Baily's Beads
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The Baily's beads, diamond ring or more rarely double diamond ring effects, are features of total and annular
solar eclipse A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby obscuring the view of the Sun from a small part of Earth, totally or partially. Such an alignment occurs approximately every six months, during the eclipse season i ...
s. Although caused by the same phenomenon, they are distinct events during these types of solar eclipses. As the
Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
covers the
Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
during a solar eclipse, the rugged topography of the lunar limb allows beads of
sunlight Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...
to shine through in some places while not in others. They are named for Francis Baily, who explained the effects in 1836. 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 A silhouette (, ) is the image of a person, animal, object or scene represented as a solid shape of a single colour, usually black, with its edges matching the outline of the subject. The interior of a silhouette is featureless, and the silhouett ...
. Lunar topography has considerable
relief Relief is a sculpture, sculptural method in which the sculpted pieces remain attached to a solid background of the same material. The term ''wikt:relief, relief'' is from the Latin verb , to raise (). To create a sculpture in relief is to give ...
because of the presence of
mountains A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher ...
,
crater A crater is a landform consisting of a hole or depression (geology), depression on a planetary surface, usually caused either by an object hitting the surface, or by geological activity on the planet. A crater has classically been described ...
s, 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
occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks f ...
s of
star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s. 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 The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...
is still visible. 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. 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 A chromosphere ("sphere of color", from the Ancient Greek words χρῶμα (''khrôma'') 'color' and σφαῖρα (''sphaîra'') 'sphere') is the second layer of a Stellar atmosphere, star's atmosphere, located above the photosphere and below t ...
(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 line A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission (electromagnetic radiation), emission or absorption (electromagnetic radiation), absorption of light in a narrow frequency ...
s. 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.


Observational history

Although Baily is often said to have discovered the cause of the feature which bears his name, Sir
Edmond Halley Edmond (or Edmund) Halley (; – ) was an English astronomer, mathematician and physicist. He was the second Astronomer Royal in Britain, succeeding John Flamsteed in 1720. From an observatory he constructed on Saint Helena in 1676–77, Hal ...
made the first recorded observations of Baily's beads during the solar eclipse of 3 May 1715.Great Britain did not adopt the
Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian cale ...
until 1752, so at the time of the eclipse, the date was recorded as 22 April 1715.
Halley described and correctly ascertained the cause of the effect in his "Observations of the late Total Eclipse of the Sun .. in the ''
Philosophical Transactions of the Royal Society ''Philosophical Transactions of the Royal Society'' is a scientific journal published by the Royal Society. In its earliest days, it was a private venture of the Royal Society's secretary. It was established in 1665, making it the second journ ...
'': The term "Baily's beads" then came into use after Baily described the phenomenon to the Royal Astronomical Society in December 1836. Having observed the solar eclipse of 15 May 1836 from
Jedburgh Jedburgh ( ; ; or ) is a town and former royal burgh in the Scottish Borders and the traditional county town of the Shires of Scotland, historic county of Roxburghshire. History Jedburgh began as ''Jedworð'', the "worth" or enclosed settlem ...
in the
Scottish Borders The Scottish Borders is one of 32 council areas of Scotland. It is bordered by West Lothian, Edinburgh, Midlothian, and East Lothian to the north, the North Sea to the east, Dumfries and Galloway to the south-west, South Lanarkshire to the we ...
, he reported that:


Double diamond ring effect

Before the diamond ring effect during a total solar eclipse, a sequence of small bits of sunlight known as Baily's Beads can be observed. These beads quickly disappear one by one until only one is left. By using precise elevation models of the Moon's irregular surface, it is now possible to predict where Baily’s Beads will converge to create the double diamond ring effect instead of just one bead. A map of the path taken by this effect was created and used to determine the cities along the path of totality during the April 8th, 2024, total solar eclipse.


In media

In 1735, painter and architect Cosmas Damian Asam completed a painting that is probably the earliest known work that realistically depicts a total solar eclipse and diamond ring. The Diamond Ring effect is seen during the credit opening sequence of '' Star Trek: Voyager'' (1995–2001), albeit from a fictitious extrasolar body, as seen from space. The Baily's beads phenomenon is seen during the credit opening sequence of the NBC TV show '' Heroes'' (2006–2010).


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* * {{DEFAULTSORT:Baily's Beads Eclipses Articles containing video clips