In many movies dealing with satelites orbiting the earth, the orbits are shown not as straight lines, but more of a wave shape. Why is this? Shouldnt the orbit be shown as a circle around the earth. I know that it may appear a little different since the charts and maps are two dimensional but I figure that should produce a barber pole effect and show stripes, but not a sine wave. Any input?
The sine wave effect is because the earth is rotating underneath the orbiting satellite. What you are seeing is the path of the satellite over the surface of the earth. The satellite reaches the northernmost point of its orbit at the same point in space, but over a different point on the earth’s surface.
An orbit is usually almost circular, with the center of the circle at the center of the earth. If the orbit is in the plane of the earth’s equator, when you draw the orbit on a Mercator projection map (rectangular world map), the orbit is just a straight line - the equator. Now, what if the orbit was tilted? If it’s tilted “up” (north) around America, the other side would have to tilt down (south) near Africa. If you draw that on a world map, you have a wavy line that crosses the equator in the Pacific, goes up to North America, crosses the equator again in the Atlantic and goes down to the Indian Ocean or thereabouts. So you have a single sine curve.
But the earth is actually rotating beneath this orbit. Say on the first orbit, at its northern limit the satellite is above Florida. On the next orbit, when it comes to the northern limit it is probably above California. If you draw successive orbits on the same map, you have multiple sine waves spaced regularly apart.
To see real-time satellite and spacecraft plots (including the wavy ground traces), go to this url:
http://liftoff.msfc.nasa.gov/RealTime/JTrack/Spacecraft.html