NED's Calculators
Coordinate Calculator
Introduction
This is an easy-to-use coordinate transformation, precession, and position angle calculator provided for your convenience.
It converts accurately between Besselian and Julian equinoxes, taking the epoch of observation into account when needed.
It assumes that Besselian dates refer to the FK4 system, that Julian dates refer to the FK5 system, and makes the appropriate transformations.
Though the International Celestial Reference Frame (ICRF) is not explicitly supported,
the FK5 optical system is consistent with ICRF to within the known errors of the FK5 system (refer to, e.g.,
Ma et al. 1998)
Data Entry
Select the input and output coordinate systems that you want to use.
They may be any of the following:
- Equatorial (default)
- Ecliptic
- Galactic
- Supergalactic
When applicable, the input and output equinoxes are either "J2000.0" or "B1950.0", with "J2000.0" being the default.
If you know the epoch of the observation (between AD 1500.0 and AD 2500.0), enter that in decimal years.
The default epoch, 2000.0, is adequate for all but high-precision conversion between the FK4 and FK5 systems.
Enter the input coordinates in decimal degrees or in sexagesimal units. Examples of supported coordinate formats are
- 09h55m52.7s +69d40m46s
- 09:55:52.7 +69:40:46
- 09 55 52.7 +69 40 46
- 148.969687d 69.679383d
The position angle (default is 0 degrees) is optional. Enter it in
decimal degrees if you need to precess it.
Results
Click on "Go" to run the calculator. The output will be displayed right below the input parameters.
If the calculator does not recognize some aspect of your input, it will display an error message.
In such cases, use your browser's "Back" button to return to the input page and correct the input.
Notes
Different systems may be used for input and output; for example,
equatorial B1950.0 coordinates on the FK4 system may be precessed and
transformed to ecliptic J2000.0 coordinates on the FK5 system.
Position angles are in degrees, measured from north through east.
The precession and coordinate conversion routines were written by J. Bennett who has also provided extensive
documentation on them.
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Page.
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Extinction Calculator
Introduction
The extinction calculator returns the foreground Galactic extinction at your input position using the
Schlafly & Finkbeiner 2011 (ApJ 737, 103, 2011) recalibration
of the
Schlegel, Finkbeiner & Davis 1998 (ApJ 500, 525, 1998; SFD98)
extinction map.
The original SFD98 extinction values are also returned for comparison purposes.
See this FAQ page
for more information and cautions on using the extinction values
returned by the calculator.
Data Entry
Select the input and output coordinate systems that you want to use.
They may be any of the following:
- Equatorial (default)
- Ecliptic
- Galactic
- Supergalactic
When applicable, the input equinox is either "J2000.0" or "B1950.0", with "J2000.0" being the default.
If you know the epoch of the observation (between AD 1500.0 and AD 2500.0), enter that in decimal years.
The default epoch, 2000.0, is adequate for all but high-precision conversion between the FK4 and FK5 systems.
Enter the input coordinates in decimal degrees or in sexagesimal units.
Examples of supported coordinate formats are
- 09h55m52.7s +69d40m46s
- 09:55:52.7 +69:40:46
- 09 55 52.7 +69 40 46
- 148.969687d 69.679383d
Results
Click on "Go" to run the calculator. The output will be displayed right below the input parameters.
If the calculator does not recognize some aspect of your input, it will display an error message.
In such cases, use your browser's "Back" button to return to the input page and correct the input.
Back to the Extinction Calculator Input
Page.
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Velocity Conversion Calculator
Introduction
Most redshifts for extragalactic objects are published as "heliocentric" redshifts -- that is, the earth's rotational and orbital motions have been removed from the measured velocity. It is often necessary to further "correct" the redshifts for other motions: Galactic rotation, peculiar motion of the Galaxy within the Local Group, "infall" of the Local Group toward the center of the Local Supercluster, and motion within the reference frame defined by the 3K microwave background radiation. This calculator enables you to make these corrections as needed. NED has several pre-defined apex vectors that you may use, or you may input your own apex vector.
NOTICE: Conversions between redshift and apparent velocity, and decomposition of an observed redshift into its physical components, are currently computed using traditional approximations
(see Huchra 2008) applicable for low redshifts.
Results accurate at all redshifts, accounting for cosmological effects (see Carr & Davis 2021), are planned for a future NED update.
Data Entry
Examples of supported coordinate formats are
- 09h55m52.7s +69d40m46s
- 09:55:52.7 +69:40:46
- 09 55 52.7 +69 40 46
- 148.969687d 69.679383d
Select the input coordinate systems that you want to use.
It may be one of the following:
- Equatorial (default)
- Galactic
- Supergalactic
When applicable, the input equinox is either "J2000.0" or "B1950.0", with "J2000.0" being the default.
Enter the redshift you wish to correct in velocity units of km/sec.
If you wish to use one of NED's
pre-defined apex vectors,
select the one defining the reference frame to which the redshift is
currently referred by clicking on the "Velocity from" button and choosing one
of the reference frames named there. Do the same for the "Velocity to" button,
choosing the reference frame to which you wish to correct the redshift.
If your redshift is currently referred to a velocity frame for which NED does not provide an apex vector, select "Yes" in the box under "Please select here to use your own apex vector", and enter the coordinates, coordinate system, and velocity in the boxes provided.
Results
Click on "Go" to run the calculator. The output will be displayed right below the input, recapturing the input parameters and providing the output velocity.
If the calculator does not recognize some aspect of your input, it will display an error message.
In such cases, use your browser's "Back" button to return to the input page and correct the input.
NED converts velocities from one reference frame to another using the
standard equation
Vcon = V + Vapex [sin(b) sin(bapex) +
cos(b) cos(bapex) cos(l - lapex)]
where l and b are the object's longitude and latitude, V is its unconverted
velocity, and the apices (with Galactic coordinates) of the various motions
are given as
| Conversion |
lapex |
bapex |
Vapex |
Source |
| Heliocentric to Galactocentric (GSR) |
87.8 deg |
+1.7 deg |
232.3 km/sec |
RC3 |
| Heliocentric to Local Group |
93 deg |
-4 deg |
316 km/sec |
AJ 111, 794, 1996 |
| Heliocentric to 3K Background |
264.14 deg |
+48.26 deg |
371.0 km/sec |
ApJ 473, 576, 1996 |
See
Courteau and van den Bergh 1999
for a review of the solar motion with respect to the Local Group.
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Conversion Input Page.
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