History of Discovery
On 15 March 2004, astronomers from Caltech, Gemini Observatory, and Yale University announced the discovery of the coldest, most distant object known to orbit the sun. The object was found at a distance 90 times greater than that from the sun to the earth - about 3 times further than Pluto, the most distant known planet.
The discovery was made on the Samuel Oschin Telescope at the Palomar Observatory east of San Diego on 14 November 2003 by the team of Mike Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale).
Here you can read a raport of discovery(you need Acrobad Reader to open this)

Observatory Palomar:
The Palomar Observatory, located in north San Diego County California, is owned and operated by the California Institute of Technology. The Observatory supports the research of the Caltech faculty, post-doctoral fellows and students, and the researchers at Caltech's collaborating institutions
. Palomar Observatory is home to the historic Hale 200-inch telescope. Other facilities on the mountain include the 60-inch, 48-inch, 18-inch and the Snoop telescopes. The 60-inch telescope is home to the Automated Transient Observing System. The 48-inch telescope is home to the Near-Earth Asteroid

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The massive dome shutters - 125 tons each - open in the
early evening to prepare for the night's run.
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The dome open below the summer Milky Way.
About discoverer
a) Mike Brown - Profesor of Planetary Astronomy Division of Geological and Planetary Sciences.He discover:
-2004 DW
b) Chad Trujillo
-He discover:
-Sedna (2003 VB12)
-binary trans-Neptunian 1998 Sm165
-binary trans-Neptunian 1999 Tc36
He curruent reserch:
-Kuiper Belt
-Moving Object Detection Software (MODS)
-useful astronomical definitions for understanding the Kuiper Belt discussion
c) David L. Rabinowitz -(born 1960) is a professor at Yale University.He Discover:
-Orcus - possibly the largest Kuiper Belt object after Pluto
- -Pholus -is a Centaur in an eccentric orbit, with a perihelion near the orbit of Saturn and aphelion near the orbit of Neptune. It is believed to have originated as a Kuiper belt object.

About Sedna

I. How to found Sedna!?
In March 2004, the location of Sedna is easily found in the evening sky to the southwest just after sunset. It is almost directly below Mars, and forms a triangle with the very bright Venus. The following sky chart was accurate for mid-March 2004 and is only left in place for an historical reference.
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II. Where are you from Sedna(What is the Oort cloud and what is its relationship to Sedna?)
The Oort cloud is a hypothetical shell of icy proto-comets in very loose orbits around the sun that extends to a distance of almost halfway to the nearest star. Occasionaly, passing stars cause a slight change in the orbit of one of these proto-comets which causes them to come steaking in to the inner solar system where we see them as comets. Though the Oort cloud has never been seen directly, the comets that we do see are very strong evidence of its existence. As can be seen in the graphic above, though, the Oort cloud is expected to be much much further out than the orbit of Sedna. So why do we think Sedna is a member of the Oort cloud? We believe that the existence of Sedna is evidence that the Oort cloud actually extends much further in towards the sun than previously thought. This "inner Oort cloud" was formed in the same manner as the previously known "outer Oort cloud." Early in the history of the solar system many many small icy bodies were orbiting the sun and getting sling-shot out by close encounters with planets. As they were travelling further and further from the sun, the orbits of these bodies were affected by distant stars, causing them to slow down and stay attached to the sun. Sedna probably suffered a similar fate, except the stars which affected it must have been much much closer than previously expected. We believe that this is evidence that the sun formed in a tight-knit group along with many other stars.
[Rozmiar: 57497 bajtów] III. The color of Sedna is very red.
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Sedna is one of the reddest known minor planets. It is similar in appearance to the very red minor planet Pholus. For Pholus, the cause of the reddening is irradiation of organic-rich ices on the surface by ultraviolet light and cosmic rays. Sedna is probably red for the same reasons.

IV. The light-scattering properties of Sedna are unusual
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For typical distant objects, there is a change in brightness that depends on the angle between the incoming sunlight and the direction to Earth (this is called the phase angle). When there is a large increase in brightness at small phase angles, it is called an opposition surge. It is an effect caused by the scattering of light from small particles of ice and dust on the surface of planetary bodies. Most distant bodies have opposition surges, but for Sedna the surge is very weak. Of all the distant bodies with measured opposition surges, only Pluto is known to have such a small surge.

V. Rotation dimeter and orbit
a) Rotation Although the changes in brightness are small, we are able to see a pattern that repeats. If this repetition is caused by the rotation of Sedna, the period of rotation would be 20 days or longer. This is unusually long for a minor planet, most of which which rotate with periods of less than one day.
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If you stay in Sedna you can see this!(artist vision)
b) Dimeter -The hardest thing was study size of Sedna.The problem was that small bodies with light color of surface can reflect solar light as well as dark giant!Even studying by thermal telescopes (which we use to check the temperature of object)doesn't help- 30 meters IRAM and 85 cm SPITZER were helpless. They didn't detect symptoms of heat where the planetoid. This is why size of globe which is announced by astronomers is only estimated. Scientists supposed that it reflect from 20 to 100 percent of light which is fallen on this surface. Joining these assessments scientist counted that Sedna in diameter is 1180-2360 km.
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Don't lock on Diameter of Sedna in this picture he is bad because this picture present first diagnosis!

c) Orbit
Now we can talk about big happiness because during 10.5 thousands years of traveling around the sun Sedna goes away from the sun much as 130 billions km (900 times farther than Earth).Now Sedna brings nearer the Sun.So we can observe it before in 72 years it will fly to the distant areas of solar system.

Why orbit is stretched??Scientists suggested two explanations.For first it can be caused by perturbations which were at the beggining of solar system example given:
flying star could entail part of matter or we have to suppose existance of next heavenly bodies nearby

The Sedna orbit( red )

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VI. Moon
When we first announced the discovery of Sedna, we noted that circumstantial evidence suggested that there is a moon around Sedna.
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Astronauts looked over 35 pictures of Sedna which made by HST(telescope Hubble)unfortunately they could not find the moon which by they're expectations should circle around Sedna.This unexpected discovery could change our views about beging and evaluation of objects which are presents on the edges.There conclusion of scientist based on rotation speed of Sedna. Massive object strongly affecting Sedna were the only explanation.It was suppoused to be the moon but it doesn't exist. Almost all of the objects in Solar System have they're rotation period within hours. Why is it called SEDNA??

Because of its frigid temperatures (-240C), the team has named the object SEDNA, after the Inuit goddess of the sea from whom all sea creatures were created.Sedna have this temperature because he are far far away from SUN.

2003 VB12 was the official temporary designation of the International Astronomical Union (IAU) Minor Planet Center, based on the year (2003) and date (14 Nov = the 22nd 2-week period of the year thus V=the 22nd letter of the alphabet. after that it is sequential based on the discovery announcement) of discovery. Once the orbit of 2003 VB12 is known well enough (probably 1 year), we will reccomend to the IAU Committee on Small Body Nomenclature -- which is responsible for solar system names -- that it be permanently called SEDNA (this has now happened, see above). Our newly discovered object is the coldest most distant place known in the solar system, so we feel it is appropriate to name it in honor of SEDNA, the Inuit goddess of the sea, who is thought to live at the bottom of the frigid arctic ocean. We will furthermore suggest to the IAU that newly discoverd objects in this inner Oort cloud all be named after entities in arctic mythologies
The legend of SEDNA SEDNA is a very significant figure in Inuit mythology. There are a number of different versions of the myth of SEDNA. I will share with you the one I prefer. As the legend goes, SEDNA was a beautiful Inuit girl who lived with her father. She was very vain and thought she was too beautiful to marry just anyone. Time and time again she turned down hunters who came to her camp wishing to marry her. Finally one day her father said to her "SEDNA, we have no food and we will go hungry soon. You need a husband to take care of you, so the next hunter who comes to ask your hand in marriage, you must marry him." SEDNA ignored her father and kept brushing her hair as she looked at her reflection in the water. Soon her father saw another hunter approaching their camp. The man was dressed elegantly in furs and appeared to be well-to-do even though his face was hidden. SEDNA'S father spoke to the man. "If you wish to seek a wife I have a beautiful daughter. She can cook and sew and I know she will make a good wife." Under great protest, SEDNA was placed aboard of the hunters kayak and journeyed to her new home. Soon they arrived at an island. SEDNA looked around. She could see nothing. No sod hut, no tent, just bare rocks and a cliff. The hunter stood before SEDNA and as he pulled down his hood, he let out and evil laugh. SEDNA'S husband was not a man as she had thought but a raven in disguise. She screamed and tried to run, but the bird dragged her to a clearing on the cliff. SEDNA'S new home was a few tufts of animal hair and feathers strewn about on the hard, cold rock. The only food she had to eat was fish. Her husband, the raven, brought raw fish to her after a day of flying off in search of food. SEDNA was very unhappy and miserable. She cried and cried and called her father's name. Through the howling arctic winds SEDNA'S' father could hear his daughter's cries. He felt guilty for what he had done as he knew she was sad. SEDNA'S father decided it was time to rescue his daughter. He loaded up his kayak and paddled for days through the frigid arctic waters to his SEDNA'S home. When he arrived SEDNA was standing on the shore. SEDNA hugged her father then quickly climbed into his kayak and paddled away. After many hours of travel SEDNA turned and saw a black speck far off into the distance. She felt the fear well up inside of her for she knew the speck was her angry husband flying in search of her. The big black raven swooped down upon the kayak bobbing on the ocean. SEDNA'S father took his paddle and struck at the raven but missed as the bird continued to harass them. Finally the raven swooped down near the kayak and flapped his wing upon the ocean. A vicious storm began to brew. The calm arctic ocean soon became a raging torrent tossing the tiny kayak to and fro. SEDNA'S father became very frightened. He grabbed SEDNA and threw her over the side of the kayak into the ocean. "Here, he screamed, here is your precious wife, please do not hurt me, take her." SEDNA screamed and struggled as her body began go numb in the icy arctic waters. She swam to the kayak and reached up, her fingers grasping the side of the boat. Her father, terrified by the raging storm, thought only of himself as he grabbed the paddle and began to pound against SEDNA'S fingers. SEDNA screamed for her father to stop but to no avail. Her frozen fingers cracked and fell into the ocean. Affected by her ghastly husbands powers, SEDNA'S fingers while sinking to the bottom, turned into seals. SEDNA attempted again to swim and cling to her father's kayak. Again he grabbed the paddle and began beating at her hands. Again SEDNA'S hands, frozen by the arctic sea again cracked off. The stumps began to drift to the bottom of the sea, this time turned into the whales and other large mammals. SEDNA could fight no more and began to sink herself. SEDNA, tourmented and raging with anger for what had happened to her, did not perish. She became, and still is today, the goddess of the sea. SEDNA'S companions are the seals, and the whales that sit with her at the bottom on the ocean. Her anger and fury against man is what drums up the violent seas and storms. Hunters have a great respect for her. Legend has it that they must treat her with respect. Shaman's from the world above must swim down to her to comb her long black tangled hair. This calms SEDNA down. Once this is done, she releases her mammals to allow the Inuit to eat from the bounty of the sea. It is for this reason in the north that after a hunter catches a seal he drops water into the mouth of the mammal, a gesture to thank SEDNA for her kindness in allowing him to feed his family.
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Planet?? yes or not
Astoundingly, no precise scientific definition of the word "planet" currently exists. It is rare for scientists to have to define a word that is already in common usage and that everybody from school children on up already understand. How does one then go about constructing a scientific definition of such a word after the fact?
In such cases, we believe that it is important to be both true to the historical and popular perception of the meaning of the word while being scientifically descriptive, accurate, and meaningful. We will use these points -- historically valid and scientifically meaningful -- as the criteria on which to judge potential definitions of the word "planet." We have identified 4 major ideas for the definition of the word "planet" (though the most common have never been written down to our knowledge):
1.Purely historical. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto are planets. Nothing else in the solar system is a planet. This definition is definitely historically valid, but fails miserably under scientific meaning. What if a new object larger than Pluto is found? What is it? Why is Pluto a planet but an object 3/4 its size, like SEDNA, is not? This definition, completely lacking in scientific motivation, makes the word "planet" meaningless as a scientific description.
2.Historical plus. Mercury through Pluto are planets, as is any newly discovered object larger than Pluto. This definition is, we believe, the one in most common colloquial use throughout the world, even if people don't realize that this is the definition they are using. Indeed, if SEDNA had been larger than Pluto, most would have hailed it as a 10th planet. This definition -- like the previous -- is historically consistent, but -- like the previous -- still fails the scientific test. Why is Pluto the cutoff size? Is there really a big enough difference in size between Pluto and SEDNA and Quaoar that one should be called a planet while the others are not? The scientific answer remains a resounding no.
3.Gravitational rounding. Any object which is round due to its own gravitational pull and which directly orbits the sun is called a planet. This definition is very different! It is strictly scientific, yet historically valid, as all objects that we call planets by the historical definitions are indeed round due to their own gravitational pull. More importantly (and by a complete coincidence) the dividing line between objects which are round and those which are not round is just a few times smaller than the size of Pluto. So why not take advantage of this coincidence and simply define planets to be objects which are round? To do so means that we must admit several other bodies to the class of "planet." SEDNA, Quaoar, the asteroid Ceres, and perhaps a dozen Kuiper belt objects are also likely to be round and thus, by this definition, planets. But these additions are perhaps a small price to pay for a definition which rests on solid scientific principles.
Unfortunately, this definition completely fails the historical sanity check. Historically, where does the criterion to be round come from, except for the near coincidence between the historical definition of planet and the transition size from round to not round? At no time in previous history has any discussion of whether or not an object is round been part of the discussion of whether or not it should be called a planet. Ceres was initially considered to be a planet, but not because it is round (which was unknown at the time), but because it was the only object known to exist between Mars and Jupiter. When other asteroids of similar sizes were found at nearly the same location it was decided to call them all members of the asteroid belt, rather than planets.
Roundness is an important physical property, and gravity is the dominant force in the solar system, so perhaps it is important to have a special word which describes the class of objects in the solar system which are round. But simply because all historical planets are round does not at all mean that it is good science to define all round objects to be planets. A much better idea is to use a different word to descibe these objects. Spheroids? Gravispheres? Actually, we prefer the word "planetoid" as a new word to descibe round objects orbiting the sun. All planets are planetoids. All planetoids are not planets.
Population classification. This definition requires a little more explanation and a little more understanding of the solar system, but, in the end, leads to the most satisfactory definition of "planet". Just like the solar system very naturally divides itself between round objects and non-round objects, it also very naturally divides itself between solitary individuals and members of large populations. The best known example of a large population is the asteroid belt. We call it a population because one region of space contains objects with a continuous range of sizes from one moderately large object (Ceres) to a handful of slightly smaller objects (Vesta, Pallas, Hermione) to a huge number of extremely small objects (rocks, dust particles). The solitary individuals are much different. In their region of space there is only them (Earth, say) and then a collection of much much smaller objects (the near-earth asteroids), with no continuous population in between. A single example helps to dramatize the difference between a continuous population and a solitary individual. Ceres, the largest asteroid, has a diameter of 900 km. The next largest asteroid, Pallas, has a diameter of 520 km. After that is Vesta at 500 km, and Hygiea at 430 km, and the list continues on down. The jump in size between asteroids is never more than a factor of two. In contrast, the earth has a diameter of about 12,000 km, while the largest other object in the earth's vicinity, the asteroid Ganymed, has a diameter of about 41 km, a factor of 300!
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune all count as solitary individuals by this definition. Pluto and Quaoar do not. Pluto is clearly a member of the Kuiper belt population, as can be seen from the fact that there are objects in the same vicinity slightly smaller than Pluto (Quaoar, 2004 DW, Varuna), and then even a larger number slightly smaller than that, and then on down.

All info is found in Internet on many internet Web. Information about Sedna is not easy to find!