astronomy

Solar eclipse of August 18, 1868

Solar eclipse of August 18, 1868 is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Solar eclipse of August 18, 1868 rather than just read about it. In short: A total solar eclipse 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 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.

Key takeaways

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Reference excerpt

A total solar eclipse 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 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. 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 Ethiopia, Eritrea, Djibouti, Yemen, India, the Andaman and Nicobar Islands, Myanmar, Thailand, Cambodia, Vietnam, Malaysia, Brunei, Indonesia, and Papua New Guinea. A partial solar eclipse was also visible for parts of East Africa, the Middle East, Central Asia, South Asia, Southeast Asia, Australia, and western Oceania. The total solar eclipse of 18 August 1868 was accurately predicted by King Mongkut of Siam, whose calculations were acknowledged as more precise than those of contemporary French astronomers. During observations of the eclipse, Pierre Janssen in India and, independently, Norman Lockyer in England detected a new yellow spectral line in the Sun's chromosphere using spectroscopes, leading to the discovery of the chemical element helium.

Observations

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 accompanied an expedition to Aden.

Discovery of helium 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.

King Mongkut's calculation

King Mongkut, Rama IV of Siam, predicted and calculated the solar eclipse two years prior. The calculations were correct as to the place, time, and type of the solar eclipse that would occur. His calculations were better — by about two seconds — than those of the French astronomers, who acknowledged his accuracy. Mongkut invited foreign dignitaries and scientists, including Sir Harry Ord, Governor of the Straits Settlements, and the French expedition led by Pierre Janssen that led to the discovery of helium. The event demonstrated Siam's engagement with modern science and diplomacy. Mongkut was exposed to malaria around this time, developing chills and fever. He died a month and a half after the eclipse, on 1 October 1868. According to the Thai Astronomical Society and NASA, this eclipse is known as "The King of Siam's eclipse".

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 This eclipse is a member of a semester series. An eclipse in a semester series of solar eclipses repeats approximately every 177 days and 4 hours (a semester) at alternating nodes of the Moon's orbit. 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.

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Illustrations

Worked examples

Example 1 — a first encounter with Solar eclipse of August 18, 1868

Start with the simplest possible case. Write down what Solar eclipse of August 18, 1868 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Solar eclipse of August 18, 1868 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Solar eclipse of August 18, 1868 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Solar eclipse of August 18, 1868

In research: Solar eclipse of August 18, 1868 appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Solar eclipse of August 18, 1868 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Solar eclipse of August 18, 1868 is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1868 in science, 19th-century solar eclipses, Astronomy in Thailand, so understanding it makes those chapters shorter.
In everyday life: Look for Solar eclipse of August 18, 1868 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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Frequently asked questions

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Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

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