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\\ & = \left ( \frac)} ^2\mbox^4) 16 \cdot 3.142 (3.959 \times 10^\ \mbox)^2} \right )^} \\ & = 173.7\ \mbox \end See: 〕 K }} 253 Mathilde is a main-belt asteroid about 50 km in diameter that was discovered by Johann Palisa in 1885. It has a relatively elliptical orbit that requires more than four years to circle the Sun. This asteroid has an unusually slow rate of rotation, requiring 17.4 days to complete a 360° revolution about its axis. It is a primitive C-type asteroid, which means the surface has a high proportion of carbon; giving it a dark surface that reflects only 4% of the light that falls on it.〔 This asteroid was visited by the NEAR Shoemaker spacecraft during June 1997, on its way to asteroid 433 Eros. During the flyby, the spacecraft imaged a hemisphere of the asteroid, revealing many large craters that have gouged out depressions in the surface. It was the first C-type asteroid to be explored and, until 21 Lutetia was visited in 2010, it was the largest asteroid to be visited by a spacecraft. ==Observation history== In 1880, Johann Palisa, the director of the Austrian Naval Observatory, was offered a position as an assistant at the newly completed Vienna Observatory. Although the job represented a demotion for Johann, it gave him access to the new refractor, the largest telescope in the world at that time. By this point Johann had already discovered 27 asteroids, and he would employ the Vienna and instruments to find an additional 94 asteroids before he retired. Among his discoveries was the asteroid 253 Mathilde, found on November 12, 1885. The initial orbital elements of the asteroid were then computed by V. A. Lebeuf, another Austrian astronomer working at the observatory. The name of the asteroid was suggested by Lebeuf, after Mathilde, the wife of Moritz Leowy—who was the vice director of the Paris Observatory.〔 〕 In 1995, ground-based observations determined that 253 Mathilde is a C-type asteroid. It was also found to have an unusually long period of rotation.〔 On June 27, 1997, the NEAR Shoemaker spacecraft passed within 1,212 km of 253 Mathilde while moving at a velocity of 9.93 km/s. This close approach allowed the spacecraft to capture over 500 images of the surface,〔 and provided data for more accurate determinations of the asteroid's dimensions and mass (based on gravitational perturbation of the spacecraft).〔 However, only one hemisphere of 253 Mathilde was imaged during the fly-by. This was only the third asteroid to be imaged from a nearby distance, following 951 Gaspra and 243 Ida. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「253 Mathilde」の詳細全文を読む スポンサード リンク
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