A Colorful Lunar Eclipse, presented by Science at NASA.
On Wednesday morning, October 8th, not long before sunrise,
the bright full Moon over North America will turn a lovely
shade of celestial red.
It's a lunar eclipse—visible from all parts of the USA.
"It promises to be a stunning sight, even from the most
light polluted cities," says NASA's longtime eclipse expert
Fred Espenak.
"I encourage everyone, especially families with curious
children, to go out and enjoy the event." From the east
coast of North America, totality begins at 6:25 am EDT.
The Moon will be hanging low over the western horizon,
probably swollen by the famous Moon illusion into a
seemingly-giant red orb, briefly visible before daybreak.
West-coast observers are even better positioned.
The Moon will be high in the sky as totality slowly plays
out between 3:25 am and 4:24 am PDT.
During a lunar eclipse, the Moon passes deep inside the
shadow of our planet, a location that bathes the the face
of the Moon in a coppery light.
A quick trip to the Moon explains the color:
Imagine yourself standing on a dusty lunar plain looking
up at the sky.
Overhead hangs Earth, nightside down, completely
hiding the sun behind it.
The eclipse is underway.
You might expect Earth seen in this way to be utterly dark,
but it's not.
The rim of the planet is on fire!
As you scan your eye around Earth's circumference, you're
seeing every sunrise and every sunset in the world,
all of them, all at once.
This incredible light beams into the heart of Earth's
shadow, filling it with a coppery glow and transforming the
Moon into a great red orb.
However, red is not the only color.
Many observers of lunar eclipses also report seeing
a band of turquoise.
The source of the turquoise is ozone.
Atmospheric scientist Richard Keen of the University of
Colorado explains: "During a lunar eclipse, most of the
light illuminating the moon passes through the stratosphere
where it is reddened by scattering.
However, light passing through the upper stratosphere
penetrates the ozone layer, which absorbs red light and
actually makes the passing light ray bluer."
This can be seen, he says, as a soft blue fringe around
the red core of Earth's shadow.
To catch the turquoise on October 8th, he advises,
"look during the first and last minutes of totality.
The turquoise rim is best seen in binoculars or a small telescope."
The depth and hue of lunar eclipse colors
depends a lot on the dustiness of the stratosphere.
When volcanoes erupt and choke the stratosphere with
aerosols, lunar eclipses can turn such a deep red that the
Moon looks almost black.
That's not the case this time, however: "Despite some
recent eruptions that look spectacular from the ground,
there have been no large injections of volcanic gases into
the stratosphere," says Keen.
"In the absence of volcanic effects, I expect a rather
normal reddish-orange lunar eclipse similar
in appearance to last April's eclipse."
In other words, this is going to be good.
Espenak notes that "The total lunar eclipse of October 8
is the second of four consecutive total lunar eclipses.
Such a set of total eclipses is known as a tetrad."
The next eclipse in the tetrad is six months from now,
in April 2015.
"Don't wait," he urges.
Mark your calendar for October 8th, wake up early,
and enjoy the show.
For more on this tetrad of lunar eclipses,
and other wonders in the night sky,
stay tuned to science.nasa.gov.