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Re: Vernal Equinox Re: day 3000 of 3rd
by Karl Palmen
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Dear Calendar People
See http://www.timeanddate.com/worldclock/sunearth.html
, which shows where it is daylight and where it is night,
Karl
10(06(24
From: East Carolina University Calendar
discussion List [mailto:CALNDR-L@...] On Behalf Of Irv
Bromberg
Sent: 20 March 2009 12:44
To: CALNDR-L@...
Subject: Re: Vernal Equinox Re: day 3000 of 3rd
On
2009.03.19, at 19:56 , Brij Bhushan Vij wrote:
However, Vernal Equinox is the point in time when SUN is directly over head and causing EQUAL 12-hours in TWO hemispheres of Earth.
The
only way that you'll reckon a 12-hour day and 12-hour night on the day of the
vernal equinox is if you use an equatorial sundial to reckon the time!
(Some
other types of sundials may also yield such readings also, but I'm less
familiar with them.)
The
ancients considered day and night equal on the day of an equinox because they
used sundials to reckon time.
If
you use a clock that proceeds at the rate of mean solar time, then the daytime
will be approximately 30 minutes longer than the nighttime.
Daytime
will be about 12h 15m, nighttime about 11h 45m.
The
exact amounts depend on the observer's latitude, and when is the actual moment
of the equinox in relation to sunrise and sunset at the observer's locale.
Due
to atmospheric refraction, when Sun is at the horizon it appears to be higher
than its actual geometric position.
Also,
Sun appears as a disk almost 1/2° in diameter, and it is daytime when any part
of that disk is above the horizon.
If
Earth had no air, and if Sun were a bright point of light, then yes, on the day
of an equinox the length of day and night would be equal.
OK,
so 3000 days have now ELAPSED since the beginning of the 3rd millennium, and
the northward equinox happened about an hour ago as I write this...
Scanned by iCritical.
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