Bath,Pa.
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Atmospheric Optics
"N O T E"
All weather articles written by the author,
weather records for Bath, Pa. USA, graphs,
graphics, pictures, are copyrighted and are owned by the author.
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Atmospheric Optics |
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Atmospheric Optics is the study of the optical characteristics of the
atmosphere which includes the study of refraction, reflection,
defraction, scattering and polarization of light produced by the atmosphere.
One of these is the appearance of the sun some 2 minutes before it
actually rises. Similarly, after setting, the sun appears to linger on the
horizon. This phenomenon is caused by refraction. The sun's light is
gradually bent as it enters the outer air and passes through the denser air
below. What we see is a mirror-like image of the sun prior to its actual
rising and setting, thus, giving us a few more minutes of sunlight.
The orange and red colors of the rising and setting sun are caused by
an increase in length of the path the rays must travel before light reaches
our eyes. The shorter (blue tones) become scattered by the lower
atmospheres thick impure-filled depths, and only red tones remain. As the
sun rises higher in the sky, its light passes through less denser air so it
loses its redder tones. The effect is the same for the moon. As the moon is
low on the horizon, the light must pass through the same atmosphere, which
cuts off shorter waves of light giving a reddish color.
One of the strongest of optical illusions is that the rising moon and sun
are larger then when they are higher in the sky. The illusion is so that
it is difficult to accept the fact that every kind of measurement shows
them to be just as large when they are high in the sky.
It is a psychological phenomenon, based on the appearance of the sun or
moon by the apparent measures or distance with respect to the horizon
and clouds.
Twilight is another phenomenon which is a period of incomplete darkness
following sunset (evening twilight) or preceding sunrise (morning twilight).
Shortly after the sun sinks below the horizon, its rays of light are
reflected from the gas molecules and impurities of the atmosphere to
produce afterglow. It is produced by scattering of fine particles of dust
suspended in the upper atmosphere. The limit of twilight is the height at
which the density of the air is sufficient to cause a perceptible amount
of scattered sunlight. The height is about 40 miles above the Earth.
