The solar rotation produces an apparent movement of any
feature of about 10¢¢ in an hour at the sun centre.
Considering that the typical duration of a CDS observation is one hour,
rastering over a region of the order of one arc min, the solar rotation
is often a non-negligible effect in observations near sun-centre, and is further
complicated by the differential rotation of the solar corona.
CDS has feature tracking software, which moves the entire instrument, but
since the accuracy of the movements is much less than the spatial resolution,
it is not generally recommended.
CDS software note #45 details the limitations, but in
short these are:
1) The minimum E-W movement is approximately 2¢¢.
2) the actual movement may often be 2¢¢ ±2¢¢ with the result that the
effect may be `worse than doing nothing', depending on what effect was
intended.
3) The default interval for updating the pointing is 600 seconds. If an
individual raster duration is less than this, no correction will ever
occur.
