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length unit
subject			fact

length unit	is a unit of length
	is a kind of unit
unit	has historical origin
	represents

Kinds of length unit :

• angstrom (6 facts) (Å) - A unit of length used when expressing wavelengths.
• astronomical unit (9 facts) (AU) - Mean distance between the Earth and the Sun: 1.495985 × 10¹¹ m., The AU is the preferred unit for distances within the solar system. Mercury, the innermost planet, lies on average 0.39 AU from the Sun; Pluto, normally the farthest planet, lies on average 39.5 AU from the Sun., The mean distance between the Earth and the Sun. The astronomical unit is defined as the length of the radius of the unperturbed circular orbit of a body of negligible mass moving around the Sun with a sidereal angular velocity of 0.017202098950 radian per day of 86400 ephemeris seconds. AU = 1.496 × 10¹³ cm ≈ 500 lt-sec., The mean distance from the earth to the sun, equal to 92.81 million miles or 499.012 light-seconds., The radius of a circular orbit in which a body of negligible mass, and free of perturbations, would revolve around the Sun in 2π / k days, where k is the Gaussian gravitational constant. This is slightly less than the semi-major axis of the Earth's orbit.
• Bohr radius (12 facts) (a₀, a₀) - A unit of length based on the radius of the first Bohr orbit of hydrogen 1.
• fermi (7 facts) - A unit of length., A unit of distance used for describing nuclear distances just as the ångström is used for atomic distances.
• light-year (9 facts) (lt-yr, ly) - Distance traveled at the speed of light for one Earth-year: 9.46 million million km., The distance light travels in one year: 5.88 trillion miles, or 9.46 trillion kilometers. The nearest star system to the Sun is 4.3 light-years away., The distance light travels in one year, equal to 5.8 × 10¹² (about six trillion) miles., The distance traveled in a vacuum by light in one year, equal to 9.46 × 10¹⁷cm., The distance that light traverses in a vacuum during one year., The distance light travels in a vacuum in 1 year. 1 lt-yr = 9.4605 × 10¹² km = 0.307 pc (c = 299792.46 km s^-1 = 186274 miles s^-1). (1 lt-min ≈ 0.13 AU.)
• meter (9 facts) (m) - A unit of length. The meter is the length equal to 1650763.73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p₁₀ and 5d₅ of the Krypton-86 atom., length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second
• micron (5 facts) (μ) - A unit of length.
• mile (2 facts) - The mile employed in this book is the statute mile, equal to 5280 feet.
• nautical mile (3 facts) - A unit of length.
• parsec (14 facts) (pc) - A unit used by astronomers to describe stellar distance. It is the distance from which the radius of the earth's orbit would subtend an angle of one second of arc. Alternatively one parsec is the distance at which one astronomical unit subtends one second of arc. The name was proposed by Professor H. H. Turner (1861-1930), Savilian Professor of Astronomy at Oxford., The distance at which one astronomical unit subtends an angle of one second of arc; equivalently, the distance to an object having an annual parallax of one second of arc. (abbreviation for parallax second), Astronomical unit of distance, equal to 3.26 light-years., The distance at which one astronomical unit subtends an angle of 1 second of arc. 1 pc = 206,265 AU = 3.086 × 10¹³ km = 3.26 light-years.
• solar radius (3 facts) - A unit of length based on radius of Sun