## Earth, Moon & Sun Moving Through Space

### Question:  When we are laying down on the ground, "being still", how fast are we moving?

Everything in space is moving all of the time.  And it's moving very fast.

But it sure doesn't look like that.

When we look up at the stars, planets and the moon we are seeing a "snapshot in time".  Everything is soooooo very far away -- even the Moon is a quarter of a million miles distance -- that there is no apparent motion.

But when we look at where the moon is night after night we see that 1) it keeps changing shape, and 2) it's moved quite a bit since the night before at the same time of night.  What we are seeing is the moon moving around the earth, one "snapshot" at a time.

Along with the Moon and planets moving around the Sun, the Earth is spinning on it's axis one complete revolution every 24 hours.  This rotation is what makes it look like the Sun and Moon are rising and setting, and the stars and planets appear to move across the night sky.  More about this later.

### Space Mathematics

There are a lot of questions about things moving through space that we can actually quite easily answer for ourselves.  Of course there are a number of place on the internet where we can find the answers, but it's good to know how to make our own estimates when we can.  Somehow it makes the numbers "more real" when we work them out by ourselves.

Once we figure it out we can always find the answer on the web and see how accurate our own calculations are.

There are some simple formulas that will work just fine for us.  Our calcs don’t have to be exact.  It’s fine for our curiosity to simplify our parameters to get a ball park figure.

### Let's keep it simple

Although the Moon’s and the planets’ orbits are actually ellipses, if we pretend that they are circles, then the calculations are simplified and the answers will be close enough for us to get a sense of the magnitude.

The formula for the circumference of a circle is:

C = 2piR   or   C = piD  (D = Diameter)

C = the Circumference of the circle.  The distance around the circle.

R = the Radius of the circle.  Distance from the center to  the      circumference.

pi = pi is the ratio of the Circumference of the circle to the Diameter.  It is always 3.14159....  That means that in every circle the circumference is 3.14159...  times longer than the circle is wide.

Although they have tried to find the EXACT value of Pi, even carrying the calculations out to billions of places on super-computers, they have not come to "the end'.

For our calculations we will use 3.14 as the value of pi.

### Doing the math

The Navigation Bar to the right offers some very informative Space Math problems worked out in a nice, simple form so we can learn how fast we are actually moving – even when we think we're "standing still".