July 11, 2010 Total Solar Eclipse
International Occultation Timing Association
Location: Hao & Hikueru Atolls, French Polynesia
Positions of IOTA's Science Team (Paul Maley and Richard Nugent/Chuck Herold) at the July 11, 2010 Total Solar Eclipse. High resolution GPS time inserted video of the Baily's Beads effect was obtained at the Hao Atoll station.
The International Occultation Timing Association (IOTA) was present at this eclipse as part of its long term study to measure solar radius variations. IOTA astronomers Paul Maley, Richard Nugent and Chuck Herold traveled to 2 Atolls in the South Pacific in the French Polynesia and set up two stations - Hikueru Atoll and Hao Atoll. Unfortunately the Hikueru station had cloud/rain problems immediately after 2nd contact. This was Maley's 38th eclipse expedition, Herold's 17th and Nugent's 21st. IOTA's method of planning eclipse stations normally places them at the north and south eclipse limits, however the path of this eclipse was just about entirely over water so Nugent/Herold and Maley set up on complementary sides of the center line: Maley at Hikueru just 10km north of the eclipse center line and Nugent/Herold at Hao 70 km south of the center line. The goal was to observe the lunar mountains race across the Sun at 2nd and 3rd contact - the diamond ring effect caused by Baily's Beads - the breaking up sunlight caused by the lunar mountains, deep valleys and craters at the edge of the Moon.
IOTA's method is currently the most accurate ground based method of determining the Sun's radius with a precision that exceeds 0.04" or 30 km at the distance of the Sun.
Why Observe the Baily's Beads effect?
The observation of the Baily's Beads effect during this eclipse provides a unique opportunity to determine the diameter of the Sun. By observing Baily's Beads at both diamond rings (2nd and 3rd contact), the duration of the eclipse can be determined accurately. This in turn allows a high precision determination of the Solar diameter. IOTA's Solar Eclipse Research Page has more information.
In the diagram below, the objective of each station was to time the beads at both contacts which, if successful, would create independent "chords" across the face of the lunar/solar disc. The chords would be calculated from the recently released Japanese Kaguya satellite data which provides the lunar topography to a precision of several meters. With accurate chord lengths, this in turn provides the exact duration of the eclipse at the particular site which in turn allows a solar disk to be fitted to match the chords. In the diagram the topography is highly exaggerated.
Above diagram of the Moon's lunar limb profile adapted from "Annular and Total Solar Eclipses of 2010" by F. Espanek and J. Anderson, NASA/TP-2008-214171
Video of the Baily's Beads at both 2nd and 3rd contacts from Hao atoll, French Polynesia. Video by Richard Nugent
Above: Composite of video frames of Baily's Beads at 2nd contact. These frames represent a 10 second time interval. From Hao Atoll-Richard Nugent
Above: Composite of video frames of Baily's Beads at 3rd contact. These frames represent a 20 second time interval. From Hao Atoll-Richard Nugent
Above: Composite of video frames of Baily's Beads at 2nd contact ~ Frames represent a 10 second time interval. From Hikueru Atoll - Paul Maley
Structure of the Solar Corona
A paper has been published on some results of this eclipse: "Towards a Unified Definition of Solar Limb During Central Eclipses and Daily Transits", C. Sigismondi, A.Raponi, C. Bazin and R. Nugent, International Journal of Modern Physics D, June 11, 2011
Left: Left to right sitting: Chuck Herold (IOTA), Dan Weller, Dave Balch, Richard Nugent (IOTA). Right: Richard Nugent with equipment used for Baily's Beads: 3.5" Duplex Questar, KIWI GPS time inserter, Supercircuits PC-164 C black & white video camera, Thousand Oaks solar filter. Dan Weller is standing in background.
Left: Half the fun was getting there. A Google map animation shows where we traveled to see the eclipse. Eclipse video by Chuck Herold. Right: Chuck used a Celestron VistaPix IS70 mm spotting scope with built in DVR.
The air temperatures during this eclipse was recorded electronically and manually by Dan Weller and Chuck Herold. Dan Weller used a digital thermometer and manually recorded temperatures every 5 minutes. His gave this data to his 5th grade students back in New Jersey to analyze. Chuck Herold recorded temperatures both at the ground level and 2 ft above ground with a digital recording temperature gauge. The results were plotted below by John and Alice Hooten of La Porte, Texas.
As expected, as the Moon slides across the Sun, the atmosphere's heat source is slowly cut off. During the 3min 38sec of totality we had at Hao Atoll centered at 8:43AM local time, the temperature dropped 3 degrees to 76°. The temperature remained low for 20 minutes after central eclipse well into the partial phases (Sun partially covered by the Moon). Prior to central eclipse, the fluctuations of temperature were due to passing clouds over the Sun plus the initial partial phases following 1st contact.
The Hao Atoll is located at 18.064°south latitude, 140.96° west longitude and is one of over 100 atolls in the French Polynesia. These atolls are "rings of land" (like snakes) in the water. The average elevation of Hao is 2 meters above the local sea level. In 1963 it became the rear base of the French Nuclear Testing Center (preparation of atomic tests and atmospheric tests - underground). Hao remained the rear base as it has a 3.4 km airstrip which has been an emergency landing site for the American Space Shuttle should a forced landing be necessary. Today Hao is the the turntable for the French Military Forces based in the French Polynesia behind the Port of Papeete on the island of Tahiti. 1,600 inhabitants live on Hao and support themselves with fishing, copra (fruit from coconuts) and pearl farming.
Left: View of Hao Atoll's 3.4km long runway looking southeast. Right: Astronaut photograph of Hao Atoll. Hao is 33 miles long x 10 miles wide.
Links to other webpages from this eclipse:
Ring of Fire Expeditions: http://www.eclipsetours.com/t10results.html
Don Gardner: http://spaceweather.com/submissions/large_image_popup.php?image_name=Donald-Gardner-Don-Gardner-IMG_2693_1278903347.jpg
Howard Duncan: http://www.eclipsehd.info/2010.html
Fritz Kleinhans: http://www.physics.iupui.edu/Starman/Astrophoto/Eclipse-Tahiti.htm
http://www.poyntsource.com/Richard/Aug_1_2008_Eclipse.htm - Total solar eclipse, August 1, 2008, Hami, China
http://www.poyntsource.com/Richard/Jan_15_2010_Eclipse.htm - Annular solar eclipse, January 15, 2010, Gulu, Uganda
http://www.poyntsource.com/Richard/Jul_11_2010_Eclipse.htm - Total solar eclipse, July 11, 2010, Hao Atoll, French Polynesia
Eclipse Home Page
The International Occultation Timing Association is the primary scientific organization that predicts, observes and analyses lunar and asteroid occultations and solar eclipses. IOTA astronomers have organized teams of observers worldwide to travel to observe grazing occultations of stars by the Moon, eclipses of stars by asteroids and solar eclipses since 1962.