The European Space Agency's galaxy-mapping Gaia probe has reached the end of its mission.
Over more than a decide, Gaia recorded the positions, motions and colours of more than a billion stars in the Milky Way.
From the data, precise three dimensional maps have been produced that are transforming our understanding of the Galaxy.
And as a bonus, Gaia's data is also providing tremendously useful resources for amateur astronomers and astrophotographers.
During January and February 2025, Gaia underwent a series of end-of-mission engineering tests.
These put the spacecraft into an orientation where its sunshield reflected more sunlight towards Earth than previously, making it feasible for amateurs to photograph it.
And that's exactly what I set out to do.
Getting the image
I captured this ground-based image showing ESA's Gaia spacecraft amongst the stars from a garden in suburban Surrey in the UK.
It shows the track of the spacecraft relative to the stars during an almost complete passage across the sky, from 20:30 UTC on 4th February 2025 to 05:30am UTC on 5th February.
During the shoot, a total of 250 frames were captured at intervals of a little over 2 minutes.
I then combined all of these frames to produce the background image of stars and sky.
To produce the track of the Gaia spacecraft in the image, I selected every third frame – 84 in total – with spacing of a little over 6 minutes between each.
The full frame version of the image provides a field of view of approximately 1.3 degrees across its width.
I also produced a cropped version to focus in more closely on Gaia.
About the image
Gaia is in a large orbit around the L2 Lagrange Point, which is about 1.5 million kilometres away from Earth in the direction opposite to the Sun. Its orbital period is about 6 months.
The sinuous shape of Gaia’s track in the image and the changing apparent speed of movement (seen in the variation in spacing between the dots) are both almost entirely a result of a parallax effect caused by Earth's rotation.
This seems fitting, given that Gaia’s data allowed distances to the stars to be calculated using parallax measurements.
Towards both ends of the track, Gaia appears gradually fainter and more orange in colour.
Earth’s atmosphere causes both these effects, which come into play more strongly when the spacecraft is low down in the sky.
In addition, the early part of the track (the upper right end) was affected somewhat by clouds. This can be seen in the variable brightness of the dots there.
Gaia’s measurements of the colours of stars was used by the processing software to calibrate the colour balance of the image.
Considering what the Gaia mission has done for astronomy and our understanding of the night sky – from mapping the positions of stars in our Galaxy, asteroids (and their moons) and black holes – it's a fitting tribute that night-sky observers and imagers like me were given the chance to see this wonderful spacecraft for ourselves.
Technical details
- Altair Hypercam 26C camera (operating at –20°C)
- Sky-Watcher 200mm Newtonian
- Sky-Watcher AZ-EQ6 mount, autoguided
- Baader MPCC coma corrector
- Image acquisition: NINA, PHD2
- Image processing: PixInsight, Photoshop
- Exposure: per frame, 60 seconds at 1000mm, f/5.1, gain 200
More ground-based images of Gaia can be seen via ESA's Cosmos Portal.
If you're an astrophotographer, whether beginner or experienced, don't forget to send us your images and they could appear in a future issue of BBC Sky at Night Magazine.
