ESA drops first test images from Euclid and they are dizzyingly good

31 Jul 2023

The 'grism' image taken by Euclid. Image: ESA/Euclid Consortium (CC BY-SA 3.0 IGO)

Euclid has sent home its first images while testing instruments on board the telescope and scientists are very pleased with what they see.

The European Space Agency (ESA) has released the first images taken by Euclid, the space telescope on a mission to make a 3D map of the night sky, indicating that the instruments on board are working well.

Released to the public today (31 July), the set of early test images are based on “minimum system tuning” and are not examples of what eventual images produced by the mission will look like. However, scientists involved in the endeavour are impressed by their quality nonetheless.

“After more than 11 years of designing and developing Euclid, it’s exhilarating and enormously emotional to see these first images,” says Euclid project manager Giuseppe Racca.

“It’s even more incredible when we think that we see just a few galaxies here, produced with minimum system tuning. The fully calibrated Euclid will ultimately observe billions of galaxies to create the biggest ever 3D map of the sky.”

Euclid was blasted into space on 2 July by the powerful SpaceX Falcon 9 rocket to probe some of the most mysterious aspects of our universe – dark matter and dark energy. Together, they account for an estimated 95pc of the universe. While invisible, astronomers have been able to infer their existence by measuring their influence on the behaviour of stars and galaxies.

Now, the latest images are a promising indication that Euclid is on track to achieve its mission objectives, and maybe even more.

“I’d say these images are absolutely amazing given that they were taken during the commissioning phase and the instruments aren’t fully tweaked yet,” Peter Coles, an astrophysicist based in Maynooth University, tells

“Over the next few weeks there will be a performance verification phase which will tell us how good Euclid will be at meeting its science goals.”

So far so good

One of the images is a highly detailed black-and-white glimpse into a small part of the night sky that cover about a quarter of the width and height of the moon. It was taken by Euclid’s Visible Instrument that is to take super-sharp images of billions of galaxies to measure their shapes.

Another, taken by the near-infrared spectrometer and photometer (NISP) aboard Euclid, is an early glimpse of the instrument’s ability to show us exactly how far away each galaxy is by measuring the brightness of light entering Euclid at a specific infrared wavelength. Both images can be seen on the ESA website here.

However, perhaps the most impressive of the first images – and Coles’ personal favourite – is the second image that has emerged from the NISP, in which light from Euclid’s telescope had passed through a ‘grism’ before it reached the detector.

The device splits light from every star and galaxy by wavelength, so each vertical streak of light in the image is one star or galaxy. This allows us to determine what each galaxy is made of and eventually evaluate its distance from Earth.

“But so far, it’s all looking very good indeed,” Coles added. “I’ve only ever seen simulations of what would come out and it’s very exciting to see what the real thing will look like!”

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The ‘grism’ image taken by Euclid. Image: ESA/Euclid Consortium (CC BY-SA 3.0 IGO)

Vish Gain is a journalist with Silicon Republic