You can be an IOTA Local or Regional Coordinator -
Help Organize and Report Occultation Observations in Your Area
For over twenty years, IOTA members have organized expeditions for
grazing occultations from the cities where they live. But now that
predictions of the paths of asteroidal occultations are becoming more
accurate, coordination of observations of these more difficult events on a
regional basis is becoming more important. In addition, many camcorders
can now directly record occultations of 5th-magnitude stars, opening up
the possibility of large numbers of accurately-timed observations of
occultations by even members of the general public who have no previous
background in astronomy. But in order to tap this potential resource, as
well as the existing resource of amateur astronomers in your area who can
increasingly be reached quickly via e-mail, local coordinators are needed.
You don't need to be a member of IOTA to help with this, although, of
course, if possible that would be preferred - our half-price rate ($15 in
North America) for on-line membership should make that more attractive.
But in any case, let us know if you can help perform some of the tasks
described below for your city or region. There is much that can be done,
so you might try to find others in your local astronomical society who
could help, with perhaps one person concentrating on asteroidal
occultations, while others organize graze expeditions and video
observations of lunar occultations of bright stars. A first step is to
announce upcoming occultations of all types in your local astronomical
society newsletter - find out from the newsletter editor what the
deadlines are for submitting short lists of the better events. When you
prepare such "stategic plans", perhaps on a monthly basis, they can also
be distributed by e-mail across your region and posted on local and/or the
IOTA Web sites (we welcome local notices on the IOTA site - that might
point some new observer in your area who first browses our site towards
your efforts). My geographically-arranged e-mail list can be used as a
starting point; you can probably add other potential observers in your
area. As the dates of important events approach and the long-range
weather forecast (and preliminary update or nominal prediction for
asteroidal occultations) appears favorable, additional work described
below should be undertaken. The IOTA Web site for most occultation
information, and for the coordination efforts, is
http://www.sky.net/~robinson/iotandx.htm
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ASTEROIDAL OCCULTATIONS: Plot the updated prediction on a small-scale
road map or aeronautical chart of your region, or just draw the path
on the map approximately from looking at the blown-up worldview map that
is available now with most asteroidal occultation updates, or just use
the provided map. Plotting the path on your own map gives more accuracy,
but that takes time and we are all busy; just do what is necessary to get
an overview of the situation. See what the coverage of the updated path
is from observers whom you have notified by e-mail, and telephone a few of
the key observers to try to get commitments that they will try the event.
Too many asteroidal occultations these days are observed from only one
station, but at least two are needed to get a measurement of the diameter
of the object, and more to better trace out its shape. If some of the
observers in your area are mobile (many are these days just to escape
light pollution), encourage them to fill in gaps of those who will observe
from home. Well before the event at convenient occasions such as star
parties or club meetings, help others practice finding target stars for
upcoming events, and distribute copies of the IOTA finder charts,
especially to those who can't obtain them from the IOTA Web sites.
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GRAZING OCCULTATIONS: For the monthly notice, at least estimate where
promising events might be seen by looking at the observer scan at the
bottom of the predictions to see which towns are close to the predicted
limit. Grazes of fainter stars can be quite interesting to observe and
give much useful data if the Moon is a crescent with small percent sunlit;
consider all conditions (Star mag., path distance, percent of Moon sunlit,
cusp angle, and Moon and Sun altitude) when selecting grazes that might be
attempted. For some of the better events, plot them on a 1:250,000-scale
map, showing the zone in which multiple events might occur based upon
examination of the predicted profile; you might get it copied in local
club newsletters or posted on a Web site, to which observers can be
referred by e-mail. Web posting is also possible for other events to
refine plans two or three days in advance if the weather forecast is
promising. For observers who don't have shortwave time signals, a local
radio station might be recorded along with shortwave time signals at one
site, so that car radios can be used with the selected local station at
other stations. A digital watch set to WWV during the meeting an hour or
so before the graze can also be used - the observer can then just call
out times to his/her continuously running tape recorder (or camcorder that
might be used as a tape recorder, if the star can't be imaged directly
with the camcorder pointed into the eyepiece of the telescope). See the
file grazein.tro for further information. After the graze, the station
locations must be determined and the timings collected before the
observers lose their tapes or forget possibly useful information that
might not have been recorded explicitely on the tape. The new report
form, email76.fnw, should facilitate reporting the observations.
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TOTAL LUNAR OCCULTATIONS OF BRIGHT STARS: Since much better stellar data
are now available, the more accurate timings that can be obtained with
video and with a few CCD systems are sought for total lunar occultations.
More observers are purchasing the inexpensive (usually less than $100; the
price varies some with different sales offers) PC23C half-ounce video
camera from www.supercircuits.com, and developing a full video capability
to record occultations of 8th mag. and fainter stars following the video
setup advice on the IOTA Web site. But even simpler for the many
observers who have camcorders is to simply point the camcorder into the
eyepiece of a telescope - occultations of 7th-mag. stars with 6-inch and
larger telescopes can be recorded quite easily that way. A hand-held view
of an occultation or graze through the eyepiece is jiggly, not making for
the best video show, but the accurate timings that we seek can be obtained
from such recordings. And now, with 30x and higher camcorders becoming
commonplace, occultations of stars as faint as 5th magnitude can be
recorded directly without a telescope.
Two major efforts are needed: Publicize suitable events in your area,
especially among amateur astronomers, reserving public efforts for the
best events, like the naked-eye Aldebaran occultation on April 18-19
visible from northwestern North America and the Regulus event visible from
most of North America on May 21-22 (events like the Jan. 26-27 Aldebaran
occultation in the western 2/3rds of North America, although not quite as
good, are also suitable for camcorder campaigns). That's the fun part;
the harder part is to measure accurate positions and determine timings,
then prepare a suitable report. So far, our efforts have not resulted in
swamping us with data and work, but hopefully some of the 1999 campaigns
will be more successful in generating many observations. If that happens
in your area, identify the most conscientious observers and enlist their
help in refining their own data, and helping with the data from a few
nearby observers as well. I have found that many new-time observers are
quite careful and want to help, so tap their talent as well as their
observations.
We have a new report form, available on the IOTA Web site, that is
easier to prepare than the old E-mail 76 form. The new form, in a file
named email76.fnw, is also limited to 76 columns per line. It can not be
used to directly report observations yet since we have not completed a
program to convert it into the format needed by the computers at the
International Lunar Occultation Center (ILOC). That program should be
ready in about a month, and will be announced by e-mail and on IOTA's Web
site then. Reports can also be prepared using the EASYILOC program
available on the IOTA Web site, as well as with the Occult and Lunar
Occultation Workbench programs; those 80-column reports can be sent as
attached files to ILOC.
Unless you have access to expensive differential GPS equipment, the
best way to determine geographical coordinates in most areas is to
carefully measure the best-scale topographic map available, or use the
computer-readable version of the map if you can obtain it. See the "Your
Station Coordinates" section of the 1999 IOTA prediction message for more
information. Measurements with a single GPS receiver are good enough for
IOTA/ILOC accuracies only if hundreds of observations obtained over at
least a 90-minute period can be averaged to reduce the large Selective
Availability errors normally introduced by GPS. More information about
determining geographical positions is on the IOTA Web site.
Just playing back a videotape and using a stopwatch to determine the
times, like repeating a visual observation, is all right for grazing
occultations, but for total lunar occultations, accurate timings are more
important. For them, an accurately time-inserted copy of the tape should
be made so that you can just find the single frame where the star
disappears or reappears and read the time from the display. A correction
might be needed if there is a rate drift, by checking the display at a
minute mark before and after the event. At present, there are only two
time inserters that give displays that can give the full video accuracy,
the time inserter designed by Peter Manly several years ago that triggers
from the 1000-Hertz or 1200-Hertz minute tones of WWV or WWVH (several
other time signals also use one of these frequencies, such as CHU), and a
newer, more expensive one that obtains time from GPS; information about
them are on IOTA's Web site (or soon will be). Both require some
electronics skills and time to fully assemble. Other devices are under
development, so there is hope that in the next few months, a more "off the
shelf" time inserter will become available. In the meantime, you can send
tapes to
Rick Frankenberger
8702 Timberbriar Drive
San Antonio, TX 78250 USA
His email address is:
rickf@stic.net
to obtain a time-inserted copy - he uses one of the Manly time inserters
to provide this service for IOTA. If you have a tape with some 1998
observations, now is the time to send it to him. When you receive the
time-inserted tape, you can then view it to obtain the timings for the
ILOC report. Procedures for this are on the IOTA Web site.
The above covers reporting observations. To obtain observations,
a local coordinator can do the following:
1. Try to videorecord (or use the PC-controlled IOTA Occultation Camera,
if you have one, currently available only in Europe) the occultation
yourself, recording, if possible, WWV, CHU, or DCF time signals, or a time
display automatically triggered by them (such as using the Cuno time
inserter that uses DCF in Europe).
2. Use your camcorder (or a borrowed camcorder, or ask a friend to do
this) to record a local TV station that will be broadcasting during
the occultation. Record the selected station along with WWV, CHU, or
other time signals to create a master tape for your area. It must be an
"over-the-air" broadcast, not a cable version of it. This is because the
cable network uses geosynchronous satellites for distribution, and even in
the same area, there can be different numbers of "hops" to and from the
satellites, causeing unknown delays in the signal in different
neighborhoods. So if you have cable, don't use it for this job; get out
rabbit ears, if you have them. The quality of the image is not important
as long as you can distinguish when scene changes occur. The recording
should cover from ten minutes before to ten minutes after the occultation
time in your area. Also record for the bright-limb event (for first-mag.
stars) if you know of other observers who will be recording the
occultation with camcorders pointed into the eyepiece of their telescope,
but who don't have time signal receivers. You will probably want to record
the occultation with the camcorder yourself, leaving a few minute gap in
the coverage. If so, just make an ordinary VCR recording of the TV
broadcast (THAT can even be cable), or arrange for someone else to do so.
It can be used as the master tape after two or three points (broadcast
scene changes) from your camcorder/WWV/CHU/DCF recording of the station
are timed accurately. If you can arrange this, please inform me or Rob
Robinson (robinson@sky.net) so we can add your selected TV station to our
list of useable stations that we will maintain on the Web. If it's
inconvenient for you to do this job, try to find someone else, perhaps a
radio ham, who might be able to perform the task. If this task can not be
performed, then observers with WWV, CHU, and/or DCF receivers, Arcron
clocks, or other sources of accurate time can be encouraged to observe.
If this task will be undertaken, proceed with the other tasks below.
3. Encourage other amateur astronomers, and other friends and
relatives in the region of visibility to record the occultation with
camcorders or small videocameras that can be attached to telescopes.
Try to borrow one if you don't own one.
4. Spread word about the occultation via bulletin boards and e-mail;
you might get permission to distribute information at your office or
school.
5. For very favorable events that can easily be recorded directly with
most camcorders, try to publicize the event in the media, at planetariums,
and/or via local high school science teachers. You can use the sample
press release below for this [Replace the local information for
Baltimore and Washington, and the event-specific and reporting
information, with the corresponding information about the occultation for
your area]. The IOTA Web site will give information about events that
might be suitable for public efforts, as well as detailed predictions and
advice on what power camcorder would be suitable. The sample event below
(Dec. 30th Aldebaran in Maryland) was good for telescope uses, but not
really suitable for the public; it was clear, and, with a 0 deg. Sun
altitude, the sky was too bright to see the star in 25x camcorders. It
would have been suitable farther to the northeast, with the Sun alt. -6
deg. or more below the horizon, but for the Dec. 30th event, it was cloudy
there.
6. Encourage those with telescopes to use it with a camcorder to
record the bright-side event.
7. Collect videotapes of the occultation made in your region, and help
observers with the determination of their longitude, latitude, and
height above sealevel to an accuracy of about 0.3" (or 10m or 30 feet),
if this has not already been done (see above).
______________________________________________________________________
****** A sample local email message/press release is below ******
Binoculars Eclipse of Bright Star Wednesday afternoon, Dec. 30th
Astronomers need your and your friends camcorder records
for lunar and solar (Earth climate) studies
Late Wednesday afternoon, December 30th, the bright orange star
Aldebaran will be eclipsed by the nearly-full Moon. The disapearance on
the dark side of the Moon can be seen with binoculars throughout the
northeastern USA, weather permitting (the forecast calls for mostly
clear skies by sunset). This event is called an "occultation"
by astronomers. A figure that will be placed on the Web Tues. evening at
shows what the occultation will look like in central Maryland. But you
only need to look to the left of the Moon, on its dark side, to locate the
bright star when it abruptly vanishes behind the oncoming edge of the
Moon. The star might be seen several minutes before it disappears, at 4:46
pm EST in Baltimore and 4:45 pm in Washington, DC (the Sun will be just
setting in the southwest, with the Moon rising in the east, about 18 deg.
above the horizon at the time). Farther to the northeast, especially in
New England and eastern Canada, the event will be more favorable, with
disappearance a few minutes later in darker twilight conditions than in
Maryland. Aldebaran will be harder to see in the glare of the nearby
sunlit part of the Moon as it reappears, at 5:39 pm in Baltimore and 5:38
pm in Washington. The bright part of the Moon will overwhelm the star a
minute or more after the reappearance, which might be seen only with the
help of binoculars or a small telescope.
[If printed, this space is for the Moon view for your city; add enough
blank lines. To prepare a local Moonview, you can print the Moonview
for several cities from the Aldebaran Moonview item on the Web site,
and copy it, cutting out the Moon's disk. Then, if your city is one of
the ones plotted, just draw the D and R line for your city by tracing;
you can label it like the one for Boston that is now on the Web site.
If the path for your city is not on the plot, use the cusp angle (CA)
or position angle (PA) or Watts angle (WA) for your city from the
prediction list, and the values for adjacent plotted cities to
interpolate the path for your city.]
In central Maryland and the Washington, DC metropolitan area, the
occultation can be videotaped by anyone with a good view to the east and a
20x or higher camcorder [as noted above, even 25x camcorders failed to
show the star directly]. We will accurately time the TV broadcasts of
WBAL, Channel 11 (Baltimore) and WJLA, Channel 7 (Washington) and
encourage as many camcorder owners as possible to record this rare event,
as well as WBAL-TV or WJLA-TV before and after the disappearance to
provide an accurate time base [on many printed copies, "reappearance" was
printed here rather than "disappearance" by mistake]. Recordings from many
locations will allow the edge of the Moon to be mapped in unprecedented
detail, with more accuracy than was obtained with the Clementine lunar
orbiter in 1994, reducing the current largest source of error for analysis
of past solar eclipse timings. These solar eclipse observations in turn
are used to measure small but climactically significant variations of the
solar diameter, possibly shedding light on the controversy of how much the
current global warming trend is due to increased burning of fossil fuels
and how much of it is due to natural variations of the Sun. But the use of
solar eclipse timings for this purpose is now limited by our knowledge of
the lunar topography.
Camcorder users should do the following:
1. At 4:40 pm (Five minutes before the disapearance in Washington, and six
minutes before it in Baltimore), turn on your camcorder and record a
minute of WBAL-TV or WJLA, aiming the camcorder at the TV screen (only
the image is needed, not the TV audio). It is important that you use
an ordinary "over the air" broadcast and not a cable version, since
cable systems introduce unknown time delays in different localities.
2. Keeping the camcorder recording, go outside and record the Moon,
zooming in on it and maintaining a good focus. Use of manual focus
might help.
3. Just after Aldebaran disappears, go back to your TV and record another
minute of WBAL-TV or WJLA, with the camcorder running the whole time.
4. Turn off the camcorder. If successful, send an e-mail message to
FritzVSch@aol.com or telephone 410-750-8786 (Eric Schindhelm).
Send the tape to:
Dr. Sara Parrott
Mt. Hebron High School
9440 Route 99
Ellicott City, MD 21042
Enclose with the tape a diagram showing about how far you were from
the center of the nearest street, and then the distance along the
street to the center of the nearest intersecting street. You can
just pace the distances; we need an accuracy of about 15 feet.
5. If you have a telescope or good pair of binoculars, watch Aldebaran
reappear. Telescope users can point a camcorder into a low-power
eyepiece and try to record the event using the timing procedures
for the disappearance above.
If your camcorder has an electronic "anti-shake" feature, turn it off. It
delays the video signal relative to the audio signal, degrading timing
accuracy. If your camcorder has a time display including seconds, keep it
running throughout. That display can be many minutes in error; it doesn't
need to be set accurately. If you have a shortwave radio, please also
record WWV time signals at 5.0 or 10.0 megahertz during the observation.
Any observations that you can provide will be greatly appreciated.
Please distribute this to others who might be interested.
IOTA Web site for more information: http://www.sky.net/~robinson/iotandx.htm
[your name], [date]
______________________________________________________________________
David Dunham, IOTA, 1998 December 31