How Euclid will scan the sky

A missive from Euclid High Command arrived yesterday confirming that ESA’s Euclid mission would be launched by SpaceX on a Falcon 9 rocket on a date between July 1st and July 30 (2023). It will soon be time to start getting nervous!

I also noticed that another video has appeared on the Euclid public website showing how the satellite will work. It’s not a traditional general-purpose observatory on which different users bid for time to observe different objects (as is the case for JWST, for example) but a dedicated mission that will compile a systematic survey with very specific science goals.

Euclid scans across the sky using a ‘step-and-stare’ method, combining separate measurements to form the largest cosmological survey ever conducted in the visible and near-infrared. Each time Euclid ‘stares’, its telescope points to a position in the sky, performing imaging and spectroscopic measurements on an area of approximately 0.5 deg² around this position. After each stare, the telescope steps to a new position.

This way the instruments will scan over a total of around 35% of the sky. This is the largest area over which one can guarantee a a complete detection of the galaxies necessary for Euclid’s cosmological studies. The rest of the sky is dominated by the high density of bright stars in our galaxy, and by the dust in the plane of our Solar System, both of which get in the way of the cosmology observations.

I hope this clarifies the situation.


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