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Lecture 18

ASTR 101 Lecture Notes - Lecture 18: Green Flash, The Moons, Red Color

Astronomy and Astrophysics
Course Code
ASTR 101
Thomas Bensky

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ASTR final study guide class questions
2. Rainbows are formed when white light from the sun hits rain drops.  Because the light
is going from thin material to a thicker one, dispersion happens.  As the light bends, it
also reflects off the rain drop, forming a rainbow once it leaves it the rain drop.  For
some reason the blue light always comes out on top, however, our eyes collect
wavelengths from multiple rain drops and thus the rainbows we see always go from red
(top) to blue (bottom)
3. The sky is blue because as white light from the sun reaches our atmosphere, blue
light is absorbed by the nitrogen.  All the other wavelengths pass right through our
atmosphere, but blue light excites nitrogen atoms and is then spit out in all directions,
causing our sky to be blue
4. Clouds are white because they reflect sunlight, which is white light
5. The green flash occurs essentially due to the same reason that makes our sky blue.
As the sun sets and the point at which you stand rotates away from the sun, white light
is still passing through the atmosphere, however; at this point the light travels much
further through the atmosphere to reach your eye and thus the blue is almost entirely
gone due to the nitrogen in the atmosphere sucking it up.  At the moment right before
the sun sets, the red light may pass right above you, as the green light meets your eye
for just a quick moment before the sun descend into the horizon
6. A mirage is basically the image of the sky on the ground.  Certain conditions must be
met for mirages the happen.  It needs to be a hot, clear, and sunny day.  The sunlight
hits the hot pavement and creates a thin layer of hot air.  As this layer of hot air rises, it
cools and becomes thicker.  At this point, when the light passes through this thicker
layer of air, the law of refraction kicks in and bends the light coming from the sun
straight into your eye, forming an image of the sky on the ground
7. The sky on the moon is black because it does not have an atmosphere
11.  The most important function of a telescope is to collect more light
13. The full moon appears red during a total lunar eclipse essentially because the
reason for the sky being blue.  Once the Earth perfectly blocks the sun during an
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