Wyniki wyszukiwania - BazTech

Ograniczanie wyników

2 Acta Astronomica

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: Ephemerides

Sortuj według:

Ogranicz wyniki do:

Error Propagation of the Computed Orbital Elements of Selected Near-Earth Asteroids

Włodarczyk I.

Acta Astronomica

2007

Vol. 57, No. 1

103--121

Computed orbital elements of asteroids contain errors depending on the errors of observations. In accordance with the procedure described by Sitarski (1998) we can find randomly selected sets of orbital elements which reasonably represent all observations with fixed mean rms residual. In this way we can obtain the error ellipse of the initial orbital elements, and that of the predicted ones. By integrating equations of motion of these computed clones we can obtain a time evolution of changes of the shape of the torus, inside which all the orbits of the clones exist. The time evolution of the configuration of the torus and its size are connected with the asteroid position inside this torus. The larger is the torus the more difficult it is to find the position of the asteroid. The shape of the torus and its time evolution depend mainly on the kind of the asteroid's orbit. If the orbit is more chaotic, then changes of the torus shape are more rapid and the size of the torus is larger. Close approaches of asteroids to planets are the main source of the chaotic motion. This is particularly important in computing their close approaches to Earth. The distances between the minor planet on the nominal orbit and the virtual minor planets around the nominal orbit can attain considerable values. In this work we computed the time necessary for the values of the mean distances of the clones to achieve the dimensions of the Earth radius. In this respect, we investigated the motion of the known earlier asteroids 433 Eros and 1943 Anteros, and the recently discovered minor planets 99942 Apophis (2004 MN4) and 2004 VD17 - the most dangerous to the Earth, according to the Impact Risk Page of NASA (http://neo.jpl.nasa.gov/risk/). It appears that time-span after which dimensions of the torus attain well defined values are strongly correlated with the stability time and they are also connected with frequent and close approaches to the planets. Furthermore, it was investigated whether the computed orbital elements of the asteroids for the epoch of the beginning, middle or end of the observation, influence the behavior of the asteroids. Also the propagation of the region of uncertainty of asteroid position was computed. This can simplify the computing of close approaches of these asteroids to the Earth and the impact risk assessment.

Warsaw Ephemeris of the Solar System: DE405/WAW

Sitarski G.

Acta Astronomica

2002

Vol. 52, No. 4

471--486

An ephemeris of the Solar System in rectangular coordinates is produced by numerical integration of equations of motion of nine planets, the Moon, and the Sun. Recurrent power series method of 26th order is applied when integrating the equations of motion in barycentric equatorial coordinates. Initial data of the JPL DE405 ephemeris were used to prepare the starting data for our integration. A comparison with the JPL ephemeris shows that our ephemeris gives e.g., the solar coordinates in accordance to within ±5×10-8 a.u. in the interval of thousand years. Starting data for integration of equations of motion of five outer planets were prepared. Initial values of barycentric coordinates and velocity components for Ceres, Pallas, Vesta, and Hygiea were also found on the base of a large number of astrometric observations of those asteroids. A subroutine providing the planetary coordinates and velocity components for any date may be included as a source of necessary planetary data in computer routines for orbital computations. For a convenient practical use, we stored values of coordinates and velocity components of the Solar System in a file for 1001 dates from 1493 January 25.0 to 2150 March 11.0 every 240 days to choose the proper starting data for planetary integration. Examples of the orbital computations using the DE405/WAW ephemeris are presented.