Comets

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Comets

• By Marie Allen

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What is a Comet?

• Comets are small, fragile, irregularly-shaped
  nuclei, sometimes surrounded by a coma and
  followed by a tail.
• Comets tend to have highly elliptical and
  eccentric orbits that take them both very close
  to the Sun and very far away, sometimes even past
  Pluto.

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What is a Comet?

• Comets are composed of the original materials
  that condensed to form the Sun and planets that
  make up our solar system.
• Many astronomers believe that collisions between
  comets and the Earth are responsible for the
  formation of our oceans.

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A Comets Nucleus

• The nucleus is made of ice and dust and is
  blacker than coal. Its black crust absorbs heat
  from the Sun, eventually leading to the creation
  of a coma.
• When a comet is far from the Sun, its nucleus is
  frozen solid and can only be seen by reflected
  sunlight.

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The Coma

• The coma is a cloud of gases and small particles
  that have broken off of the nucleus. Its size
  and brightness increase as the comet gets closer
  to the sun.
• The coma reflects sunlight, causing the comet to
  fluoresce and become more visible.

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The Coma

• As a comet approaches the Sun, the nucleus warms
  causing ices beneath the surface to turn to gases
  and expand. When this occurs, portions of the
  surface bulge and eventually burst under the
  pressure, shooting gas and small particles
  outward. This expulsion is known as a jet.

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The Tail

• A comets tail is a result of the Suns radiation
  and pressure and the solar wind. Gases and dust
  particles that have been expelled from the
  nucleus are accelerated at certain rates,
  depending on their size, away from the comets
  head. These differing accelerations may
  sometimes cause the appearance of multiple tails.
  Relatively massive dust tails accelerate more
  slowly, causing them to curve, while the ion
  tail, made up of gases, is accelerated more
  quickly, causing it to be straighter.

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Halleys Comet

• Halleys Comet has been observed since at least
  240 B.C., maybe even as early as 1059 B.C.
• This comet appeared in the sky in 1066, the night
  before the Battle of Hastings, and is depicted on
  the Tapestrie de Bayeux.
• Edmund Halley, in 1705, predicted its orbital
  period to be about 76 years.

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Halleys Comet

• Perihelion distance .587 au
• Dimensions 16x8x8 km
• In 1984 and 1985, 5 spacecrafts from Russia,
  Japan, and Europe were launched to observe the
  characteristics of this comet only 4 other
  comets had been studied in this way in the past.
• These ventures told us, among other things, that
  the comets nucleus has a density of 0.1 grams
  per cubic centimeter. Therefore, the nucleus is
  obviously porous.
• Halleys next perihelion passage is predicted to
  occur in 2061.

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Hale-Bopp Comet

• Discovered by two different astronomers, one
  professional (Alan Hale) in New Mexico and one
  amateur (Thomas Bopp) in Arizona, in July 1995.
• It is a very large comet, having a diameter of
  30-40 km.

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Hale-Bopp Comet

• The Hale-Bopp Comet holds the record for
  remaining visible with the naked eye for the
  longest period of time 19 months.
• It is estimated that around 81 of Americans have
  seen this comet.
• The Hale-Bopp Comet has received much attention
  in the media, mostly due to the Heavens Gate
  cult. Thirty-seven members of this cult took
  their own lives, all at the same time, believing
  that there wasa kind of UFO behind the Hale-Bopp
  Comet that would take them to paradise.

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Conclusion

• Comets are beautiful to look at and have been
  perceived for centuries as everything from bad
  omens to one-way tickets to Heaven.
• They have been observed extensively and have
  provided much information about the beginnings of
  the universe.

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Sources

• http//cometography.com/educate/comintro.html
• http//csep10.phys.utk.edu/astr161/lect/comets/hal
  ley.html
• http//www.psi.ed/hbinfo.html
• http//seds.lpl.arizona.edu/nineplanets/nineplanet
  s/halley.html
• http//www.sipe.com/halebopp/preface_current.htm
• http//www.solarviews.com/eng/comet.htm