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The nautical mile (nmi) was originally defined as the arc length of a minute of latitude on a spherical Earth, so the actual Earth's circumference is very near 21600nmi. A minute of arc is π/10800 of a radian. A second of arc, arcsecond (arcsec), or arc second, denoted by the symbol ″, [ 2 ] is 1/60 of an arcminute, 1/3600 ...
Angular resolution. A series of images representing the magnification of M87* with an angular size of some microarcseconds, comparable to viewing a tennis ball on the Moon (magnification from top left corner counter−clockwise to the top right corner). Angular resolution describes the ability of any image-forming device such as an optical or ...
CHARA array. The CHARA (Center for High Angular Resolution Astronomy) array is an optical interferometer, located on Mount Wilson, California. The array consists of six 1-metre (40 in) telescopes operating as an astronomical interferometer. Construction was completed in 2003.
However, Einstein noted in 1915 in the process of completing general relativity, that his 1911 result (and thus Soldner's 1801 result) is only half of the correct value. Einstein became the first to calculate the correct value for light bending: 1.75 arcseconds for light that grazes the Sun. [21] [22]
At radio wavelengths, image resolutions of a few micro-arcseconds have been obtained, and image resolutions of a fractional milliarcsecond have been achieved at visible and infrared wavelengths. One simple layout of an astronomical interferometer is a parabolic arrangement of mirror pieces, giving a partially complete reflecting telescope but ...
Parallax in astronomy. Stellar parallax motion from annual parallax. Half the apex angle is the parallax angle. Parallax is an angle subtended by a line on a point. In the upper diagram, the Earth in its orbit sweeps the parallax angle subtended on the Sun. The lower diagram shows an equal angle swept by the Sun in a geostatic model.
A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10 −6 or 1⁄1,000,000) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is to one second, as one second is to approximately 11.57 days. A microsecond is equal to 1000 nanoseconds ...
Small-angle approximation. Approximately equal behavior of some (trigonometric) functions for x → 0. The small-angle approximations can be used to approximate the values of the main trigonometric functions, provided that the angle in question is small and is measured in radians: These approximations have a wide range of uses in branches of ...