Comets

=Project Documents:=

Rubric: [[file:Space Exploration Adventure Rubric.doc]], [[file:Space Exploration Adventure Rubric.pdf]]
**__Written Information__**

__**What are comets?**__
"Comet" originally came from the Greek words "//aster kmetes"//, literally meaning as "hairy" or "long-haired star". Comets are made of dust, ice, and assorted gasses such as frozen methane.

__The Orbit__
Comets orbit the sun in __elliptical__ shapes, which are long ovals. They spend most of their time in the outer regions of the solar system; in some cases, well beyond Neptune and Pluto. __Short-period__ comets only get as far as between Jupiter and Neptune. __Non-period__ comets only appear in the inner solar system once. Their orbits may be __prograde__ or __retrograde__, meaning with the same direction as the planets or in the opposite direction, respectively. Comets make rare, short, but beautiful through the inner solar system (Mercury to Mars) as they approach the sun.

__Tails on a Comet__
If a comet's path takes it close enough to the sun, the suns' radiation causes the center of the comet to melt and give off gasses and dust. This process is called __outgassing.__ These materials are swept behind the comet's orbital path by the solar wind to form the stretched out tail we see. The comet Hyakutake had a tail of about 40 degrees, one of the longest recorded.

__Halley's Comet__
Halley's comet has been streaking through the sky periodically for over two thousand years. In 240 BCE, it was first recorded, and has been documented every time it passes Earth since then. For a long time, comets were viewed as bad omens responsible for human catastrophes and earthly disasters. When the comet was first spotted in 240 BCE, the Chinese noted its presence and blamed it for the death of an empress. Babylonians recorded its appearance in 164 BCE and 87 BCE. When the Romans spotted Halley's Comet in 12 BCE, they held it responsible for the death of statesman Marcus Vipsanius Agrippa. Several other sightings were recorded before the observations of Edmund Halley (British astronomer, 1656-1742) in 1682.

Until Halley began studying comets, no one knew where comets came from or what paths they followed. Johannes Kepler (German astronomer and mathematician, 1571-1630) observed Halley's comet in 1607, although it wasn't known by that name yet. He concluded that comets followed straight lines, coming from and disappearing into infinity. Later, Johannes Hevelius (German astronomer, 1611-1687) suggested that comets follow slightly curved lines. Georg Samuel Dorffel (German astronomer) suggested that comets follow a __parabolic__ course, a curve that looks like the curve of a rocket.

Although comets appeared unaffected by gravity as they traveled through the sky, Halley wondered if the force influenced them in some way. He carefully analyzed the paths of twenty-four comets. With the help of Sir Isaac Newton (English physicist and mathematician, 1642-1727), he found three comets--those occurring in the years 1531, 1607, and the one he viewed himself in 1682, with nearly identical paths. This led him to the conclusion that what observers had seen was actually one comet passing by Earth three different times. This also led to the idea that comets follow an elliptical orbit around the sun, instead of parabolic.

Halley found problems with this theory though. The time between the first and second sightings was a year longer than the time between the second and third sightings. Also, the comet was not found in the same place in the sky every time it reappeared. To solve these problems, Halley suggested the comet's path was thrown a little off course by the gravitational fields of Jupiter and Saturn as it passed by those large planets. After long, detailed, calculations that included the influences of Jupiter and Saturn, Halley predicted the same comet would return in 1758. Although he didn't live to see it, Halley was correct, and the comet was named after him.

After the death of Halley in 1742, others continued to plot the course of Halley's Comet. Alexis Clairut, Joseph Lalande, and Nicole-Reine Lepaute (all French astronomers) made calculations on when Halley's comet would be seen again. The results were so exact that their predictions were only a month off from when the comet actually returned. They determined Halley's comet completes one orbit in just about seventy-six years.

Halley's comet produces two meteor showers seen from Earth each year. Eta Aquarids is seen in May and the Orionids is observed in October. Halley's comet will return in the year 2061.

__Hyakutake__
Comet Hyakutake, visible to Earthlings in the spring of 1996, was the brightest and closest comet to Earth in two decades. It was so bright, you could see it without a telescope, even in places with light pollution. This caused it to become known as the Great Comet of 1996. it came much closer to Earth than Halley's comet ever has. Hyakutake was discovered by Yuji Hyakutake (Amateur Japanese astronomer, 1950-2002) just two months before its arrival, using only a pair of binoculars. It was his second comet discovery in two months. The comet was first visible in the Nothern Hemisphere in mid-March, and reached its closest point to Earth on March 25th. Near the end of April, the comet looped around the sun and returned to pass by Earth again in May. When it passed in May it was visible to people in the Southern Hemisphere. Then it traveled off into space, continuing its long orbit around the sun. Because Hyakutake was such a suprise, scientists had very little time to prepare for observation. The scientists who were able to study the comet discovered Hyakutake was an icy center surrounded by jets of dust. It appeared that gas and dust were escaping through holes in the comet's surface. Hyakutake was unusual because it had a second smaller tail made of dirt particles. Scientists found that the comet emitted x-rays, which scientists hadn't before connected to comets. The 1996 visit was the only chance humans alive today would have to see Hyakutake. It won't pass by Earth for another ten to twenty thousand years.

** __Visuals__ **
 * [[image:http://callisto.ggsrv.com/imgsrv/FastFetch/UBER1/00017835 caption="http://ic.galegroup.com/ic/scic/ReferenceDetailsPage/ReferenceDetailsWindow?displayGroupName=Reference&disableHighlighting=false&prodId=SCIC&action=e&windowstate=normal&catId=&documentId=GALE%7CCV2640050062&mode=view"]] || [[image:http://callisto.ggsrv.com/imgsrv/FastFetch/UBER1/00102012 caption="Halley's comet" link="http://ic.galegroup.com/ic/scic/ImagesDetailsPage/ImagesDetailsWindow?total=11&query=BS+Halley%27s+Comet&prodId=SCIC&windowstate=normal&mode=view&limiter=AC+y&displayGroupName=Images&currPage=7&sortBy=relevance%2Cdescending&action=e&catId=&view=docDisplay&documentId=GALE%7CCV2210078171"]] ||

__**Works Cited**__ **Sources**
 * //Iconn.com//. Web. .


 * //Iconn.com//. Web. .

Your Source List: [] [] [] []
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__**Topic and Research Focus**__
 * I am doing my research project on comets. The focus of my research is comets in general as well as Halley's Comet.**

Comets are small bodies that orbit the sun. For at least part of their orbit, they have an atmosphere, a tail, or both. The nucleus of a comet is made up of rock, ice, and gas; the comet's tail and atmosphere are created by the sun's radiation acting on its nucleus. Because of their unusual shape and sudden appearances, ancient civilizations often interpreted comets as warnings or signs of great news. Aristotle was among those who believed comets were atmospheric phenomena, and he also suggested that comets were signs related to weather, a view that kept fear of comets alive for centuries. As soon as printing was widespread, every appearance of a comet was followed by pamphlets with titles such as "News of the Terrible and Fearsome Comet." In 1456, the comet that would later be known as Halley's Comet appeared just three years after the Turks had conquered Constantinople, lending credence to this view. Nonetheless, some people looked at this phenomenon scientifically. Johann Müller (1436-1476), also called Regiomontanus, observed a bright comet in 1472. He followed its path in the sky and made such accurate measurements that Edmond Halley (1656-1742) used them to calculate the comet's orbit in the early eighteenth century. Two other early observers, Girolamo Fracastoro (ca. 1478-1553) and Peter Bennewitz (1501-1552), published reports stating that the comets they observed always kept their tails pointed away from the sun. Johannes Kepler (1571-1630), who observed the comet of 1607, concluded that comets followed straight lines, coming from and disappearing into infinity. Johannes Hevelius (1611-1687) disagreed, suggesting comets followed slightly curved lines. Georg Samuel Dörffel (1643-1688) contradicted both Kepler and Hevelius, hypothesizing that comets might follow a parabolic course. When the comets of 1680 and 1682 appeared, Halley set out to calculate their orbits definitively. He looked back at past comet appearances as described by careful observers, and noticed that a few orbits were the same. He claimed the comet of 1682 was the same one seen in 1456, 1531, and 1607. He predicted it would return in 1758. Even though he died before its return, Halley lives on in the comet's name. Halley's comet and others had elliptical orbits, so astronomers of the time believed there were two types of comets with differing orbits: periodic comets that had elliptical orbits and nonperiodic comets that were one-time visitors with parabolic orbits. Further study revealed that comets followed elliptical paths much more frequently than parabolic ones. Parabolic paths were believed to be caused by the gravitational forces of stars and planets the comet encountered or passed near during its flight. Depending on the velocity and proximity of the two bodies at the crucial juncture, the comet's path might be altered only slightly, or it could change drastically. Comets, therefore, appeared to be residents of the solar system, though occasional disturbances such as gravity might cause some to disintegrate or exit the solar system. Modern scientists speculate that there might be a reservoir of comet nuclei surrounding the solar system. Dutch astronomer Jan Oort (1900-1992) pioneered this theory with his assertion that these inactive comets would have a very low temperature and number in the billions; such comets would remain inactive until a significant astronomical occurrence--the passing of star, for example--would pull a comet into the solar system by means of its gravitational force. This hypothetical reservoir is now referred to as the Oort Cloud. Astronomers have studied the composition of comets extensively. They used spectroscopes to analyze comets, but by the late nineteenth century, these results were inconclusive because the spectrogram indicated mostly reflected sunlight. Harvard astronomer Fred Whipple (1906-) coined the phrase "dirty snowball" to explain his understanding of comets' composition; his view is now generally accepted, and comets' nuclei are believed to be formed from dust and rocky material mixed with frozen methane, ammonia, and water. However, as of 2006, there is still controversy about the proportions of these materials, which can vary from comet to comet. In March 1986, five spacecrafts passed near the long-awaited Halley's Comet. The most daring craft, Giotto, flew in toward the comet's center and sent back the first pictures of Halley's nucleus. These shots revealed a potato-shaped object darker than coal measuring 7.5 miles (12 km) in length. Two bright jets of dust extended 9 miles (14.5 km) from the nucleus toward the sun. These jets were caused by the sun's heat, and they are responsible for causing comets to deviate from their scheduled appearances. The mid-1990s produced a bumper crop of interesting comets. In 1994, comet Shoemaker-Levy 9 collided spectacularly with Jupiter. The comet had broken into numerous fragments during a previous orbit of the giant planet; it elongated into a string of pieces that crashed into Jupiter during the summer of 1994, providing the first directly observed collision between two objects in the solar system. Astronomers around the world debated how its impact would affect Jupiter's atmosphere; after observing the gigantic clouds that resulted, they spent the months afterward studying the results. In 1996, comet Hyakutake passed a mere 9 million miles from Earth, its tail stretching some 40 degrees across the sky. In 1997, the more distant but intrinsically brighter comet Hale-Bopp swung by. Both these comets follow large orbits, and they will not return to the inner solar system for thousands of years. However, astronomers and other scientists made detailed observations that yielded important new information about comets' composition and rotation periods. A variety of studies continue to reveal comets' secrets. In 2004, NASA spacecraft Stardust collected particle samples from comet Wild 2. Scientists evaluating Stardust's data in 2006 found some surprises, including minerals formed near the sun or other hot stars. This data may change the way scientists understand comet formation. In addition, pictures from Stardust revealed the comet's surface to be quite complex, including craters and spires. In 2005, NASA initiated the Deep Impact mission. A 770-pound copper projectile launched into comet 9P/Tempel 1 created a large crater that allowed scientists to study the comet's interior as well as the debris resulting from the impact. Scientists found some of the substances they expected, but they found clay and carbonates as well, which were not thought to require liquid water to form. In addition, scientists found aromatic hydrocarbons, chemicals found in auto exhaust and never before seen in comets. In 2004, spacecraft Rosetta left on a 10-year mission to observe comet 67P/Churyumov-Gerasimenko. In 2014, Rosetta is expected to achieve the first comet landing when it releases a lander onto Churyumov-Gerasimenko; this landing should return the most detailed information about comets yet collected. In 2012, NASA researchers conducted laboratory research that revealed that amino acids found on comets could survive entry through Earth's atmosphere and the subsequent collision with the surface. The combination of amino acids, water, and energy could produce proteins.

Halley's comet, formally called 1P/Halley, has been seen streaking through the sky periodically for over two thousand years. The first record of its appearance dates to 240 bce. Since that date, its re-appearance has been documented every time it has passed by Earth. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">For example, in 240 <span class="smallLetters" style="background-color: transparent; font-size: 10px; vertical-align: baseline;">bce, the Chinese noted the comet's presence and blamed it for the death of an empress. Its appearance was also recorded by the Babylonians in 164 <span class="smallLetters" style="background-color: transparent; font-size: 10px; vertical-align: baseline;">bce and 87 <span class="smallLetters" style="background-color: transparent; font-size: 10px; vertical-align: baseline;">bce. In 12 <span class="smallLetters" style="background-color: transparent; font-size: 10px; vertical-align: baseline;">bce, the Romans thought the comet was connected with the death of Roman statesman Marcus Vipsanius Agrippa (c. 63-12<span class="smallLetters" style="background-color: transparent; font-size: 10px; vertical-align: baseline;">bce ). Several other sightings of the comet were recorded before the observations of British astronomer and mathematician Edmund Halley (1656-1742) in 1682. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">Until Halley's study of comets, no one knew where comets came from or what paths they followed. German astronomer and mathematician Johannes Kepler (1571-1630) observed Halley's comet in 1607, although it had not yet been given that name. Kepler concluded that comets follow straight lines, coming from and disappearing into infinity. Somewhat later, German astronomer Johannes Hevelius (1611-1687) suggested that comets follow slightly curved lines. In the latter half of the 1600s, German astronomer Georg Samuel Dörffel suggested that comets follow a parabolic course, a curve with the shape of the nose cone of a rocket. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">Although comets appeared free from the effects of gravity as they traveled through the sky, Halley wondered if gravity somehow influenced their movement. He carefully analyzed the paths of twenty-four comets. With the help of his friend, English physicist and mathematician Sir Isaac Newton (1642-1727), he found three comets--those occurring in the years of 1531, 1607, and the one he viewed himself in 1682--with nearly identical paths. This discovery led him to the conclusion that what observers had seen was really a single comet passing by Earth three different times. It also suggested that comets follow a long, elliptical (oval-shaped) orbit around the Sun. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">Halley, however, found some problems with this theory. First, the period between the first and second sightings was a year longer than the period between the second and third sightings. Second, the comet was not found in the same place in the sky each time it re-appeared. To deal with these inconsistencies, Halley suggested that the comet's path was thrown a little off course by the gravitational fields of Jupiter and Saturn as it passed by those large planets. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;"> Predicting the Comet's Orbit <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">After long, detailed calculations that took into account the influences of Jupiter and Saturn, Halley predicted that this same comet would return in 1758. He published his findings in 1705 in A Synopsis of the Astronomy of Comets. Although Halley did not live to see it, his prediction was correct, and the comet was named after him. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">After Halley's death in 1742, others continued to plot more accurately the course of Halley's comet. First, French mathematician Alexis Clairaut (1713-1765) made precise calculations of the gravitational interactions between Jupiter, Saturn, Earth, and the comet. He was joined by French astronomers Joseph Lalande (1732-1807) and Nicole-Reine Lepaute (1723-1788), who was the leading female astronomer in France at the time. Their results were so exact that their predictions were only a month different from the comet's actual return. They determined that Halley's comet completes one orbit in just over seventy-six years. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">In 1986, when Halley's comet was scheduled to pass near the Sun and Earth, it attracted a great deal of attention among both scientists and the general public. Over one thousand astronomers from forty countries coordinated the International Halley Watch. Soviet, Japanese, and European space probes were sent to get a close look at the comet, while other spacecraft and telescopes were used for observation. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">The European Space Agency's probe, Giotto, flew toward and took pictures of the comet's center on March 14, 1986. These pictures showed the nucleus to be a 9.3-mile-long, 6-mile-wide, (5.8 kilometers long and 3.7 kilometers wide) coal-black, potato-shaped object marked by hills and valleys. Two bright jets of gas and dust, each 9 miles (5.6 kilometers) long, shot out of the nucleus. Giotto 's> instruments detected the presence of water, carbon, nitrogen, and sulfur molecules. It also found that the comet was losing about thirty tons of water and five tons of dust each hour. This fact means that although the comet will survive for hundreds more orbits, it will eventually disintegrate. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">Halley's comet produces two meteor showers seen from Earth each year. The Eta Aquarids is observed around May and the Orionids is seen in October. The comet is next due to pass by Earth in the year 2061 <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">Comet Hyakutake (hi-yah-koo-tah-kay), visible to Earthlings in the spring of 1996, was the brightest and closest comet to come close to Earth in two decades. It was brilliant enough to have been witnessed even by naked-eye viewers in light-polluted cities. Such a spectacle caused it to be nicknamed The Great Comet of 1996. This comet came much closer to Earth than Halley's comet ever did in its greatly anticipated (and quite disappointing) 1985 fly-by. The closest Halley came on that trip was 39 million miles (63 million kilometers) from Earth. Hyakutake, on the other hand, approached within 9.3 million miles (15 million kilometers), just forty times the distance to the Moon. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">Comet Hyakutake, formally called C/1996 B2, took the world by surprise. It had been discovered (January 30, 1996) only two months before its arrival by Japanese amateur astronomer Yuji Hyakutake (1950-2002) using a pair of binoculars. Comet Hyakutake was Yuji's second comet discovery in two months. He had given the same name to the first, a much fainter comet, which is now officially named C/1995 Y1. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">Comet Hyakutake was first visible in the Northern Hemisphere in mid-March and reached its closest point to Earth on March 25. At the end of April, the comet looped around the Sun, and in May it passed by Earth again. This time it was visible to people in the Southern Hemisphere. It then traveled off into space, continuing its long orbit around the Sun. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">While astronomers usually have years to prepare for the arrival of a comet, Hyakutake posed a different problem. They had relatively little time to set up ground-based cameras and had to divert telescopes from other projects. They also prepared the Hubble Space Telescope to capture detailed images of the comet. What they discovered was an icy nucleus surrounded by jets of dust. It appeared that gas and dust were escaping through holes in the comet's surface. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">The description of Comet Hyakutake fits the general view of comets as being "dirty snowballs," nothing more than clumps of rocky material, dust, and ice (made of frozen methane, ammonia, and water). In addition, as comets are known to do, Hyakutake had an ion tail (made mostly of electrically charged hydrogen compounds) that pointed away from the Sun. This tail is formed when some of the comet melts as it nears the Sun and the gas is swept back by the solar wind. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">Hyakutake was unusual, however, in that it also had a second, smaller tail made of dirt particles. The Ulysses spacecraft, a robotic probe designed to study the Sun, traveled through the comet's tail on May 1996. It found that its longer tail was about 353 million miles 568 million kilometers) in length--the longest length so far found on a comet. It was also unusual because scientist found that the comet emitted X rays, which had never before been found associated with comets. Astronomers contend that ionized particles from the Sun interact with neutral atoms in the comet's atmosphere (coma) to produce the X rays. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">Hyakutake was estimated to be about 10 miles (16 kilometers) across, about the same size as Halley's comet. It traveled at about 93,000 miles (150,000 kilometers) per hour--forty-five times faster than a speeding bullet. At 9.3 million miles (15 million kilometers) away, however, it appeared to stand still in the sky. The comet's change in position could only be detected from night to night, as it showed up in progressively westward locations. <span style="background-color: #ffffff; color: #333333; font-family: Helvetica,Arial,sans-serif; font-size: 14px; vertical-align: baseline;">The 1996 visit of Hyakutake was the only chance humans alive today will have to see the comet. It will not pass this way again for another ten thousand to twenty thousand years.