At all annular eclipses and some total eclipses we attempt observation of the marvelous Baily's Beads (named for Sir Francis Baily after his observation of a solar eclipse in 1836) which appear at central eclipse. Our first attempt at observing near the limit of the eclipse path where the beads are best seen occurred at the annular eclipse in 1973 but our application of video to the task was initiated in Indonesia ten years later. The appearance of these features that result from sunlight streaming through the valleys at the moon's north and south polar regions are crucial to pinning down the solar radius at each eclipse. While the sun is a fluid body and moon a solid one, the moon's topography is known with relative certainty. The bead features can be predicted with relatively high accuracy and can be subsequently compared to observed beads. Timing of these features cannot be done from cruise ships or aircraft, only from land based expeditions where site locations can be ascertained with high accuracy using modern day GPS.

Since the 1980's the International Occultation Timing Association, an amateur-professional astronomical group, has begun studies to ascertain if the solar radius is varying between the time frame of consecutive eclipses. To be sure there are variations on much shorter time scales suspected; however, our goal is to secure reliable, high definition information on the appearance, disappearance, merging of individual beads during the eclipse process and recording them on videotape along with precise time signals. Because the moon moves rather quickly from west to east as it covers the sun, the bead features are very distinct and their appearance as small dots which expand as deeper valleys cover the sun.

Weather is always a major challenge since the eclipse can influence the local temperature and cloud formation. We endeavor to locate places where the likelihood of good weather is high and observation can be conducted from a safe location.

The NASA JSC Astronomical Society's public outreach allows anyone who has an interest in eclipse observing to join our expeditions and also to participate in the Baily's Beads research project. To participate in this at annular eclipses, we set up observation sites within several kilometers of the north and south edge of the eclipse path. Annular eclipses are essentially a cross between a partial eclipse and a total eclipse. The sky does not get dark as at a total eclipse. At the north edge or limit, features from the south pole of the moon (a rugged area with deep valleys) project onto this limit line. The edge/limit is the mathematical track along the earth's surface that defines the projection of the exact solar and lunar disk edges. At the south edge, corresponding features from the north pole of the moon (a somewhat flatter, less rugged area with shallow valleys and low mountain peaks) are monitored for the formation of the beads. Equipment you can use include the following. All equipment are the responsibility of the participants and are not provided by IOTA.

1.small portable telescope, preferably with a clock driven mount (aperture between 3.5 and 8 inches)

2.video camera attached to the prime focus of a telescope (preferably a black and white Supercircuits model PC-23C) with cables to output to a VCR

3.portable time signal receiver

4.portable VCR (such as any Sony VCR with RCA jacks and fold out monitor) with input ports from video cameras

5.Neutral density 5 filter to fit in front of the telescope aperture

6.portable GPS receiver

Safety in observation is assured by keeping the solar filter in front of the telescope, since the beads are active sunlight and present a hazard to the eye.

It is important to only have about a 120 degree arc along the sun's edge in the video field of view. Using a telescope with too high magnification or too large an aperture does not allow effective data to be obtained, hence the smaller apertures noted above. The beads migrate from limb to the other, and the observer must be vigilant in keeping track of them as they move. If totality is experienced at the site, one must be prepared for the reappearance of a bead area after totality has ended on a successive part of the limb. In order to ensure that we are set up at the correct location, we determine the optimal site locations and will direct you in the proper procedures for data collection.

At total solar eclipses, we set up similar equipment at the limit lines, usually within 0.5 to 1.5km south of the north edge and the same distance north of the south edge. The limit/edge of a total eclipse defines the track between a 100% total obscuration of the sun and 99.9% or less. The farther away from the center line one travels, the less totality. When one cross the limit/edge line you are in 'partial eclipse territory' where Baily's Beads are not effectively observed.

Since most total eclipse observers wish to observe the total phase where the sun's light is completely extinguished, for the most amount of time, the totality observed at the edge is normally no more than about 30 seconds, regardless of the length of time of total eclipse at the center line. However, all the grand features seen at the centerline are also observed at the edge. The one feature that cannot be seen for any length of time at the center is prolonged enormously at our edge stations. These are the Baily's Beads which appear as dazzling points of sunlight of varying size. They slowly appear from nowhere and move gently along the sun's limb. Sometimes they can appear for 3 minutes, although some individual single beads may be observed as early as 20 minutes before central eclipse, though this is somewhat exceptional. At the eclipse limit line there are always few observers and little traffic to fight. Competing for the best observing sites is never a problem here. This experiment can be completed using 'off the shelf' equipment rather than exotic, bulky, and difficult to operate hardware. For example, a small CCD TV camera is available for less than US$100.00 while camcorders are sold for less than $US400.

The challenge is for data at both limits to be successfully collected in order to produce enough information for the sun's radius to be determined by this method. IOTA members in various countries spend their own money and time to volunteer to collect data for this ambitious multi-decade project. We scout suitable ground for setting up our equipment and attempt to shield it from wind and passing vehicles. The sun's image must be steady, in-focus and of highest quality.

The video camera is used to record the bead formation process at 30 frames per second. The time signals from the radio are recorded on the audio channel of the camcorder (or camera) and can be used after the fact by those who reduce the tapes. It does not require any significant expertise, just an abundant interest in contributing to a very interesting project. Again, IOTA, NASA JSCAS or Ring of Fire Expeditions does not furnish equipment. You must obtain your own. Photos of the beads are of generally of minimal use, since we require detailed timings of coincidence between beads events (formation and dissipation) and known lunar features. Data from modern eclipses are being used for future comparison with data at older eclipses for which similar edge data is being researched today.

IOTA is also involved in the collection of data by observing occultations of stars by the moon. Grazing occultations involve the passage of stars behind lunar peaks at the north/south polar regions. By timing these events, information on the topographic heights of these areas can be even further improved. Such a program by IOTA has been in place for almost 40 years and has expanded the baseline reference for lunar topography known as the 'Watt's Charts' produced by C.B. Watts in 1963. Amateur astronomers have played a key role in collecting thousands of timings which have been of enormous contribution in reducing the general error of Watt's Charts from 1000 ft (350m) to less than 300 ft (100m). The recent evolution of GPS has reduced position error from 100 ft (30m) to about 5 feet (1.6m). The human timing error has been overcome by the use of video.

Bead videos can also be recorded on other international video formats such as PAL and SECAM and on VHS as well as 8mm or Hi-8, etc. Time signals must be recorded on the video track in order for the data to be useful. In the reduction process, a highly precise time inserter is used to inject a time code to the nearest hundredth of a second to enable the greatest accuracy in linking features with time.

In addition to current and future eclipses, we are also investigating accounts into past eclipses particularly in the United States and the UK. If you are possibly interested in joining an upcoming expedition, please contact us as early as possible.

Carlson Wagonlit Travel