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Lettris is a curious tetris-clone game where all the bricks have the same square shape but different content. Each square carries a letter. To make squares disappear and save space for other squares you have to assemble English words (left, right, up, down) from the falling squares.
Boggle gives you 3 minutes to find as many words (3 letters or more) as you can in a grid of 16 letters. You can also try the grid of 16 letters. Letters must be adjacent and longer words score better. See if you can get into the grid Hall of Fame !
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1.the distance light travels in a vacuum in one second; approximately 300,000 kilometers
unité de longueur (fr)[Classe]
light second (n.)
|299.79×103 km||299.79×106 m|
|2.0040×10−3 AU||31.688×10−9 ly|
|US customary / Imperial units|
|186.28×103 mi||983.57×106 ft|
A light-second is a unit of length useful in astronomy, telecommunications and relativistic physics. It is defined as the distance that light travels in free space in one second, and is equal to exactly 299,792,458 metres. It is just over 186,000 miles and almost 9.84×108 feet.
Just as the second forms the basis for other units of time, the light-second can form the basis for other units of length, ranging from the light-nanosecond (just under one U.S. or imperial foot) to the light-minute, light-hour and light-day, which are sometimes used in popular science publications. The more commonly-used light-year is also presently defined to be equal to precisely 31557600 light-seconds, since the definition of a year is based on a Julian year (not Gregorian year) of exactly 365.25 days, each of exactly 86400 SI seconds.
|“||The metre is the length of the path traveled by light in vacuum during a time interval of 1⁄299792458 of a second.||”|
Communications signals on Earth rarely travel at precisely the speed of light in free space, but distances in fractions of a light-second are still useful for planning telecommunications networks as they indicate the minimum possible delay between sender and receiver.
The light-second is a convenient unit for measuring distances in the inner Solar System, because it corresponds very closely to the radiometric data used to determine them (the match is not exact for an Earth-based observer because of a very small correction for the effects of relativity). The value of the astronomical unit in light seconds is a fundamental measurement for the calculation of modern ephemerides (tables of plantary positions): it is usually quoted as "light-time for unit distance" in tables of astronomical constants, and its currently accepted value is 499.004786385(20) s.
Multiples of the light-second can be defined, although apart from the light-year they are more used in popular science publications than in research works. For example, a light-minute is 60 light-seconds and the average distance from the Earth to the Sun is 8.317 light-minutes.
|light-second||2.997924580×108 m||2.998×105 km||1.863×105 mi||average distance from the Earth to the Moon is about 1.282 light-seconds|
|light-minute||60 light-seconds||1.798754748×1010 m||1.799×107 km||1.118×107 mi||average distance from the Earth to the Sun is 8.317 light-minutes|
= 3600 light-seconds
|1.079252849×1012 m||1.079×109 km||6.706×108 mi||semi-major axis of Pluto's orbit is about 5.473 light-hours|
= 86400 light-seconds
|2.590206837×1013 m||2.590×1010 km||1.609×1010 mi||Sedna is currently 0.52 light-days from the Sun; on an orbit that varies from a perihelion of 0.44 light-days to an aphelion of 5.41 light-days|
= 604800 light-seconds
|1.813144786×1014 m||1.813×1011 km||1.127×1011 mi||The Oort cloud is thought to extend between 41 and 82 light-weeks out from the Sun|
= 31557600 light-seconds
|9.460730473×1015 m||9.461×1012 km||5.879×1012 mi||Proxima Centauri is the nearest star to the Sun, about 4.24 light-years away|