Photometry of a photometer

TL;DR

This paper presents photometric and astrometric observations of the Herschel Space Observatory from its L2 orbit, confirming brightness variations align with reported logs and demonstrating observational methods from a distant spacecraft.

Contribution

It provides a novel methodology for photometry and astrometry of a spacecraft from Earth-based observations at L2, validating the observed brightness variations against official logs.

Findings

Brightness variations match reported logs

Observational techniques effective at L2 distance

Data reduction methods successfully applied

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.