Draw a horizontal line and write
'east' at the left end and 'west'
at the right end. Now draw in
the path of the Sun across the
sky.
Answers
Astronomical twilight is defined when the sun's center is 18 degrees below the horizon, nautical twilight is at 12 degrees, and civil is at 6 degrees. According to www.weatherunderground.com, today's (January 12th) twilight times are as follows: Astronomical twilight began at 5:46 a.m. and ended at 6:20, nautical began at 6:20 and ended at 6:56, and civil began at 6:56, then sunrise was at 7:28 a.m. Since they are all segments of 6 degrees of rotation, how can the times between them be different? Additionally, if the average time it takes to travel 6 degrees is 34 minutes, and there are 60 groups of 6 degrees, it would mean that there are 2,040 minutes in a day, which isn't true, there are only 1,440. How can these things be explained?
You ask some good questions. This will take a little time to explain.
Let me start by trying to draw a picture showing the path of the Sun through the sky. In the figure below, I'm standing in the middle of a big, flat field, looking to the South (away from the viewer, so you see the back of my head). It's late in the afternoon, and the Sun is starting to set in the western portion of the sky. I've drawn in gold the path the Sun makes as it rises in the East, reaches its highest point at noon, then sets in the West.
can't see the Sun at night, because it lies below the horizon, and its light is blocked by the body of the Earth. But if I could make the Earth into a transparent sphere of glass, I would see the Sun at all times, and I could draw the path it makes: rising in the East, reaching a maximum altitude in the South at noon, setting in the West, then dropping farthest below the horizon to the North at midnight, and then climbing up again towards the East for the next day's sunrise.
