- A blood moon lunar eclipse wasn't always something
to look forward to.
When the moon turned red thousands
of years ago, the ancient Mayans
and Mesopotamians feared that something monstrous
and evil was eating the moon.
They would shout at the night sky
to try and fend off the ravenous beasts
and since the average lunar eclipse lasts
around 100 minutes, and the moon returns
to normal afterward, they were probably convinced
that their whooping and howling actually worked.
We know now that the moon doesn't need our protection,
but why does it turn red in the first place?
Whenever you look up at a full moon,
you're seeing sunlight that's reflected
off the lunar surface,
so if something were to block that sunlight
say, the earth, then in theory,
the moon should disappear from view
but during a total lunar eclipse
when the moon passes through the earth's shadow,
we get a red moon, not a vanishing one.
So what's going on?
To figure it out, let's take a quick trip
to the lunar surface.
This is a NASA simulation of what the earth looks like
during a total lunar eclipse.
Notice the red ring around our planet.
Everywhere you see that ring is either a sunrise
or a sunset, and while it's true that no direct
sunlight is reaching the lunar surface
at this moment, earth's atmosphere is bending
the red wavelengths of light around the planet,
so that redness you see during a blood moon eclipse
is a combination of light from every sunrise
and sunset on earth, all happening at once.
So the moon appears red for the same reason
that sunrises and sunsets on earth are red
because of a phenomenon called Rayleigh Scattering.
Named after the British physicist, John William Strutt,
also known as Lord Rayleigh, who discovered it
in the late 19th century.
It describes how different colors of sunlight interact
with the earth's atmosphere.
Look at the sky during daytime, for example.
It appears blue because air molecules
in earth's atmosphere scatter blue light more easily
than red, but during sunrise and sunset,
the light travels through more of earth's atmosphere
before reaching your eye which has two consequences.
First, it means more overall sunlight is scattered,
making the sun appear dimmer.
That's why you can easily gaze upon the sun at sunset
compared to at high noon.
And secondly, more scattering means more blue light is
scattered away, leaving the redder wavelengths behind.
Similarly, the ring around earth
during a total lunar eclipse is red
because the sunlight travels through a long stretch
of earth's atmosphere, from one end
of the planet to the other.
So rather than fear a blood moon like the ancient Mayans
and Mesopotamians, why not think of it as a romantic moment?
After all, it's the only time when you can see the sunrise
and sunset simultaneously.