August 1, 2008 Solar Eclipse South Limit Science Team
International Occultation Timing Association
Positions of IOTA's Science Team at the August 1, 2008 Total Solar Eclipse near Hami, China. High resolution GPS time inserted video of the Baily's Beads effect was obtained at both stations.
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 and Chuck Herold traveled to the city of Hami, China on the eastern side of the Gobi desert to set up two stations located just barely inside the south eclipse limit - Nugent's at 1.4 km inside the limit and Herold's at 3.4 km inside the limit. Science teams from Europe set up a total of six stations covering both north and south limits complementing our stations. This was Nugent's 19th eclipse and Herold's 14th eclipse. While most eclipse chasers strive to get the center line of the Moon's shadow to maximize the duration of totality (nearly 2 minutes for this eclipse), Nugent and Herold had another goal in mind - to observe the lunar mountains graze past the Sun, maximizing the Baily's Beads effect. Here they had only 15-20 seconds of totality, but some 70-80 seconds 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 members Dave Ombrello and Maureen Price and Bhanu Sharma were also at Chuck Herold's site observing and taking digital photos of the Beads effect. Baily's Beads are prolonged at the eclipse limits.
1.4 km Site: Richard Nugent's equipment setup (above): Questar 3.5" and a Watec 902H Ultimate video camera fed high resolution video in a DVR. The time reference was obtained from GPS satellites and overlaid onto the video providing Universal Time with an accuracy of ±0.03 second. This site with the convenient concrete table just off the road was found quite by accident and proved to be very private for the observations.
3.4 km Site: Chuck Herold's equipment setup: Celestron NexStar 5", Supercircuits PC-164C video camera, and KIWI GPS time inserter fed the Baily's Beads into a digital camcorder. As with Nugent's site, the time of each frame can be extracted to ±0.03 second. Joining Chuck Herold was Dave Ombrello, Maureen Price and Bhanu Sharma.
The path of the Moon's shadow (blue lines) determines the eclipse limits. IOTA astronomers Richard Nugent and Chuck Herold observed just outside of Hami, China at the south shadow limit.
Richard Nugent, Space Shuttle Astronaut Claude Nicollier and Chuck Herold at the Hami, China Airport
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 1.4 km inside the south limit. Video taken by Richard Nugent.
A paper entitled "Baily's Bead Atlas in 2005-2008 Eclipses" co-authored by Richard Nugent, Chuck Herold and others has been published in the journal Solar Physics in July 2009. See it here.
A second paper "Measuring Solar Disk Shape up to Relativistic Accuracy: The Role of Scintillation in ancient naked Eye Data", authored by Costantino Sigismondi, Richard Nugent and Gerhard Dangl was presented at the Proceedings of the 3rd Stueckelberg Workshop on Relativistic Field Theories, in Pescara, Itlay, July 2010, p. 303, ISBN 978-1-904868-73-6.
33 second freeze frame sequence of Baily's Beads:
From Richard Nugent's video the above sequence of the Baily's Beads phenomena covers 18 frames. The time of the first frame starts at 11:09:3.42 UT and the last frame is 11:09:36.19 UT. As the rugged lunar mountains glide past the Sun's edge, the sunlight is broken up into "beads". This phenomena was first noticed by the English stockbroker turned astronomer Francis Baily during the annular eclipse of May 15, 1836 over Scotland.
Photos of the eclipsed Sun by photographer Dave Ombrello:
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 analyzes 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.