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5th century BC – Democritus proposes that the bright band in the night sky known as the Milky Way might consist of stars. 4th century BC – Aristotle believes the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which ...
Size (left) and distance (right) of a few well-known galaxies put to scale. There are an estimated 100 billion galaxies in all of the observable universe. [1] On the order of 100,000 galaxies make up the Local Supercluster, and about 51 galaxies are in the Local Group (see list of nearest galaxies for a complete list).
One of the galaxies is an ungravitationally bound background object. The other "galaxy" is instead an extension of the interacting system — a tidal stream caused by the merger. The group is, therefore, more properly called HCG 79; the name refers to the visual collection and not the group. HCG 79 lies 190 million light-years away in the ...
The timeline of the Universe lists events from its creation to its ultimate final state. For a timeline of the universe from the present to its presumed conclusion, see: Timeline of the far future Chronology of the universe
Cosmic inflation expands space by a factor of the order of 10 26 over a time of the order of 10 −36 to 10 −32 seconds. The universe is supercooled from about 10 27 down to 10 22 Kelvins. [18] The strong interaction becomes distinct from the electroweak interaction. Electroweak epoch ends 10 −12 s 10 15 K (150 GeV)
In this map of the Observable Universe, objects appear enlarged to show their shape. From left to right celestial bodies are arranged according to their proximity to the Earth. This horizontal (distance to Earth) scale is logarithmic.
c. 16th century BCE – Mesopotamian cosmology has a flat, circular Earth enclosed in a cosmic ocean. [1]c. 15th–11th century BCE – The Rigveda of Hinduism has some cosmological hymns, particularly in the late book 10, notably the Nasadiya Sukta which describes the origin of the universe, originating from the monistic Hiranyagarbha or "Golden Egg".
Friedrich Bessel successfully uses the method of stellar parallax, the effect of Earth's annual movement around the Sun, to calculate the distance to 61 Cygni, the first star other than the Sun to have its distance from Earth measured. Bessel's is a truly accurate measurement of stellar positions, and the parallax technique establishes a ...