Astronomers have been conducting an ongoing survey of the outer solar system using the Palomar QUEST camera and the Samuel Oschin Telescope at Palomar Observatory in Southern California. This survey has been operating since the fall of 2001, with the switch to the QUEST camera happening in the summer of 2003. To date they have found around 40 bright Kuiper belt objects. To find objects, Astronomers have taken three pictures of a small region of the night sky over three hours and look for something that moves. The many billions of stars and galaxies visible in the sky appear stationary, while satellites, planets, asteroids, and comets appear to move. Objects in the inner Oort cloud are extremely distant and so move extremely slowly.
(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. The existence of Sedna is evidence that the Oort cloud actually extends much further in towards the sun than previously thought).
These are two slightly differently processed views of the same 3 discovery images. The total area of sky shown in the bottom image is equivalent in size to the head of a pin held at arm's length. Incidentally, that is how big the Sun would appear from Sedna:
Even more interestingly, the orbit of Sedna is extreme elliptical, in contrast to all of the much closer planets, and it takes 10,500 years to circle the sun.
Here is an image of the orbit and position compared to all the known solar system objects:
In our discovery images, we see only a point of light. We can't directly measure the size of Sedna from this point. The light that we see has traveled from the sun, been reflected off the surface of Sedna, and come back to us where we can see it in the images like the discovery images below. So a small icy object and a large coal-covered object, for example, would both look about the same brightness in the discovery images, because both objects could reflect about the same amount of sunlight.
Astronomers measured Sedna's size using a thermal telescope, which measures the heat coming from the surface. They know how far away Sedna is, so they know that the surface temperature is about 400 degrees below zero Fahrenheit. A large object of that temperature will give off much more heat than a small object of that temperature. A 30 meter diameter IRAM telescope and a Spitzer Space Telescope were used. Sedna was too small to be detected in either. This tells us that Sedna is at most about 1800 km in diameter: about halfway in size between Pluto and the largest known Kuiper belt object Quaoar. Even though all we know for certain is that Sedna is smaller than 1800 km, we have evidence which suggests that the size might be pretty close to this number. They are virtually certain that the size is larger than the 1250 km size of Quaoar, though this object has shown many unexpected characteristics, so they can't completely rule out a smaller size.
Sedna is about 20.5 magnitudes in R, considerably fainter than 2004 DW and Quaoar. It is beyond the reach of almost all amateurs astronomers (though, interestingly, the first confirmation of the existence of Sedna was made at Tenagra Observatory, an extremely high-end amateur telescope run by Michael Schwartz in southern Arizona).
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.
When astronomers first announced the discovery of Sedna, we noted that circumstantial evidence suggested that there is a moon around Sedna. Soon after, we acquired the images below with the Hubble Space Telescope. Much to our surprise no moon is visible!
But In December 2005 astronomers finally discovered a moon for sedna they called it (Gabriel).
1 Comments:
Its ok, i had to write this post long because all the informations are very important and very interesting ^_^
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