| Solar eclipse of August 18, 1868 | |
|---|---|
 Map | |
| Type of eclipse | |
| Nature | Total |
| Gamma | −0.0443 |
| Magnitude | 1.0756 |
| Maximum eclipse | |
| Duration | 407 sec (6 m 47 s) |
| Coordinates | 10°36′N 102°12′E / 10.6°N 102.2°E |
| Max. width of band | 245 km (152 mi) |
| Times (UTC) | |
| Greatest eclipse | 5:12:10 |
| References | |
| Saros | 133 (37 of 72) |
| Catalog # (SE5000) | 9207 |
A total solar eclipse occurred on August 18, 1868, also known as "The King of Siam's eclipse". A solar eclipse occurs when the Moon passes between Earth 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.
The eclipse was predicted more precisely by King Mongkut of Thailand than it was by French astronomers. The eclipse allowed for the discovery of helium by both Pierre Janssen and Norman Lockyer, who observed Solar prominences with spectroscopes.
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Several expeditions were sent to observe the eclipse.
French astronomer Pierre Janssen observed the eclipse from Guntur in Madras State, British India. 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 on October 26, 1868.[5][6]
King Mongkut, also known as Rama IV of Siam, was able to calculate and predict the solar eclipse two years earlier.[7] 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, then developed chills and fever. He died on October 1, 1868.[8] According to the Thai Astronomical Society and NASA, this eclipse is known as "The King of Siam's eclipse".[7][9]
It is a part of solar Saros 133.
Solar Inex series 2013 May 10
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