| 释义 |
Oort Astr.|ʊət|
The name of Jan Hendrik Oort (b. 1900), Dutch astronomer, used attrib. and in the possessive to designate concepts proposed by him or arising out of his work, as Oort('s) (comet) cloud, a cloud of small bodies that Oort proposed orbited the sun well beyond the orbit of Pluto and acted as a cometary reservoir; Oort('s) constant, either of two constants in the equation relating the radial velocity of a star in the galaxy to its distance from the sun (see quot. 1977).
1941B. J. & P. F. Bok Milky Way v. 106 The ‘Oort’ constant..measures the maximum effect [of differential rotation] at a standard distance. Ibid. 108 The best value of Oort's constant A is between five and six kilometers per second for a distance of one thousand light years. 1966McGraw-Hill Encycl. Sci. & Technol. VI. 12/1 The radial velocities may be closely represented by the equation Radial velocity = rA sin 2l where r is the distance to the object from the Sun, l its galactic longitude, and A, known as Oort's constant, depends on many factors including the mass of the galaxy and the distance of the Sun from the galactic center. Its value is approximately 18 km/(sec) (1000 parsecs). 1968D. C. Knight Comets 38 The American astronomer Fred L. Whipple recently proposed that a yet-to-be-seen comet belt, distinct from Oort's ‘comet cloud’, lies near the orbit of Pluto. 1976Nature 29 Jan. 290/1 Some theories go even further and predict that, in addition to these comets in the Oort cloud, the remains of a primaeval comet belt may still exist at a distance of ∼50 AU. 1976National Observer (U.S.) 24 Apr. 6/1 Van Flandern's work also casts doubt on ‘Oort's Cloud’, one of the more cherished concepts of comet studies. 1977J. Narlikar Struct. Universe iii. 62 Oort expressed the transverse velocity of the star in the following form T = r{ob}B + A cos 2(l—l0){cb}. Here r is the distance of the star from the Sun, l its galactic longitude, and l0 is the galactic longitude of the galactic centre. A and B are constants called Oort's constants. |