Naturalists' Worksite

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'

MM J100026.36+021527.9 (a.k.a. "Mambo-9"), is a dusty, star forming galaxy formed when the universe was very young.  The galaxy is so far away that space has expanded during the time it took for light to get here. That expansion has shifted the light from the galaxy by a factor of 5.85. Light that left the galaxy in the visible spectrum (~ 500 nm) reached us with a wavelength of 2.9 micrometres (in the infrared)  In the region that Mambo-9 resides, galaxies are moving away from us at 95.8%

In the last class of Recent Discoveries in Astronony, we discussed dark matter and in one example, the total mass of the galactic cluster Abell 1689. The total mass and hence the amount of dark matter was determined by using the lensing of distant galaxies beyond the cluster.  The question was asked how the astronomers knew the distance to those galaxies and I did not have the answer.  The distance is needed to do the calculation of the mass causing the gravitational