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The
Speed of Light
-
Galileo
tried to measure (unsuccessfully) the speed of light (early 1600s)
-
Romer
measured speed of light using eclipses of Jupiter's moons in 1676
-
period
of moon's orbits were known
-
went
behind Jupiter (eclipsed) at regular intervals
-
about
6 months later, the eclipses were happening 16.5 minutes late!
-
Romer's
value can be expressed in minutes per AU since the precise value of 1 AU
was not known at the time (what was Romer's number?)
-
Fizeau
and Foucalt measured the speed of light more precisely in 1850. Modern
value:
c
= 299,792.458 km/s
c
= 3 x 105 km/s
c
= 3 x 108 m/s
-
Implications
in everyday life:
-
Thunder
and lightening
-
Sound
has a speed too, about 0.3 km/s or 600 mi/hr
-
Thunder
is delayed relative to lightening
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