120 Chapter 2 From the Solar System to the Milky Way
Kant brought about a revolution in epistemology by providing a rebuttal to the existing
assertion of empiricists at that time—that all knowledge and concepts held by mankind arise
through experience. Kant asserted that cognitive contents provided through experience are
processed intellectually, enabling people to continue to gain further knowledge or new con-
cepts (this is considered to be a synthesis of rationalism and empiricism).
Kant also turned his thoughts toward the universe. He became aware of the disc-
shaped model of the galaxy early on and wrote that the reason systems like the Milky Way
galaxy can be seen is that stars are often organized in a lens-shaped pattern. Incidentally,
Herschel may have read this and may have begun counting stars to try to scientifically prove
Kant’s idea, but we don’t know for sure.
Kant’s greatest insight related to understanding the universe is his hypothesis that the
entire universe contains many “island universes,” which are systems (or collections) of stars
like the many islands in the ocean. The stars that mankind had observed until then were
just one island universe called the Milky Way. Kant suggested that there were also countless
other similar island universes, which together constituted the whole universe.
In the latter half of the 18th century, when Kant was active, many other nonstellar
heavenly bodies came to be known because of advances in observation technology. These
were named nebulas because they shone faintly like clouds.
For example, the “Great Andromeda Nebula” and the Large and Small Magellanic
Clouds, which are classified today as galaxies, exist in ancient records, since they could
be seen even by the naked eye. However, soon after telescopes were available, it became
apparent that these objects that were thought to be cosmic clouds were actually uncount-
able collections of stars.
If the Milky Way is considered to be a collection of stars and the galactic structure is
explained on that basis, then a nebula is also probably a cluster of stars. Kant’s theory was
really quite insightful.
*
How Did Technology for Observing the Universe
Progress?
Mankind’s conception of the universe has changed and developed over time based on
observational science as well as logical reasoning. The results of astronomy throughout the
19th and 20th centuries, after Herschel, are presented in Chapter 3. This section gives a
simple overview of the technology we use today to generate new observational data.
We’ve already mentioned that telescopes were invented at the beginning of the 17th
century and that Galileo built one himself and made many discoveries with it. Amazingly,
given how crude such early telescopes were, Galileo was able to observe some of the faint
stars composing the Milky Way galaxy and thus prove Democritus‘s theory that the Milky
Way was an aggregation of stars. In 1612, the German astronomer Simon Marius observed
the Andromeda galaxy (in those days, the “Great Andromeda Nebula”), which appears next
to the Milky Way in the night sky, but he still did not recognize that it was an aggregation of
stars. If he had discovered at that time that Andromeda was the same as the Milky Way, the
structure of the universe might have become clearer much sooner.
* However, we should note that Kant expanded upon the unique ideas found in Thomas Wright’s An Original Theory or
New Hypothesis of the Universe (1750). In this work, which precedes Kant’s hypothesis, Wright proposes that we are
immersed within a “flat layer of stars.”

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