Euclid’s wide and deep surveys

This graphic shows the location of the fields on the sky that will be covered by Euclid's wide (blue) and deep (yellow) surveys. The sky is shown in the Galactic coordinate system, with the bright horizontal band corresponding to the plane of our Milky Way galaxy, where most of its stars reside.

Euclid is an ESA mission that will image billions of galaxies across the Universe to investigate dark matter and dark energy mapping the past ten billion years of our cosmic history. The largest fraction of the mission's observations will be devoted to a wide survey, covering more than one third of the sky.

The portions of the sky that will be covered by the wide survey are outlined by in blue in this image. Other regions are avoided because they are dominated by Milky Way stars and interstellar matter, or by diffuse dust in the Solar System – the so-called zodiacal light. The wide survey is complemented by a deep survey, taking about 10% of the total observing time and repeatedly observing just three patches of the sky called the Euclid Deep Fields, highlighted in yellow in this image.

The Euclid Deep Field North – highlighted in yellow, towards the top left in this view – has an area of 20 square degrees and is located very close to the Northern Ecliptic Pole, in the constellation Draco, the dragon. The proximity to the ecliptic pole ensures maximum coverage throughout the year; the exact position was chosen to obtain maximum overlap with one of the deep fields surveyed by NASA's infrared workhorse, the Spitzer Space Telescope.

The Euclid Deep Field Fornax – highlighted in yellow, in the lower right of the image – spans 10 square degrees and is located in the southern constellation Fornax, the furnace. It encompasses the much smaller Chandra Deep Field South, a 0.11 square degree region of the sky that has been extensively surveyed in the past couple of decades with NASA's Chandra and ESA's XMM-Newton X-ray observatories, as well as the NASA/ESA Hubble Space Telescope and major ground-based telescopes.

The third and largest of the fields is the Euclid Deep Field South – highlighted in yellow, between the Large Magellanic Cloud and the Euclid Deep Field Fornax. It covers 20 square degrees in the southern constellation of Horologium, the pendulum clock. This field has not been covered to date by any deep sky survey and so has a huge potential for new, exciting discoveries. It has been planned to be observed from the ground by the Vera C. Rubin Observatory.

[Image description: This is an oval image showing a projection of the night sky with fields that will be covered by Euclid’s survey. Blue patches show Euclid’s wide survey, and yellow spots depict the deep surveys. An horizontal bright line in the oval shows the plane of our Milky Way where most stars reside.]