Astronomical Objects, Near and Far

The Hubble Ultra Deep Field (HUDF) is the “deepest” optical observation of the Universe: eleven days of Hubble Space Telescope observations concentrated on a tiny patch of sky.

I recently came across this three-dimensional mockup of the HUDF, using our measurements of the redshifts (related to the distances) of each of the galaxies in the field. I assume that these are what we call “photometric redshifts”, using broad measurements of the color of a galaxy to estimate its distance, rather than the much more difficult spectroscopic redshifts that give much more accurate results. Also, the galaxies are, I think, not to scale: there is somewhat more empty space in the Universe — I’m possibly wrong about this, as per Ted Bunn’s comment below. (Unfortunately, I couldn’t find much information on how or by whom the video was put together, although it refers to the site and to NASA/ESA animations.)

Today is also the peak of the summer Perseid meteor shower. If you haven’t looked already, you should be able to see it at dusk tonight. Even Google has taken notice.

One response to “Astronomical Objects, Near and Far”

  1. Ted Bunn avatar

    I’m not an expert on this, but the scale (size of galaxies relative to spacing between them) looks OK to me. I think bright galaxies are spaced out, on average, about a few Mpc apart from each other, which is ~100 times their diameters. By eye, the movie doesn’t look far off from that.