Still, when the sun lines up perfectly on the opposite side of the Earth from the moon, as it did on January 4, 1912, it increases the tidal effect slightly.

CNN: The sun, the moon and the Titanic

The overall strength of the moon's gravity, as well as its differential (tidal) effect, is greatest when the moon is closest to the Earth, as on January 4, 1912.

CNN: The sun, the moon and the Titanic

Moons that orbit their planet too closely will experience strong tidal heating and a runaway greenhouse effect that would boil away any surface water.

MSN: News editor