How we see the Universe Expansion.

 

As we look out into our universe we (astronomers) see billions of galaxies. A most impressive image made by the Hubble space telescope of the galaxy cluster Abell 370.  That is Abell 370 below with lots galaxies and distorted lensed background galaxies.  Everything in the image is a galaxy.  

Abell 370 is xxx Mpc from Earth. z = 0.375  4 billion ly away in Cetus.

Hubble telescope has taken some images of the most distant galaxies known 

The Image below is only 2.3' x 2' arc and required 22.5 days of exposure time from July 2002 thru March 2012. Location in the Constellation of Fornax: position: RA = 03h 32m 38.5s, dec = -27° 47' 0.0"

The eXtreme Deep Field, or XDF the  deepest image of the universe ever taken and contains about 5,500 galaxies even within its smaller field of view.

More than 2,000 images of the same field were taken with Hubble's two premier cameras – the Advanced Camera for Surveys and the Wide Field Camera 3, which extends Hubble's vision into near-infrared light – and combined to make the XDF. reveals galaxies that span back 13.2 billion years in time. The youngest galaxy found in the XDF existed just 450 million years after the universe's birth in the big bang.

Magnificent spiral galaxies similar in shape to our Milky Way and the neighboring Andromeda galaxy appear in this image, as do the large, fuzzy red galaxies where the formation of new stars has ceased. These red galaxies are the remnants of dramatic collisions between galaxies and are in their declining years. Peppered across the field are tiny, faint, more distant galaxies that were like the seedlings from which today's striking galaxies grew. The history of galaxies – from soon after the first galaxies were born to the great galaxies of today, like our Milky Way – is laid out in this one remarkable image.

[From https://hubblesite.org/contents/media/images/2012/37/3098-Image.html ]

 

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