In Astronomy, which etymologically means law of the stars, (from Greek: αστρονομία = άστρον + νόμος) is a science involving the observation and explanation of events occurring outside Earth and its atmosphere. It studies the... astronomy, the cosmic light horizon is a " For the television programme, see Horizon. For the frigate, see Horizon. For the JPL Horizons Ephemeris System, see JPL Horizons Ephemeris System. For the Epcot attraction, see Horizons. Horizon The horizon is the line that separates earth from sky. More precisely, it is the line that divides all of the... horizon" which marks the edge of the The deepest visible-light image of the cosmos. Hubble Ultra Deep Field. Image Credit: NASA, ESA, S. Beckwith (STScI) and the HUDF team. In the first half of the 20th century, the word universe was used to mean the whole spacetime continuum in which we exist, together with all the... visible universe. This horizon is the edge of a For other uses, see sphere (disambiguation). A sphere is, roughly speaking, a ball-shaped object. In non-mathematical usage, the term sphere is often used for something solid (which mathematicians call ball). But in mathematics, sphere refers to the boundary of a ball, which is hollow. This article deals with... sphere, centered upon the Earth, also known as the Earth or Terra, is the third planet outward from the Sun. It is the largest of the solar systems terrestrial planets, and the only planetary body that modern science confirms as harboring life. The planet formed around 4.5 billion (4.5×109) years... Earth, which is approximately 13.7 billion A light year, abbreviated ly, is the distance light travels in one year: roughly 9.46   1012 kilometres (9.46 petametres, or about 5.88   1012 miles). More specifically, a light year is defined as the distance that a photon would travel, in free space and... light years or 130 A yottametre (American spelling: yottameter) (symbol: Ym) is a unit of length equal to 1024 metres. Yottametres could be used for measuring intergalactic distances, but astronomers have been long accustomed to use light-years and parsecs instead. 1 Ym is equal to 105700000 light-years or 32408000 parsecs diameter of... Ym in The word radius (Latin for wheel spoke; plural radii, pronounced ray-dee-eye) has several meanings in English: In classical geometry, a radius of a circle or sphere is any line segment with one endpoint on the circle (i.e., the circular boundary) and the other at the center of... radius; this figure is sometimes referred to as the "lookback distance" because Wikipedia does not yet have an article with this exact name. Start the AstroNomer article If you have created this page in the past few minutes and it has not yet appeared, it may not be visible due to a delay in updating the database. Please wait and check again... astronomers, who view distant objects, are "looking back" into the History is a term for information about the past. When used as the name of a field of study, history refers to the study and interpretation of the record of human societies. The term history comes from the Greek ιστορία historia, an account of... history of the The deepest visible-light image of the cosmos. Hubble Ultra Deep Field. Image Credit: NASA, ESA, S. Beckwith (STScI) and the HUDF team. In the first half of the 20th century, the word universe was used to mean the whole spacetime continuum in which we exist, together with all the... universe since it takes 13.7 billion years for the light to reach Earth. The general homogeneity of Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. General description The formal properties of temperature are studied in thermodynamics. Formally, temperature is that property which governs the transfer of thermal... temperatures, at the edge of the cosmic horizon, is part of the Evidence is: Any observable event which tends to prove or disprove a proposition, see scientific method and reality. In law, any testimony (eg. oral or written statements, such as an affidavit), exhibit (eg. physical objects) or other documentatry material which is admissible (ie. allowed to be considered by the trier... evidence for the " According to the Big Bang theory, the universe originated in an infinitely dense and physically paradoxical singularity. Space has expanded with the passage of time, objects being moved farther away from each other. In cosmology, the Big Bang theory is the scientific theory that concerns the early development and shape... Big Bang".

See also:

• The comoving distance or conformal distance of two objects in the universe is the distance divided by a time-varying scale factor representing the expansion of the universe. As a result the comoving distances on average are not increasing with time. The scale factor is usually taken to be one... comoving distance
• Cherenkov effect in a swimming pool nuclear reactor. The effect is due to electrons moving faster than the speed at which light moves in water. The speed of light (denoted as c, reputedly from the Latin celeritas, speed, and also known as Einsteins constant) in a vacuum is exactly... Speed of light