The fall equinox is just a few days away
marking the end of summer and the beginning of autumn
and everybody remembers what the equinox is because of its name
equinox: latin for "equal night"
it's the time of year that comes once in March
and once in September
in which night and day are the same length, everywhere in the world.
Lies, friends. All lies.
I know! That's what the name says that it is
and that's what most of us were taught in schools
but science, guys
science is always making sure that stuff is more interesting than it sounds.
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for starters, the equinox isn't even a day
it's a moment
a specific moment of astronomical alignment
when the earth's axis is exactly perpendicular to the sun
neither pointing toward it or away from it
this alignment occurs when the geometric center of the sun
is directly above the equator.
now, on these days it is indeed true
that the center of the sun appears above the horizon for twelve hours
but for several reasons, the day is actually longer than the night.
the first reason is that the sun is just freakin huge
so at sunrise the disk of the sun appears above the horizon
several minutes before the center does
and likewise, even after the center drops below the horizon in the evening
it's not officially sunset until the top edge of the disk disappears.
secondly, we observe the sun
through our beautiful, breathable atmosphere
which refracts the sun's rays
so we can actually see the top edge of the sun before it even rises above the horizon
in the morning, and in the evening
we can see it for a few minutes after it has actually set.
this causes every day, including the days of the equinoxes,
to appear at least six minutes longer
than it physically is
and also, helps cause some awesome sunsets,
so you can thank it for that too.
And both of these effects are actually
amplified the farther away you get from the equator
if you're sittin' with your butt on the equator
watching the path of the sun on equinox day
you'd see that both at sunrise and sunset
it would intersect with the horizon at exactly ninety degrees
but at higher latitudes, the angle of the sun's approach to the horizon gets smaller
and the sun takes a lot longer to rise and set
at a shallow angle than when it's going straight up and down.
So you put these effects together
and it seems like it starts to add up:
for example, in Quito, Ecudaor, just below the equator
the length of an equinox day is about twelve hours and six point five minutes
In Shanghai, at thirty degrees north latitude,
it's twelve hours and eight minutes
and in St. Petersburg, Russia, at sixty degrees north latitude, it's twelve hours and sixteen minutes
Not a huge difference but still
the 'nox' is not quite 'equi'
Stupid Latin! Also stupid astronomers always making up Latin terms
that aren't quite accurate.
This makes me so angry!
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