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I was wondering if you could tell me about the
moon and about eclipses. Why is it harmful to
your vision? Ive heard that eclipses of the sun
hurt your eyes. My teacher said hes seen moon
eclipses that looked red. Why would that happen?
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Question Date: 1999-03-11 | | Answer 1:
I'm not sure exactly what you want to know about
the moon, but I can certainly tell you about
eclipses of the moon. Let's start with the phases
of the moon.
As the earth is orbiting the sun, the
moon is orbiting the earth. So, you could picture
a flat plane in your head, and in it lies the sun
at the center, with the earth traveling around it,
and the moon traveling around the earth. Sunlight
is always being reflected off of the half of the
moon that is facing the sun at any given time.
However, based on our position relative to the
moon, we may only see a half, crescent or no moon.
The reason is this: for example, with a half
moon...there is one whole side of the moon that is
lit up by the sun, but we are only seeing half of
it...so we see it as a half moon. A new moon is
when the other side of the moon is being lit up,
relative to our position.
An eclipse (lunar), on the other
hand, happens when the earth gets between the sun
and the moon and blocks the light. The earth is
actually casting a shadow on the moon. (I don't
know why it might be red, sorry!) A lunar (moon)
eclipse is totally safe to look at.
A solar
eclipse happens when the moon gets between the
earth and the sun, and the moon's shadow is
actually blocking out most of the sun. It is
dangerous to look at a solar eclipse for the same
reason it is dangerous to look directly into the
sun. Because the moon doesn't completely block out
the sun, there is still an area of direct rays
coming out around the rim of the circle, which can
be damaging to your eyes. I hope this helps you! | | Answer 2:
The moon formed about 4500 million years ago
(write this out on a piece of paper and have your
teacher make sure you have all the zeros!!) when a
body about the size of Mars collided with the
earth. This giant impact created a huge vapor
plume of vaporized rock that got put into orbit
around the earth and eventually condensed to form
the moon.
An eclipse happens when one body, say the
moon, passes into the shadow of another. The
redness occurs because the small amount of light
that does illuminate the surface of the moon is
mostly red light because red light has a longer
wavelength and scatters less than blue
light.
YOU SHOULD NEVER LOOK DIRECTLY AT
THE SUN WITH YOUR NAKED EYE OR THROUGH A TELESCOPE OR
BINOCULARS. The intensity of sunlight will
burn(DESTROY) your eyes because your eyes are not
built to deal with INTENSE LIGHT. YOU SHOULD NEVER
LOOK DIRECTLY AT A LASER LIGHT FOR THE SAME
REASON.
I hope this helps. | | Answer 3:
Your questions are very good and ones that confuse
a lot of people. There are two kind of eclipse,
lunar and solar, and each one works a little
differently.
Lunar eclipses happen during
the full moon when the earth is between the sun
and the moon. Normally, the full moon is bright
because the light of the sun is shining on the
full surface of the moon that is facing the earth.
Sometimes, the earth comes into and exact line
between the sun and the moon and blocks the light
of the sun. The shadow of the earth moves across
the moon until we can't see the moon anymore and
this is a lunar eclipse. The moon becomes red
during these eclipses because some of the sunlight
shines through the earth's atmosphere before
reaching the moon and is refracted so that more
red light reaches the moon. This is like what
happens at sunset when the sun gets close to the
horizon and looks red because its light travels
through so much atmosphere and is refracted. In
some eclipses, even the light that goes through
the earth's atmosphere doesn't reach the moon and
it becomes completely dark before turning red
again and the going back to the usual color of the
full moon at the end of the eclipse.
Solar
eclipses happen when the moon, traveling in its
orbit, comes between the earth and the sun so we
can't see the sun anymore. Although the sun is
much much bigger than the moon, the moon is much
closer so they appear about the same size in the
sky. The moon can sometimes completely block the
sun but this is very rare because they are close
to the same size. Often you see a little bit of
the sun ringing the moon or on one side of it.
When an eclipse like this happens, most of the
light from the sun is blocked so the sky gets
darker, and everything gets a little colder for a
few minutes. Still, a little of the sun shows
from around the moon and it is still much too
bright for your eyes. This is a very dangerous
time because everything seems darker and so you
want to look at the eclipse but it's just as
dangerous to look at the sun, even with
sunglasses.
| | Answer 4:
Eclipses occur when the sun, moon, and the earth
are in a line so that the earth passes through the
moon's shadow (solar eclipse) or the moon passes
through the earth's shadow (lunar eclipse). Why
do you think the moon is always full for a lunar
eclipse and new for a solar eclipse?
I
found a pretty good website at:
eclipse
There are some links to other sites too.
You should never look at the sun because the lens
of the eye focuses light onto the retina. The sun
is so bright that it can cause damage before you
know it. During a total lunar eclipse light from
the sun gets refracted through the atmosphere and
hits the moon which then gets reflected back to
us. Can you think of a reason why it's mostly red
light that we see?
| | Answer 5:
You asked several questions so I'll take them in
turn.
Moon and Eclipses: As you know the moon
revolves about the earth in a 28 day (1 lunar
month) orbit. At the same time, both the
earth and the moon orbit the sun in a much
larger (93,000,000 miles) and slower (365.256
days = 1 year) orbit. The solar orbit is slightly
inclined to the lunar orbit-- if you drew
circles to represent the orbits, you would
need two sheets of paper on which to draw
the circles. Also, the moon at 238,000 miles is
about 1/2 an angular degree wide and the sun at
93,000,000 miles is also about 1/2 a
degree.
So, now at one time each month, the
moon is between the earth and the sun -- but
only rarely is it exactly between so it casts a
shadow on the earth. (The shadow is a solar
eclipse). 1/2 month later, the earth is between
the sun and the moon -- and if this happens
where the two planes (paper sheets above) the
earth casts a shadow on the moon -- the make a
lunar eclipse.
Although you can watch a
lunar eclipse without protection, it is very
dangerous to look at a solar eclipse. Typical
sunlight is much brighter than you might think,
and staring into the sun is just like burning
paper with a magnifying glass -- in this case
the magnifier is your eye lens and cornea, and
the "paper" that is burned is your retina-- The
part of your eye that is sensitive to
light.
The danger in a eclipse, is that a
significant part of the light of the sun (and
all of the heat) is invisible to your eye. During
the eclipse, the sun appears dimmer (and it is)
but it is still dangerously bright. Worse, your
eye gets used to the overload -- and stops
sending warning signals to you (i.e. pain) so
significant damage can occur at the point of
focus, and to parts of the eye which are sensed by
nerves that are hit. The simplest safe way to
view an eclipse is to poke a small hole with a
pin in a card and look at the image of the sun
on another sheet of paper held a few feet behind.
(The same effect can be seen during a partial
eclipse if you walk through trees -- you see
hundreds of partial eclipses on the ground).
Finally, the standard argument for why a
lunar eclipse looks red is that red light has a
longer wavelength than yellow, green, or blue
light,
so is less easily scattered by the dust in the
earth's atmosphere. Some of the light falling
on the moon during the eclipse went very close to
the earth and went a long way through the air
before going back into space and hitting the
moon. Blue, green, and some yellow light
is scattered into other directions, but the red
light goes straight. At the moon, it is the
only light left -- so the moon appears red
as well.
What would happen if the lunar
and solar orbits were exactly in the same
plane? How often would we have an eclipse?
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