern Yucatan and southern
Baja California. M-class (metallic spectra) asteroids are now of special
interest with the recent radar discovery of the dogbone shape of the
largest M asteroid, 216 Kleopatra, whose unusual shape was first hinted at
from observations of an occultation in 1991 (that was one reason why
Kleopatra was selected as the first main-belt target with the recently
upgraded Arecibo radio telescope).
3. GPS is more accurate with S/A turned off, but several minutes of averaging
are still needed to have high confidence in meeting IOTA's needed
accuracy in longitude, latitude, and height above sealevel.
4. An occultation e-group has been formed to discuss occultation recording
and timing equipment and techniques, among other things; you are
invited to join our initial trial period to see how it works.
____________________________________________________________________________
____________________________________________________________________________
1. Possible eta Aquarid lunar impacts have been videorecorded by Frank Anet
in California; confirmation is sought. A 6th-mag. impact was recorded
probably near Manilius on U.T. May 7 at 4:52:41.6 UTC (Sat. evening
local time) and another "quite bright" one occurred at 4:22:26.6 UTC
(half an hour earlier than the first-discovered flash) near Mare Nectaris.
On UTC May 9 at 5:04:26, a flash was seen in real time near Archimedes in
Mare Imbrium, and examination of the tape shows 5 flashes, the brightest
two being 6th mag., in an arc with each spaced roughly 30 arc seconds
apart (but NOT with uniform separation). At the time, the Moon alt.
was 23 deg., so others in western North America hopefully also have
this interesting meteor cluster in their videotape. If you videotaped
the dark side of the Moon during these times, please check and let us
know if you can confirm any of these events or not. Frank observed with
his wife Ragini from their new home in Valencia - his e-mail is
anet@chem.ucladot edu. More information about these observations can be
found at http://iota.jhuapldot edu
In addition, around 2:42:00 UT on 8 May 2000, Brian Cudnik
spotted a possible 7th magnitude flash north of Plato, on the north
"shore" of Mare Frigoris (near W. Bond Crater). Aside
from this, he is 95% certain that flashes brighter than magnitude 9.0 did
not occur during his observing periods of 1:44 to 2:27UT and 2:35 to 3:16UT.
Also, using a smaller telescope on May 9, UT, he thought he
saw a half-dozen or so within a four minute period randomly distributed
throughout the Mare Vaporum and points South region, between 2:04 and
2:08UT. Each was near the limit of visibility. Another
candidate was spotted just southeast of Mare Nubium (about an arcminute
southeast of its "shore" in lunar coordinates) at 2:22:22.0. This one
was possibly 6th magnitude or so. The final candidate was observed
around 2:42:30 just west of the Theophilus crater, Southwest of Sinus
Asperitany (lunar coordinates again), this one being about 7th
magnitude.
Brian Cudnik
____________________________________________________________________________
2. Preliminary update for the occultation of 7.2-mag. SAO 210027 by the
M-class
asteroid 382 Dodona shows only a small shift north from the nominal
path the night of May 16-17, putting the likely path across central
Cuba and central Mexico (including the northern Yucatan and southern
Baja California. M-class (metallic spectra) asteroids are now of special
interest with the recent radar discovery of the dogbone shape of the
largest M asteroid, 216 Kleopatra, whose unusual shape was first hinted at
from observations of an occultation in 1991 (that was one reason why
Kleopatra was selected as the first main-belt target with the recently
upgraded Arecibo radio telescope). The occultation shape of Kleopatra
was published in my planetary occultation highlights article in the
January 1992 issue of Sky and Telescope, while the new, more detailed
"dogbone" shape is at http://www.jpl.nasadot gov/pictures/kleopatra
Of course, all M-class asteroids probably don't have as extreme shapes as
Kleopatra, but probably the possibility of a surprising shape is more
likely with these objects.
My prediction gives a shift from Goffin's nominal prediction
(available in the small world view, along with a detailed finder chart,
in the asteroidal occultation section of
http://www.lunar-occultations.com/iota ) of 0.06" north (1.2 path-widths,
but with a 1-sigma uncertainty of about the same size) in the path and
-3.1 minutes (+/-0.6 min.) in time. These are formal uncertainties;
Jan Manek, being able to use observations over a longer arc of the orbit
of Dodona, has just calculated a better prediction that is two path-
widths north of my path; details, including the updated path, will
soon be placed on the IOTA Web site mentioned above. The star is in
Sagittarius at
J2000 RA 18h 21m 19.9s, Dec -32 deg. 10' 50"; if it is occulted, there
will be a 6-mag. drop in the star's light, unless the star is a previously
unresolved close double, which is possible with its A3 spectral type.
The updated path is expected to be 104 km wide (due to projection)
with its center passing about 150 km south of Havana, Cuba at 7:45 UT (the
UT date is May 17 for all; note that Manek's updated path is almost two
path-widthws north of this one so that Havana is a short distance inside
the southern limit), about 220 km north of Mexico City at 7:51 UT
(but about 400 km north of Mexico City, according to Manek),
and about 120 km south of La Paz, Baja California at 7:54 UT (with the
southern limit near La Paz with Manek's prediction). Edited
path data are given below; more extended data will be placed on the
IOTA web site mentioned above soon.
OCCULTATION OF 7.24-MAG. SAO 210027 (Goffin ID ACT 7397 00183,
SPECTRAL TYPE A3) BY 382 Dodona ON 2000 May 17
DIAMETER= 61. KM = 0.048 SECONDS OF ARC, CENTRAL OCCN. = 13.594 SECONDS
DIAMETER OF STAR= 0.176 ARC MILLISECONDS= 225.4 METERS= 0.859 FRINGES
CENTER PATH IS ABOUT 104. KM WIDE AT THE COORDINATES LISTED BELOW
*** But Jan Manek's predicted path is about two path-widths
north of this and is probably a better prediction ***
UNIV. TIME Dodona SUN MOON
LONGITUDE LATITUDE H M S ALT. AZI. ALT. AZI. ALT.
79.85 W 22.17 7 44 37.3 35.5 176.1 -34.8 43.9 32.4
82.56 W 21.76 7 45 34.9 35.7 173.5 -36.6 42.0 34.5
85.29 W 21.45 7 46 32.7 35.7 171.0 -38.4 39.9 36.6
92.12 W 21.08 7 48 55.9 34.9 164.6 -42.2 33.9 41.5
94.85 W 21.10 7 49 51.9 34.2 162.2 -43.4 31.2 43.2
97.57 W 21.21 7 50 46.9 33.3 159.8 -44.5 28.3 44.9
100.29 W 21.42 7 51 40.4 32.3 157.6 -45.3 25.2 46.3
102.99 W 21.73 7 52 32.4 31.1 155.4 -46.0 22.0 47.7
105.67 W 22.13 7 53 22.4 29.7 153.4 -46.4 18.7 48.8
108.34 W 22.62 7 54 10.3 28.2 151.5 -46.6 15.3 49.7
110.98 W 23.20 7 54 55.8 26.6 149.6 -46.5 11.9 50.4
113.59 W 23.87 7 55 38.7 24.9 147.9 -46.3 8.5 50.8
___________________________________________________________________________
3. GPS is more accurate with S/A turned off, but several minutes of averaging
are still needed to have high confidence in meeting IOTA's needed.
From the following from Joe Hobart, Flagstaff, AZ, it is
clear that some averaging is preferred to obtain the
accuracy that IOTA would like in positions. Probably
10 minutes would be sufficient in almost all cases, but
a reasonably unobstructed view and reasonably good
satellite geometry are important - with them, probably
even only two or three minutes would be all right.
But if you are not sure how good the geometry is, then
record for 10 minutes. If that shows some periods of
large excursions, record for 5 or 10 more minutes so
that either obviously discordant data can be removed,
or to ensure that the averaged position is accurate
enough. These are my impressions, to achieve 15m
accuracy that IOTA would prefer to have - others might
have some better advice after more observations are
made. Of course, longer averaging times will always
give a better result, but times longer than 10 - 15
minutes become impractical when more than a few
stations need to be surveyed for a distant lunar
grazing or asteroidal occultation expedition. In any
case, now I agree that scaling positions from USGS
maps will soon become passe as observers acquire
inexpensive GPS receivers. The maps may be useful
for checking (or determining) heights above sealevel
(which can be obtained from online versions of the
maps, such as those at www.topozone.com), but I think
even for heights, several minutes of GPS measurements
will usually be good enough. When getting heights
from other sources, be sure that the coordinates are
all referenced to the same datum. That is another
reason to use just GPS measurements, which usually
use the GPS WGS84 datum, since maps always give the
heights relative to the local geodetic datum. More
information on GPS accuracies will be posted on
IOTA's site at http://lunar-occultations.com/iota
as it becomes available. Note that for lunar
occultation observations, IOTA prefers an accuracy
of +/-16 meters (about 50 feet) or better in each
coordinate. 30 - 50m accuracy is all right for
most asteroidal occultation observations.
The next step will be
to build something like the Japanese GHS clock
(GPS-based for video time insertion) that can be
used with commonly-available inexpensive GPS
receivers (the GHS clock only works with the
Japanese Jupiter GPS receiver, which doesn't
seem well-suited for averaging positional
observations). Information about it is on the
IOTA Web site at
http://www.lunar-occultations.com/iota
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
From: <jrh@nofs.navy.mil>
Date: Tue, 2 May 2000 06:53:22 -0700
To: dunham@erols.com
Hello All,
And SA is indeed off!!
Despite what others say about being within feet, the following
were observed:
For some time after SA was turned off the altitude was 2100 meters
or about 25 meters above my "reference". It later improved to
about 4 meters above my "reference". Also there was one time of
five to ten minutes when the error was as much as 18 meters in
horizontal (18 meters at 171 degrees true). This was very
obviously due to poor statellite configuration.
These figures were taken from the SA Watch program with a Motorola
GT+ GPS receiver running without differential corrections. The
antenna is mounted on top of an unused wood stove chimney about
six meters above ground.
Preliminary report for the first eight hours without SA:
Average: 35 05 59.21 N 111 41 34.86 2078 meters altitude
Reference: 35 05 59.20 N 111 41 34.87 W 2074 meters
Difference is 0.4 meter @ 051 degree true from a position
determined by MONTHS of averaging with SA turned on.
For this eight hour period,
Percent of readings Were within
99 10 meters
95 10 meters
68 4 meters
50 3 meters
Life is good. "Gimme a Bud!!!"
Joe Hobart
Flagstaff, AZ
____________________________________________________________________________
4. An occultation e-group has been formed to discuss occultation recording
and timing equipment and techniques, among other things; you are
invited to join our initial trial period to see how it works. It was
formed before the announcement of GPS S/A being turned off, a natural
subject for this group.
Date: Tue, 02 May 2000 19:28:49 -0500
From: Rob Robinson <webmaster@lunar-occultations.com>
Subject: new outlet
To: David Dunham <dunham@erols.com>
I created an account at egroups.com for IOTAoccultations.
It can be accessed via:
http://www.egroups.com/group/IOTAoccultations
I did this for several reasons:
1) it is open to anyone who has an interest to ask questions, discuss, etc.
2) if for some reason timely information needs to be disseminated, and I am
not available, it can be posted there, with an email directing members to it.
3) it may spur interest in IOTA by non-IOTA members browsing the postings
4) IOTA and IOTA/ES will have a common ground to share and discuss.
5) It may prove more fruitful than the bulletin board I have on the main
page (which I am thinking of removing).
We can try this for a 90 day period and see what activity it generates. If
it looks like a dying ship, then I will remove it.
You might send a mass email to the general membership regarding this new
feature, and encourage them to use it, than private email on discussions on
such topics as the GPS time deal. That way it would be open to more
discussion by a larger audience.
====================================================================
Rob Robinson Bonner Springs KS, USA
Vice President of Occultation Services - IOTA
Webmaster for the IOTA Lunar Occultation Homepage
http://www.lunar-occultations.com/iota
94.8932 West 39.0579 North 249.7 Meters
====================================================================
____________________________________________________________________________
Joan and David Dunham
7006 Megan Lane
Greenbelt, MD 20770
(301) 474-4722
dunham@erols.com
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