Kreutz Sungrazers

As a Kreutz - group (English Kreutz Sungrazers ) a group of comets is called, which are very close during their perihelion the sun. They form a subgroup of the Sungrazer ( sungrazer sun or scratches). The comets of the Kreutz group are probably fragments of a much larger comet that broke around the sun during revolution several centuries ago. They were named after the astronomer Heinrich Kreutz, who first recognized the group membership.

Several members of the Kreutz group developed into very bright comets that were themselves during the day in addition to the sun visible, such as the comet Ikeya - Seki published in 1965, which is considered one of the brightest comets of the last millennium.

Since the commissioning of the SOHO spacecraft in 1995, several hundred smaller comets of the group were discovered, partly by amateur astronomers.

Discovery and historical observations

The first comet whose orbit could be determined to be very sonnennah, was the Great Comet of 1680 the comet pulled in just 200,000 km or 0.0013 astronomical units (AU ) at the solar surface over -. Representing about half the distance between the Earth and moon. The astronomers of the time, including Edmond Halley, suspected that it might be the same comet that was visible in the daytime 1106. 163 years later, the Great Comet of 1843, which also vorbeizog extremely close to the sun appeared. The determination of its orbit showed a periodicity of several hundred years. Some astronomers saw it as the return of the comet of 1680. 1880 appeared a bright comet that was moving on a very similar path as the comet of 1843. 1882 again a very conspicuous comet was visible, which was known as the Great September Comet.

This led some astronomers suspect that they might be one and the same comet at all observations, with its orbital period must have been greatly reduced over time, for example due to deceleration by a denser medium near the sun.

One other argument after it was fragments of a larger comet. This first expressed in the 1880 thesis was supported, as was observed that the Great Comet of 1882 broke up into several pieces after the perihelion passage. 1888 Heinrich Kreutz published a work in which he explained that it could be at the comet of 1843, 1880 and 1882 are fragments of a giant comet, which was broken in previous passages. The comet of 1680, however, do not belong to this group.

Another comet, which could be assigned on the basis of its orbit characteristics of the group appeared in 1887, the next but again only in 1945 In the 1960s, then appeared in quick succession two. 1963, the comet Pereyra and 1965 Ikeya - Seki, which in just before the perihelion passage three parts broke. The appearance of two comets of the Kreutz - group in such short intervals led to study more carefully the dynamics of the group.

Dynamics

A 1967 employees by Brian Marsden study was the first attempt to determine the origin of the body of the Kreutz group. All known members of the group were observed until 1965, had a similar orbital inclination of about 144 ° and similar Perihellängen of 280-282 °, with occasional deviations occurred, although they were due to inaccurate orbit determination. Larger deviations arose, however, regarding the Perihelarguments and the length of the ascending node.

According to Marsden, the Kreutz group can in turn be divided into two groups that had arisen due to the multiple breakup of the source body. A comparison of the orbits of Ikeya - Seki and the comet of 1882 led to the conclusion that it was fragments that had arisen at the same perihelion passage of the comet origin. The most likely candidate for this was the comet of 1106. Comets of 1689, 1702 and 1945 could also to this " subgroup I " belong, although their paths could not be determined accurately enough.

The orbits of the comets of 1843 and 1963 have each other also on similarities. In the re-calculation of the tracks, however, there is a larger difference. These members of the " subgroup II ", which include the comets of 1668, 1695, 1880 and 1963 belong, are believed to have originated in several Periheldurchgängen.

The subdivision into two subgroups leads to the conclusion that they are descended from two different comets. This could, however, turn represent fragments of an even larger source body. As a candidate comes a comet in question, which was 373 BC by Aristotle and Ephorus observed (Great Comet of 373 BC ). Ephorus reported that the comet had broken into two pieces. At the origin of comets have it must be traded with an estimated 100 km in diameter to a very large specimen (for comparison, the bright comet Hale- Bopp had a diameter of about 40 km).

So far, many comets subgroup I were four times as discovered when members of the subgroup II This suggests that the origin of comet broke up into different-sized sections.

Although the orbit of the comet of 1680 of which the two sub-groups is quite different, it is probably also attributable to the Kreutz group, where he was made a long time ago by fragmentation.

The Kreutz group is probably not a unique phenomenon. Studies show that comets with a large inclination and Periheldistanzen of less than 2 AU can develop as a result of the gravitational effect of the sun to Sungrazern. There is a 15% chance for the comet Hale- Bopp.

Recent studies

Due to the close distance to the sun most of the Kreutz group comets from Earth are difficult to observe. Except for the very bright representative of most remained unnoticed in the past.

In the 1980s, discovered two particular for solar observation satellites, several new members of the group. Since the commissioning of the SOHO spacecraft in 1995, it is possible to observe the comet in the near vicinity of the Sun. Since then, several hundred Sungrazer were discovered, of which approximately 90 % of the Kreutz group are attributable. Some reported only diameter of several meters. None of the discovered by SOHO Sungrazer survived the perihelion passage. Some plunged directly into the sun, the other vaporized near the sun. An exception to this rule is C/2011 W3 ( Lovejoy ), which thus far the only observed comet of the Kreutz group apparently largely unscathed continued his path in December 2011 after the perihelion passage.

About a third of the discovered by SOHO Sungrazer was discovered by amateur astronomers who were evaluating the photos of the satellite on the internet. Thus, the Briton Michael Oates found the immense number of 144 comets, the German Rainer Kracht 156 (November 2005)

The SOHO observations showed that the Kreutz comets appear often in pairs at a distance of a few hours. These fragments have obviously formed at greater distance from the sun.

The Kreutz comets are likely to be identified also further thousands of years as an independent group. Their orbits by the gravitational influence of large celestial body will probably change in the solar system. In the long term, the group will disband by further fragmentation and evaporation near the sun.

The last bright comet of the group was published in 1970 the White- Ortiz- Bolelli. It is currently impossible to predict when the next flashy Kreutz comet appears. If, however, based on sets that were visible with the naked eye in the last 200 years, at least 10, this is likely to happen in the not too distant future.