Grigg-Skjellerup is a comet that was first discovered in 1808 by the French comet-hunter, Jean-Louis Pons. At first, it was named 1808 III because it was the third comet to be discovered that year. It was observed once more 23rd of July, 1902 by an amateur astronomer named John Grigg (from Thames, New Zealand). Between 23rd of July and 3rd of August, the comet was observed 14 times. Due to a waxing moon, it was not possible to observe the comet after these 11 days. The result of this was that only a vague path could be calculated.

Many years went by, until the comet was again observed on the 17th of May, 1922, by J. Frank Skjellerup. According to Skjellerup, the comet looked like an extremely faint nebula, and was "about twice the diameter of Jupiter".

At that time, astronomers did not know that the comet discovered by Grigg and Skjellerup was the same comet. In 1927 R. T. Crawford and W. F. Meyer compared the path-calculations with the one made after Grigg's discovery in 1808, they claimed that it was the same comet, and renamed it Grigg-Skjellerup. They measured its period to be 5 years.

Due to Jupiter's enormous amount of gravity, the comet's perihelion distance increases from year to year. In 1725 this distance was 0.77 AU and in 1922 it was 0.89 AU.

During 1986, a Slovakian astronomer named Lubor Kresak suggested that Grigg-Skjellerup could be the same comet discovered by Jean-Louis Pons in 1808.

On 10th of July, 1992, a probe named Giotto tried to photograph Grigg-Skjellerup. Since Giotto originally was built to photograph Halley's Comet 6 years earlier, the camera was set for a different trajectory than Grigg-Skjellerup's, and therefore missed by a mere 100 to 200 km.

  • Comets - A Descriptive Catalogue, G.W.Kronk, Enslow Publishers (1984)
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