A total

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 ...

occurred at the Moon's ascending node of orbit on Tuesday, August 18, 1868 (also known as "The King of Siam's eclipse"), with a magnitude of 1.0756. A

occurs when 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 ...

passes between

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

and the Sun, thereby totally or partly obscuring the image of the Sun for a viewer on Earth. A total solar eclipse occurs when the Moon's apparent diameter is larger than the Sun's, blocking all direct sunlight, turning day into darkness. Totality occurs in a narrow path across Earth's surface, with the partial solar eclipse visible over a surrounding region thousands of kilometres wide. Occurring about 6.5 days after perigee (on August 17, 1868, at 22:35 UTC), the Moon's apparent diameter was larger. The path of totality was visible from parts of modern-day

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India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

, the

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, and

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. A partial solar eclipse was also visible for parts of

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, the

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, and western

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. The eclipse was predicted more precisely by King Mongkut of

than it was by French astronomers. The eclipse allowed for the discovery of

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

by both Pierre Janssen and Norman Lockyer, who observed Solar prominences with spectroscopes.

Observations

Solar eclipse 1868Aug18-Bullock.png, Bullock sketch of the eclipse, ''Total Eclipses of the Sun'', 1900. Sketches of the total solar eclipse, 1868 (19745966082).jpg, M. Stephan sketches of the eclipse, ''Archives des missions scientifiques et littéraires'', 1868. Map of the solar eclipse of August 18, 1868 (19757912091).jpg, Map of the forecast path of the total eclipse, ''Archives des missions scientifiques et littéraires'', 1868. Several expeditions were sent to observe the eclipse. * One of two expeditions from Germany was sent to Aden. The expedition was led by Gustav Spörer. * The second expedition was sent to the west coast of India. The expedition was led by Friedrich Tietjen. *Captain Bullock observed from the Celebes sea, sketching the appearance of the corona, while

Gustav Fritsch Gustav Theodor Fritsch (5 March 1838 – 12 June 1927) was a German anatomist, anthropologist, traveller and physiologist from Cottbus. Fritsch studied natural science and medicine in Berlin, Breslau and Heidelberg. In 1874 he became an asso ...

accompanied an expedition to

Aden Aden () is a port city located in Yemen in the southern part of the Arabian peninsula, on the north coast of the Gulf of Aden, positioned near the eastern approach to the Red Sea. It is situated approximately 170 km (110 mi) east of ...

Discovery of helium

French astronomer Pierre Janssen observed the eclipse from

Guntur Guntur (), natively spelt as Gunturu, is a city in the States and union territories of India, Indian state of Andhra Pradesh and the administrative headquarters of Guntur district. The city is part of the Andhra Pradesh Capital Region and is lo ...

in Madras State,

British India The provinces of India, earlier presidencies of British India and still earlier, presidency towns, were the administrative divisions of British governance in South Asia. Collectively, they have been called British India. In one form or another ...

. It was the first total eclipse since Gustav Kirchhoff's 1859 theory that the Fraunhofer lines in the solar spectrum correspond to the emission line of the different chemical elements present in the Sun. Correspondingly, Janssen observed the eclipse with the aid of a spectroscope. He noticed a bright yellow line ( ''λ'' = 587.49 nm) in the spectra of the solar prominences that could not be due to sodium as had previously been assumed, and was subsequently able to observe the same line even without the need for an eclipse. The same result was found independently by British astronomer Norman Lockyer, and both Janssen's and Lockyer's communications were presented to the

French Academy of Sciences The French Academy of Sciences (, ) is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French Scientific method, scientific research. It was at the forefron ...

on October 26, 1868.

King Mongkut's calculation

King Mongkut, also known as Rama IV of Siam, was able to calculate and predict the solar eclipse two years earlier. The calculations were correct as to the place, the time and the type of the solar eclipse that would happen. The eclipse took place precisely as the king had predicted, the total phase lasting six minutes and 46 seconds. In fact, his calculations were better — by about two seconds — than those of the French astronomers, who acknowledged his accuracy. Mongkut was exposed to

malaria Malaria is a Mosquito-borne disease, mosquito-borne infectious disease that affects vertebrates and ''Anopheles'' mosquitoes. Human malaria causes Signs and symptoms, symptoms that typically include fever, Fatigue (medical), fatigue, vomitin ...

, then developed chills and fever. He died on October 1, 1868. According to the Thai Astronomical Society and NASA, this eclipse is known as "The King of Siam's eclipse".๒๐๐ ปี พระบาทสมเด็จพระจอมเกล้าเจ้าอยู่หัว พระบิดาแห่งวิทยาศาสตร์ไทย

Eclipse details

Shown below are two tables displaying details about this particular solar eclipse. The first table outlines times at which the moon's penumbra or umbra attains the specific parameter, and the second table describes various other parameters pertaining to this eclipse.

Eclipse season

This eclipse is part of an eclipse season, a period, roughly every six months, when eclipses occur. Only two (or occasionally three) eclipse seasons occur each year, and each season lasts about 35 days and repeats just short of six months (173 days) later; thus two full eclipse seasons always occur each year. Either two or three eclipses happen each eclipse season. In the sequence below, each eclipse is separated by a fortnight.

Related eclipses

Eclipses in 1868

* A penumbral lunar eclipse on February 8. * An annular solar eclipse on February 23. * A penumbral lunar eclipse on March 8. * A penumbral lunar eclipse on August 3. * A total solar eclipse on August 18. * A penumbral lunar eclipse on September 2.

Metonic

* Preceded by: Solar eclipse of October 30, 1864 * Followed by: Solar eclipse of June 6, 1872

Tzolkinex

* Preceded by: Solar eclipse of July 8, 1861 * Followed by: Solar eclipse of September 29, 1875

Half-Saros

* Preceded by: Lunar eclipse of August 13, 1859 * Followed by: Lunar eclipse of August 23, 1877

Tritos

* Preceded by: Solar eclipse of September 18, 1857 * Followed by: Solar eclipse of July 19, 1879

Solar Saros 133

* Preceded by: Solar eclipse of August 7, 1850 * Followed by: Solar eclipse of August 29, 1886

Inex

* Preceded by: Solar eclipse of September 7, 1839 * Followed by: Solar eclipse of July 29, 1897

Triad

* Preceded by: Solar eclipse of October 17, 1781 * Followed by: Solar eclipse of June 20, 1955

Solar eclipses of 1866–1870

The partial solar eclipses on April 15, 1866 and October 8, 1866 occur in the previous lunar year eclipse set, and the solar eclipses on June 28, 1870 (partial) and December 22, 1870 (total) occur in the next lunar year eclipse set.

Saros 133

Metonic series

All eclipses in this table occur at the Moon's ascending node.

Tritos series

Inex series

Notes

References

NASA chart graphics
*
Googlemap
*
NASA Besselian elements

''Observations of the Total Solar Eclipse of August 18, 1868'' by Charles G. Perrins

Drawing of Corona
* {{Commons category, Solar eclipse of 1868 August 18 1868 08 18 1868 in science 1868 08 18 Helium August 1868 Astronomy in Thailand