This is a help page specific to using Precess online. For more information, please consult the CIAO Precess help page here.

Input Coordinates

The user may enter the input coordinates or resolve a Target Name using the Resolve Name button.

Coordinate System

Select the coordinate system to convert from/to. Precess supports the following choices:

• Equatorial(B1950) - Equatorial w/ Besselian epoch B1950
• Equatorial(J2000) - Equatorial w/ Julian epoch J2000
• Equatorial(Xxxxx) - Equatorial w/ specified Besselian or Julian epoch
• Galactic - Galactic
• Ecliptic(B1950) - Ecliptic w/ Besselian epoch B1950
• Ecliptic(Bxxxx) - Ecliptic w/ specified Besselian epoch
• (CONVERT "TO" ONLY) Constellation - Returns the constellation located at the given input position

Note about Ecliptic: Precess does not allow conversions from one Ecliptic system to another Ecliptic system. The GUI therefore will allow Ecliptic to be in either the Input list or the Output list, but not both at the same time.

Equinox

Specify the epoch. This is enabled only if the selected Coordinate System is Equatorial(Xxxxx) or Ecliptic(Bxxxx).

Coordinates

Input a set of coordinates in the format of the selected coordinate system or resolve a target name which will set the RA/Dec coordinates in J2000. The supported coordinate ranges are listed below.

• EQUATORIAL - RA - Right Ascension, given in either sexagesimal or decimal format. Sexagesimal values are specified as "hh mm [ss[.ss]]" (that is, hours and minutes are required, seconds and fractions of seconds are optional). The range for RA is:
  Sexagesimal 00 00 00.00 to 24 00 00.00
  Decimal 00.00 to 360.00
  
• EQUATORIAL - Dec - Declination, given in either sexagesimal or decimal format. Sexagesimal values are specified as "sdd mm [ss[.ss]]". The range for Dec is:
  Sexagesimal -90 00 00.00 to 90 00 00.00
  Decimal -90.00 to 90.00
  
• GALACTIC - L2 - Longitude, given in either sexagesimal or decimal format. Sexagesimal values are specified as "hh mm [ss[.ss]]". The range for L2 is:
  Sexagesimal 00 00 00.00 to 24 00 00.00
  Decimal 00.00 to 360.00
  
• GALACTIC - B2 - Latitude, given in either sexagesimal or decimal format. Sexagesimal values are specified as "sdd mm [ss[.ss]]". The range for B2 is:
  Sexagesimal -90 00 00.00 to 90 00 00.00
  Decimal -90.00 to 90.00
  
• ECLIPTIC - EL - Ecliptic Longitude, given in either sexagesimal or decimal format. Sexagesimal values are specified as "hh mm [ss[.ss]]". The range for EL is:
  Sexagesimal 00 00 00.00 to 24 00 00.00
  Decimal 00.00 to 360.00
  
• ECLIPTIC - EB - Ecliptic Latitude, given in either sexagesimal or decimal format. Sexagesimal values are specified as "sdd mm [ss[.ss]]". The range for EB is:
  Sexagesimal -90 00 00.00 to 90 00 00.00
  Decimal -90.00 to 90.00
  

Target Name

Enter a valid target name and click the Resolve Name button. This will query the catalog[s] specified in the Name Resolver field. If one, and only one entry is found, the coordinates will be displayed in J2000. If no entry is found or more than one entry is retrieved, the user will be asked to modify the Target Name and try again.

Name Resolver

Name of the service or services that will be used to resolve the target name when the Resolve Name button is pressed. The services will be chosen in the specified order. For example, "NED/SIMBAD" will first search for the target name in NED and then, if the name was not found, in SIMBAD.

Constellation Output

The output is the constellation in which the given input position lies. Positions are precessed to B1875.0 and compared with the Delporte (1935) constellation definitions.

Output Format

The output is provided in two formats.

• Sexagesimal: hh mm ss.ss & sdd mm ss.ss
• Decimal: ddd.dddd & sdd.dddd