In the summer of 2016, the Milky Way doubled in size.

By which we mean, the number of stars it was previously believed to contain was found to be only about half what it actually contains.

It was around that time when the first batch of data from Gaia — a space telescope that’s been scanning the sky since July 2014, capturing images using a one billion pixel camera — was released.

“There’s maybe 100, 200, 300 billion stars, near the high end of that range,” says Professor Gerry Gilmore, from Cambridge University, in the UK.

“What we know is that there’s maybe twice as many stars as we previously thought, and that’s just in the bit of the Milk Way that Gaia has measured.”

Gilmore is head of the team at Cambridge’s Institute of Astronomy using the images from Gaia — 120 billion in its first 14 months — to make the most detailed and accurate map of our home galaxy ever.

“The fact that Gaia has such high spatial resolution, (it) can tell the difference between two or three stars that are very close together, but nevertheless are separate stars, whereas previously from our images from the ground, blurry sort of things, it merged into what we thought was one star.”

By the end of its five year mission, Gaia will have observed each part of the sky 70 times, and measured the exact position of the stars, their distances, and their motions. This will enable the European team that designed and are operating the mission, to create a three-dimensional structural map of at least one billion stars, or about half the Milky Way galaxy.