January 15, 2010 Annular Solar Eclipse
North Limit Science Team
International Occultation Timing Association
Google map of the eclipse path over Africa, extreme south India and Sri Lanka.
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 Richard Nugent, Chuck Herold and Paul Maley traveled to northern Uganda to set up two stations within 1 km of the north eclipse limit. Science teams from IOTA/European Section and in India set up stations covering the south limits complementing our stations. Unfortunately the south limit stations in Uganda had cloud/rain problems. This was Nugent's 20th eclipse expedition, Herold's 16th and Maley's 37th. While most eclipse chasers strive to get the center line of the Moon's shadow to maximize the duration of annularity (nearly 8 minutes for this eclipse), Nugent/Herold and Maley had another goal in mind - to observe the lunar mountains graze past the Sun, maximizing the Baily's Beads effect. Here they had 2 minutes of 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 of measuring the Baily's Beads at the north and south eclipse limits 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. Ring of Fire Expeditions member Bhanu Sharma was also at Nugent's site observing and taking digital photos. Baily's Beads are prolonged at the eclipse limits.
Close up of the eclipsed Sun showing individual Baily's Beads. From video by Richard Nugent. UT of frame is 5h 25m 46.381 sec.
Why Observe the Eclipse at the Edge?
The observation of a solar eclipse from the edge from north and south eclipse limits provides a unique opportunity to determine the diameter of the Sun. By observing Baily's Beads at both the north and south eclipse limits, the width of the Moon's shadow on the ground can be determined accurately. This in turn allows a high precision determination of the Solar diameter. For a diagram illustrating this concept please go to IOTA's Solar Eclipse Research Page.
The video link below (click on picture) shows the Baily's Beads effect from the north eclipse limit. Video taken by Richard Nugent.
Positions of IOTA's Science Team at the January 15, 2010 Annular Solar Eclipse near Gulu, Uganda. High resolution GPS time inserted video of the Baily's Beads effect was obtained at both stations.
Analysis of the data obtained at Nugent's north limit station is analyzed here: "Towards A Unified Definition of Solar Limb During Central Eclipses and Daily Transits (authors-C. Sigismondi, A. Raponi, C. Bazin, R. Nugent, International Journal of Modern Physics D, March 2011). It will be combined with the results of the previous eclipse over China on August 1, 2008 (see "Baily's Bead Atlas in 2005-2008 Eclipses" co-authored by R. Nugent, C. Herold, D. Dunham, C. Sigismondi, and 23 co-authors published in the journal Solar Physics in July 2009).
Richard Nugent shares his views of the eclipse with the local people of Uganda
Left to right: Bhanu Sharma, Carolyn Whitfield, Byron Braswell, Richard Nugent, Dr. Lynn Palmer, Paul Maley, Chuck Herold, Barbara Flack, Jeffrey and Linda Pohlman
Southern Limit Expedition
At the southern eclipse limit in Sri Lanka, off the coast of India, Saraj Gunasekera organized a team of observers to record Baily's Beads. They were located in Arachchikattuwa on the west coast of Sri Lanka 1.5 km inside the south eclipse limit. The team used a Vixen 80mm refractor piggyback on a Meade 12" SCT.
limit Science team, left to right: Sachintha Abeykoon,
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
More from this expedition:
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.