Small Wanderers, Dirty Snowballs

Part of Solar System? Largest Object in System?


- Looooong Ellipses (where's the Sun?)

  1. Long Period Comets
  2. Short Period Comets. Short- and Intermediate-period comets (like Comet Halley), stay within the orbit of Pluto for a significant fraction of their orbits.
  3. Invisible Comets
  4. Eccentric Comets
  5. Dead Comets
  6. Ejected Comets


  1. As Old as the Sun
  2. Are they all from this Solar System?
  3. Oort Cloud
  4. The Kuiper Belt is a disk-shaped region past the orbit of Neptune, roughly 30 to 100 A.U. from the Sun


Print version of comet diagram.

  1. Nucleus -- relatively solid and stable, mostly ice and gas with small amount of dust and other solids (d usually <10km)
  2. Coma -- dense cloud of water, carbon dioxide and other neutral gases sublimed from the nucleus
  3. Hydrogen cloud -- huge (millions of km in diameter) but very sparse envelope of neutral hydrogen
  4. Tails


C0042677-Comet Shoemaker-Levy and Jupiter, diagram-SPL.jpg

1. Dust tail -- 10 million km long.
  • Composed of smoke-sized dust particles driven off the nucleus by escaping gases.
  • This is the most prominent part of a comet to the unaided eye;
2. Ion tail -- several 100 million km long
  • Plasma
  • Laced with rays and streamers caused by interactions with the solar wind


  1. Chinese records of Halley -- 240 BC.
  2. Bayeux Tapestry, shows the conquest of England in 1066, has Comet Halley.
  3. 878 comets cataloged (as of 1995) and their orbits at least roughly calculated.
  4. 184+ are periodic (orbital periods less than 200 years). Some of the others are likely periodic, but their orbits are not precisely known.
  5. Satellite Flyby of Halley in 1984
  6. HST detected Kuiper Belt objects that are small and faint (perhaps only 20 km). There may be as many as 100 million such comets.


  • Could Comets be the origin of life? ...They may be the origin of organic materials
  • Does every star system have an Oort?


Edwards, Jonathan. "Sun." World Book Encyclopedia. NY: Collier International. 1972. Vol 18, p313.

Sagan, Carl. Comet. New York: Random House. 1985.

"Sun." Online. October 17, 2001.

<!- Comet Hyakutake C/1996 B2 March 25, 1996 Hubble Space Telescope Comet Borrelly & Deep Space 1 Halley's Detachment Event ->

Countdown to 500 Comets

Posted by --Starseeker 14:55, 13 October 2007 (UTC)

Press Release

CLOUDCROFT, NEW MEXICO. The Earthrise Institute is pleased to announce its inaugural educational project, entitled ≥Countdown to 500 Comets.≤ The project takes its name and focus from Earthrise Institute founder and President Alan Haleπs quest to observe 500 comets, a quest he began over 37 years ago. He has recently collected his 400th comet and, in his words, ≥Iπve decided to share my quest for comet number 500 with the astronomy students of the world.≤

Dr. Hale is best known as being co-discoverer of Comet Hale-Bopp, which shone brightly in Earthπs nighttime skies ten years ago. ≥Comets can be among the most spectacular of objects we see in our skies,≤ notes Hale. ≥Comets like Hale-Bopp and the very recent Comet McNaught ≠ which became bright enough to view during the daytime during January before becoming an incredible nighttime sight for our friends in the southern hemisphere ≠ have always acted to inspire us to examine the universe around us.≤ While Hale remarks that brilliant comets like these are quite uncommon and that most of those he observes are much dimmer, ≥they are nevertheless fascinating objects for examination and study.≤

Students of all ages and nationalities are invited to participate in ≥Countdown.≤ The goal of ≥Countdown≤ is for students to observe as many of Dr. Haleπs next 100 comets as they are able, either by viewing them through a telescope, and/or by taking images of them with appropriately equipped telescopic cameras. Special awards will be presented to any student who successfully observes ten of Dr. Haleπs next 100 comets. Hale estimates that it will take five to seven years for him to collect those 100 comets, and thus there are plenty of opportunities for participation.

Within the next two years the Earthrise Institute expects to establish the first operational telescope at its planned dark-sky facility east of Cloudcroft, New Mexico. Once this telescope is operating it will be available for remote-control utilization for, among other projects, imaging of comets in the ≥Countdown≤ program.

Experienced amateur and professional astronomers, and astronomy clubs and other similar organizations, are being solicited to act as mentors and to assist in other ways with ≥Countdown,≤ and any individual or organization so interested is invited to contact the Institute. A sponsor is also being sought to name the comet observing awards that will be provided to successful participants of the project.

Additional information about "Countdown to 500 Comets," specific information about the comets being observed, photographs and images of the various comets, and information about assisting astronomers and organizations, is available at

The Earthrise Institute, formerly known as the Southwest Institute for Space Research, is a private non-profit organization with the goals of promoting science research and education, and for using astronomy and other activities as tools for bringing humanity together. Information about its mission, programs, and activities is available at its web site,