# Galileo's Astronomy and Newton's Gravitation 

## Example 1: the moon is moving right along!

**The Question:** 

How fast is the Moon traveling, using modern parameters?

**The Answer:**

The Moon’s actual distance from the center of the earth used by Newton was $D_M=1,031,400,000$  ft and the period is roughly 30 days, actually 27.3 days, or  $2..36 \times 10^{6}$ seconds (I asked Mr Google). The more modern value for this distances is  $1,261,000,000$ ft,  or $1.26$ billion feet or…  $1.26 \times 10^9$ feet.

So the speed is the distance around divided by the time to go around:

$$
\begin{align*}
v_M &= \frac{
\end{align*}
$$


That’s about 2287 mph. Moving right along, that thing is. You’ll next be asked to do the same thing for a familiar orbiting object.