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The comoving distance from an observer to a distant object (e.g. galaxy) can be computed by the following formula (derived using the Friedmann–Lemaître–Robertson–Walker metric): = ′ (′) where a(t′) is the scale factor, t e is the time of emission of the photons detected by the observer, t is the present time, and c is the speed of ...
A light-year, alternatively spelled light year ( ly or lyrr [3] ), is a unit of length used to express astronomical distances and is equal to exactly 9,460,730,472,580.8 km ( Scientific notation: 9.4607304725808 × 10 12 km), which is approximately 5.88 trillion mi.
In acoustics, the sound pressure of a spherical wavefront radiating from a point source decreases by 50% as the distance r is doubled; measured in dB, the decrease is still 6.02 dB, since dB represents an intensity ratio. The pressure ratio (as opposed to power ratio) is not inverse-square, but is inverse-proportional (inverse distance law):
Trilinear coordinates. In geometry, the trilinear coordinates x : y : z of a point relative to a given triangle describe the relative directed distances from the three sidelines of the triangle. Trilinear coordinates are an example of homogeneous coordinates. The ratio x : y is the ratio of the perpendicular distances from the point to the ...
Distance moduli are most commonly used when expressing the distance to other galaxies in the relatively nearby universe. For example, the Large Magellanic Cloud (LMC) is at a distance modulus of 18.5, [ 2 ] the Andromeda Galaxy 's distance modulus is 24.4, [ 3 ] and the galaxy NGC 4548 in the Virgo Cluster has a DM of 31.0. [ 4 ]
109.36 yd. 3 937.0 in. The hectometre ( International spelling as used by the International Bureau of Weights and Measures; SI symbol: hm[ 1]) or hectometer ( American spelling) is a unit of length in the International System of Units (SI), equal to one hundred metres [ 2] and to one tenth of a kilometre. The word comes from a combination of ...
The distance (or perpendicular distance) from a point to a line is the shortest distance from a fixed point to any point on a fixed infinite line in Euclidean geometry. It is the length of the line segment which joins the point to the line and is perpendicular to the line. The formula for calculating it can be derived and expressed in several ways.
The great-circle distance, orthodromic distance, or spherical distance is the distance between two points on a sphere, measured along the great-circle arc between them. This arc is the shortest path between the two points on the surface of the sphere. (By comparison, the shortest path passing through the sphere's interior is the chord between ...