Hawai'i Observatories Play Critical Role in Adding Color to the Euclid Space Mission

Full color image of a UNIONS field with data from CFHT, Subaru and Pan-STARRS. credit: UNIONS team


What is the Universe made of? What is the mysterious dark matter? How has the structure of the Universe evolved over billions of years? After twelve years of planning, the European Space Agency launched its Euclid satellite from Cape Canaveral, Florida today, with the goal of answering these and many other questions. But Euclid’s incredible dataset will need a big helping hand from observations taken at three observatories in Hawai’i.

The Euclid mission plans to observe billions of galaxies across more than a third of the sky, building a 3D map of the Universe. Unlike the James Webb Space Telescope,, which observes a tiny portion of the Universe in great detail, Euclid will survey a large portion of the sky, to see the entire image. Prior to Euclid’s launch, the work of creating the map began in Hawai’i through the UNIONS project, an ambitious imaging survey of the northern sky in the optical and near-infrared conducted by three Hawai’i based telescopes since 2017: the Canada-France-Hawaiʻi Telescope (CFHT), Japan’s Subaru Telescope on Maunakea, and the University of Hawaiʻi Institute for Astronomy (IfA) Pan-STARRS telescope on Haleakalā, Maui. UNIONS is co-led by Jean-Charles Cuillandre CEA Saclay/Université Paris-Saclay, along with Ken Chambers at the University of Hawaiʻi Institute for Astronomy (IfA), Alan McConnachie at Dominion Astrophysical Observatory (DAO) in Canada, Oguri Masamune at Chiba University in Japan, and Mike Hudson at the University of Waterloo in Canada.

“The superb observing conditions in Hawaiʻi led to the unprecedented collection of galaxies over a very large area of the sky with each telescope playing a critical role by adding different filters or colors to the Euclid data” said Cuillandre, a former CFHT staff astronomer. “While a critical part of the original motivation to obtain the UNIONS data was the Euclid mission, the data will have an impact extending far beyond the space mission.”

By observing more than one-third of the observable sky outside the Milky Way, Euclid will image billions of targets out to a distance of ten billion light years. Astronomers estimate the distances to these galaxies - and thus convert 2-dimensional images to a 3-d map of the Universe - using their observed brightness in different color filters. The more filters are used, the better the distance estimate. But Euclid has only four filters - one that spans most of what we see as visible light, and three that cover infrared wavelengths, beyond what our eyes can see. The Hawaiʻi telescopes will add observations in five visible-light filters, spanning the rainbow from the violet to far-red. In other words, the three Hawaiʻi telescopes turn the black and white 2D images from Euclid into a full color, 3D map of the Universe. Because Euclid is mapping such a huge swath of sky, and ground-based telescopes have different capabilities, multiple observatories have to contribute to provide all the data.

“The idea for one filter from space and additional filters from ground-based telescopes was the Euclid plan from the beginning. Subaru observations add far-red and green, Pan-STARRS adds red and CFHT adds blue, enhancing the one filter images that Euclid will produce. UNIONS is a consortium of telescopes in Hawai‘i,” said Professor Satoshi Miyazaki, director of Subaru Telescope. “ Not only with Euclid, UNIONS scientists are also sharing data to conduct research collaborations based on Hawai‘i.”

Dark matter does not emit light like the more familiar planets, stars, and galaxies. However, dark matter has gravity and can be detected by observing large clusters of galaxies. In some cases, the immense gravity of a galaxy or cluster of galaxies can bend light from an object behind it, known as gravitational lensing. Ground-based observations will assist astronomers working on the Euclid gravitational lensing project.

“I have worked on the Euclid mission for 12 years and it is very satisfying to see the mission launch,” said Jean-Gabriel Cuby, CFHT executive director and Euclid board member. “Much like with the James Webb Space Telescope, Euclid will surprise us and lead to insights we do not fully anticipate. Insights enabled by the efforts of the teams at CFHT, Subaru, and Pan-STARRS.”

The Euclid mission will spend more than 6 years in space to accomplish the mission and involve more than 2,000 scientists, including astronomers in Hawaiʻi. The IfA team is especially interested in using this data to measure the parameters that characterize the properties of the universe.

“The Euclid mission will provide a next generation measurement of these characteristics and we may discover we have made a mistake or series of small mistakes along the way, or we may find that dark energy is more complicated than in Einstein's formulation. Or there might be something else, some new aspect of the universe that we are presently unaware of,” explained Chambers.

The first images from the Euclid mission are expected in around two months. Euclid will build up a large archive of unique data, unprecedented by volume for a space-based mission, enabling research over all disciplines in astronomy. The data will be archived at the Canadian Astronomy Data Center (CADC) and accessible to astronomers around the world. The CADC will also provide color information based on the observations from the Hawaiʻi based telescopes.

"The Euclid images will be beautiful to look at, above and beyond the considerable scientific value of the data. I'm looking forward to seeing them,"said Stephen Gwyn, Science Data Specialist at the Canadian Astronomy Data Centre. “Ultimately, data from the Hawai’i telescopes - CFHT, Subaru, and Pan-STARRS - will turn the images into a three-dimensional map of our Universe.



With the Moon waning, the ground-based telescopes shifted to optical instruments. Using MegaCam, Euclid was observed for 1.5hr on July 11, 2023. The sequence of 26 images (3mn integration each). The GIF animation captures Euclid crossing a single CCD (the video frame is 9' wide and 7' tall), and Jean-Charles Cuillandre (CEA) created a visual to give the context in the sky and the observation. Euclid is moving within the Ecliptic plane and in consequence CFHT captured a couple of moving Solar objects on the line of sight just in that small portion of the MegaCam field-of-view.

Euclid is traveling to L2, a million miles away from the Earth and one of the Earth's Lagrange points. Lagrange points are spots where the forces of gravity of the Sun and Earth form essentially a parking spot for satellites where they sit with minimal orbit corrections. The James Webb Space Telescope is also at L2. In the gif, Euclid is the oblong shape moving through the stars. It’s moving faster than the stars, which is why we see motion in the image. When CFHT takes images of close objects in the solar system, there are two choices— move the telescope at the same speed as the object across the sky (which makes the object its actual shape and the stars look funny) or move the telescope at the speed of the stars (which makes the stars round and the object oblong). In this case, the telescope couldn't fast enough. At Euclid is “only” about 600,000 miles (920,000km) away, so it’s oblong, and the stars are round. The telescope is too small for us to detect its actual shape.

Mahalo to Klaus Merz (ESA), Stephen Gwyn (CADC), Jean-Charles Cuillandre (CEA) and the CFHT observing team for their key contribution to this effort. Image credit: Cuillandre (CEA)

Additional Links

University of Hawai'i News Story
Subaru Telescope News Story

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Mary Beth Laychak
Director of Communications and Community Engagement, Canada-France-Hawai'i Telescope