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Click on thumbnail above for larger picture.
These shots were taken on 27 March 1996 from Baleshare, North Uist, Western Isles, Scotland (57deg 31'N 07deg 21'W) one of the finest viewing sites in the U.K. (no light pollution!). Time was 0107 hrs U.T. (+/- 2 mins).
The comet was approaching zenith and Polaris (the North Star) can be made out in the bottom left hand corner.
Exposure was 180 seconds onto Kodak Ultra Gold 400 using an Olympus OM-10 35mm SLR (tripod mounted) on B-lock.
In this second (computer enhanced) shot some of the features of the coma and tail start to become apparent.
You can find more cometary photos I took at my Comet Hale-Bopp page.
Comets-a brief discussion
Since the work of the American astronomer Fred L. Whipple (1906~) in 1950, comets have been thought of as 'dirty snowballs' - lumps of ice mixed with silicate particles. Far from the Sun, a comet is an inert lump. As it approaches the Sun, solar heating evaporates some ice containing fine dust particles, so a comet loses material in the formation of an expanding gaseous envelope and a long tail (such as was seen with Comet Hyakutake).
A typical comet thus consists of several components: the key component is the compact nucleus, only a few kilometres across; surrounding the nucleus is coma, an ephemeral atmosphere of tenuous gas and dust particles, from which extends the long tail directed away from the Sun. Sunlight reflected from dust particles in the coma and tail makes them visible, while fluorescence of ionized gas also adds a glow.
During the 1910 appearance of the famous comet Halley, its magnificent tail streamed over no less than 40 deg of the night sky. Comet Hyakutake was even more spectacular and I 'guesstimated' the tail extending to at least 90 deg (in the crystal clear and unpolluted Hebridean night sky).
Comet tails extend over such large parts of the inner Solar System that planetary orbits inevitably intersect them. When the Earth passes through a comet tail, minute particles bum up in the atmosphere, but few meteorites which reach the ground seem to be derived from comets. Much more rarely, the nucleus of a comet hits the Earth. A minor event of this sort may have taken place at Tunguska in Siberia in 1908, when a violent explosion flattened more than several thousand square kilometres of forest.
The Comet Halley spacecraft encounters in 1986 supported the 'dirty snowball' hypothesis. They showed that the comet nucleus was actually a peanut-shaped object, about 16km x 8km in size. Estimates of its density were surprisingly low, about 0.25 x 103 kg m-3. Such a low density is consistent with an icy composition; the ice vaporizing near the Sun to provide the gaseous envelope of the coma and leaving cavities in the interior. On each of its passages past the Sun, a comet loses some fraction of its volatile icy material. Ultimately, it will all be lost, leaving only a rocky and carbonaceous residue. Some Earth-crossing asteroids have highly elliptical orbits similar to comets. It is possible that they are the burned-out husks of old comets. It is tempting to argue in such cases that all that is left of the original 'dirty snowballs' is the dirt.
A single comet, however inspiring to behold, is an insignificant object in terms of mass. What comets may lack individually, however, they make up for in numbers. Jan Oort (1900-1992), a Dutch astronomer, suggested in 1950 that most comets reside in an essentially spherical cloud surrounding the Sun at a distance of 20 000-100 000 AU. (The nearest stars, in the Alpha Centauri group, are about 270 000 AU, or 4 light years distant.) This Oort cloud may contain about 1012 comets, with a cumulative mass some 25 times that of the Earth. There is now direct observational evidence for the existence of many comets, and astrophysicists accept the merit of Oort's statistical arguments.
Click here for more information on Hyakutake and comets in general.
There are some ongoing cometary exploration missions to keep an eye on.
The first is called STARDUST and is a Discovery mission (like the highly successful Mars Pathfinder). Stardust's objectives are to gather particles flying off the nucleus of Comet Wild-2 and return them to Earth for scientific analysis, and to collect and return samples of interstellar dust flowing through our solar system. Stardust is the first spacecraft ever launched on a mission to bring back material from beyond the Moon. It is also the first U.S. mission to a comet. Stardust's sample return capsule is due to parachute into Earth's atmosphere and land on the U.S. military's Utah Test and Training Range near Salt Lake City on January 15, 2006. It was launched in February 1999.
NASA's CONTOUR Mission Readies for Summer 2002 Launch
Capping nearly two years of detailed development and assembly, engineers at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, are putting the last touches on the CONTOUR spacecraft, which will provide the closest and most detailed look ever into the icy heart of a comet.
Slated to launch July 1, 2002, CONTOUR (Comet Nucleus Tour) will encounter at least two diverse comets as they zip through the inner solar system. From as close as 100 miles (160 kilometers) away, the spacecraft will snap high-resolution photos of the comet nucleus, map the types of rock and ice on the nucleus, and analyze the composition of the surrounding gas and dust. CONTOUR's targets include comet Encke in November 2003 and Schwassmann-Wachmann 3 in June 2006 - though the mission team can send the spacecraft to an as-yet undiscovered comet should such a valuable opportunity arise.
The second comet sample return mission (now regrettably cancelled) was called the Champollion Project also referred to as Space Technology 4 (previously Deep Space 4). Champollion was part of the New Millennium program which has a strong emphasis on proving new technology. This spacecraft was due to be launched in 2003 to rendezvous with Comet Temple 1 to survey and map it. It was then proposed to land a small vehicle to undertake drilling the surface of the comet nucleus!. I hope to post archive Web pages of this cancelled Project in the near future.
The International Rosetta Mission was approved in November 1993 by the European Space Agency (ESA) Science Programme Committee as the Planetary Cornerstone Mission in ESA's long-term space science programme. The mission goal is a rendezvous with comet 46 P/Wirtanen. On its eight-year journey to the comet, the spacecraft will pass close to two asteroids, (Otawara and Siwa are now the planned targets). Rosetta will study the nucleus of comet Wirtanen and its environment in great detail for a period of nearly two years, the near-nucleus phase starting at a heliocentric distance of about 3.25 AU, with far-observation activities leading ultimately to close observation (from about one km distance). Rosetta will be launched in January 2003 by an Ariane-5 from Kourou, French Guiana..
Preliminary data on this Comet Hyakutake observation
Ecl. Long. and Lat. 99deg 25' 22'' 65deg 20' 6''
Distance from Earth 0.0489 AU (7,315,070 km).
Distance from the Sun 1.007 AU (150,600,000 km) - about the same distance as planet Earth from the Sun.
Visual Magnitude -0.23
Copyright © 1997-2002 John Gruson
