While not as spectacular as a
solar eclipse, a lunar eclipse
can still be a beautiful and amazing spectacle. It's also a lot easier to
see a total lunar eclipse than its solar equivalent!
A lunar eclipse always occurs at night,
during a Full Moon; you
should be able to see the eclipse if it occurs during your nighttime,
and you have a view of the Moon. But what you will see depends on the
specific type of the eclipse.
By the way, since a lunar eclipse occurs at night, when the Sun
isn't around, it's always safe to look at a lunar eclipse.
The Shadow on the Moon
As described in Mechanics of Lunar Eclipses, the Earth's shadow during a lunar eclipse
has two parts: the penumbra,
where the Sun's light is only partly blocked from the Moon; and the
umbra, where the Earth totally
blocks the Sun's light.
If the Moon touches the penumbra, a penumbral eclipse will
be seen (although, in practice, this type of eclipse is subtle; most
penumbral eclipses can't bee seen with the naked eye); if the Moon
touches the umbra, a partial umbral
eclipse will be seen; and if the Moon completely enters the umbra, the
result is a total umbral eclipse, or total lunar eclipse.
A total eclipse is always preceded and followed by a partial eclipse;
which is in turn preceded and followed by a penumbral eclipse. Hence,
we say that a total eclipse goes through a penumbral stage, then a
partial stage, then the total stage, then partial, then penumbral,
before finishing.
What Can You See?
Penumbral Eclipse
The penumbral stage of a lunar eclipse (or a lunar eclipse that is
only penumbral) is essentially impossible to see, unless the Moon is
deeply inside the penumbral shadow; even then, all parts of the Moon are
still receiving light from the Sun, and therefore quite bright.
Still, in a deep penumbral eclipse, sharp-eyed observers should
see a subtle but distinct shading across the Moon at maximum eclipse.
This should be fairly obvious in a
total penumbral eclipse.
Partial Umbral Eclipse
A partial eclipse, or the partial stage of a total eclipse, is
heralded by the Earth's shadow beginning to take a bite out of one
side of the Moon. The remainder of the Moon will still be quite
bright, as normal; but the Earth's shadow will gradually move across
the face of the Moon, and the light level will drop noticeably.
Total Eclipse
When the Earth's umbral shadow completely covers the Moon, the drama
begins! The Moon darkens, but rather than vanishing totally, it turns
a dark red or coppery-red colour. This is an amazing sight, and is
caused by the refraction of sunlight through the Earth's atmosphere;
although the Sun is totally blocked from the Moon, this scattered
light, filtered by the atmosphere, ensures that a total lunar eclipse
is a sight worth seeing.
This amazing image, by Michele Whitlow, illustrates the stages of the
total lunar eclipse of 8 Oct, 2014,
from the beginning of the partial eclipse, through the total eclipse, to the
end:
Depending on the prevailing condition of the Earth's atmosphere, in
terms of cloud cover and dust from volcanic eruptions, the actual
colour of the Moon at totality can vary from near black (particularly
at mid-totality), rust, brick red, and bright copper-red or orange.
Large Moons
The Moon is quite visibly larger when it's close to the horizon, as
in when it's rising or setting — how does this affect an eclipse?
Well, things are not quite what they seem — in fact, this is
just an optical illusion. You can prove this by taking a picture of the
Moon near the horizon, and another when it's high in the sky; with the
same lens settings, the two Moon pictures will be the same size. This
effect is known as
the Moon Illusion.
Vantage Points
So where do you have to go to see a lunar eclipse? The good
news is that this isn't too hard.
A lunar eclipse is much easier to see than a solar eclipse. When
the Moon moves into the Earth's shadow, half of the Earth — the night
side, where the Moon is above the horizon — can observe the event.
The type of eclipse you will see doesn't depend on where on Earth you
are; as long as you can see the Moon, you will see the same view of
what's happening to it at any given moment as everyone else.
Your ability to see the Moon, of course, is governed by the
Earth's rotation; as the Earth spins, the Moon, as seen from any given
point, appears to rise in the East, move across the sky, and set in
the West. Since a lunar eclipse can last for hours, you may find that
from your location, the Moon rises or sets part way through, and you
only see part of the eclipse; or you may see it all, or none of it.
As an illustration of this, the following map shows the total area
of the Earth which witnessed the total lunar eclipse on July 16, 2000:
The orange and yellow shaded areas on the map will see only the
beginning of the total eclipse, as the Moon sets in the West; the cyan
and blue shaded areas will see just the end, as the Moon rises; and the
light area (covering Australia and east Asia in this case) will see the
entire spectacle. The green tag in the centre shows where the Moon was
directly overhead at the moment of maximum eclipse.
Bear in mind that if you're very near the edge of the area of visibility,
the Moon will be low on the horizon; depending on your view of the horizon,
you might not actually be able to see it.
The other good news is that a lunar eclipse, even a total eclipse,
generally goes at a pretty relaxed pace (the total phase often lasts
an hour or more); with that, and the lack of any need for eye
protection, there's plenty of time to enjoy the view, take pictures,
and have a good time!
And yes, that's right — a lunar eclipse can't damage your eyes.
The Moon is no brighter during a lunar eclipse than at any other time,
and nowhere near bright enough to cause blindness. (If you're looking at the Sun,
that's not a lunar eclipse — and it is dangerous.)
