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Solar eclipse of August 18, 1868

{{Short description|Total eclipse named after Rama IV of Siam}}

{{Infobox solar eclipse|1868Aug18

| previous = Solar eclipse of February 23, 1868

| next = Solar eclipse of February 11, 1869

}}

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.{{cite web|title=Moon Distances for London, United Kingdom, England|url=https://www.timeanddate.com/astronomy/moon/distance.html?year=1868&n=136|publisher=timeanddate|access-date=3 September 2024}}

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 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.

Observations

{{Location map+|AFC|width=400|caption=Observation points of the solar eclipse |places=

{{Location map~|AFC|lat= 12.7633 |long= 45.054|label={{nowrap|Fritsch}}|position=bottom}}

{{Location map~|AFC|lat= 0.53 |long= 123.48|label={{nowrap|Bullock}}|position=top}}

{{Location map~|AFC|lat= 15.70 |long= 59.25|label={{nowrap|Rennoldson}}|position=top}}

{{Location map~|AFC|lat= 16.60 |long= 75.294|label={{nowrap|Herschel}}|position=top}}

{{Location map~|AFC|lat= 16.34 |long= 75.5|label={{nowrap|Tietjen}}|position=top}}

{{Location map~|AFC|lat= 16.5917 |long= 75.7367|label={{nowrap|Spörer}}|position=bottom}}

{{Location map~|AFC|lat= 16.33 |long= 80.45|label={{nowrap|Tennant}}|position=right}}

{{Location map~|AFC|lat= 11.7097 |long= 99.7494|label={{nowrap|Tisserand }}|position=right}}

{{Location map~|AFC|lat= 4.595 |long= 113.98|label={{nowrap|Hennesy}}|position=right}}}}

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.{{cite book|author=Gustav Spoerer|title=Die Reise nach Indien zur Beobachtung der totalen Sonnenfinsterniss am 18. August 1868: Vortrag gehalten in der Singakademie zu Berlin am 16. Januar 1869|url=https://archive.org/details/bub_gb_PkBSAAAAcAAJ|year=1869|publisher=Engelmann}}
  • The second expedition was sent to the west coast of India. The expedition was led by Friedrich Tietjen.{{cite book|title=Zeitschrift|url=https://books.google.com/books?id=BTNCAQAAMAAJ&pg=PA608|year=1870|publisher=D. Reimer|pages=608–}}
  • Captain Bullock observed from the Celebes sea, sketching the appearance of the corona,{{cite book|author=Edward Walter Maunder, British Astronomical Association|title=The Indian Eclipse, 1898: Report of the Expeditions Organized by the British Astronomical Association to Observe the Total Solar Eclipse of 1898 January 22|url=https://archive.org/details/indianeclipsere00assogoog|year=1899|publisher=Hazell, Watson, and Viney|page=[https://archive.org/details/indianeclipsere00assogoog/page/n131 113]}} while Gustav Fritsch accompanied an expedition to Aden.Standard Encyclopaedia of Southern Africa

=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.{{citation | url = https://www.wired.com/thisdayintech/2009/08/dayintech_0818/ | publisher = wired.com | access-date = 2010-03-18 | title = Aug. 18, 1868: Helium Discovered During Total Solar Eclipse | date = August 18, 2009 | first = Hadley | last = Leggett}}.{{citation | journal = C. R. Acad. Sci. Paris | volume = 67 | year = 1868 | pages = 836–841 | url = http://gallica.bnf.fr/ark:/12148/bpt6k3024c.image.r=comptes-rendus+hebdomadaires+Acad%C3%A9mie+des+Sciences.f836.langFR |title=Comptes rendus hebdomadaires des séances de l'Académie des sciences}}.

= King Mongkut's calculation =

File:King Mongkut Solar Eclipse Expedition.jpg

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, then developed chills and fever. He died on October 1, 1868.{{cite web|url= http://www.bradleyfoundation.org/genealogies/Bingley/tobg88.htm#21153|title= Descendants of Danyell Broadley de West Morton

|access-date= 9 August 2013 |first1= Saul M. |last1= Montes-Bradley

|first2= W.L. |last2= Bradley |author2-link= William Lee Bradley|date= 10 January 2006|format= 964-word excerpt from Siam then, the foreign colony in Bangkok before and after Anna, Pasadena, California, 1981.|work= Eighth Generation|publisher= Thomas Osgood Bradley Foundation

|archive-url= https://web.archive.org/web/20150210165538/http://www.bradleyfoundation.org/genealogies/Bingley/tobg88.htm|archive-date= 2015-02-10|url-status= live|quote= King Mongkut's prediction surpassed those of European scientists. "In the 19th century, King Mongkut of Siam (now Thailand), an amateur astronomer, paid the ultimate price for eclipse-chasing: his life.

}} According to the Thai Astronomical Society and NASA, this eclipse is known as "The King of Siam's eclipse".[http://thaiastro.nectec.or.th/library/kingmongkut_bicentennial/kingmongkut_bicentennial.html ๒๐๐ ปี พระบาทสมเด็จพระจอมเกล้าเจ้าอยู่หัว พระบิดาแห่งวิทยาศาสตร์ไทย]. {{in lang|th}}{{cite web|last1=Candey|first1=Robert. M.|title=Solar Eclipses of Historical Interest|url=https://eclipse.gsfc.nasa.gov/SEhistory/SEhistory.html#1868|publisher=NASA|access-date=25 April 2017|language=en|date=28 Sep 2009}}

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.{{cite web|title=Total Solar Eclipse of 1868 Aug 18|url=https://eclipsewise.com/solar/SEprime/1801-1900/SE1868Aug18Tprime.html|publisher=EclipseWise.com|access-date=3 September 2024}}

class="wikitable" align="{{{align|left}}}" style="margin:{{#ifeq:{{{align}}}|left|0 0 0.5em 1em|0 1em 0.5em 0}}"

|+August 18, 1868 Solar Eclipse Times

! Event

! Time (UTC)

First Penumbral External Contact

| 1868 August 18 at 02:34:50.2 UTC

First Umbral External Contact

| 1868 August 18 at 03:27:59.0 UTC

First Central Line

| 1868 August 18 at 03:29:29.6 UTC

First Umbral Internal Contact

| 1868 August 18 at 03:31:00.1 UTC

First Penumbral Internal Contact

| 1868 August 18 at 04:24:13.7 UTC

Greatest Duration

| 1868 August 18 at 05:08:35.7 UTC

Ecliptic Conjunction

| 1868 August 18 at 05:11:42.5 UTC

Greatest Eclipse

| 1868 August 18 at 05:12:09.6 UTC

Equatorial Conjunction

| 1868 August 18 at 05:13:17.9 UTC

Last Penumbral Internal Contact

| 1868 August 18 at 06:00:03.7 UTC

Last Umbral Internal Contact

| 1868 August 18 at 06:53:18.8 UTC

Last Central Line

| 1868 August 18 at 06:54:49.0 UTC

Last Umbral External Contact

| 1868 August 18 at 06:56:19.2 UTC

Last Penumbral External Contact

| 1868 August 18 at 07:49:29.4 UTC

class="wikitable" align="{{{align|right}}}" style="margin:{{#ifeq:{{{align}}}|right|0 0 0.5em 1em|0 1em 0.5em 0}}"

|+August 18, 1868 Solar Eclipse Parameters

! Parameter

! Value

Eclipse Magnitude

| 1.07561

Eclipse Obscuration

| 1.15693

Gamma

| −0.04434

Sun Right Ascension

| 09h51m00.1s

Sun Declination

| +13°02'06.8"

Sun Semi-Diameter

| 15'48.4"

Sun Equatorial Horizontal Parallax

| 08.7"

Moon Right Ascension

| 09h50m57.4s

Moon Declination

| +12°59'28.9"

Moon Semi-Diameter

| 16'42.8"

Moon Equatorial Horizontal Parallax

| 1°01'20.3"

ΔT

| 2.2 s

{{clear}}

Eclipse season

{{See also|Eclipse cycle}}

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.

class="wikitable"

|+ Eclipse season of August–September 1868

! August 3
Descending node (full moon)
!! August 18
Ascending node (new moon)
!! September 2
Descending node (full moon)

200px
align=center

| Penumbral lunar eclipse
Lunar Saros 107

Total solar eclipse
Solar Saros 133		Penumbral lunar eclipse
Lunar Saros 145

Related eclipses

= Eclipses in 1868 =

= Metonic =

= Tzolkinex =

= Half-Saros =

= Tritos =

= Solar Saros 133 =

= Inex =

= Triad =

= Solar eclipses of 1866–1870 =

{{Lunar year eclipse set info}}

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.

class="wikitable mw-collapsible mw-collapsed"

!class="nowrap" colspan="7" | Solar eclipse series sets from 1866 to 1870

scope="col" colspan="3" | Descending node

| rowspan="6" | 

! scope="col" colspan="3" | Ascending node

style="text-align: center;"

! scope="col" | Saros

! scope="col" | Map

! scope="col" | Gamma

! scope="col" | Saros

! scope="col" | Map

! scope="col" | Gamma

style="text-align: center;"

| 108

| March 16, 1866
150px
Partial

| 1.4241

| 113

|

|

style="text-align: center;"

| 118

| March 6, 1867
150px
Annular

| 0.7716

| 123

| August 29, 1867
150px
Total

| −0.7940

style="text-align: center;"

| 128

| February 23, 1868
150px
Annular

| 0.0706

| 133

| August 18, 1868
150px
Total

| −0.0443

style="text-align: center;"

| 138

| February 11, 1869
150px
Annular

| −0.6251

| 143

| August 7, 1869
150px
Total

| 0.6960

style="text-align: center;"

| 148

| January 31, 1870
150px
Partial

| −1.2829

|

| 153

| July 28, 1870
150px
Partial

| 1.5044

= Saros 133 =

{{Solar Saros series 133}}

= Metonic series =

{{Metonic eclipse set info}} All eclipses in this table occur at the Moon's ascending node.

class="wikitable mw-collapsible mw-collapsed"

!colspan=5|24 eclipse events between March 25, 1819 and August 20, 1906

March 25–26

!January 11–12

!October 30–31

!August 18–20

!June 6–7

107

!109

!111

!113

!115

style="text-align:center;"

|150px
March 25, 1819

|150px
January 12, 1823

|150px
October 31, 1826

|150px
August 18, 1830

|150px
June 7, 1834

117

!119

!121

!123

!125

style="text-align:center;"

|150px
March 25, 1838

|150px
January 11, 1842

|150px
October 30, 1845

|150px
August 18, 1849

|150px
June 6, 1853

127

!129

!131

!133

!135

style="text-align:center;"

|150px
March 25, 1857

|150px
January 11, 1861

|150px
October 30, 1864

|150px
August 18, 1868

|150px
June 6, 1872

137

!139

!141

!143

!145

style="text-align:center;"

|150px
March 25, 1876

|150px
January 11, 1880

|150px
October 30, 1883

|150px
August 19, 1887

|150px
June 6, 1891

147

!149

!151

!153

style="text-align:center;"

|150px
March 26, 1895

|150px
January 11, 1899

|150px
October 31, 1902

|150px
August 20, 1906

= Tritos series =

{{Solar Tritos series 2010 July 11}}

= Inex series =

{{Solar Inex series 2013 May 10}}

Notes

{{reflist}}

References

  • [http://eclipse.gsfc.nasa.gov/5MCSEmap/1801-1900/1868-08-18.gif NASA chart graphics]
  • [http://eclipse.gsfc.nasa.gov/SEsearch/SEsearchmap.php?Ecl=18680818 Googlemap]
  • [http://eclipse.gsfc.nasa.gov/SEsearch/SEdata.php?Ecl=18680818 NASA Besselian elements]
  • [http://www.starwrite.org/eclipse.html www.starwrite.org: Solar Astronomy in 1868] {{Webarchive|url=https://web.archive.org/web/20110728054656/http://www.starwrite.org/eclipse.html |date=2011-07-28 }}
  • [https://www.jstor.org/pss/112360 Observations of the Total Solar Eclipse of August 18, 1868 by Charles G. Perrins]
  • [http://xjubier.free.fr/site_stickers/solar_corona_shape/1868_08_18_Bullock.jpg Drawing of Corona]
  • {{cite book|author=Mabel Loomis Todd|title=Total Eclipses of the Sun|url=https://books.google.com/books?id=FI0-AAAAYAAJ|year=1900|publisher=Little, Brown}}

{{Solar eclipses}}

{{Commons category|Solar eclipse of 1868 August 18}}

1868 08 18

Category:1868 in science

1868 08 18

Category:Helium

Category:August 1868

Category:Astronomy in Thailand