QUIZ-of-the-WEEK QUESTION:
Does the speed of light ever change or is it constant?
CONGRATULATIONS TO THIS WEEK'S GEM SCHOLARS: ALEXIS K. IN VA, CAROLINE H. IN MA, ERIN R. IN KY,  JESSICA D. IN VT, KATHRYN T. IN VA, KELLY B. IN PA, MAGGIE K. IN CT.

September 6, 2002
A: The speed of light in a vacuum is constant.
The speed of light in a vacuum is exactly 299,792,458 m/s (metres per second)

When people refer to the speed of light, they refer to the definition
above - the speed of light in a vacuum.

The speed of light is normally rounded to 300 000 kilometers per second or
186 000 miles per second.

The speed of light depends on the material that the light moves through -
for example: light moves slower in water, glass and through the atmosphere
than in a vacuum. The ratio whereby light is slowed down is called the
refractive index of that medium.

In general, the difference in the speed of light in other mediums is
ignored.