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So if the matter that originally emitted the oldest CMBR photons has a present distance of 46 billion light-years, then the distance would have been only about 42 million light-years at the time of decoupling. The light-travel distance to the edge of the observable universe is the age of the universe times the speed of light, 13.8 billion light ...
The human eye discards what it sees from split-second to split-second, but photographic film gathers more and more light for as long as the shutter is open. The resulting image is permanent, so many astronomers can use the same data. It is possible to see objects as they change over time (SN 1987A is a spectacular example).
Visible-light astronomy has existed as long as people have been looking up at the night sky, although it has since improved in its observational capabilities since the invention of the telescope, which is commonly credited to Hans Lippershey, a German-Dutch spectacle-maker, [1] although Galileo played a large role in the development and ...
The light-month, roughly one-twelfth of a light-year, is also used occasionally for approximate measures. [37] [38] The Hayden Planetarium specifies the light month more precisely as 30 days of light travel time. [39] Light travels approximately one foot in a nanosecond; the term "light-foot" is sometimes used as an informal measure of time. [40]
The particle horizon is the boundary between two regions at a point at a given time: one region defined by events that have already been observed by an observer, and the other by events which cannot be observed at that time. It represents the furthest distance from which we can retrieve information from the past, and so defines the observable ...
As an example, the Milky Way is roughly 100,000–180,000 light-years in diameter, [54] [55] and the nearest sister galaxy to the Milky Way, the Andromeda Galaxy, is located roughly 2.5 million light-years away. [56] Because humans cannot observe space beyond the edge of the observable universe, it is unknown whether the size of the universe in ...
This is followed shortly by Haidinger's brush." He commented that not all observers see it in the same way. Some see the yellow pattern as solid and the blue pattern as interrupted, as in the illustrations on this page. Some see the blue as solid and the yellow as interrupted, and some see it alternating between the two states.
The Hubble length or Hubble distance is a unit of distance in cosmology, defined as cH −1 — the speed of light multiplied by the Hubble time. It is equivalent to 4,420 million parsecs or 14.4 billion light years. (The numerical value of the Hubble length in light years is, by definition, equal to that of the Hubble time in years.)