Photometry of a photometer

Abstract

In this draft photometry and astrometry is presented from the Herschel Space Observatory (HSO). This spacecraft orbits the second Lagrangian point (L2) of the Sun -- Earth system, yielding a mean distance of a million miles (~ 1.5 million kms) for HSO. From such a distance, HSO is observable as a 17-23 magnitude object moving relatively fast (apparently several arcseconds in a minute) and the actual observed brightness highly depends on the spatial orientation of the spacecraft. This draft describes briefly how observations from this observatory and the subsequent data reductions have been carried out. Our conclusion is really reassuring, namely the brightness variations of HSO are in accordance with the publicly available reported logs and target coordinates of this spacecraft.