time

Question 1:  The Sun appears to be about 0.5° in diameter.  On the equator, approximately how long does it take for the Sun to set, from first contact with the horizon to complete disappearance below the horizon?

If the sun appears to be about 0.5 in diameter, once the sun has made contact with the horizon, I believe it would take about 2 minutes for it to disappear below the horizon completely. This is due to the fact that our planet rotates 360 within a 24 hour period. So you would take the 360 degrees divide it by 24 hours in a day, which equals 15. Meaning, we’re rotating at 15 degrees per hour. 15 degrees divided by 0.5 (sun’s diameter) = 30 then divide 60 (minutes in an hour) by 30 and you get 2.

Question 2:     If you were standing on the South Pole at the time of the autumnal equinox, where would you expect the Sun to be at midday?   Here are some possible options:  A)    in your zenith,  B)     23.5° above the horizon,  C)     well below your horizon,  D)    on your horizon.

The sun crosses the celestial equator halfway around during the autumnal equinox. At that time, Earth’s axis of rotation is perpendicular (at a 90 degree angle) to the line joining the sun to the earth. (similar to the vernal equinox). With that being said, if you were standing on the South Pole during the autumnal equinox, it would be on your horizon midday. This is also because during this event the day and night are of equal length.