if Earth rotates so fast, why does it always look still from outer space?

Question

if Earth rotates so fast, why does it always look still from outer space?

In: 0

Answer 1

The numbers you’re hearing are linear speed, not angular speed.

vᵣ=rω where v is the linear speed, r is the radius of rotation and ω is the angular speed.

For earth, r = 3950 mi, and ω = 15°/h. This gives vᵣ= 3950×15×π÷180=1034.107666 mi/h (π÷180 is just a unit conversion) at the equator. Sound familiar?

Now, what really matters is ω – that 15°/h. This is half the angular speed of the hour hand on a clock. The hour hand on a clock goes around twice in a day, which works out to 30°/h. That’s not a movement we can easily perceive when viewed from altitudes like the one the *Blue Marble* photo was taken at, the perspective we have of the earth is very similar to the perspective we have of a clock. The angular speed is just slow enough we can’t perceive it.

Edit: unit errors in my math