Today is Valentine's Day. I hope you enjoy it with a sweetheart. Remember the sky is free and always available for sharing with another.

Tonight the nearly five-day-old crescent moon is in the western sky after sunset at 6:09 p.m.

A crescent moon is a beautiful naked-eye sight, but it is even more spectacular if you view it in a small telescope. In my opinion, the moon looks more impressive through a small telescope than it does on the best of photographs. Along the terminator of the moon, partially lit craters stand out in bold relief and are stunning even at very low powers.

Do not confuse the moon's terminator with Arnold Schwarzenegger's "Terminator."

The moon's terminator is the dividing line between the lit and unlit portions of the moon.

When the moon is in a waxing (growing more lit) phase, the terminator is the sunrise line slowly moving along the moon's surface. When the moon is in a waning (growing less lit) phase, the terminator is the sunset line moving slowly along the moon's surface.

Craters and mountains on the moon on the terminator are lit by a low-altitude sun either rising or setting on the moon. They cast long shadows and stand out far more than when the moon is full and the sun is overhead on the moon. At full moon, craters and mountains cast very shallow shadows and are much more difficult to discern.

The moon sets tonight at 10:54. If you look toward the south and southwest at that time, you can see Orion the Hunter, Canis Major the Greater Dog, Canis Minor the Lesser Dog, and overhead Gemini the Twins.

What a way to finish off Valentine's Day.

Moon Watch

The moon is a waxing (growing larger) crescent attaining first quarter on Sunday.

Contact Tim Hunter at skyspy@azstarnet.com