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.
Description
Galactic U,V,W express space velocity along Galactic-center, rotation and north directions.
Galactic U,V,W express space velocity along Galactic-center, rotation and north directions. Proper motion contributes transverse speed through distance, with RA* already including the cosine of declination.1
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.
When to use Galactic Space Velocity Uvw
Use this tool to 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.
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 Galactic Space Velocity Uvw 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, distanceParsecs, raStarProperMotionArcsecPerYear, decProperMotionArcsecPerYear, radialKmPerSecond using the field table and calculation rules, then run the tool.
- Read uKmPerSecond, vKmPerSecond, wKmPerSecond. 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 |
| distanceParsecs | Distance parsecs | number | Required |
| raStarProperMotionArcsecPerYear | RA* = RA proper motion × cos(declination), in arcseconds per Julian year. | number | Required |
| decProperMotionArcsecPerYear | Dec proper motion arcsec per year | number | Required |
| radialKmPerSecond | Radial km per second | number | Required |
Enter RA/Dec degrees, positive distance pc, signed radial km/s and RA*/Dec proper motions in arcsec/year. The tool builds the Cartesian ICRS velocity and applies the fixed Galactic matrix, returning U toward the center, V along rotation and W north in km/s.
vICRS=radial × line + 4.74047 distancePc(μRA* east+μDec north); UVW=GalacticRotation × vICRS Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.
| Output field | Meaning | Value type |
|---|---|---|
| uKmPerSecond | U km per second | number |
| vKmPerSecond | V km per second | number |
| wKmPerSecond | W km per second | number |
{
"input": {
"raDegrees": 0,
"decDegrees": 0,
"distanceParsecs": 1,
"raStarProperMotionArcsecPerYear": 0,
"decProperMotionArcsecPerYear": 0,
"radialKmPerSecond": 1
},
"output": {
"uKmPerSecond": -0.0548755604162154,
"vKmPerSecond": 0.4941094278755837,
"wKmPerSecond": -0.8676661490190047
}
}Limitations and assumptions
These are heliocentric velocities without a solar-motion or local-standard-of-rest correction. Units, frame and proper-motion convention must match; uncertainties and epoch propagation are separate.
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 Icrs To Galactic Coordinates: Apply the fixed ICRS/J2000 Galactic rotation to a sky direction; this is not an epoch propagation. For a complementary task, use Rectilinear Astrometric Epoch Propagation: Propagate a Cartesian constant-space-velocity astrometric state using RA* proper motion and Julian years; light-time, gravity and reference-frame precession are excluded.
References
-
Galactic Space Velocity Uvw — tool.io
Similar or alternative tools
- Icrs To Galactic Coordinates
Apply the fixed ICRS/J2000 Galactic rotation to a sky direction; this is not an epoch propagation.
- Rectilinear Astrometric Epoch Propagation
Propagate a Cartesian constant-space-velocity astrometric state using RA* proper motion and Julian years; light-time, gravity and reference-frame precession are excluded.