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Observing a Lunar Graze

Subj: Good Aldebaran occ'n Sat. am; need coordinators & observers
Date: 98-09-09 10:16:35 EDT
From: dunham@erols.com (Joan and David Dunham)

Local and Regional Coordinators, and OBSERVERS are needed for Saturday morning's spectacular Aldebaran Occultation and Graze

Aldebaran is the brightest star, other than the Sun, that can be occulted by the Moon. Saturday morning's occultation will be the last naked-eye occultation of Aldebaran visible from the eastern USA until 2015. Time is short, but please try to make the most of this opportunity, not only for obtaining science but for public outreach. Local coordinators are critical for public participation to obtain unprecedented large quantities of accurate timings of the occultation, now that we know that national broadcasts via cable can't be used for accurate timing. Much information about the occultation is on IOTA's Web site at http://www.sky.net/~robinson/iotandx.htm - please visit it.

Tasks that might be undertaken during a Lunar Graze.

1. Use your camcorder (or a borrowed camcorder) to record a strong local station that will be broadcasting during the occultation. Record the selected station along with WWV 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 reappearance in your area. Also record for the disappearance 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 WWV 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 recording of the station are timed accurately. WWV is preferred since IOTA's video time inserter is designed to trigger its time display from WWV's signal, not from other signals.

If you can arrange this, please inform me or Rob Robinson (robinson@sky.net; let him know after 0h UT Sept. 11 = 8 pm EDT Thurs. evening when I will no longer have e-mail access while travelling to Nashville for the graze and IOTA meeting) 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 (especially the case for those who are participating in one of the many graze expeditions), 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 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.

As of early Sept. 9th, arrangements have been made to create a master tape with WWV for only one station, WBAL, Channel 2 in Baltimore, Maryland. So observers in central Maryland are encouraged to use it to time the occultation with camcorders, if they don't have a WWV receiver. Other stations will be listed on the IOTA Web site as they are added.

2. Encourage other amateur astronomers, and other friends and relatives in the region of visibility to record the occultation with camcorders. Try to borrow one if you don't own one.

3. Spread word about the occultation via bulletin boards and e-mail; you might get permission to distribute information at your office or school. For example, information about the occultation will soon be distributed widely in high schools in Howard County, Maryland.

4. Contact Local Newspapers and TV Stations to inform them of the event, and the need for camcorder observations. Use the sample local press release below for this [you need to fill in the blanks about the local TV broadcast that should be used]. Prepare a local moonview; I will prepare one upon request if it will be used in a newspaper or on television.

5. Encourage those with telescopes to use it with a camcorder to record the disappearance, as well as the reappearance without the telescope (in the scope, the R may be too far from the cusp and difficult to locate).

6. A dark-limb graze of such a bright star is a rare treat; gradual events revealing the star's angular diameter will be noticeable, one of the few cases where this is true even with binoculars. If the graze path is within reasonable range, join one of the IOTA expeditions, or make your own independent effort. If the latter, try to get others to join you, and let us know so we can inform others via the IOTA Web page. Very detailed information about the graze, and expeditions for it from Llano and Waco, Texas, to southern Maine, is on the IOTA Web site. If a 1:250,000-scale plot of the path has not been prepared for your area, one might be supplied upon request.

7. Collect videotapes of the occultation made in your region.

David W. Dunham, IOTA email: dunham@erols.com phone: 301-474-4722
Office: fax 240-228-1093 david.dunham@jhuapl.edu 240-228-5609

P.S. A general press release about the occultation is being distributed to several newspapers and television stations in the region of visibility, but LOCAL releases specifying a TV station that can be used locally for timing will be more effective.

****** A sample local press release is belew ******

Items that you need to complete are in [ ]
A completed example for one county (where the times
are accurate to 1 minute across the county) is on the
IOTA web site.

Naked-Eye Eclipse of Bright Star Sat. Morning, Sept. 12

Astronomers need your camcorder records for lunar and solar (Earth climate) studies

Early Saturday morning, September 12th, the bright orange star Aldebaran will be eclipsed by the last-quarter Moon. The reappearance on the dark side of the Moon will be easy to see with the naked eye throughout the Midatlantic States. This event is called an "occultation" by astronomers. The figure below shows what the occultation will look like in [your region]. For locations south of [your region], the path behind the Moon will be closer to the Moon's center. For example, at [city to south], the star will reappear at the 2 o'clock position rather than the 1 o'clock position shown below for [your city; change the clock positions depending on where you are. North of [your area], the path is higher on the Moon. At [give city on or near the limit line], the northern limit of the occultation, the path will be a line that just touches (is tangent to) the Moon's disk, and parallel to the [your city] path [delete this sentence if your city is more than about 150 miles from the graze line]. But you only need to look near the top of the Moon, on its dark side, to locate the bright star when it blazes back into view from behind the retreating edge of the Moon. The star might be seen several minutes before it disappears. But Aldebaran will be harder to see then in the glare of the nearby sunlit part of the Moon. The bright part of the Moon will overwhelm the star a minute or more before the disappearance, which might be seen only with the help of binoculars or a small telescope.

[This space is for the Moon view for your city; add enough blank lines]

In [your region], the occultation can be videotaped by anyone with a camcorder. We will accurately time the broadcast of Wxxx, Channel # [specify the station and channel], and encourage as many camcorder owners as possible to record this rare event, as well as Wxxx before and after the reappearance to provide an accurate time base. 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 buring 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.

The time of the occultation varies by several minutes across the [specify your] region. The times of the disappearance and reappearance are given on two separate maps [these regional maps are available now on the IOTA Web site for most areas of the USA in the occultation zone] that have lines drawn at one-minute intervals. Several cities are identified by the first two letters of their name. For example [give an example like this, replacing the city and times with one in your area], looking at the maps, it can be seen that for Frederick, Maryland (labelled "Fr"), Aldebaran will disappear at 3:19 am and will reappear at 3:41.

Camcorder users should do the following:

1. Set your alarm to wake up at least 20 minutes before the reappearance, or stay up for it. You might want to get up earlier to see Aldebaran before it disappears.

2. Five minutes before the reappearance, turn on your camcorder and record a minute of Wxxx. 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.

3. 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.

4. Just after Aldebaran reappears, go back to your TV and record another minute of Wxxx, with the camcorder running the whole time.

5. Turn off the camcorder. If successful, send the tape to [give your name and address, or that of an IOTA coordinator for your region]. 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 10 feet.

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. 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.

[Include this paragraph only if your city is within about 200 miles of the northern limit] Within a mile or two of the northern limit graze line shown on the maps, the star will just graze the northern edge of the Moon, disappearing and reappearing several times among the lunar mountains and craters. "X" marks the approximate location of expeditions that IOTA plans to record this spectacular graze. Anyone who lives within, or can travel to, the narrow graze zone can see this interesting phenomenon with binoculars or possibly with the naked eye if most of the bright part of the Moon can be blocked from view.

Aldebaran is the brightest star, other than the Sun, that the Moon can eclipse. Saturday morning's occultation is the last one of Aldebaran that will occur under good enough conditions to be seen with the naked eye from the eastern USA until the year 2015.

IOTA Web site for more information: http://www.sky.net/~robinson/iotandx.htm

[your name], September 9, 1998


If regional maps might be used by the media in your area, I could supply a version without the hand labels, and could also add more cities and towns, if you supply their names to me in a list using all capital letters, preceded (with no space) with the state abbreviation. For example, for Baltimore, Ocean City, and Easton, Maryland, the list would be:

MDBALTIMORE
MDOCEAN CITY
MDEASTON

Unfortunately, my database of US State boundaries is rather crude, with gaps (many filled in manually) and errors of at least a few miles in some areas. I am seeking a better database of the State boundaries. The locations of the plotted cities relative to the timelines are accurate. Notice that there are some differences with lists of event times, since the latter were computed with the Occult program that adjusts the times for lunar mountains and valleys, while my program that generates the timelines just uses a spherical "smooth" Moon.

P.S. Observers are reminded of the other occultations on the Web, including the Hyades events preceding Aldebaran, and the good occultation reappearances of 4.5-mag. mu Ceti (ZC 405) tomorrow morning, Sept. 10th, visible from east of the Appalachians, and of 4.3-mag. 5 Tauri (ZC 508) visible from the eastern half of the USA Friday morning, September 11th. U.T.'s for a few cities are given on p. 97 of the Jan. issue of Sky and Telescope, and possibly for several more on IOTA's Web site, if we get a chance to generate and post them there.

David Dunham, 1998 September 9



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