Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Asteroid shopping experience:

1. Compare - without doubt the biggest advantage that the Asteroid offers shoppers today is the ability to compare thousands of Asteroid at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.

2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about

3. Testimonials - don't know anybody that has bought a Asteroid? Wrong! If the Asteroid is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.

4. Questions - Got a question about Asteroid then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

5. Reputation - Never heard of the company selling Asteroid? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Asteroid and build up a picture of their reputation for sales, returns, customer service, delivery etc.

6. Returns - still worried that even after all of the above your Asteroid wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Asteroid then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Asteroid site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Asteroid, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Asteroid, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.

, a C-type asteroid.Asteroids, also called minor planets or planetoids, are a class of astronomical objects. The term asteroid is generally used to indicate a diverse group of small celestial bodies in the solar system that orbit around the Sun. Asteroid (Greek for "star-like") is the most commonly used word in the English literature for minor planets, which has been the term preferred by the International Astronomical Union; some other languages prefer planetoid (Greek: "planet-like"), because it more accurately describes what they are. In late 2006 redefinition of planet, the IAU introduced the term "small solar system body" (SSSBs), which includes most objects thus far classified as minor planets, as well as comets. At the same time they introduced the term dwarf planet for the largest minor planets. This article deals specifically with the minor planets that orbit in the inner solar system (roughly up to the orbit of Jupiter (planet)). For information on other types of objects, such as comets, Trans-Neptunian objects, and Centaur (planetoid)s, see Small solar system body.

The first asteroid to be discovered, Ceres (dwarf planet), is the largest asteroid known to date and is now classified as a dwarf planet. All others are currently classified as small solar system bodies. The vast majority of asteroids are found within the main asteroid belt, with ellipse orbits between those of Mars (planet) and Jupiter. It is thought that these asteroids are remnants of the protoplanetary disc, and in this region the accretion (astronomy) of planetesimals into a larger planet or planets during the formative period of the solar system was prevented by large gravitational perturbations by Jupiter. Some asteroids have Asteroid moon or are found in co-orbiting pairs known as binary asteroids.

Asteroids in the solar system (white) and the Trojan asteroids (green)Hundreds of thousands of asteroids have been discovered within the solar system and the present rate of discovery is about 5000 per month. As of July 31, 2007, from a total of 378,546 registered minor planets, 160,508 have orbits known well enough to be given astronomical naming conventions. Of these, 13,889 have official names.trivia: about 650 of these names require diacritics The lowest-numbered but unnamed minor planet is ;{{cite web].{{cite web|title=Discovery Circumstances: Numbered Minor Planets (155001)-(160000)|accessdate=2007-07-31|url=http://www.cfa.harvard.edu/iau/lists/NumberedMPs150001.html-->Current estimates put the total number of asteroids above 1 km in diameter in the solar system to be between 1.1 and 1.9 million. The largest asteroid in the inner solar system is 1 Ceres, with diameters of 975×909 km. Two other large inner solar system belt asteroids are 2 Pallas and 4 Vesta; both have diameters of ~500 km. Vesta is the only main belt asteroid that is sometimes visible to the naked eye (in some very rare occasions, a near-Earth asteroid may be visible without technical aid; see 99942 Apophis)., 1 Ceres, Earth's MoonThe mass of all the asteroids of the Main Belt is estimated to be about 3.0-3.6 kg, or about 4% of the mass of our moon. Of this, Ceres (dwarf planet) comprises 0.95 kg, some 32% of the total. Adding in the next three most massive asteroids, 4 Vesta (9%), 2 Pallas (7%), and 10 Hygiea (3%), brings this figure up to 51%; while the three after that, 511 Davida (1.2%), 704 Interamnia (1.0%), and 3 Juno (0.9%), only add another 3% to the total mass. The number of asteroids then increases rapidly as their individual masses decrease.

Asteroid classification Asteroids are commonly classified according to two criteria: the characteristics of their orbits, and features of their reflectance visible spectrum.

Orbit groups and families Many asteroids have been placed in groups and families based on their orbital characteristics. It is customary to name a group of asteroids after the first member of that group to be discovered. Groups are relatively loose dynamical associations, whereas families are much "tighter" and result from the catastrophic break-up of a large parent asteroid sometime in the past.V. Zappalà et al Asteroid Families: Search of a 12,487-Asteroid Sample Using Two Different Clustering Techniques, Icarus, Vol. 116, p. 291 (1995.)

For a full listing of known asteroid groups and families, see minor planet and asteroid family.

===Spectral classification=== shows the view looking from one end of the asteroid across the gouge on its underside and toward the opposite end. Features as small as 35 m across can be seen.

In 1975, an asteroid taxonomy system based on colour, albedo, and spectral line was developed by Clark R. Chapman, David Morrison, and Ben Zellner. These properties are thought to correspond to the composition of the asteroid's surface material. Originally, they classified only three types of asteroids:



This list has since been expanded to include a number of other asteroid types. The number of types continues to grow as more asteroids are studied. See Asteroid spectral types for more detail or :Category:Asteroid spectral classes for a list.

Note that the proportion of known asteroids falling into the various spectral types does not necessarily reflect the proportion of all asteroids that are of that type; some types are easier to detect than others, biasing the totals.

Problems with spectral classification Originally, spectral designations were based on inferences of an asteroid's composition:



However, the correspondence between spectral class and composition is not always very good, and there are a variety of classifications in use. This has led to significant confusion. While asteroids of different spectral classifications are likely to be composed of different materials, there are no assurances that asteroids within the same taxonomic class are composed of similar materials.

At present, the spectral classification based on several coarse resolution spectroscopic surveys in the 1990s is still the standard. Scientists have been unable to agree on a better taxonomic system, largely due to the difficulty of obtaining detailed measurements consistently for a large sample of asteroids (e.g. finer resolution spectra, or non-spectral data such as densities would be very useful).

Asteroid discovery and its moon Dactyl, the first satellite of an asteroid to be discovered.

Historical methods Asteroid discovery methods have drastically improved over the past two centuries.

In the last years of the 18th century, Baron Franz Xaver von Zach organized a group of 24 astronomers to search the sky for the "missing planet" predicted at about 2.8 Astronomical unit from the Sun by the Titius-Bode law, partly as a consequence of the discovery, by Sir William Herschel in 1781, of the planet Uranus (planet) at the distance "predicted" by the law. This task required that hand-drawn sky charts be prepared for all stars in the zodiacal band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, be spotted. The expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers.

Ironically, the first asteroid, 1 Ceres, was not discovered by a member of the group, but rather by accident in 1801 by Giuseppe Piazzi, director of the observatory of Palermo in Sicily. He discovered a new star-like object in Taurus (constellation) and followed the displacement of this object during several nights. His colleague, Carl Friedrich Gauss, used these observations to determine the exact distance from this unknown object to the Earth. Gauss' calculations placed the object between the planets Mars (planet) and Jupiter (planet). Piazzi named it after Ceres (mythology), the Roman goddess of agriculture.

Three other asteroids (2 Pallas, 3 Juno, and 4 Vesta) were discovered over the next few years, with Vesta found in 1807. After eight more years of fruitless searches, most astronomers assumed that there were no more and abandoned any further searches.

However, Karl Ludwig Hencke persisted, and began searching for more asteroids in 1830. Fifteen years later, he found 5 Astraea, the first new asteroid in 38 years. He also found 6 Hebe less than two years later. After this, other astronomers joined in the search and at least one new asteroid was discovered every year after that (except the wartime year 1945). Notable asteroid hunters of this early era were John Russell Hind, Annibale de Gasparis, Karl Theodor Robert Luther, Hermann Mayer Salomon Goldschmidt, Jean Chacornac, James Ferguson (astronomer), Norman Robert Pogson, Ernst Wilhelm Leberecht Tempel, James Craig Watson, Christian Heinrich Friedrich Peters, Alphonse Louis Nicolas Borrelly, Johann Palisa, the Paul Henry and Prosper Henry and Auguste Charlois.

In 1891, however, Maximilian Franz Joseph Cornelius Wolf pioneered the use of astrophotography to detect asteroids, which appeared as short streaks on long-exposure photographic plates. This drastically increased the rate of detection compared with previous visual methods: Wolf alone discovered 248 asteroids, beginning with 323 Brucia, whereas only slightly more than 300 had been discovered up to that point. Still, a century later, only a few thousand asteroids were identified, numbered and named. It was known that there were many more, but most astronomers did not bother with them, calling them "vermin of the skies".

Manual methods of the 1900s and modern reporting Until 1998, asteroids were discovered by a four-step process. First, a region of the sky was photographed by a wide-field telescope (usually an Astrograph). Pairs of photographs were taken, typically one hour apart. Multiple pairs could be taken over a series of days. Second, the two films of the same region were viewed under a stereoscope. Any body in orbit around the Sun would move slightly between the pair of films. Under the stereoscope, the image of the body would appear to float slightly above the background of stars. Third, once a moving body was identified, its location would be measured precisely using a digitizing microscope. The location would be measured relative to known star locations.

These first three steps do not constitute asteroid discovery: the observer has only found an apparition, which gets a provisional designation in astronomy, made up of the year of discovery, a letter representing the week of discovery, and finally a letter and a number indicating the discovery's sequential number (example: ).

The final step of discovery is to send the locations and time of observations to Brian Marsden of the Minor Planet Center. Dr. Marsden has computer programs that compute whether an apparition ties together previous apparitions into a single orbit. If so, the object gets a number. The observer of the first apparition with a calculated orbit is declared the discoverer, and he gets the honour of naming the asteroid (subject to the approval of the International Astronomical Union) once it is numbered.

Computerized methods is the centre dot being followed by the sequence; the object that flashes by during the clip is an artificial satellite.There is increasing interest in identifying asteroids whose orbits cross Earth's, and that could, given enough time, collide with Earth (see Earth-crosser asteroids). The three most important groups of near-Earth asteroids are the Apollo asteroid, Amor asteroid, and Aten asteroid. Various asteroid deflection strategies have been proposed, as early as the 1960s.

The near-Earth object asteroid 433 Eros had been discovered as long ago as 1898, and the 1930s brought a flurry of similar objects. In order of discovery, these were: 1221 Amor, 1862 Apollo, 2101 Adonis, and finally 69230 Hermes, which approached within 0.005 Astronomical Unit of the Earth in 1937. Astronomers began to realize the possibilities of Earth impact.

Two events in later decades increased the level of alarm: the increasing acceptance of Walter Alvarez' hypothesis that an impact event resulted in the Cretaceous–Tertiary extinction event, and the 1994 observation of Comet Shoemaker-Levy 9 crashing into Jupiter (planet). The U.S. military also declassified the information that its military satellites, built to detect nuclear explosions, had detected hundreds of upper-atmosphere impacts by objects ranging from one to 10 metres across.

All of these considerations helped spur the launch of highly efficient automated systems that consist of Charge-Coupled Device (Charge-coupled device) cameras and computers directly connected to telescopes. Since 1998, a large majority of the asteroids have been discovered by such automated systems. A list of teams using such automated systems includes:



The LINEAR system alone has discovered 84,764 asteroids, as of August 28, 2007. Between all of the automated systems, 4711 near-Earth asteroids have been discovered including over 600 more than 1 km in diameter.

Naming asteroids Overview: naming conventions A newly discovered asteroid is given a Provisional designation in astronomy consisting of the year of discovery and an alphanumeric code (such as ). Once its orbit has been confirmed, it is given a number, and later may also be given a name (e.g. 433 Eros). The formal naming convention uses parentheses around the number (e.g. (433) Eros), but dropping the parentheses is quite common. Informally, it is common to drop the number altogether, or to drop it after the first mention when a name is repeated in running text.

Asteroids that have been given a number but not a name keep their provisional designation, e.g. (29075) 1950 DA. As modern discovery techniques are discovering vast numbers of new asteroids, they are increasingly being left unnamed. The first asteroid to be left unnamed was for a long time (3360) 1981 VA, now 3360 Syrinx; as of November 2006, this distinction is now held by . On rare occasions, a small body's Provisional designation in astronomy may become used as a name in itself: the still unnamed gave its name to a group of Kuiper belt objects which became known as cubewanos.

Numbering asteroids Asteroids are awarded with an official number once their orbits are confirmed. With the increasing rapidity of asteroid discovery, asteroids are currently being awarded six-figure numbers. The switch from five figures to six figures arrived with the publication of the Minor Planet Circular (MPC) of October 19, 2005, which saw the highest numbered asteroid jump from 99947 to 118161. This change caused a small "Y2k"-like crisis for various automated data services, since only five digits were allowed in most data formats for the asteroid number. Most services have now widened the asteroid number field. For those which did not, the problem has been addressed in some cases by having the leftmost digit (the ten-thousands place) use the alphabet as a digit extension. A=10, B=11,…, Z=35, a=36,…, z=61. A high number such as 120437 is thus cross-referenced as C0437 on some lists.

Sources for names The first few asteroids were named after figures from Graeco-Roman mythology, but as such names started to run out, others were used —famous people, literary characters, the names of the discoverer's wives, children, and even television characters.

The first asteroid to be given a non-mythological name was 20 Massalia, named after the city of Marseilles. For some time only female (or feminized) names were used; Alexander von Humboldt was the first man to have an asteroid named after him, but his name was feminized to 54 Alexandra. This unspoken tradition lasted until 334 Chicago was named; even then, oddly feminised names show up in the list for years afterward.

As the number of asteroids began to run into the hundreds, and eventually the thousands, discoverers began to give them increasingly frivolous names. The first hints of this were 482 Petrina and 483 Seppina, named after the discoverer's pet dogs. However, there was little controversy about this until 1971, upon the naming of 2309 Mr. Spock (which was not even named after the Star Trek character, but after the discoverer's cat who supposedly bore a resemblance to him). Although the International Astronomical Union subsequently banned pet names as sources, eccentric asteroid names are still being proposed and accepted, such as 4321 Zero, 6042 Cheshirecat, 9007 James Bond, 13579 Allodd, 24680 Alleven, 128036 Rafaelnadal or 26858 Misterrogers.

Special naming rules Asteroid naming is not always a free-for-all: there are some types of asteroid for which rules have developed about the sources of names. For instance Centaur (planetoid) (asteroids orbiting between Saturn and Neptune) are all named after mythological centaurs, Trojan asteroid after heroes from the Trojan War, and trans-Neptunian objects after underworld spirits.

Another well-established rule is that comets are named after their discoverer(s), whereas asteroids are not. One way to "circumvent" this rule has been for astronomers to exchange the courtesy of naming their discoveries after each other. A particular exception to this rule is 96747 Crespodasilva, which was named after its discoverer, Lucy d'Escoffier Crespo da Silva, because she died shortly after the discovery, at age 22. A few objects are also cross-listed as both comets and asteroids, such as 4015 Wilson-Harrington = 107P/Wilson-Harrington.

Asteroid symbols The first few asteroids discovered were assigned symbols like the ones traditionally used to designate Earth, the Moon, the Sun and planets. The symbols quickly became ungainly, hard to draw and recognise. By the end of 1851 there were 15 known asteroids, each (except one) with its own symbol(s).

{| class="wikitable"|- align="center" style="align:center; background:#ffc0c0"! Asteroid || Symbol |-| Ceres (dwarf planet) || |-| 2 Pallas ] || |-| 4 Vesta ] || |-| 6 Hebe ] || |-| 8 Flora ] || |-| 10 Hygiea ] || |-| 12 Victoria ] || Never assigned.|-| 14 Irene ] || |-| 28 Bellona ] || |-| 37 Fides ] made a major change in the Berliner Astronomisches Jahrbuch (BAJ, "Berlin Astronomical Yearbook") for 1854. He introduced encircled numbers instead of symbols, although his numbering began with 5 Astraea, the first four asteroids continuing to be denoted by their traditional symbols. This symbolic innovation was adopted very quickly by the astronomical community. The following year (1855), Astraea's number was bumped up to 5, but Ceres through Vesta would be listed by their numbers only in the 1867 edition. A few more asteroids (28 Bellona, 35 Leukothea, and 37 Fides) would be given symbols as well as using the numbering scheme. The circle would become a pair of parentheses, and the parentheses sometimes omitted altogether over the next few decades.

Asteroid exploration Until the age of space travel, asteroids were merely pinpricks of light in even the largest telescopes and their shapes and terrain remained a mystery.

The first close-up photographs of asteroid-like objects were taken in 1971 when the Mariner 9 probe imaged Phobos (moon) and Deimos (moon), the two small moons of Mars (planet), which are probably captured asteroids. These images revealed the irregular, potato-like shapes of most asteroids, as did subsequent images from the Voyager program probes of the small moons of the gas giants.

, the first asteroid to be imaged in close up.The first true asteroid to be photographed in close-up was 951 Gaspra in 1991, followed in 1993 by 243 Ida and its moon Dactyl (asteroid), all of which were imaged by the Galileo spacecraft en route to Jupiter (planet).

The first dedicated asteroid probe was NEAR Shoemaker, which photographed 253 Mathilde in 1997, before entering into orbit around 433 Eros, finally landing on its surface in 2001.

Other asteroids briefly visited by spacecraft en route to other destinations include 9969 Braille (by Deep Space 1 in 1999), and 5535 Annefrank (by Stardust (spacecraft) in 2002).

In September 2005, the Japanese Hayabusa probe started studying 25143 Itokawa in detail and may return samples of its surface to earth. The Hayabusa mission has been plagued with difficulties, including the failure of two of its three control wheels, rendering it difficult to maintain its orientation to the sun to collect solar energy. Following that, the next asteroid encounters will involve the European Rosetta space probe (launched in 2004), which will study 2867 Šteins and 21 Lutetia in 2008 and 2010.

In September 2007 NASA launched the Dawn Mission, which will orbit 1 Ceres and 4 Vesta in 2011-2015, with its mission possibly then extended to 2 Pallas.

It has been suggested that asteroids might be used in the future as a source of materials which may be rare or exhausted on earth (asteroid mining), or materials for constructing space habitats (see Colonization of the asteroids). Materials that are heavy and expensive to launch from earth may someday be mined from asteroids and used for space manufacturing and construction.

Asteroids in fiction Asteroids and asteroid belts are a staple of science fiction stories. Asteroids play several potential roles in science fiction: as places which human beings might colonize; as resources for extracting minerals; as a hazard encountered by spaceships travelling between two other points; and as a threat to life on Earth due to potential impacts.

References

See also

External links


(asteroid navigator) | 1 Ceres | ...

, a C-type asteroid.Asteroids, also called minor planets or planetoids, are a class of astronomical objects. The term asteroid is generally used to indicate a diverse group of small celestial bodies in the solar system that orbit around the Sun. Asteroid (Greek for "star-like") is the most commonly used word in the English literature for minor planets, which has been the term preferred by the International Astronomical Union; some other languages prefer planetoid (Greek: "planet-like"), because it more accurately describes what they are. In late 2006 redefinition of planet, the IAU introduced the term "small solar system body" (SSSBs), which includes most objects thus far classified as minor planets, as well as comets. At the same time they introduced the term dwarf planet for the largest minor planets. This article deals specifically with the minor planets that orbit in the inner solar system (roughly up to the orbit of Jupiter (planet)). For information on other types of objects, such as comets, Trans-Neptunian objects, and Centaur (planetoid)s, see Small solar system body.

The first asteroid to be discovered, Ceres (dwarf planet), is the largest asteroid known to date and is now classified as a dwarf planet. All others are currently classified as small solar system bodies. The vast majority of asteroids are found within the main asteroid belt, with ellipse orbits between those of Mars (planet) and Jupiter. It is thought that these asteroids are remnants of the protoplanetary disc, and in this region the accretion (astronomy) of planetesimals into a larger planet or planets during the formative period of the solar system was prevented by large gravitational perturbations by Jupiter. Some asteroids have Asteroid moon or are found in co-orbiting pairs known as binary asteroids.

Asteroids in the solar system (white) and the Trojan asteroids (green)Hundreds of thousands of asteroids have been discovered within the solar system and the present rate of discovery is about 5000 per month. As of July 31, 2007, from a total of 378,546 registered minor planets, 160,508 have orbits known well enough to be given astronomical naming conventions. Of these, 13,889 have official names.trivia: about 650 of these names require diacritics The lowest-numbered but unnamed minor planet is ;{{cite web].{{cite web|title=Discovery Circumstances: Numbered Minor Planets (155001)-(160000)|accessdate=2007-07-31|url=http://www.cfa.harvard.edu/iau/lists/NumberedMPs150001.html-->Current estimates put the total number of asteroids above 1 km in diameter in the solar system to be between 1.1 and 1.9 million. The largest asteroid in the inner solar system is 1 Ceres, with diameters of 975×909 km. Two other large inner solar system belt asteroids are 2 Pallas and 4 Vesta; both have diameters of ~500 km. Vesta is the only main belt asteroid that is sometimes visible to the naked eye (in some very rare occasions, a near-Earth asteroid may be visible without technical aid; see 99942 Apophis)., 1 Ceres, Earth's MoonThe mass of all the asteroids of the Main Belt is estimated to be about 3.0-3.6 kg, or about 4% of the mass of our moon. Of this, Ceres (dwarf planet) comprises 0.95 kg, some 32% of the total. Adding in the next three most massive asteroids, 4 Vesta (9%), 2 Pallas (7%), and 10 Hygiea (3%), brings this figure up to 51%; while the three after that, 511 Davida (1.2%), 704 Interamnia (1.0%), and 3 Juno (0.9%), only add another 3% to the total mass. The number of asteroids then increases rapidly as their individual masses decrease.

Asteroid classification Asteroids are commonly classified according to two criteria: the characteristics of their orbits, and features of their reflectance visible spectrum.

Orbit groups and families Many asteroids have been placed in groups and families based on their orbital characteristics. It is customary to name a group of asteroids after the first member of that group to be discovered. Groups are relatively loose dynamical associations, whereas families are much "tighter" and result from the catastrophic break-up of a large parent asteroid sometime in the past.V. Zappalà et al Asteroid Families: Search of a 12,487-Asteroid Sample Using Two Different Clustering Techniques, Icarus, Vol. 116, p. 291 (1995.)

For a full listing of known asteroid groups and families, see minor planet and asteroid family.

===Spectral classification=== shows the view looking from one end of the asteroid across the gouge on its underside and toward the opposite end. Features as small as 35 m across can be seen.

In 1975, an asteroid taxonomy system based on colour, albedo, and spectral line was developed by Clark R. Chapman, David Morrison, and Ben Zellner. These properties are thought to correspond to the composition of the asteroid's surface material. Originally, they classified only three types of asteroids:



This list has since been expanded to include a number of other asteroid types. The number of types continues to grow as more asteroids are studied. See Asteroid spectral types for more detail or :Category:Asteroid spectral classes for a list.

Note that the proportion of known asteroids falling into the various spectral types does not necessarily reflect the proportion of all asteroids that are of that type; some types are easier to detect than others, biasing the totals.

Problems with spectral classification Originally, spectral designations were based on inferences of an asteroid's composition:



However, the correspondence between spectral class and composition is not always very good, and there are a variety of classifications in use. This has led to significant confusion. While asteroids of different spectral classifications are likely to be composed of different materials, there are no assurances that asteroids within the same taxonomic class are composed of similar materials.

At present, the spectral classification based on several coarse resolution spectroscopic surveys in the 1990s is still the standard. Scientists have been unable to agree on a better taxonomic system, largely due to the difficulty of obtaining detailed measurements consistently for a large sample of asteroids (e.g. finer resolution spectra, or non-spectral data such as densities would be very useful).

Asteroid discovery and its moon Dactyl, the first satellite of an asteroid to be discovered.

Historical methods Asteroid discovery methods have drastically improved over the past two centuries.

In the last years of the 18th century, Baron Franz Xaver von Zach organized a group of 24 astronomers to search the sky for the "missing planet" predicted at about 2.8 Astronomical unit from the Sun by the Titius-Bode law, partly as a consequence of the discovery, by Sir William Herschel in 1781, of the planet Uranus (planet) at the distance "predicted" by the law. This task required that hand-drawn sky charts be prepared for all stars in the zodiacal band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, be spotted. The expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers.

Ironically, the first asteroid, 1 Ceres, was not discovered by a member of the group, but rather by accident in 1801 by Giuseppe Piazzi, director of the observatory of Palermo in Sicily. He discovered a new star-like object in Taurus (constellation) and followed the displacement of this object during several nights. His colleague, Carl Friedrich Gauss, used these observations to determine the exact distance from this unknown object to the Earth. Gauss' calculations placed the object between the planets Mars (planet) and Jupiter (planet). Piazzi named it after Ceres (mythology), the Roman goddess of agriculture.

Three other asteroids (2 Pallas, 3 Juno, and 4 Vesta) were discovered over the next few years, with Vesta found in 1807. After eight more years of fruitless searches, most astronomers assumed that there were no more and abandoned any further searches.

However, Karl Ludwig Hencke persisted, and began searching for more asteroids in 1830. Fifteen years later, he found 5 Astraea, the first new asteroid in 38 years. He also found 6 Hebe less than two years later. After this, other astronomers joined in the search and at least one new asteroid was discovered every year after that (except the wartime year 1945). Notable asteroid hunters of this early era were John Russell Hind, Annibale de Gasparis, Karl Theodor Robert Luther, Hermann Mayer Salomon Goldschmidt, Jean Chacornac, James Ferguson (astronomer), Norman Robert Pogson, Ernst Wilhelm Leberecht Tempel, James Craig Watson, Christian Heinrich Friedrich Peters, Alphonse Louis Nicolas Borrelly, Johann Palisa, the Paul Henry and Prosper Henry and Auguste Charlois.

In 1891, however, Maximilian Franz Joseph Cornelius Wolf pioneered the use of astrophotography to detect asteroids, which appeared as short streaks on long-exposure photographic plates. This drastically increased the rate of detection compared with previous visual methods: Wolf alone discovered 248 asteroids, beginning with 323 Brucia, whereas only slightly more than 300 had been discovered up to that point. Still, a century later, only a few thousand asteroids were identified, numbered and named. It was known that there were many more, but most astronomers did not bother with them, calling them "vermin of the skies".

Manual methods of the 1900s and modern reporting Until 1998, asteroids were discovered by a four-step process. First, a region of the sky was photographed by a wide-field telescope (usually an Astrograph). Pairs of photographs were taken, typically one hour apart. Multiple pairs could be taken over a series of days. Second, the two films of the same region were viewed under a stereoscope. Any body in orbit around the Sun would move slightly between the pair of films. Under the stereoscope, the image of the body would appear to float slightly above the background of stars. Third, once a moving body was identified, its location would be measured precisely using a digitizing microscope. The location would be measured relative to known star locations.

These first three steps do not constitute asteroid discovery: the observer has only found an apparition, which gets a provisional designation in astronomy, made up of the year of discovery, a letter representing the week of discovery, and finally a letter and a number indicating the discovery's sequential number (example: ).

The final step of discovery is to send the locations and time of observations to Brian Marsden of the Minor Planet Center. Dr. Marsden has computer programs that compute whether an apparition ties together previous apparitions into a single orbit. If so, the object gets a number. The observer of the first apparition with a calculated orbit is declared the discoverer, and he gets the honour of naming the asteroid (subject to the approval of the International Astronomical Union) once it is numbered.

Computerized methods is the centre dot being followed by the sequence; the object that flashes by during the clip is an artificial satellite.There is increasing interest in identifying asteroids whose orbits cross Earth's, and that could, given enough time, collide with Earth (see Earth-crosser asteroids). The three most important groups of near-Earth asteroids are the Apollo asteroid, Amor asteroid, and Aten asteroid. Various asteroid deflection strategies have been proposed, as early as the 1960s.

The near-Earth object asteroid 433 Eros had been discovered as long ago as 1898, and the 1930s brought a flurry of similar objects. In order of discovery, these were: 1221 Amor, 1862 Apollo, 2101 Adonis, and finally 69230 Hermes, which approached within 0.005 Astronomical Unit of the Earth in 1937. Astronomers began to realize the possibilities of Earth impact.

Two events in later decades increased the level of alarm: the increasing acceptance of Walter Alvarez' hypothesis that an impact event resulted in the Cretaceous–Tertiary extinction event, and the 1994 observation of Comet Shoemaker-Levy 9 crashing into Jupiter (planet). The U.S. military also declassified the information that its military satellites, built to detect nuclear explosions, had detected hundreds of upper-atmosphere impacts by objects ranging from one to 10 metres across.

All of these considerations helped spur the launch of highly efficient automated systems that consist of Charge-Coupled Device (Charge-coupled device) cameras and computers directly connected to telescopes. Since 1998, a large majority of the asteroids have been discovered by such automated systems. A list of teams using such automated systems includes:



The LINEAR system alone has discovered 84,764 asteroids, as of August 28, 2007. Between all of the automated systems, 4711 near-Earth asteroids have been discovered including over 600 more than 1 km in diameter.

Naming asteroids Overview: naming conventions A newly discovered asteroid is given a Provisional designation in astronomy consisting of the year of discovery and an alphanumeric code (such as ). Once its orbit has been confirmed, it is given a number, and later may also be given a name (e.g. 433 Eros). The formal naming convention uses parentheses around the number (e.g. (433) Eros), but dropping the parentheses is quite common. Informally, it is common to drop the number altogether, or to drop it after the first mention when a name is repeated in running text.

Asteroids that have been given a number but not a name keep their provisional designation, e.g. (29075) 1950 DA. As modern discovery techniques are discovering vast numbers of new asteroids, they are increasingly being left unnamed. The first asteroid to be left unnamed was for a long time (3360) 1981 VA, now 3360 Syrinx; as of November 2006, this distinction is now held by . On rare occasions, a small body's Provisional designation in astronomy may become used as a name in itself: the still unnamed gave its name to a group of Kuiper belt objects which became known as cubewanos.

Numbering asteroids Asteroids are awarded with an official number once their orbits are confirmed. With the increasing rapidity of asteroid discovery, asteroids are currently being awarded six-figure numbers. The switch from five figures to six figures arrived with the publication of the Minor Planet Circular (MPC) of October 19, 2005, which saw the highest numbered asteroid jump from 99947 to 118161. This change caused a small "Y2k"-like crisis for various automated data services, since only five digits were allowed in most data formats for the asteroid number. Most services have now widened the asteroid number field. For those which did not, the problem has been addressed in some cases by having the leftmost digit (the ten-thousands place) use the alphabet as a digit extension. A=10, B=11,…, Z=35, a=36,…, z=61. A high number such as 120437 is thus cross-referenced as C0437 on some lists.

Sources for names The first few asteroids were named after figures from Graeco-Roman mythology, but as such names started to run out, others were used —famous people, literary characters, the names of the discoverer's wives, children, and even television characters.

The first asteroid to be given a non-mythological name was 20 Massalia, named after the city of Marseilles. For some time only female (or feminized) names were used; Alexander von Humboldt was the first man to have an asteroid named after him, but his name was feminized to 54 Alexandra. This unspoken tradition lasted until 334 Chicago was named; even then, oddly feminised names show up in the list for years afterward.

As the number of asteroids began to run into the hundreds, and eventually the thousands, discoverers began to give them increasingly frivolous names. The first hints of this were 482 Petrina and 483 Seppina, named after the discoverer's pet dogs. However, there was little controversy about this until 1971, upon the naming of 2309 Mr. Spock (which was not even named after the Star Trek character, but after the discoverer's cat who supposedly bore a resemblance to him). Although the International Astronomical Union subsequently banned pet names as sources, eccentric asteroid names are still being proposed and accepted, such as 4321 Zero, 6042 Cheshirecat, 9007 James Bond, 13579 Allodd, 24680 Alleven, 128036 Rafaelnadal or 26858 Misterrogers.

Special naming rules Asteroid naming is not always a free-for-all: there are some types of asteroid for which rules have developed about the sources of names. For instance Centaur (planetoid) (asteroids orbiting between Saturn and Neptune) are all named after mythological centaurs, Trojan asteroid after heroes from the Trojan War, and trans-Neptunian objects after underworld spirits.

Another well-established rule is that comets are named after their discoverer(s), whereas asteroids are not. One way to "circumvent" this rule has been for astronomers to exchange the courtesy of naming their discoveries after each other. A particular exception to this rule is 96747 Crespodasilva, which was named after its discoverer, Lucy d'Escoffier Crespo da Silva, because she died shortly after the discovery, at age 22. A few objects are also cross-listed as both comets and asteroids, such as 4015 Wilson-Harrington = 107P/Wilson-Harrington.

Asteroid symbols The first few asteroids discovered were assigned symbols like the ones traditionally used to designate Earth, the Moon, the Sun and planets. The symbols quickly became ungainly, hard to draw and recognise. By the end of 1851 there were 15 known asteroids, each (except one) with its own symbol(s).

{| class="wikitable"|- align="center" style="align:center; background:#ffc0c0"! Asteroid || Symbol |-| Ceres (dwarf planet) || |-| 2 Pallas ] || |-| 4 Vesta ] || |-| 6 Hebe ] || |-| 8 Flora ] || |-| 10 Hygiea ] || |-| 12 Victoria ] || Never assigned.|-| 14 Irene ] || |-| 28 Bellona ] || |-| 37 Fides ] made a major change in the Berliner Astronomisches Jahrbuch (BAJ, "Berlin Astronomical Yearbook") for 1854. He introduced encircled numbers instead of symbols, although his numbering began with 5 Astraea, the first four asteroids continuing to be denoted by their traditional symbols. This symbolic innovation was adopted very quickly by the astronomical community. The following year (1855), Astraea's number was bumped up to 5, but Ceres through Vesta would be listed by their numbers only in the 1867 edition. A few more asteroids (28 Bellona, 35 Leukothea, and 37 Fides) would be given symbols as well as using the numbering scheme. The circle would become a pair of parentheses, and the parentheses sometimes omitted altogether over the next few decades.

Asteroid exploration Until the age of space travel, asteroids were merely pinpricks of light in even the largest telescopes and their shapes and terrain remained a mystery.

The first close-up photographs of asteroid-like objects were taken in 1971 when the Mariner 9 probe imaged Phobos (moon) and Deimos (moon), the two small moons of Mars (planet), which are probably captured asteroids. These images revealed the irregular, potato-like shapes of most asteroids, as did subsequent images from the Voyager program probes of the small moons of the gas giants.

, the first asteroid to be imaged in close up.The first true asteroid to be photographed in close-up was 951 Gaspra in 1991, followed in 1993 by 243 Ida and its moon Dactyl (asteroid), all of which were imaged by the Galileo spacecraft en route to Jupiter (planet).

The first dedicated asteroid probe was NEAR Shoemaker, which photographed 253 Mathilde in 1997, before entering into orbit around 433 Eros, finally landing on its surface in 2001.

Other asteroids briefly visited by spacecraft en route to other destinations include 9969 Braille (by Deep Space 1 in 1999), and 5535 Annefrank (by Stardust (spacecraft) in 2002).

In September 2005, the Japanese Hayabusa probe started studying 25143 Itokawa in detail and may return samples of its surface to earth. The Hayabusa mission has been plagued with difficulties, including the failure of two of its three control wheels, rendering it difficult to maintain its orientation to the sun to collect solar energy. Following that, the next asteroid encounters will involve the European Rosetta space probe (launched in 2004), which will study 2867 Šteins and 21 Lutetia in 2008 and 2010.

In September 2007 NASA launched the Dawn Mission, which will orbit 1 Ceres and 4 Vesta in 2011-2015, with its mission possibly then extended to 2 Pallas.

It has been suggested that asteroids might be used in the future as a source of materials which may be rare or exhausted on earth (asteroid mining), or materials for constructing space habitats (see Colonization of the asteroids). Materials that are heavy and expensive to launch from earth may someday be mined from asteroids and used for space manufacturing and construction.

Asteroids in fiction Asteroids and asteroid belts are a staple of science fiction stories. Asteroids play several potential roles in science fiction: as places which human beings might colonize; as resources for extracting minerals; as a hazard encountered by spaceships travelling between two other points; and as a threat to life on Earth due to potential impacts.

References

See also

External links


(asteroid navigator) | 1 Ceres | ...



BBC NEWS | Science/Nature | Asteroid makes close Earth pass
A 250m-wide asteroid known as 2007 TU24 makes a relatively close pass of Earth. ... An asteroid some 250m (820ft) across has swept past the Earth. There was no chance of it hitting ...

BBC NEWS | UK | Asteroid danger in 2014 downplayed
A potentially continent-crushing asteroid is detected, but UK analysts say there is little chance it will hit Earth.

Asteroid - Wikipedia, the free encyclopedia
Asteroids, also called minor planets or planetoids, are Solar System bodies smaller than planets but larger than meteoroids (which are commonly defined as being 10 meters across or ...

Asteroid Introduction
Background information, details on selected asteroids, image gallery.

Definition: asteroid from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.

The Official Asteroid Website
Welcome The Asteroid Website is undergoing a complete makeover. In the mean time you can find all the information at Myspace...or e-mail us at contact@asteroid.se

Hayabusa probe prepares to punch an asteroid - space - 03 November ...
The Japanese craft will perform three daring smash-and-grabs, as planetary scientists puzzle over close-up images of the space rock

It's called Apophis. It's 390m wide. And it could hit Earth in 31 ...
It's 390m wide. And it could hit Earth in 31 years time. Scientists call for plans to change asteroid's path Developing technology could take decades

 

Asteroid



 
Copyright © 2008 Hintcenter.com - All rights reserved.
Home | Terms of Use | Privacy Policy
All Trademarks belong to their repective owners. Many aspects of this page are used under
commercial commons license from Yahoo!