Autumnal Equinox and GPS

[GroundBound]

It would appear that the autumnal equinox is on 23rd September. The equinox is when day and night are equal length, yes? So, I presume that means that sunset is 12 hours after sunrise.

On my GPS, for 23 September, sunrise is shown as 05:28 utc and sunset as 17:40 utc. i.e 12 hours and 12 minutes. So the night is shorter than the day.

Now, on 26th September, sunrise is 05:33 and sunset 17:33 - equal day and night.

A quick visit on the web to a selection of world clocks and almanacs confirms the times in my GPS.

So why isn't the 26th September the equinox? Or else, the equinox is not the date on which day and night are equal.

Or is it just me?

GB

[UV]

To do with Leap years and other problems.
See here..
http://scienceworld.wolfram.com/astr...alEquinox.html
UV

[bookworm]

Originally Posted by GroundBound

So why isn't the 26th September the equinox? Or else, the equinox is not the date on which day and night are equal.

The equinox is defined by a 12 hour period between the geometric centre of the sun passing through the horizon. However, the atmosphere bends light slightly, so apparent sunset or sunrise occurs when the sun is geometrically about 0.57 degrees below the horizon. Hence the day is slightly longer than 12 hours.

http://aa.usno.navy.mil/faq/docs/RST_defs.html

[Ringway Flyer]

It all depends on exactly where you are.... just have a look at the variations in SR and SS times across the UK in your flight guide. If you REALLY want to get confused, try 'Google-ing' sundials!