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THESE ARE THE DIRECTIONS. DELETE THIS PART WHEN MAKING YOUR PAGE.

Skill Builder 1C - Topic: Comets

Use the listed topic and accompanying text to create a simple web page.  You are not required to use all of the text. You just need to be sure to include the correct coding for each of the following requirements. 

1.  use a DOCTYPE declaration for transitional XHTML 
2.  use title tags, head tags, and body tags correctly 
3.  use list tags to create an ordered list and set the numbering style (i.e, 1, I) 
4.  create a second page called page2.html and create an internal link to a page named page2.html 
5.  use blockquote tag 
6.  use definition list
7.  create an external link to http://stardust.jpl.nasa.gov/ and make the link open in a NEW browser window 
8.  create an external link to http://stardust.jpl.nasa.gov/ and make the link open in the SAME browser window
9.  use super or subscript for something 
10.  use headings and text alignment 
11.  add a graphic of your choice. For ideas go to http://stardust.jpl.nasa.gov/photo/index.html
12.  create an EXTERNAL style sheet. Call it cometstyle.css. 
13.  create style rules for your external style sheet. Set formatting using styles including including AT LEAST one font type, font style, font color using hexidecimal numbers 
14.  define the background color using a hexidecimal number 
15.  use an XHTML validator and indicate the validator used at the bottom of the page
16.  use a CSS validator and indicate the validator used at the bottom of the page

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Comets are a mixture of ices including water and frozen gases, along with dust. They don't contain fire. They include materials that weren't incorporated into planets when the solar system was formed, so they contain a rich record of the history. Nearly 900 comets have been cataloged and their orbits calculated. However they rarely come more than a few million miles of Earth.

Parts of a Comet
Comets are normally invisible. However when a comet nears the sun, the heat melts the ices in the nucleus releasing dust particles that can be seen from Earth. Distinct parts of the comet can be identified including the nucleus, coma, hydrogen cloud, dust tail, and ion tail.

Comets in Human History
Throughout human history, people have observed comets. As early as 240BC, the Chinese recorded sightings of Comet Halley. Edmond Halley was the first person to recognize that this comet was periodic. It's next close appearance won't take place until 2060.

The Bayeux Tapestry which depicts the Norman Conquest of England in 1066 includes Comet Halley.

1P Halley               76.1 yrs.  1986-02-09                                                                          
2P Encke                3.30 yrs.  2003-12-28                                                                               
6P d'Arrest             6.51 yrs.  2008-08-01  
9P Tempel 1             5.51 yrs.  2005-07-05
19P Borrelly            6.86 yrs.  2001-09-14
21P Giacobini-Zinner    6.52 yrs.  1998-11-21            
26P Grigg-Skjellerup    5.09 yrs.  1992-07-22
                                                                                         
Viewing Comets
Comets can best be observed using a telescope or binoculars. Every five or six years, a comet can be viewed with the naked eye. Comets with long tails are only seen every 10-12 years. Below is a list of selected comets and their orbital periods:
Comet Hale-Bopp (C/1995 01)
Comet Hyakutake (C/1996 B2)
Comet West (C/1975 V1=1976 V1)
Comet Kohoutek (1973 E1=1973 XII)
Comet White-Ortiz-Bolelli (C/1970 K1=1970 VI)
Comet Bennett (C/1969 Y1=1970 II)

Comet News

Project Stardust, NASA's recent Comet Sample Return Mission
http://stardust.jpl.nasa.gov/
Launched in 1999, the Stardust spacecraft is the first U.S. space mission dedicated solely to the exploration of a comet. On January 2, 2004, the spacecraft flew within 236 kilometers of the comet Wild 2 and survived an impact. 

Play at cool game called Tails of Wonder at http://spaceplace.jpl.nasa.gov/en/kids/stardust/index.shtml

Definitions
anti-tail. Also known as anomalous tail, this occurs when a comet's tail appears to be pointing toward the Sun. Of course, it's not actually pointing toward the sun because comets orbit the Sun. When a comet produces heavy dust particles, they are left along the comet's orbit instead of being pushed away from the Sun.

apparition. This is the time when a comet is under observation. The term probably comes from the ghostly appearance of comets.

coma. Also known as the comet's head, the coma is the dense, hazy cloud of water, carbon dioxide, another gases around the comet's nucleus. The head and tail are the only things we see from Earth.

dust tail. Composed of dust particles from the nucleus and up to 10 million kilometers long, this is the most prominent element of the comet.

hydrogen cloud. A large, sparse envelope of neutral hydrogen.

ion tail. Composed of plasma laced with rays and streamers from solar wind, this tail can be several hundred million kilometers long.

long-period comets. Orbit periods of more than 200 years.

nucleus. Made up of ice, gas, dust, and small amounts of other materials, this core is solid and stable.

outburst. A comet sometimes experiences an unexpected increase in brightness for a short time due to the release of dust and gas into the coma from the nucleus. This is known as an outburst.

perihelion. The point in a comet's orbit when it is closest to the Sun.

short-period comets. Also known as periodic comets, they have orbit periods of less than 200 years. These coments have a P/ before their name.

I see myself as a huge fiery comet, a shooting star. Everyone stops, points up and gasps "Oh look at that!" Then - whoosh, and I'm gone... and they'll never see anything like it ever again, and they won't be able to forget me - ever. - Jim Morrison