Editing Sungrazing comet (section)

== History of sungrazers ==

=== Pre-19th century ===
One of the first comets to have its orbit computed was the sungrazing comet (and Great Comet) of 1680, now designated [[C/1680 V1]].  It was observed by [[Isaac Newton]] and he published the orbit results in 1687.<ref name=Marsden>{{cite journal|last=Marsden|first=Brian G.|title=Sungrazing Comets|journal=Annual Review of Astronomy & Astrophysics|date=September 2005|volume=43|issue=1|pages=75–102|doi=10.1146/annurev.astro.43.072103.150554|bibcode=2005ARA&A..43...75M}}</ref> Later, in 1699, [[Jacques Cassini]] proposed that comets could have relatively short orbital periods and that C/1680 V1 was the same as a comet observed by [[Tycho Brahe]] in 1577, but in 1705 [[Edmond Halley]] determined that the difference between the perihelion distances of the two comets was too great for them to be the same object.<ref>{{cite journal|last=Cassini|first=JD|journal=Hist. Acad. R. Sci. Paris|date=1699|volume=Amsterdam ed. 1734|pages=95–100}}</ref><ref>{{cite journal|last=Halley|first=Edmund|journal=Phil. Trans.|date=1705|volume=24|issue=297|pages=1882–1899|doi=10.1098/rstl.1704.0064|title=IV. Astronomiæ cometicæ synopsis, Autore Edmundo Halleio apud Oxonienses Geometriæ Professore Saviliano, & Reg. Soc. S|doi-access=free|bibcode=1704RSPT...24.1882H}}</ref> However, this marked the first time that it was hypothesized that Great Comets were related or perhaps the same comet. Later, [[Johann Franz Encke]] computed the orbit of C/1680 V1 and found a period of approximately 9000 years, leading him to conclude that Cassini's theory of short period sungrazers was flawed. C/1680 V1 had the smallest measured perihelion distance until the observation in 1826 of comet C/1826 U1.<ref name=Marsden />

=== 19th century ===
Advances were made in understanding sungrazing comets in the 19th century with the Great Comets of [[C/1843 D1|1843]], C/1880 C1, and [[C/1882 R1|1882]]. C/1880 C1 and C/1843 D1 had very similar appearances and also resembled the [[X/1106 C1|Great Comet of 1106]], therefore Daniel Kirkwood proposed that C/1880 C1 and C/1843 D1 were separate fragments of the same object.<ref name=Kirkwood />   He also hypothesized that the [[parent body]] was a comet seen by [[Aristotle]] and [[Ephorus]] in 371 BC because there was a supposed claim that Ephorus witnessed the comet splitting after perihelion.<ref name=Marsden />

Comet [[C/1882 R1]] appeared only two years after the previously observed sungrazer so this convinced astronomers that these bright comets were not all the same object.  Some astronomers theorized that the comet might pass through a resisting medium near the Sun and that would shorten its period.<ref name=Marsden />   When astronomers observed C/1882 R1, they measured the period before and after perihelion and saw no shortening in the period which disproved the theory.  After perihelion this object was also seen to split into several fragments and therefore Kirkwood's theory of these comets coming from a parent body seemed like a good explanation.

In an attempt to link the 1843 and 1880 comets to the comet in 1106 and 371 BC, Kreutz measured the fragments of the 1882 comet and determined that it was likely a fragment of the 1106 comet.  He then designated that all sungrazing comets with similar orbital characteristics as these few comets would be part of the [[Kreutz Sungrazers|Kreutz Group]].<ref name=Marsden />

The 19th century also provided the first spectrum taken of a comet near the Sun which was taken by Finlay & Elkin in 1882.<ref>{{cite journal|last=Finlay|first=W.H.|author2=W.L Elkin |title=Observations of the Great Comet 1882|journal=[[Monthly Notices of the Royal Astronomical Society]]|date=November 1992|volume=43|pages=21–25|doi=10.1093/mnras/43.1.21|bibcode=1882MNRAS..43...22E|url=https://zenodo.org/record/1431845|doi-access=free}}</ref> Later the spectrum was analyzed and [[Iron|Fe]] and [[Nickel|Ni]] spectral lines were confirmed.<ref>{{cite journal|last=Orlov|first=A.|journal=Astron. Zh.|date=1927|volume=4|pages=1–9}}</ref>

=== 20th century ===
The first sungrazing comet observed in the 20th century was in 1945 and then between 1960 and 1970 five sungrazing comets were seen (C/1961 O1, [[comet Seki-Lines|C/1962 C1]], [[Comet Pereyra|C/1963 R1]], [[Comet Ikeya–Seki|C/1965 S1]], and [[comet White–Ortiz–Bolelli|C/1970 K1]]). The 1965 comet (Comet Ikeya-Seki) allowed for measurements of spectral emission lines and several elements were detected including Iron, marking this the first comet since the Great Comet of 1882 to show this feature.  Other emission lines included [[Potassium|K]], [[Calcium|Ca]], Ca<sup>+</sup>, [[Chromium|Cr]], [[Cobalt|Co]], [[Manganese|Mn]], [[Nickel|Ni]], [[Copper|Cu]], and [[Vanadium|V]].<ref>{{cite journal|last=Dufay|first=J.|author2=Swings, P. |author3=Fehrenbach, Ch. |title=Spectrographic Observations of Comet Ikeya-Seki (1965f)|journal=Astrophysical Journal|date=November 1965|volume=142|pages=1698|doi=10.1086/148467|bibcode=1965ApJ...142.1698D|url=http://orbi.ulg.ac.be/bitstream/2268/71503/1/SWINGS_1965_spectographic-observations.pdf}}</ref><ref>{{cite journal|last=Curtis|first=G. Wm.|author2=Staff, The Sacramento Peak Observatory|title=Daylight observations of the 1965 F comet at the Sacramento Peak Observatory|journal=The Astronomical Journal|date=April 1966|volume=71|pages=194|doi=10.1086/109902|bibcode=1966AJ.....71..194C|doi-access=free}}</ref><ref>{{cite journal |last=Thackeray |first=A. D. |author2=Feast, M. W. |author3=Warner, B. |author-link3=Brian Warner (astronomer) |date=January 1966 |title=Daytime Spectra of Comet Ikeya-Seki Near Perihelion |journal=The Astrophysical Journal |volume=143 |pages=276 |bibcode=1966ApJ...143..276T |doi=10.1086/148506}}</ref><ref>{{cite journal|last=Preston|first=G. W.|title=The spectrum of Ikkeya-Seki (1965f)|journal=The Astrophysical Journal|date=February 1967|volume=147|pages=718|doi=10.1086/149049|bibcode=1967ApJ...147..718P|doi-access=free}}</ref><ref>{{cite journal|last=Slaughter|first=C. D.|title=The Emission Spectrum of Comet Ikeya-Seki 1965-f at Perihelion Passage|journal=The Astronomical Journal|date=September 1969|volume=74|pages=929|doi=10.1086/110884|bibcode=1969AJ.....74..929S|doi-access=free}}</ref> Comet Ikeya-Seki also led to separating the Kreutz sungrazers into two subgroups by Brian Marsden in 1967.<ref>{{cite journal|last=Marsden|first=B. G.|title=The sungrazing comet group|journal=The Astronomical Journal|date=November 1967|volume=72|pages=1170|doi=10.1086/110396|bibcode=1967AJ.....72.1170M}}</ref> One subgroup appears to have the 1106 comet as the parent body and members are fragments of that comet, while the other group have similar dynamics but no confirmed parent body associated with it.

==== Coronagraphic observations ====
The 20th century greatly impacted sungrazing comet research with the launch of [[coronagraphic]] telescopes including [[P78-1|Solwind]], [[Solar Maximum Mission|SMM]], and [[Solar and Heliospheric Observatory|SOHO]].  Until this point, sungrazing comets were only seen with the [[naked eye]] but with the coronagraphic telescopes many sungrazers were observed that were much smaller and very few have survived perihelion passage.  The comets observed by Solwind and SMM from 1981 to 1989 had [[Apparent magnitude|visual magnitudes]] from about -2.5 to +6 which is much fainter than Comet Ikeya-Seki with a visual magnitude of about -10.<ref name=Marsden />

In 1987 and 1988 it was first observed by SMM that there could be pairs of sungrazing comets that can appear within very short time periods ranging from a half of a day up to about two weeks. Calculations were made to determine that the pairs were part of the same parent body but broke apart at tens of AU from the Sun.<ref>{{cite journal|last=Sekanina|first=Zdenek|title=Secondary Fragmentation of the ''Solar and Heliospheric Observatory'' Sungrazing Comets at Very Large Heliocentric Distance|journal=The Astrophysical Journal|date=20 October 2000|volume=542|issue=2|pages=L147–L150|doi=10.1086/312943|bibcode=2000ApJ...542L.147S|s2cid=122413384|doi-access=free}}</ref> The breakup velocities were only on the order of a few meters per second which is comparable to the speed of rotation for these comets. This led to the conclusion that these comets break from [[tidal force]]s and that comets C/1882 R1, C/1965 S1, and C/1963 R1 probably broke off from the Great Comet of 1106.<ref>{{cite journal|last=Sekanina|first=Zdenek|author2=Chodas, Paul W. |title=Common Origin of Two Major Sungrazing Comets|journal=The Astrophysical Journal|date=10 December 2002|volume=581|issue=1|pages=760–769|doi=10.1086/344216|bibcode=2002ApJ...581..760S|doi-access=free}}</ref>

Coronagraphs allowed for measuring the properties of the comet as it reached very close to the Sun.  It was noted that sungrazing comets tend to peak in brightness at a distance of about 12.3 [[Solar radius|solar radii]] or 11.2 solar radii.  It is thought that this variation stems from a difference in dust composition.  Another small peak in brightness has been found at about 7 solar radii from the sun and it is possibly due to a fragmentation of the comet nucleus.<ref name=Marsden /> An alternative explanation is that the brightness peak at 12 solar radii comes from the sublimation of [[Amorphous solid|amorphous]] [[olivine]]s and the peak at 11.2 solar radii is from the sublimation of [[Crystallinity|crystalline]] olivines.  The peak at 7 solar radii could then be the [[Sublimation (phase transition)|sublimation]] of [[pyroxene]].<ref>{{cite journal|last=Kimura|first=H|title=Dust Grains in the Comae and Tails of Sungrazing Comets: Modeling of Their Mineralogical and Morphological Properties|journal=Icarus|date=October 2002|volume=159|issue=2|pages=529–541|doi=10.1006/icar.2002.6940|bibcode=2002Icar..159..529K}}</ref>