Orwell Astronomical Society (Ipswich)
Gaia Astrometric Satellite, 30 January - 23 February 2025
ESO's astrometric satellite Gaia was launched on 19 December 2013. Its purpose was to measure the positions, distances and motions of stars with unprecedented precision. On 08 January 2014, the craft entered an L2 Earth-Sun orbit (approximately 1.5 million km from Earth on the opposite side to the Sun) and, on 25 July 2014, it began scientific operations.
In January 2025, the craft exhausted the nitrogen gas which it used to maintain orientation. Scientific operations ended, and ground controllers manoeuvred the craft in a way which made it much brighter, increasing its magnitude from approximately 21 to approximately 15, putting it within the scope of observations by amateur astronomers. More details on the visibility of Gaia.
On 30 January there was a spell of clear weather. Observations were possible during a two-hour period, which terminated when cloud returned. Gaia was at a distance of 1.4 million km and I could detect it in individual 60 second exposures, estimating it at between magnitude 15.6 and 16.
On 02 February I observed the craft again. At this time, it was at approximately magnitude 15.6.
At the end of the month, Gaia was still undergoing technology tests following termination of observations. On 22 February, I had another attempt at observing it. The craft was described as medium bright, between magnitudes approximately 15 and 21. I found that it was no longer visible in individual 60 second frames but was marginally visible in a stack of 250 such frames (all aligned on its expected position), below. I estimate its magnitude as 19 or so (a guess, as I have no means of measuring it).
There will be one last opportunity to see Gaia at circa magnitude 15 on 04 March 2025.
Nigel Evans