Star Properties

Defining a Star

The Definition page for a star enables you to define Position, Proper Motion, Annual Parallax and to record visual magnitude.

Reference Frame

The epoch position of the star may be specified in either the J2000 or ICRF reference frame.

Julian Epoch

Specify the epoch of the star position information as a Julian epoch (yyyy.yy). The Julian epoch is related to the Julian date by the expression

JD = 2451545.0 + (yyyy.yy – 2000.0) x 365.25

where 2451545.0 (TT) represents the standard J2000 epoch.

Position

Define the star's position at the specified reference epoch.

Option	Description
Right Ascension	The angle in the equatorial plane measured in a right-handed sense about the inertial Z-axis from the inertial X-axis.
Declination	The angle from the inertial equator measured toward the inertial positive Z-axis.

Proper Motion

Define the motion of the star relative to the solar system barycenter expressed in arc seconds per year. Access computations correctly take proper motion into account.

Option	Description
Right Ascension	Motion in the equatorial plane measured in a right-handed sense about the inertial Z-axis from the inertial X-axis. Note that this field corresponds to .
Declination	Motion from the inertial equator measured towards the inertial positive Z-axis, normally designated as .

Magnitude

Use the Magnitude option to define the visual brightness of the star.

Currently, values entered in the Magnitude field do not affect the definition of the star in STK, but you can use this field to record and save magnitude values for individual stars.

Annual Parallax

Parallax is the motion of a star due to changes in the Earth's position relative to the solar system barycenter. Enter an annual value in arc seconds. Access computations correctly take annual parallax into account.