On Friday, 18 March 2016 07:08:24 UTC, vidcapper wrote:
On 18/03/2016 04:14, Tudor Hughes wrote:
On Friday, 18 March 2016 00:40:43 UTC, jumper wrote:
Why is the spring equinox on the 20th March, when at my location
today we had 12 hrs daylight / nighttime? On the 20th March we
have 12hrs 12 mins daylight.

--- This email has been checked for viruses by Avast antivirus
software. https://www.avast.com/antivirus

Refraction. When the sun appears to be on the horizon it's
geometrically below it by just over half a degree because the rays
are bent downwards due to the higher density of the atmosphere at
lower levels.

But the earth rotates at 15°/hr, so it would only take 2 minutes to turn
half a degree, not enough to account for the 12 minute difference
noted above...


--

Paul Hyett, Cheltenham

The sun's path relative to the horizon is not at right angles, not in these latitudes so it takes longer than the theoretical 2.2 minutes for the sun to rise or set. At 52° the figure is 2.2/cos 52 (at the equinoxes) which is 3.6 minutes at each end of the day, total 7.2 minutes which is about the figure. At the pole the sun would rise over a day earlier than straightforward geometry would indicate.

Tudor Hughes