Question: What causes the distance from Earth to the Moon to vary?
Answer: The celestial mechanics of the Moon's motion are very complex. When the distance to the Moon is measured at different times of the month, it is found to vary by more than 10 percent because the Moon's orbit is basically an ellipse, with Earth at one focus. The Moon may come as close as 356,334 kilometers (220,927 miles) to Earth's center and then move as far away from it as 406,610 kilometers (252,098 miles). The dates when the Moon is at apogee (the point in its orbit farthest from Earth) and perigee (the point in its orbit closest to Earth) can be found on each month's calendar page in The Old Farmer's Almanac. However, to understand the "mechanics," as mentioned above, we recommend consulting a basic astronomy textbook.