Phase 2 Proposal Instructions for Cycle 10

3.5 Equinox for Coordinates [Equinox]

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Specify the year of the equator and equinox to which the coordinates are referred, optionally preceded by a J or B to indicate the Julian or Besselian system. Integer or decimal values for the year may be used. If the year is given without a prefix (for example, 1975), the Besselian system is assumed for years prior to 2000 and the Julian system is assumed for the year 2000 and beyond. If a prefix is given, it must be B for years prior to 2000 and J for the year 2000 and beyond.

The values J2000 and B1950 correspond to commonly used catalogs; it is recommended that one of these be specified unless there is a good reason to use something else. It is not necessary to apply precession corrections to coordinates from positional catalogs. The Guide Star Catalog and the Hipparcos Input Catalogue both use the J2000 equinox. (Note, however, that the Hipparcos output catalogue is epoch 1991.25, which means proper motions can have significant effects if you are not careful.)

An Equinox value is required.

For some notes on Equinox, Epoch, and units, see3.13Getting Coordinates Coordinated.