What are 'Standard International units'?
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Strange Attractor, c/ PO Box 9, Fitzroy, VIC 3065, AustraliaThe seven Système International d'Unités (SI) base units: second, mole, metre, kilogram, kelvin, candela, ampere (National Physical Laboratory)The seven Système International d'Unités (SI) base units: second, mole, metre, kilogram, kelvin, candela, ampere (Wikipedia)The base units (Bureau International des Poids et Mesures)The SI system kicked off after 1799 (The National Institute of Standards & Technology)Moon Unit Zappa, child of Frank Zappa (Wikipedia)The 'cubit' was the length from the tip of one's middle finger to the bottom of the elbow (Wikipedia)History of length measurement: From cubits to lasers (National Physical Laboratory)A history of all the weird units of measurement from ye olde ancient times (Encyclopaedia Britannica)A history of the kilogram (National Physical Laboratory)Standard time was introduced from the mid-1800s around the world with the coming of the railways (Wikipedia)The Allegheny Observatory used to provide accurate time updates via telegraph in North America (Wikipedia)A history of timekeeping devices (Wikipedia)The second used to be defined as 1/86,400 of a day, but now it's "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" (Wikipedia)A brief history of the second (The National Institute of Standards & Technology)"A new optical clock ticks so consistently that if it had started at the dawn of the universe, it would have lost less than two minutes" (The Independent)The strontium optical clock (OSA Publishing)Where are atomic clocks? They're everywhere now (HyperPhysics, Georgia State University)Clock synchronisation around the world is really important for computers & stuff (Wikipedia)International Atomic Time tells us at which speed our clocks should tick (Time and Date)What is needed to synchronise time across atomic clocks in the world? (Quora)How to improve time accuracy on iPhone & Apple Watch (iPhone Tricks)Security implications of the humble computer clock (Network World)Who invented the second? Claudius Ptolemy around 150 C.E. (Reference)Why is a minute divided into 60 seconds, an hour into 60 minutes, yet there are only 24 hours in a day? (Scientific American)The book Johnny was talking about by Dava Sobel: 'Longitude: The true story of a lone genius who solved the greatest scientific problem of his time' (Wikipedia)See John Harrison's original clocks in the museum at Greenwich, London (Royal Museums Greenwich)We had the second for ages, then the kelvin was first defined in 1743, the kilogram & metre followed in 1793, the amp in 1881, the mole in 1900, & the candela in 1946, but they've been refined now (Wikipedia)The metre was originally defined as one ten-millionth of the distance from the equator to the North Pole (Wikipedia)The metre is now defined as the distance travelled by light in 1/299,792,458th of a second (Wikipedia)A brief history of the metre (The National Institute of Standards & Technology)The speed of light: 299,792,458 metres per second (Encyclopaedia Britannica)People debating pool tolerance & why timing isn't more accurate in swimming (Reddit)Meet the kilogram - a.k.a 'La Grande K' or 'Big K' (Wikipedia)There did used to be someone who went around checking stuff - the 'city meter' - "checking both the weights of goods as sold & the accuracy of the metal weights used" (Hall Genealogy Website)The International Prototype Kilogram (IPK) & its copies - Australia has one (Wikipedia)If someone knocks a chunk off the IPK, the definition of a kilogram changes (Wikipedia)A list of the prefixes for metric units of measurement: e.g. 'kilo' just means a thousand (The National Institute of Standards and Technology)"The magnitude of many of the units comprising the SI system...are highly dependent upon the stability of a 137-year-old, golf-ball-sized cylinder of metal stored in a vault in France" (Wikipedia)The new kilogram is due out in 2018 - stay tuned (The National Institute of Standards and Technology)Redefining the kilogram: Mass, Planck & Einstein (The National Institute of Standards and Technology)Redefining the kilogram: The 'Watt balance' (The National Institute of Standards and Technology)After a fraught few years, experiments to redefine the kilogram have reached agreement (Nature)What is a mole? Not the burrowing kind with small eyes (The National Institute of Standards & Technology)Avogadro's number & the mole (Wikipedia)What is a mole & why are moles used? (About Education, Chemistry)Hello kelvin - this unit is 1/273.16 of the thermodynamic temperature of the triple point of water (The National Institute of Standards & Technology)What is the triple point of water? (Wikipedia)What is Celsius? (Wikipedia)Deep breath: "The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, & placed 1 metre apart in a vacuum, would produce between these conductors a force equal to 2 x 10-7 newton per metre of length" (The National Institute of Standards & Technology)What is the difference between voltage & current (amperes)? (The Charging Point)Everything you wanted to know about charging your iPhone or iPad (Apple, Communities)iPhone & iPad chargers appear to be around 1-2 amps according to this (Apple, Communities)I believe you now Johnny: Turns out the coloured rings for electric toothbrushes really are to tell family members' brush heads apart (Electric Teeth)Meet the candela, "the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1,012 hertz & that has a radiant intensity in that direction of 1/683 watts per steradian" (The National Institute of Standards & Technology)What is black body radiation? (Cosmos, Swinburne University)We can use luminous intensity to measure how far away stars are (Science, How Stuff Works)'Intrinsic luminosity' is how bright something is & 'apparent brightness' is how bright it looks - knowing these details helps us measure how far away stars are (Department of Astronomy & Astrophysics, Penn State)Stellar brightness (Department of Astronomy, The Ohio State University)Brightness, luminosity & the magnitude scale (Department of Astronomy, Cornell University)What is a standard candle? (Cosmos, Swinburne University)(non SI) Units for quantities that describe biological effects (Bureau International des Poids et Mesures)The future - proposed redefinition of SI base units (Wikipedia)A more fundamental International System of units (Physics Today)Corrections
Sorry Johnny, you got latitude & longitude mixed up - latitude is north-south, longitude is east-west (Encyclopaedia Britannica)Cheeky review? (If we may be so bold)
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