Orbit Determination

Abstract

The classical aim of orbit determination is to obtain the orbital elements of a planet, comet, or minor planet from the smallest possible number of observed positions. This is therefore essentially the opposite to determining an ephemeris, where positions are obtained from known orbital elements. Any observation made from Earth at a specific time gives two spherical coordinates. We may chose whether these relate to the celestial equator (right ascension and declination) or to the ecliptic (ecliptic longitude and latitude). On the other hand, the distance cannot be measured, so knowledge of it cannot be used in orbit determination. To derive six orbital elements, the same number of independent observational values are required, so three observations must be available.