When is sunrise?

Question: At what time is sunrise considered sunrise - I see the sunlight coming in my window yet the sunrise time (posted during the weather report) is still many minutes away?

Answer: According to Joe Ammerman, meteorologist at the National Weather Service in Louisville: Sunrise is defined as “when the leading edge of the sun passes the horizon.” Which horizon is used to set the time is decided by the U.S. Naval Observatory. For Lexington, it is longitude W84.5, latitude N38.1. Go to The Naval Observatory website to check this information from locations across the United States and the world. The naval observatory website also states “the actual times depend on unpredictable atmospheric conditions that affect the amount of refraction at the horizon. Thus, even under ideal conditions (e.g., a clear sky at sea) the times computed for rise or set may be in error by a minute or more. Local topography (e.g., mountains on the horizon) and the height of the observer can affect the times of rise or set even more.”