NORFOLK, Va. — The old saying goes “it’s not the heat, it’s the humidity!” And while that may be true, it’s only half of the story. It’s the “dew point” that really matters. But what is the dew point?

Dew point/relative humidity questions come up fairly often and this is a good one. Water vapor in the atmosphere is pretty important for deep-sky observing and photography. The atmosphere can only ...

The dew point temperature (or simple dew point) is the air temperature at which the air is totally saturated with water vapor. Let’s take it step by step. As air is heated, its ability to hold water ...