UNIVERSE
In Big Bang cosmology, the observable universe consists of the galaxies and other matter that can, in principle, be observed from Earth in the present day—because light (or other signals) from those objects has had time to reach the Earth since the beginning of the cosmological expansion
Universe shape Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe is a spherical volume (a ball) centered on the observer, regardless of the shape of the universe as a whole. Every location in the universe has its own observable universe, which may or may not overlap with the one centered on Earth.
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The Big Bang theory developed from observations of the structure of the Universe and from theoretical considerations.
In 1912 Vesto Slipher measured the first Doppler shift of a "spiral nebula" (spiral nebula is the obsolete term for spiral galaxies), and soon discovered that almost all such nebulae were receding from Earth. |
