Limits of Human Detection

Galaxy Eye by ~darkening (http://darkening.deviantart.com/art/Galaxy-Eye-37360468)

Science released an article a year ago which stated the farthest galaxy we have detected (Link).  This was done by Hubble's Ultra Deep Field exposure lasting 87 hours and the galaxy was 13.2 billion light years away or 77 sextillion miles.  This is incredible to imagine, our ability to see back into the infancy of the known universe.  To put this to scale, the new observation is 100 millions year further into the past than the previous record holder, made three months prior to this observation (October 2010).  This still needs direct spectroscopic observation to truly confirm its distance.  However, the concept is amazing and this got me searching for other extremes on seeing objects near and far.

Without the use of telescopes the human eye can actually see some far away galaxies.  The Andromeda Galaxy has an apparent magnitude, relative to a viewer on earth, of 3.44.  The apparent magnitude measurement is logarithmic and Wikipedia has a full chart here.  It can be seen on a clear night and is 2.5 million light years from Earth.   If it's a very clear night, then the Triangulum Galaxy, 3.14 million light years away, can be observed (Link). 

The naked human eye can theoretically see an amoeba or paramecium, which are close to the smallest things we can see at about 100 microns or micrometers (Link).  At a standard distance for eyesight acuity testing, 6 meters, a human eye can separate 1 arc minute or distinguish 2 lines set 1.75 millimeters apart (Link Video).  How about the smallest things we can "see" with technology and science?  Our current understanding is that quarks are the smallest building blocks of matter (Link).  There are also particles we can detect that don't have mass like photons but understanding what makes an atom is much more complicated.  The LHC aims at describing the constituents of matter down to one twenty thousandth of the size of a proton or the zeptometer range (Link).  Just think how our range of detecting objects small and far has changed over time and what we may be able to see in the future.