Hubble Ultra-Deep Field fly-through

Today's image at NASA's Astronomy Picture of the Day site inspires one's sense of wonder:


Several times now the Hubble Space Telescope has taken an extremely long-exposure image while aimed at an apparently empty patch of sky. In this case the total exposure was 412 orbits, with each orbit lasting 97 minutes. The resulting image is of very distant galaxies as they looked in a much earlier stage of the universe, when the light started on its journey to us.

The universe is expanding and the farther away a galaxy is, the faster it's moving away from us. The Doppler effect that lowers the pitch of a receding siren similarly lengthens the wavelengths of light from those receding galaxies. Since the longest wavelengths we can see are red, this effect is called "red shift," but it doesn't mean the galaxies look reddish; it means that the pattern of spectral lines is shifted in that direction.

In order to create this animation, each galaxy's red shift was converted into a distance based on the Hubble Constant, a relationship between distance and speed originally worked out by Edwin Hubble, the astronomer the telescope is also named for, and significantly revised since then based on new measurements.

More links:
Today's NASA Astronomy Picture of the Day (APOD)
NASA APOD website
Technical details on the Ultra-Deep Field

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