WHEN IS THE BEST TIME FOR THE PHYSICAL
OBSERVATIONS OF ASTEROIDS?
J. GAO1,2, J. ZHU 2,3
1
.Department of Astronomy, Beijing Normal University, Beijing 100875, P. R. CHINA.
Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012, P. R.
CHINA.
3
CAS-PKU Jointly Beijing Astrophysics Center, Peking University, Beijing 100871, P. R.
CHINA.
2
The astrometric observations of asteroids are often performed near their
oppositions, where they have faster apparent motions and brighter visual
magnitudes. However, the physical observations of asteroids (photometric
and spectral) often require longer exposure times as well as bright
magnitudes for better signal-to-noise ratio, which are combined effects of
both apparent moving speeds and visual magnitudes. We derive the equations
of the apparent motion of asteroid in geocentric ecliptic coordinates.
Comparison of the apparent magnitudes of asteroid at opposition and at
stationary shows that the magnitude differences in the two cases are around 1
magnitude in average for main belt asteroids, but are much larger for some
NEAs and some special orbit asteroids. Spacial and magnitude distributions
of asteroids in different types at stationary are presented
from calculations based on both numerical simulation and the real data of the
first 20,000 numbered asteroids. The influence of sky background brightness
of the observation site, telescope diameter, and pixel size of CCD on the
physical observations of asteroids are also discussed.