No, I’m not referring to the ever-popular Twilight movies.
I’m talking about that time of day when the sun is shining light into our atmosphere — just before sunrise and just after sunset.
However, few people realize that there are actually 3 different definitions of twilight:
- Civil Twilight: This refers to the period of time when the sun is 6 degrees below the horizon. It’s before the morning civil twilight and after the evening civil twilight when artificial outdoor lighting is generally needed to conduct outdoor activities. The horizon is clearly seen and bright stars can be made out if the moon is not up.
- Nautical Twilight: At this point, the sun is 12 degrees below the horizon in the morning or in the evening. You might be able to see the outlines or profiles of objects on the ground without the use of other light, but it’s too dark too really see any detail well. The horizon is not well seen.
- Astronomical Twilight: With the sun 18 degrees below the horizon, any type of sunlight virtually cannot be seen in the sky before morning astronomical twilight or after evening astronomical twilight.