Icrs To Galactic Coordinates
Apply the fixed ICRS/J2000 Galactic rotation to a sky direction; this is not an epoch propagation.
Description
Galactic and ICRS/J2000 axes are related by a fixed three-dimensional rotation.
Galactic and ICRS/J2000 axes are related by a fixed three-dimensional rotation. Rotating a direction changes its coordinates without advancing the object's epoch.1
Apply the fixed ICRS/J2000 Galactic rotation to a sky direction; this is not an epoch propagation.
When to use Icrs To Galactic Coordinates
Use this tool to apply the fixed ICRS/J2000 Galactic rotation to a sky direction; this is not an epoch propagation.
Prepare the source, detector or coordinate measurements. Confirm frame, epoch, angular units, axis directions and the stated RA proper-motion convention before entering values.
How to use Icrs To Galactic Coordinates and understand its results
- Prepare the source, detector or coordinate measurements. Confirm frame, epoch, angular units, axis directions and the stated RA proper-motion convention before entering values.
- Enter raDegrees, decDegrees using the field table and calculation rules, then run the tool.
- Read longitudeDegrees, latitudeDegrees. The explanation below defines the units, signs, ordering and any flags or placeholder values.
- If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.
| Input field | Meaning | Value type; see rules below | Requirement |
|---|---|---|---|
| raDegrees | Ra degrees | number | Required |
| decDegrees | Dec degrees | number | Required |
Enter finite RA and declination degrees, with declination within ±90. The tool converts the direction to a Cartesian unit vector, applies the fixed Galactic rotation matrix and recovers longitude wrapped to [0,360) and latitude degrees.
Galactic unit vector=fixed 3×3 rotation × ICRS unit vector Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| longitudeDegrees | Longitude degrees | number |
| latitudeDegrees | Latitude degrees | number |
{
"input": {
"raDegrees": 0,
"decDegrees": 0
},
"output": {
"longitudeDegrees": 96.33727234341762,
"latitudeDegrees": -60.18855326759371
}
}Limitations and assumptions
This does not perform proper-motion propagation, precession or a different catalog frame realization. Input coordinates must already use the stated ICRS/J2000 convention.
Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.
Alternative or Complementary methods
Use Galactic Space Velocity Uvw: Transform ICRS proper motion (RA*=RA·cos Dec), distance and radial velocity into heliocentric U toward Galactic center, V along rotation, W north; no solar-motion correction is applied. For a complementary task, use Equatorial Ecliptic Axis Rotation: Rotate a sky direction between equatorial and ecliptic axes using supplied obliquity; the same epoch must be used for both frames.
References
-
Icrs To Galactic Coordinates — tool.io
Similar or alternative tools
- Galactic Space Velocity Uvw
Transform ICRS proper motion (RA*=RA·cos Dec), distance and radial velocity into heliocentric U toward Galactic center, V along rotation, W north; no solar-motion correction is applied.
- Equatorial Ecliptic Axis Rotation
Rotate a sky direction between equatorial and ecliptic axes using supplied obliquity; the same epoch must be used for both frames.