No, definitely not. First, it can only possibly happen when the moon is at its point in orbit where it is directly opposite the earth from the sun. This only occurs once per orbit (called the synodic month - approximately 29.5 days). If the moon rotated around the earth in the same plane as the earth rotates around the sun (picture all three objects lying on a flat surface like a table, tracing out their almost-circular orbits), then there would be an eclipse every month (at every full moon). However, those orbits are NOT in the same plane. The moon's orbit is inclined approximately 5 degrees from that of the earth around the sun (the latter is called the ecliptic plane). Thus, the moon is only in the same plane as the earth and the sun once every ~13.7 days (that's half of a sidereal month - the time it takes the moon to rotate around the earth. It differs from the synodic month because the earth's movement around the sun doesn't matter for the sidereal month). In order for a lunar eclipse to occur, BOTH of those situations have to occur: the moon must be at its furthest point from the sun in its rotation (i.e. the moon must be full), and it must be at the point in its orbit when it is very close to the ecliptic.
|