The Baily's beads, diamond ring or more rarely double diamond ring effects,[1] are features of total and annular solar eclipses. Although caused by the same phenomenon, they are distinct events during these types of solar eclipses. As the Moon covers the Sun during a solar eclipse, the rugged topography of the lunar limb allows beads of sunlight to shine through in some places while not in others. They are named for Francis Baily, who explained the effects in 1836.[2][3] The diamond ring effects are seen when only one or two beads are left, appearing as shining "diamonds" set in a bright ring around the lunar silhouette.[4]
Lunar topography has considerable relief because of the presence of mountains, craters, valleys and other topographical features. The irregularities of the lunar limb profile (the "edge" of the Moon, as seen from a distance) are known accurately from observations of grazing occultations of stars. Astronomers thus have a fairly good idea which mountains and valleys will cause the beads to appear in advance of the eclipse. While Baily's beads are seen briefly for a few seconds at the center of the eclipse path, their duration is maximized near the edges of the path of the umbra, lasting around 90 seconds.
It is not safe to view Baily's beads or the diamond ring effect without proper eye protection because in both cases the photosphere is still visible.[5]
Observers in the path of totality of a solar eclipse see first a gradual covering of the Sun by the lunar silhouette for just a small duration of time from around one minute to four minutes, followed by the diamond ring effect (visible without filters) as the last bit of photosphere disappears. As the burst of light from the ring fades, Baily's beads appear as the last bits of the bright photosphere shine through valleys aligned at the edge of the Moon.[6] As the Baily's beads disappear behind the advancing lunar edge (the beads also reappear at the end of totality), a thin reddish edge called the chromosphere (the Greek chrōma meaning "color") appears. Though the reddish hydrogen radiation is most visible to the unaided eye, the chromosphere also emits thousands of additional spectral lines.[7]
Beaded solar eclipses occur during an eclipse when the Sun and Moon have nearly identical apparent sizes. During a beaded eclipse, the rim of the Moon displays Baily's beads at many points all around the Moon and the brightness of the Sun remains from around 2000x to 10x greater than a complete total eclipse (ranging from about magnitude 99.8% to slightly more than 100.00%). The use of a smooth mean lunar radius to mathematically determine totality versus annularity does not take into account the deeper lunar valley floors which display the beaded photosphere points. Some authors have argued that since the Sun's photosphere is not fully extinguished during the beaded totality of the shortest hybrid total eclipses (such as the solar eclipse of 3 October 1986), these eclipses should be classified as only annular eclipses. The diamond ring effects in the moments just before and after a beaded eclipse are often referred to as diamond tiaras. Beaded annularity or totality duration is very short - less than about 12 seconds. However, the annularity duration before and after beaded hybrid totality and beaded annularity can be longer.
- ^ Staff (27 December 2023). "Searching for the Double Diamond Ring". PhotoEphemeris.com. Archived from the original on 30 December 2023. Retrieved 30 December 2023.
- ^ Baily (1836). "I. On a remarkable phenomenon that occurs in total and annular eclipses of the sun". Monthly Notices of the Royal Astronomical Society. 4 (2): 15–19. doi:10.1093/mnras/4.2.15.
- ^ Littmann, Mark; Willcox, Ken; Espenak, Fred (1999). Totality – Eclipses of the Sun. Oxford University Press. pp. 65–66. ISBN 978-0-19-513179-6.
- ^ O. Staiger. "The Experience of Totality".
- ^ "Solar Eclipse Observing – The Diamond Ring and Baily's Beads".
- ^ Pasachoff, J. M. & Covington, M. The Cambridge Eclipse Photography Guide (Cambridge Univ. Press, 1993)[page needed]
- ^ Pasachoff, Jay M. (2009). "Solar eclipses as an astrophysical laboratory". Nature. 459 (7248): 789–795. Bibcode:2009Natur.459..789P. doi:10.1038/nature07987. PMID 19516332. S2CID 205216683.