Q. How are the times of sunrise and sunset determined for the weather report? What if my location is well above sea level and hilly?

A. What goes into the forecast is based on calculation, not observation, and the calculation is done without reference to local topography or visibility.

The National Weather Service gets its sunrise and sunset times from data computed by the United States Naval Observatory.

The conventional definition for both is the time at which the upper edge of the disk of the Sun meets the horizon. Atmospheric conditions are assumed to be average, and the observer is assumed to be at sea level with an unobstructed view.

The observatory’s calculations do include corrections for visibility and for the average amount of refraction, or light bent by the atmosphere. But it is not practical to include exact local conditions in routine computations of sunrise and sunset.