Nella notte su mercoledì gli orologi atomici di tutto il mondo si fermeranno un secondo per “aspettare” la Terra. Il movimento di rotazione del nostro pianeta viene infatti progressivamente rallentato dall'attrito di oceani, maree e atmosfera. Il primo luglio durerà così un secondo in più.
Gli orologi atomici sono più precisi rispetto alla Terra e per questo motivo, progressivamente ma ad intervalli impossibili da prevedere, la rete di osservatori che misura la rotazione della Terra e che costituisce il “Servizio internazionale sulla rotazione terrestre e i sistemi di riferimento” (IERS) decide che è il momento di fermare gli orologi atomici per un secondo per sincronizzarli con il movimento della Terra.
Il secondo in più è stato introdotto il 30 giugno 1972 (il primo luglio per l'Italia). Da allora è accaduto per 25 volte, l'ultima delle quali nel 2012. Quest'anno i 350 orologi atomici di tutto il mondo faranno scattare il secondo in più alla mezzanotte del 30 giugno (le due del mattino del primo luglio in Italia). In questo modo la misura standard registrata dal Tempo Coordinato Universale (UTC) verrà “riallineata” con la rotazione terrestre.
RG delle 18.30 del 30.06.15; il servizio di Elisa Raggi
RSI Svizzera 30.06.2015, 20:13
Red.MM/ATS/Swing
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