The SkyCorr () form plots an error ellipse (or rectangle or other similar figure) on the sky defined by errors in the longitude and latitude directions, and a correlation between the two errors.
The error in longitude is considered to be premultiplied by the cosine of the latitude, i.e. both errors correspond to angular distances along a great circle.
The supplied correlation is a dimensionless value in the range -1..+1 and is equal to the covariance divided by the product of the lon and lat errors. The covariance matrix is thus:
[ lonerr*lonerr lonerr*laterr*corr ] [ lonerr*laterr*corr laterr*laterr ]
This plot type is suitable for use with the
ra_error
, dec_error
and ra_dec_corr
columns in the Gaia source catalogue.
Note however that Gaia positional errors are generally quoted
in milli-arseconds (mas),
while this plotter requires lon/lat errors in degrees,
so to plot true error ellipses
it is necessary to divide the Gaia error values by 3.6e6.
In most plots, Gaia position errors are much too tiny to see!
Example SkyCorr plot
SkyCorr form configuration panel
The configuration options are:
ra_dec_corr
value
supplied in the Gaia source catalogue.