Solar eclipse of August 18, 1868

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Solar eclipse of August 18, 1868
Course of the total solar eclipse on August 18, 1868
Course of the total solar eclipse on August 18, 1868
classification
Type Total
area Africa , Asia , Australia
Total: East Africa , Arabian Peninsula , India , Southeast Asia , Australia
Saros cycle 133 (37 of 72)
Gamma value −0.0444
Greatest eclipse
Duration 6 minutes 47 seconds
place Gulf of Thailand
location 10 ° 36 '  N , 102 ° 13'  E Coordinates: 10 ° 36 '  N , 102 ° 13'  E
time August 18, 1868 3:12:08   UT
size 1.0756

The total solar eclipse of August 18, 1868 ran from East Africa across the southern part of Asia to the western Pacific . Their maximum total duration was extremely long at 6 minutes and 47 seconds. During this eclipse, the astronomer Jules Janssen discovered an emission line in the solar spectrum that could not be associated with any previously known element . It was assigned to an element occurring on the sun, which was given the name helium ( ancient Greek ἥλιος hélios , German 'sun' ) and was only detected on earth 14 years later.

The cause of the particularly long totality was, on the one hand, that the (new) moon was very close to the earth during the eclipse, was almost in its perigee and its apparent diameter was thus almost maximum. On the other hand, the eclipse ran near the equator , where the absolute rotational speed of the earth's surface is greatest. The earth's surface moving to the east is least easily “detached” by the moon shadow, which is also “fleeing” to the east.

The solar eclipse of 1868 was the second longest eclipse of the Saros cycle 133. It was only exceeded by the previous eclipse of the same cycle on August 7th, 1850, whose totality was 3 seconds longer at 6 minutes and 50 seconds.

One of the observers was King Mongkut of Siam , who personally calculated the time and place of this solar eclipse . In the course of his observations, he became infected with malaria, from which he eventually died.

course

The umbra of the moon first hit the earth in East Africa in the highlands of Abyssinia near Lake Tana . Then the zone in which the sun could be seen totally darkened, moved over the Bab al-Mandab , the extreme southwest of the Arabian Peninsula and the Arabian Sea to India . From there, the shadow path continued in an east-southeast direction over the Bay of Bengal , crossed the Isthmus of Kra and after crossing the Gulf of Thailand reached the Mekong Delta . In the further course there were a few more Southeast Asian islands in the totality zone, including Borneo and Celebes . At the end of the eclipse, the totally eclipsed sun could be observed in the evening hours in southern New Guinea and in the far north of the Australian Cape York Peninsula .

Observation sites

The opportunity to use the only a few years old method of spectroscopy for the first time in a total solar eclipse attracted numerous European scientists to the orbit of the umbra, whereby the respective colonies offered themselves depending on the country of origin : British India , Dutch East Indies (today Indonesia ) and French Indochina . The latter could not be used, however, because the umbra only grazed the coast of Vietnam with its inaccessible mangrove swamps . The monsoon caused great concern , as it brought many clouds and rain from the southwest in August. The observation sites in Jamkhandi and Thailand were chosen mainly because they expected "rain shadows" from the mountain ranges to the west. Other observers took advantage of the fact that they lived near the shadow orbit and could reach it relatively easily.

The following observation locations are known: (  Map with all coordinates in this section: OSM ) f1Georeferencing

Drawing by Captain Carl Bullock
  • In Aden (Yemen) , a group of photographers from Berlin with Gustav Theodor Fritsch and the photo chemist Hermann Wilhelm Vogel succeeded in taking six pictures during the totality of only three minutes. The astronomers Edmund Weiss and Theodor von Oppolzer from Austria had chosen the same place .
  • To the east of Aden in theIndian Ocean,four hand sketches of prominences were madeon the steamerRangoon.
  • In Jamkhandi (India) Lieutenant John Herschel and his helpers observed the solar eclipse. The son of the 76-year-old British astronomer Sir John Herschel was actually a geodesist and had received instruments and precise instructions from William Huggins .
  • After Mulvad (spelling in the records "Moolwar") near Bijapur (India), another German group had traveled under the direction of Prof. Gustav Spörer , where however bad weather prevented the observations.
  • In Guntur (India) a group led by Major James Francis Tennant also made six photographs. In the same place Jules Janssen discovered the spectral line of helium (see below ).
  • The researchers Stephan, Rayet and Tisserand (see below ) had chosen the east coast of the isthmus of Kra . The place name is called "Wha-Tonne".
  • King Mongkut of Siam (see below ) also had an observation station built near the French near Waghor
  • J. Pope Hennessy, Governor of Labuan , traveled only one night to Cape Baram on the north-west coast of Borneo . One of the four ships of the Dutch expedition had the same goal.
  • On the tiny island Mantawaloc-Kéké off the coast of Sulawesi in the Gulf of Tomini who built Jesuit Federico Fauro, Juan Ricart and Jaime Nonell (in the source, the names are Germanized) their instruments. They had come from Manila on the Serpent steamer , where they operated an observatory. The serpent's captain , Carl Bullock, made the drawing shown above. Another Dutch ship anchored nearby with Prof. Jean Abraham Chrétien Oudemans on board. The third ship of his expedition lay further north of Gorontalo on the edge of the shadow zone.
  • The fourth Dutch ship anchored off Ambon .

The discovery of helium

In the summer of 1868, the technique of spectroscopy could be used for the first time during a total solar eclipse. For this reason some expeditions traveled to India from Europe, two from Great Britain, two French, one German and one Spanish. The aim was to research the spectrum of the solar atmosphere and especially the prominences . As expected, bright emission lines were observed in the spectrum of the prominences by various observers , which indicated hydrogen . The French astronomer Jules Janssen (1824–1907) in Guntur was one of these observers . In contrast to the other scientists who had traveled, Janssen stayed in India, because during the darkness he had the idea that the bright emission lines of the protuberances would have to be recognizable even in normal daylight if the intensity of the Stray light reduced. When he pointed his telescope at the edge of the no longer eclipsed sun the next day , he saw his suspicion confirmed, because he could see the same emission lines as the day before, including a strange yellow “ sodium line”. It was surprising that a comparatively heavy element such as sodium should appear in the protuberances, and the wavelength of the emission line seemed to be slightly shorter than that of sodium known so far.

Two years before this eclipse, the English astronomer Norman Lockyer (1836–1920) commissioned the manufacture of a special spectroscope with which he wanted to study the solar corona and the prominences. Without ever having seen a total solar eclipse, he had the idea that the spectrum of the protuberances should also be able to be analyzed in normal daylight. His spectroscopic telescope, however, was not yet ready in the summer of 1868, so that he missed the solar eclipse and did not travel to India. On October 20, 1868, it was finally ready for use. In Cambridge , he aimed it at the sun and saw his suspicions confirmed: the emission lines of the protuberances could be seen. He immediately wrote to the French Academy of Sciences , where his report happened just a few minutes after Janssens. Both reports were read out one after the other at the meeting on October 26, 1868 at the Academy. The French academy honored both scientists and later had a coin minted with the likeness of both.

Lockyer then made further observations of the spectrum of the prominences, and he too noticed this strange yellow emission line. Perhaps his instruments were more precise because he was not satisfied with explaining that they were due to sodium. After all, the unknown line was at 587.6 nm (5876  Å ), a long way from that of sodium at 589.3 nm. Neither Lockyer nor Janssen was able to reproduce this spectral line under laboratory conditions, but Lockyer was in 1870 sure to have discovered a new chemical element , which only existed on the sun and not on earth. He called it helium  - after the Greek word hélios for "sun". Most other scientists had doubts and did not recognize the method of postulating a new element solely on the basis of the existence of an emission line in the solar spectrum. It was not until 1882, 14 years later, that Luigi Palmieri succeeded in detecting the element helium on earth for the first time using the spectral analysis of Vesuvius lava, and in 1895 the Scottish chemist William Ramsay (1852-1916) observed the same spectral line when analyzing the mineral Cleveit , a variant of radioactive uraninite . He was able to isolate the gas, just like William Crookes , Per Teodor Cleve and Nicolas Langlet together independently in the same year . These collected sufficient quantities of the gas to be able to determine its atomic mass .

The next solar eclipse that both Janssen and Lockyer traveled to was the December 22, 1870 solar eclipse . But both Janssen in Algeria and Lockyer in Sicily were unlucky, because the clouds did not allow a view of the darkened sun. Lockyer later made several more trips to observe total solar eclipses. He was twice in India, both on December 12, 1871 and on January 22, 1898 . This may contribute to the fact that it is often falsely claimed that both of them first observed the emission line in the same eclipse in India.

The King of Siam

King Mongkut on his observation post

Probably the most prominent observer of the solar eclipse was Mongkut (Rama IV.), The king of Siam , today's Thailand . Before he could ascend the throne in 1851, he lived for many years, first as a monk and later as abbot in the monastery of Wat Bowonniwet . There he dealt intensively with western culture, languages ​​and sciences, in particular with astronomy . With the help of this knowledge, he calculated the location and time of the solar eclipse two years in advance. His court astrologers, however, thought the calculations were wrong.

In the vicinity of the village of หว้า กอ (Waghor) in the province of Prachuap Khiri Khan , he cleared a free area in the jungle and built a large observation pavilion along with numerous accommodation buildings. The place was roughly where the central line of darkness intersected the coastline. It was therefore not only easily accessible from the royal steamships, but it was also the place on the Thai mainland with the longest total duration, as the maximum occurred about eight minutes later over the Gulf of Thailand. He invited numerous foreign dignitaries to observe, including Sir Harry Ord , Governor of the Straits Settlements ( Singapore ).

The French scientists' observation post

A group of French scientists also had an observation station built just under two kilometers to the southwest. It had not been easy to get a permit from the Bangkok authorities. The officials in charge could hardly believe that such effort and expense would be expended in observing an event that was to last only a few minutes. On July 25, scientists Édouard Jean-Marie Stephan , Georges Rayet and Félix Tisserand arrived at their observation station. They established foundations for a variety of instruments to enable precise measurements.

The letter from King Mongkut
to Édouard Jean-Marie Stephan

A few days before the solar eclipse, Mongkut landed with a fleet of twelve steamships of the royal navy, and nearly a thousand people from his farm came by land, bringing many cattle, horses and fifty elephants. The king visited the French station and then wrote a letter to Stephen in which he expressed his admiration for the modern equipment and gave details of his astronomical knowledge.

To the satisfaction of the king, the solar eclipse was exactly what he had calculated. While the French researchers unwound a sophisticated program of measurements and observations, King Mongkut had fanfares blown and a cannon fired and carried out a ceremonial "bath of cleansing". After returning to his palace, he confronted the court astrologers and, when they were unable to explain their misjudgment, had them perform degrading work as a punishment.

However, the king and his son Chulalongkorn soon developed a severe fever. The observation station was in an area full of swarms of mosquitoes that had infected many people with malaria . Mongkut succumbed to the disease two months later. His son survived and took the throne that same year.

King Mongkut received the nickname "Father of Science" because of his impulses for modernization. Near the observation stations (they are untraceable) is now the King Mongkut Memorial Park of Science and Technology 11 ° 43 '  N , 99 ° 46'  O .

literature

Web links

Commons : Solar eclipse of August 18, 1868  - Collection of images, videos and audio files

Individual evidence

Notes with individual references to the coordinates

  1. ↑ Coordinates of the lighthouse on the "Peninsula Aden", in the vicinity of which, according to "Development of solar research" on page 156, the observations took place in two bungalows
  2. ↑ Les Mondes gives a southern latitude on page 296, but correctly it must be the northern latitude.
  3. ↑ a b Coordinates of the place named in Gaea Vol. 5, pages 1–2, the exact coordinates of the observation positions are not known.
  4. ↑ The center of Guntur, in Les Mondes , a house in this city is mentioned on page 296
  5. ^ In the report on page 547 the exact north latitude is given. The eastern length results from the coastline, since the station was directly on the sea.
  6. ↑ According to the report on page 544, the king's station was about a mile (meaning the nautical mile = 1852 m) to the northeast.
  7. ↑ Coordinates in Provinciale Overijsselsche ( Memento of the original from December 4, 2012 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 1.4 MB) on page 2 @1@ 2Template: Webachiv / IABot / resources2.kb.nl
  8. ↑ Prof. Fauro mentions two different coordinates in his observations on page 4, the island lies exactly between them.
  9. ↑ Coordinates according to Verslag over de waarneming on page 74

Further individual evidence

  1. ^ A b c d e f Édouard Jean-Marie Stephan: L'eclipse de soleil du 18 Août 1868. In: Archives des missions scientifiques et littéraires. Commission des missions scientifiques et littéraires, 1868, pp. 535-584 , accessed April 18, 2012 (French).
  2. ↑ a b Herm. J. Klein: The results of the observations of the total solar eclipse of August 18, 1868. In: Gaea - Nature and Life, Volume 5. Herm. J. Klein, 1869, pp. 1-2 , accessed April 18, 2012 .
  3. ^ Edmund Weiss: Reports of the Austrian expedition undertaken to Aden to observe the total solar eclipse of 1868 . In: Imperial Academy of Sciences, Vienna (Hrsg.): Astronomische Nachrichten . tape 77 , 1871, pp. 177-202 , doi : 10.1002 / asna.18710771202 .
  4. ^ F. Moigno: Astronomie physique. In: Les Mondes. Bureaux des mondes, 1868, p. 296 , accessed April 26, 2012 (French).
  5. ^ Barbara J. Becker: Unraveling Starlight. 2011, pp. 151–152 , accessed on April 24, 2012 (English).
  6. ↑ Dr. H. Schellen: The spectral analysis. 1871, p. 299 , accessed April 18, 2012 .
  7. ^ J. Pope Hennessy: Governor Hennessy's Observations. (PDF) 1868, p. 71 , accessed on April 26, 2012 (English).
  8. ↑ a b c J. AC Oudemans: Verslag over de waarneming the total zoneclips in 1868. In: Natuurkundig Tijdschrift voor Nederlandsch-Indië. Koninglijke natuurkundige vereeniging in Nederlandsch-Indië, 1870, pp. 51-89 , accessed on April 26, 2012 (Dutch).
  9. ↑ Prof. Friedrich Fauro: Observations of the total solar eclipse on August 18, 1868 made by the fathers of the Society of Jesus in Manila in the Philippines. Letter from PF Fauro to PA Secchi. 1869, pp. 1-16 , accessed April 26, 2012 .
  10. ↑ McEvoy: Solar Eclipse. The story of a sensational phenomenon. Page 157ff
  11. ^ Littmann, Espenak, Willcox: Totality: Eclipses of the Sun. Pages 77–85
  12. ↑ a b c McEvoy: Solar eclipse. The story of a sensational phenomenon. Page 159–167
  13. ↑ AL Cortie: Sir Norman Lockyer, 1836-1920. In: Astrophysical Journal. 53: 233-258, May 1921 ( online )
  14. ↑ Incorrect representation, for example here: Leon Golub, Jay M. Pasachoff: The Solar Corona. Second Edition, page 43, Cambridge University Press, New York 2010, ISBN 978-0-521-88201-9
  15. ^ A b c L. Robert Morris: The 1868 solar eclipse and the King of Siam. In: History of Nova Scotia. December 25, 2000, accessed May 3, 2012 .
  16. ^ A b Samuel J. Smith: EVENTS IN SIAM. Connected With The Eclipse Of 1868. In: The Siam Repository Vol. I. Samuel J. Smith, January 1869, pp. 2-3 , accessed April 18, 2012 (English).
  17. ↑ www.a2o.com.sg/a2o/public/html/online_exhibit/odetoFriendship/html/King_IV/index.htm ( Memento from December 5, 2010 in the Internet Archive ) National Archives of Singapore
  18. ↑ David Streckfuss: Truth on Trial in Thailand. 2011, p. 338 , accessed on May 3, 2012 (English).
This version was added to the list of articles worth reading on June 1, 2012 .