English: Euclid’s telescope and its optics are designed to deliver a large view of the sky in one shot. This is crucial for a mission whose primary goal is to map, at a high sensitivity, more than one-third of the celestial sphere within six years.
This figure shows an overlay of an image of the Moon on top of an image of the sky recorded simultaneously by the 36 detectors of Euclid’s VIS instrument. The VIS image was obtained in one single shot during the initial months of testing of the spacecraft. It illustrates that the area of the sky that Euclid can observe within one pointing of the telescope, is larger than that of the full Moon. The aperture angle of the Moon’s diameter is approximately 0.5 degrees. Euclid’s gaze captures in one single observation a square area of the sky of about 0.7 times 0.7 degrees.
To achieve this, VIS is equipped with 36 CCDs (Charge Coupled Devices, a type of camera sensor), arranged in a 6x6 grid; each sensor having more than 4000x4000 pixels. The NIPS instrument is fitted with a 4x4 grid of near-infrared sensors of more than 2000x2000 pixels each. While VIS measures the shapes of the galaxies, NISP measures their brightness (and how it changes over wavelengths), requiring a smaller number of detector arrays that have larger pixels.
Euclid is the only telescope that currently can observe such a large area of the sky in one single sitting with such sharpness, in visible and near-infrared light.