Sunrise & Sunset

DAY: Roughly, the time it takes for the Earth to complete one rotation on its axis.

Back to top

SUNRISE: Sunrise is the time at which the leading edge of the Sun first rises above the horizon.

SUNSET: Sunset is the time at which the trailing edge of the Sun disappears below the Horizon.

Note: As sunrise and sunset are calculated from the leading and trailing edges of the Sun (and not the center), this slightly lengthens "day" relative to "night".

This also extends full days of sunlight around the summer solstice - and provides more sunlight around the winter solstice - even though the Sun can be mostly hidden below the horizon.

If the Sun was like a light bulb that turned "on" or "off" when the middle of it hit the horizon, the days of full sunlight and full darkness would be equal (See June 21 and Dec. 22 on the Arctic Circle).

Back to top

TWILIGHT: This is light from the sky when the Sun is just below the horizon - such as we see just before the Sun comes up in the morning and just after it sets in the evening.

In the polar regions twilight also occurs when the Sun comes to just below the horizon - but does not come up high enough to actually rise.

Think of twilight as having enough light to not have to turn your lights on.