that they will return about a century apart, between 670 and 960 years after the break-up. Comet Ikeya–Seki Comet Ikeya–Seki is the most recent very bright Kreutz sungrazer. It was discovered independently by two Japanese amateur astronomers on September 18, 1965, within 15 minutes of each other, and quickly recognised as a Kreutz sungrazer. It brightened rapidly over the following four weeks as it approached the Sun, and reached apparent magnitude 2 by October 15. Its perihelion passage occurred on October 21, and observers across the world easily saw it in the daytime sky. A few hours before perihelion passage on October 21 it had a visible magnitude from −10 to −11, comparable to the first quarter of the Moon and brighter than any other comet seen since 1882. A day after perihelion its magnitude decreased to just −4. Japanese astronomers using a coronagraph saw the comet break into three pieces 30 minutes before perihelion. When the comet reappeared in the morning sky in early November, two of these nuclei were definitely detected with the third suspected. The comet developed a very prominent tail, about 25° in length, before fading throughout November. It was last detected in January 1966. Dynamical history and evolution A study by Brian G. Marsden in 1967 was the first attempt to trace back the orbital history of the group to identify the progenitor comet. All known members of the group up until 1965 had almost identical orbital inclinations at about 144°, as well as very similar values for the longitude of perihelion at 280–282°, with a couple of outlying points probably due to uncertain orbital calculations. A greater range of values existed for the argument of perihelion and longitude of the ascending node. Marsden found that the Kreutz sungrazers could be split into two groups, with slightly different orbital elements, implying that the family resulted from fragmentations at more than one perihelion. Tracing back the orbits of Ikeya–Seki and the Great Comet of 1882, Marsden found that at their previous perihelion passage, the difference between their orbital elements was of the same order of magnitude as the difference between the elements of the fragments of Ikeya–Seki after it broke up. This meant it was realistic to presume that they were two parts of the same comet which had broken up one orbit ago. By far the best candidate for the progenitor comet was that seen