One of the reasons for launching the Hubble Space Telescope in
1990 was to eliminate the filter of the atmosphere that affects
earth-bound observations of the night sky. The results speak for
themselves: more than 10 000 peer-reviewed papers using Hubble
data, around 98% of which have citations (only 70% of all
astronomy papers are cited). There are plenty of other filters
at work on Hubble's data: the optical system, the electronics of
image capture and communication, space weather, and even the
experience and perceptive power of the human observer. But it's
clear: eliminating one filter changed the way we see the cosmos.
What is a filter? Mathematically, it's a subset of a larger set.
In optics, it's a wavelength-selection device. In general, it's
a thing or process which removes part of the input, leaving some
output which may or may not be useful. For example, in seismic
processing we apply filters which we hope remove noise, leaving
signal for the interpreter. But if the filters are not under our
control