|Why does the moon turn red at times? And why is
the sky blue? Can the sky turn into another color,
and if so what color?|
|Question Date: 2015-01-15|
This is a fantastic question! I had to go out
and do some research of my own to learn why the
moon turns red sometimes. Most of the information
below is from a video produced by NASA. I included
a link to the video below. You should watch it
after you read through this answer... It turns out
that the moon turns red during a “total lunar
eclipse”, when the moon is in Earth’s shadow.
The moon orbits around the Earth over a period
of about 29.5 days (relative to the sun).
Sometimes the moon passes through Earth’s shadow,
causing an eclipse. This happens (on average)
about twice per year. When the moon passes through
the middle of Earth’s shadow, red light from the
fringes around Earth beam onto the surface of the
moon, turning it red. Why is there red light
around the fringes of Earth when facing toward the
sun? Light passes a long distance through the
atmosphere in this direction, and the gases in the
atmosphere let the red light pass through.
Okay, maybe that sounds a little confusing… So I
have included two different illustrations to help
illustration 1 shows the
position of the moon during a full lunar eclipse,
when it’s bathed in red light. The
illustration 2 explains
why there is red light bent into Earth’s shadow.
This is a good transition into the second part of
your question. Why does the sky appear
blue? It can turn into other colors, like
pink, red, and orange during sunset. Why is
that? You should never look directly at the
sun without the right kind of filter because the
intense light can hurt your eyes. But, if you
were to look directly at the sun (DON’T DO THIS)
you would see that the light is white. The same is
true for a light bulb in your house (you can look
at this and pretend it’s the sun). White light is
a combination of light of all different colors,
from red to violet. Different colors have
different “wavelengths”– purple and blue light has
a shorter wavelength than red light. When the
colors are combined, we cannot see them
individually and they appear white. There are
certain ways that the colors can be separated out
of white light, and this happens in the atmosphere
of the Earth. Gas molecules in the atmosphere
“scatter” the different wavelengths of light, and
it turns out that blue light is scatted the
We see the scattered (blue) light when we look at
the sky, so it appears blue. During sunrises and
sunsets, the sun is low in the sky, so light that
reaches us travels a long distance through the
atmosphere. The blue light is strongly absorbed by
water vapor and dust and the red and pink light
pass directly through (nasa.gov). I have included
a picture illustrating this phenomenon and have
also included a link to another informative NASA
video about eclipses and red moons:
video about the color of the sky:
video-audio click here
Thanks of the very interesting question. The
reason why the moon appears red sometimes, is the
same reason why the sky appears blue.
Sunlight is made of different colors of light
with different intensity for each color, combined
together. White light is made of all the colors in
equal intensity. An interesting experiment: When
white light or sunlight is passed through a prism,
one can see the different colors split, because
different colored light travels with different
speed in certain objects such as a prism. This
experiment was very important to establish the
nature of light by Newton and Huygens.
It happens that our atmosphere scatters blue
light more than red. This is called "Rayleigh's
scattering". Therefore out of all the colors
in the sunlight, blue light is the one that is
scattered and reaches our eyes during the day.
During a lunar eclipse, the moon turns
red. A lunar eclipse is when moon, earth and
sun align in a straight line with the earth in
between the sun and the moon (like so: O---o---.).
When this happens, light from the sun first hits
the earth. Most of the light hits the earth in the
middle, but some of the light passes through the
earth's atmosphere. Because the atmosphere
scatters blue more than red, all the blue light is
"filtered out" of the sunlight due to scattering.
But red light that don't scatter remain and
reaches the moon after passing through the earth's
atmosphere. It is this red light that hits the
moon and reflects back to our eyes, and cause the
The next time you watch a beautiful sunset,
observe the color of the clouds that float. They
will be bright orange. This also happens when
there is fire in the nearby woods. Those sunsets
are very beautiful with multiple colors decorating
the sky. This is because smoke scatters
different shades of red light. The sky can
appear redder if our atmosphere is filled with
Although, a smoke-full atmosphere will
certainly be a beautiful sight to watch, it will
trap the heat from the sun and raise the
temperature of the earth making it uninhabitable
for living beings, which of course includes us.
This is called "global warming", and is an
increasing problem because of the smoke from cars,
coal burning, etc..
1. Light from the moon is a mixture of different
colors (two examples are blue and red).
2. You can think of blue light as a wave that has
a shorter wavelength than a wave from red light.
Now that we understand these, I can explain why
we see a red moon. When light from the moon
reaches Earth, both blue and red light bump with
molecules in the air. But because blue light is
shorter than red light, the molecules in the air
are more able to block the blue light and scatter
them away. What you're left with is the red light,
which is a little more difficult for air molecules
to deflect. Those red light waves are then able to
pass through our atmosphere and reach our eyes.
This is why it looks like the moon has turned
red. So you can see that you need a lot of
molecules so more blue light can get scattered.
Pollution in the air can cause the moon to turn
red, because it brings up a lot of dust
particles to the sky.
Now, for your second question. The sky is blue
because of the same process that we just talked
about. During a nice, beautiful day, what you're
seeing is the blue light being scattered in all
different directions by many molecules up in the
sky. You're probably thinking, "well, if the moon
can turn red, can the sky do that too?” Yes, it
actually can. That's what happens if you've ever
watched a sunset. The sky turns reddish and
yellowish due to the same process that makes the
moon turn red. When the sun is low in the horizon
(just like what happens during a sunset), light
from the sun (which is also a mixture of different
colors) gets blocked and scattered by the
molecules in the air. So the sky turns red.
I realized this is a really long answer, but
you have very interesting questions. Good luck
with your studies!
The sky is blue because blue light scatters off of
air molecules more than red light does. Violet
light scatters even more, but so little of the
sun's light is violet that we see the sky as being
The moon appears red during a lunar eclipse
because it is in the shadow of the Earth. I do not
know whether the red color is filtered through
dust in the Earth's atmosphere as light bends
around the planet, or if it is reflected light
from the night side of the Earth.
Light is a very interesting phenomenon. Light that
is visible to our eyes can have all the colors
that you see in a rainbow. If light with two
different colors gets mixed together, it will
become a third color. For example, green light and
red light taken together becomes yellow, blue
light and red light becomes magenta (close to
pink) and so on. The light that comes from the sun
contains all the colors together and therefore
However as light travels in a straight line
from the sun into your eyes it needs to get
through the atmosphere. Small particles or gas in
the atmosphere “take out” a lot of the blue light
and only very little of the red light. Thus, when
you look at the sun, a lot of the blue light has
been taken out by particles in the atmosphere and
the sun looks yellow (Do not look at the sun
without the right equipment. It will hurt your
eyes very much!). The particles in the atmosphere
cannot hold on to the blue light forever so they
throw it back out in random direction. We say that
the light gets “scattered”. Some of this
light gets scattered back into space and is lost
and some of the light reaches your eye. Thus, when
you look at the sky, what you see is the blue
light that was “taken out” from the sunlight by
particles in the atmosphere and was then scattered
around and reached your eye.
At the beginning or the end of the day, when
the sun is very low on the horizon, the path of
the light through the atmosphere is very long and
a lot of the blue light gets lost along.
Therefore, the sky will appear red and orange. The
same is true when the atmosphere is very “dirty”
for example because of pollution from cars or when
a volcano erupts and spits ash into the air.
Again, the particles scatter off the blue light
and when enough of it gets lost, all that is left
is the red light.
Now you can understand why the moon can be red.
The moon just reflects the white light from the
sun and sends it to the earth.
So similarly to the sun, when the moon is low
in the sky, the light has to travel a long way
through the atmosphere and a lot of the blue light
gets lost. The moon appears red. The other way
to get a red moon is when there are a lot of
particles in the air due to pollution.
Finally, the moon can be red when the sun is
on the other side on the earth and positioned so
that the moon does not receive any direct white
light from the sun any more. The only light it
receives is the red light that made it through the
atmosphere of the earth. Therefore the moon
now reflects red light back to the earth and
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