In 1838, the first measurement of
the distance to a star was made by
Friedrich Bessell. He used the "Parallax
Technique" - a method of determining
the distance to a star by measuring the
angle or the apparent shift in its
position. The star 61 Cygnus was
measured to be 11.4 light years away.
In the 1800s, astrophotography and
spectroscopy (the study of the interaction
of matter and the wavelengths of light) made
it possible to research the composition
of stars from a distance. This
contributed to the establishment and
advancement of what we now know as
astrophysics (a branch of astronomy that
employs the principles of physics and
chemistry to ascertain the nature of
astronomical objects, rather than their
positions or motions in space).
A simplified illustration of the parallax of an object against a distant background due to a perspective shift. When viewed from "Viewpoint A", the object appears to be in front of the blue square. When the viewpoint is changed to "Viewpoint B", the object appears to have moved in front of the red square.
1925: Cecilia Payne discovered that
hydrogen is the most abundant
element in the Sun's atmosphere, and
accordingly, the most abundant
element in the universe.
1929: The existence of the Earth's
galaxy, the Milky Way, as its own group
of stars was proven along with the
existence of "external" galaxies. The
observed recession of those galaxies
led to the Edwin Hubble’s discovery of
the "Expansion of the Universe" and
Georges Lemaître’s formulation of the
“Big Bang Theory”.