You may think Ein­stein’s the­o­ries have noth­ing to do with you, but with­out them your mo­bile phone would not be able to tell you your lo­ca­tion

Sky at Night Magazine - - MYSTERIOUS GRAVITY -

The satel­lites of the Global Po­si­tion­ing Sys­tem, on which smart­phones and sat­nav rely to de­ter­mine lo­ca­tion, move in highly elon­gated el­lip­ti­cal or­bits around Earth. When each swings in to its clos­est point to the planet, it ex­pe­ri­ences stronger grav­ity and its on-board clock slows down; when it re­cedes to its farthest point from the planet, the clock speeds up. This is ac­cord­ing to Ein­stein’s gen­eral the­ory of rel­a­tiv­ity. How­ever, an ef­fect of Ein­stein’s spe­cial the­ory of rel­a­tiv­ity causes the clocks to slow down when they are mov­ing fastest. Both of these ef­fects must be taken into con­sid­er­a­tion by the soft­ware that, un­be­knownst to you, cal­cu­lates your ex­act lo­ca­tion on the Earth’s sur­face.

Satel­lites in or­bit also have to com­pen­sate for grav­i­ta­tional ef­fects to work prop­erly

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