Comets: Windows into Time 1981 NASA 7min
more at
http://scitech.quickfound.net/astro/asteroid_news
.html
"
Presents three parts on comets. Reveals that comets were born with the sun some
4.5 billion years ago but, unlike planets, the primitive ice and dust of coments have remained unchanged.
Shows that they are windows into time, into the origins of the solar system. Defines comets and gives a historical account of them, including
Halley's comet in
Part One.
Looks at new studies investigating comets at short range, presently only from observations on
Earth, but new space probes will allow the close-up study of comets."
Public domain film, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization.
http://en.wikipedia.org/wiki/
Comet
A comet is an icy small
Solar System body that, when close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere) and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet.
Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. Comets have been observed since ancient times and have traditionally been considered bad omens.
Comets have a wide range of orbital periods, ranging from a few years to hundreds of thousands of years. Short-period comets originate in the
Kuiper belt, or its associated scattered disc, which lie beyond the orbit of
Neptune. Longer-period comets are thought to originate in the
Oort cloud, a hypothesized spherical cloud of icy bodies in the outer Solar System
...
Comets are distinguished from asteroids by the presence of a coma or a tail...
As of January 2011 there are a reported 4,185 known comets of which about 1,
500 are
Kreutz Sungrazers and about 484 are short-period. This number is steadily increasing. However, this represents only a tiny fraction of the total potential comet population: the reservoir of comet-like bodies in the outer Solar System may number one trillion. The number visible to the naked eye averages roughly one per year, though many of these are faint and unspectacular. Particularly bright or notable examples are called "
Great Comets"...
http://en.wikipedia.org/wiki/Halley's_Comet
Halley's Comet or
Comet Halley (officially designated 1P/Halley) is the best-known of the short-period comets, and is visible from Earth every 75 to 76 years. Halley is the only short-period comet that is clearly visible to the naked eye from Earth, and thus the only naked-eye comet that might appear twice in a human lifetime. Other naked-eye comets may be brighter and more spectacular, but will appear only once in thousands of years.
Halley's returns to the inner Solar System have been observed and recorded by astronomers since at least 240
BCE.
Clear records of the comet's appearances were made by
Chinese, Babylonian, and medieval
European chroniclers, but were not recognized as reappearances of the same object at the time. The comet's periodicity was first determined in 1705 by
English astronomer
Edmond Halley, after whom it is now named. Halley's comet last appeared in the inner Solar System in
1986 and will next appear in mid-2061.
During its 1986 apparition, Halley became the first comet to be observed in detail by spacecraft, providing the first observational data on the structure of a comet nucleus and the mechanism of coma and tail formation. These observations supported a number of longstanding hypotheses about comet construction, particularly
Fred Whipple's "dirty snowball" model, which correctly predicted that Halley would be composed of a mixture of volatile ices -- such as water, carbon dioxide and ammonia -- and dust...
http://en.wikipedia.org/wiki/Halley_Armada
The Halley Armada is the generally accepted and popularly used name of five space probes sent to examine Halley's Comet during its 1986 sojourn through the inner solar system,[1] connected with apparition "1P/
1982 U1"...
Probes involved (in order of closest approach):
-
Giotto, the first space probe to get close-up color images of the nucleus of a comet. (
ESA)
-
Vega 1, which dropped a balloon probe and lander on
Venus before going on to Halley. (
USSR/
France Intercosmos)
- Vega 2, which dropped a balloon probe and lander on Venus before going on to Halley. (USSR/France Intercosmos)
- Suisei, also known as
PLANET-A.
Data from Sakigake was used to improve upon Suisei for its dedicated mission to study Halley. (
ISAS)
- Sakigake,
Japan's first probe to leave the
Earth system, mainly a test of interplanetary mission technology. (ISAS)