# 55P/Tempel–Tuttle

55P/Tempel–Tuttle (commonly known as Comet Tempel–Tuttle) is a retrograde periodic comet with an orbital period of 33 years. It fits the classical definition of a Halley-type comet with a period of between 20 and 200 years. It was independently discovered by Wilhelm Tempel on 19 December 1865, and by Horace Parnell Tuttle on 6 January 1866. It is the parent body of the Leonid meteor shower.

## Characteristics

The nucleus of the comet was observed by Hubble Space Telescope during the 1998 apparition, and assuming an albedo of 0.04, its nucleus was estimated to have a mean radius of 1.8 km. The nucleus has a reddish color, with a B−V 0.75 ± 0.05 and V−R 0.51 ± 0.05. A jet was observed emanating from the nucleus and based on its movement the rotation period was calculated to be 15.31 ± 0.03 and 14.79 ± 0.02 hours.
The spectrum of the comet revealed the presence of diatomic carbon, NH2 and [Oi]. The relative production rates indicate that the comet is depleted in diatomic carbon when compared with Halley's comet. The gas-to-dust ratio also indicated it was gas rich compared with Halley's comet. The infrared spectrum of the comet closely resembled that of a black body with a temperature of 330 K and lacked silicate emission that has been detected in other comets.
William Huggins observed the spectrum of the comet in January 1866, making it the second time spectrographic observations of a comet were obtained.

## Sightings

In 1699, it was observed by Gottfried Kirch but was not recognized as a periodic comet until the discoveries by Tempel and Tuttle during the 1866 perihelion. In 1933, S. Kanda deduced that the comet of 1366 was Tempel–Tuttle, which was confirmed by Joachim Schubart in 1965. On 26 October 1366, the comet passed 0.0229 AU (3,430,000 km; 2,130,000 mi; 8.9 LD) from Earth. It is possible the comet was also observed in October 1234, however it is only mentioned briefly by a single Japanese source, and also a comet observed in China in January 1035 could be comet Temple–Tuttle, however unless it had undergone a major outburst, it would have been too dim to observe with the naked eye.
Comet Tempel–Tuttle was recovered by J. Schubart in images taken by Michiel John Bester on 30 June 1965 using the 10-inch telescope of Boyden Observatory, South Africa. At that time the comet had an apparent magnitude of 16. The presence of the comet was confirmed in plates obtained by Palomar Observatory on 30 June. These were the only two observations of the comet during the 1965 apparition.
The comet was recovered on 4 March 1997 by Karen Meech, Olivier Hainaut and James "Gerbs" Bauer, at the University of Hawai`i. At the time it was very faint (22.5 mag), but the recovery proved that it was returning on schedule and that its orbit was very well determined. During the 1998 apparition the comet brightened more than predicted and reached an apparent magnitude of 7.4–7.8 in late February and could be observed with binoculars. It was last observed on 5 July 1998.

## Orbit

The retrograde orbit of 55P/Tempel–Tuttle causes meteors to impact Earth at a high speed of 70 km/s. The orbit intersects that of Earth nearly exactly, hence streams of material ejected from the comet during perihelion passages do not have to spread out much over time to encounter Earth. The comet currently has an Earth-MOID of 0.008 AU (1,200,000 km; 740,000 mi). This coincidence means that past streams from the comet at perihelion are still dense when they encounter Earth, resulting in the 33-year cycle of Leonid meteor storms. For example, the 1833 meteor storm was created by the previous 1800 perihelion passage. Between 2021–2030, Earth will often pass through the meteoroid stream left behind from the 1733 orbit.
55P/Tempel–Tuttle Earth approaches :
| Year | Nominal geocentric distance (AU) |
| 1366 | 0.023 AU (3.4 million km) |
| 1699 | 0.064 AU (9.6 million km) |
| 1832 | 0.171 AU (25.6 million km) |
| 1998 | 0.356 AU (53.3 million km) |
| 2031 | 0.791 AU (118.3 million km) |
| 2163 | 0.132 AU (19.7 million km) |
55P/Tempel–Tuttle is estimated to have a nucleus of mass 1.2×10$^{13}$ kg and radius 1.8 km and a stream of mass 5×10$^{12}$ kg.