Editing Sungrazing comet (section)

{{Short description|Comet that is extremely close to the sun during part of its orbit}}
[[File:Kreutz Comet Orbits.ogv|thumb|300px|The representative orbit of a sungrazing comet.]]

A '''sungrazing comet''' is a [[comet]] that passes extremely close to the [[Sun]] at [[perihelion]] – sometimes within a few thousand kilometres of the Sun's surface. Although small sungrazers can completely [[evaporation|evaporate]] during such a close approach to the Sun, larger sungrazers can survive many perihelion passages. However, the strong evaporation and [[tidal force]]s they experience often lead to their fragmentation.

Up until the 1880s, it was thought that all bright comets near the Sun were the repeated return of a single sungrazing comet. Then, German astronomer [[Heinrich Kreutz]] and American astronomer [[Daniel Kirkwood]] determined that, instead of the return of the same comet, each appearance was a different comet, but each were related to a group of comets that had separated from each other at an earlier passage near the Sun (at [[perihelion]]).<ref name=Kirkwood>{{cite journal|last=Kirkwood|first=Daniel|title=On the great southern comet of 1880|journal=The Observatory|date=November 1880|volume=3|pages=590–592|bibcode=1880Obs.....3..590K}}</ref>   Very little was known about the population of sungrazing comets until 1979 when [[coronagraph]]ic observations allowed the detection of sungrazers.  As of October 21, 2017, there are 1495 known comets that come within ~12 solar radii (~0.055 AU).<ref>[http://ssd.jpl.nasa.gov/sbdb_query.cgi#x JPL Small-Body Database Search Engine]</ref>  This accounts for nearly one third of all comets.<ref>{{cite web |last=Johnston |first=Robert |title=Known populations of solar system objects |url=http://www.johnstonsarchive.net/astro/sslist.html |date=27 July 2013 |access-date=30 July 2013}}</ref>  Most of these objects vaporize during their close approach, but a comet with a nucleus radius larger than 2–3&nbsp;km is likely to survive the perihelion passage with a final radius of ~1&nbsp;km.

Sungrazer comets were some of the earliest observed comets because they can appear very bright. Some are even considered [[Great Comet]]s. The close passage of a comet to the Sun will brighten the comet not only because of the reflection off the comet nucleus when it is closer to the Sun, but the Sun also vaporizes a large amount of gas from the comet and the gas reflects more light. This extreme brightening will allow for possible naked eye observations from Earth depending on how [[Volatility (chemistry)|volatile]] the gases are and if the comet is large enough to survive perihelion. These comets provide a useful tool for understanding the composition of comets as we observe the outgassing activity and they also offer a way to probe the effects solar radiation has on other Solar System bodies.