<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I was watching a great show on Einstein’s miracle year the other night and I thought I heard the scientist who was narrating say that special relativity is why we are constantly adjusting the clocks on satellites. Is this correct? I could see the need for course corrections, but time adjustments? If this is true are the adjustments different depending on which direction relative to the Earths rotation the satellite is traveling? D.K.A. <br />Posted by dkaakd</DIV><br /><br />There are actually two corrections, one caused by the speed around the earth, and another caused by the earth's lower gravity at that height. They partially cancel out, so the net correction is something like 37 microsends a day. We just discussed that in another thread, I'll see if I can find it. Note particularly that one effect is due to SPecial Relativity, and the other is due to General Relatively. It's astounding Einstein figured this out in his head befroe there was a way to test it. Now that GPS satellites are in widespread use, millions of pople prove his theories every day!</p><p> </p><p>Yes speedfreak posted this in the time dilation thread:</p><p>"</p><p>From
<font size="2">Real-World Relativity: The GPS Navigation System </font></p><p>"The current GPS configuration consists of a network of 24 satellites in high orbits around the Earth. Each satellite in the GPS constellation orbits at an altitude of about 20,000 km from the ground, and has an orbital speed of about 14,000 km/hour (the orbital period is roughly 12 hours - contrary to popular belief, GPS satellites are not in geosynchronous or geostationary orbits).</p><p>Because an observer on the ground sees the satellites in motion relative to them, Special Relativity predicts that we should see their clocks ticking more slowly. Special Relativity predicts that the on-board atomic clocks on the satellites should fall behind clocks on the ground by about 7 microseconds per day because of the slower ticking rate due to the time dilation effect of their relative motion</p><p>Further, the satellites are in orbits high above the Earth, where the curvature of spacetime due to the Earth's mass is less than it is at the Earth's surface. A prediction of General Relativity is that clocks closer to a massive object will seem to tick more slowly than those located further away. As such, when viewed from the surface of the Earth, the clocks on the satellites appear to be ticking <em>faster</em> than identical clocks on the ground. A calculation using General Relativity predicts that the clocks in each GPS satellite should get ahead of ground-based clocks by 45 microseconds per day.</p><p>The combination of these two relativitic effects means that the clocks on-board each satellite should tick faster than identical clocks on the ground by about 38 microseconds per day (45-7=38)! This sounds small, but the high-precision required of the GPS system requires nanosecond accuracy, and 38 microseconds is 38,000 nanoseconds. If these effects were not properly taken into account, a navigational fix based on the GPS constellation would be false after only 2 minutes, and errors in global positions would continue to accumulate at a rate of about 10 kilometers each day."</p><p>MW</p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
Basic Error: The accelerating Universe conclusion - reason
The US is now at risk of losing to China in the race to send people back to the Moon’s surface
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