Thanks for the very fascinating question. I had no idea that this was the case.
The first thing I did was check a sunrise/sunset chart for 2005.
Rhode Island - Sunrise Sunset Chart
And, indeed the days that straddle the 12 hours between sunrise and
sunset point are March 16th and 17th!
The next thing I did was research facts about the Vernal Equinox. What
I found was the following:
The vernal equinox - fact and fiction
Quote: "'Equal night'... more or less: Equinox translates to 'equal
night.' Twice a year the sun shines directly on the equator, providing
equal amounts of light and darkness all over the earth. The vernal, or
spring, equinox usually occurs on March 20 or 21, and the autumnal
equinox takes place on September 22 or 23. You would think, then, that
we would have exactly 12 hours of daylight on March 20, right? Not
exactly. Due to the refraction of the sun's rays through our
atmosphere, the sunrise we see precedes the actual sunrise, and the
apparent sunset arrives similarly later to our eyes, so we actually
have a few minutes of extra daylight on the equinox. Strange, but
Confirming this information and adding other interesting details is:
Quote: "The discrepancy arises from the frame of reference for each
event. On the day of an equinox, the geometric center of the sun
crosses the equator, and this point is above the horizon for 12 hours
everywhere on Earth....But the sun is not simply a geometric point,
it's a disk. Sunrise is calculated when the leading edge of the sun's
disk becomes visible on the horizon, and sunset is the instant when
the trailing edge of the disk disappears below the horizon....As the
edge of the sun appears or disappears, the actual center of the sun's
disk is below the horizon. In addition, the refraction or bending of
light by the atmosphere causes the sun to appear higher in the sky
than it would if Earth had no atmosphere. This combination adds up to
several minutes at sunrise and sunset to account for the discrepancy."
Search Strategy (on Google):
* "sunset chart" 2005
* equinox before March 21
* equinox "equal amounts"
I hope this helps!