Timing Baily’s Beads during the August 21, 2017 Total Solar Eclipse

Precise timings of beading phenomena made near the northern and southern limits of the umbral path (i.e., the graze zones), may be useful in determining the diameter of the Sun relative to the Moon at the time of the eclipse. Such measurements are essential to an ongoing project to try to detect changes in the solar diameter.

Because of the conspicuous nature of the eclipse phenomena and their strong dependence on geographical location, scientifically useful observations can be made with relatively modest equipment.  For more detailed information on observing techniques for Baily’s Beads, see the information in the free IOTA Observer’s Manual (Chapter 11 specifically covers Solar Eclipse observing).

IOTA is organizing a citizen science effort to observe the 2017 eclipse from locations near the edges of the path of totality, to see how well it can be defined. Details are at . Besides the effort at the southern limit in Minden, Nebraska described there, work has started on organizing similar efforts at the path edges in St. Louis (northern limit) and Kansas City (southern limit).

St Louis Expo Documents:

Observations from Past Eclipses for Reference:

Videos showing Baily’s Beds:

Eclipse edge observation techniques and instructions can be found at the top of this web page: (to be updated about Jul 23).

For more information contact:

Richard Nugent at