Atmospheric refraction,twinkling of stars,advance sunrise and delayed sunset

3. Atmospheric refraction is the deviation of light or other
electromagnetic wave from a straight line as it passes
through the atmosphere due to the variation in air
density as a function of altitude.
This refraction is due to the velocity of light through
decreasing with increasing density.
Refraction not only affects light rays but all
electromagnetic radiation, although in varying degrees.
Atmospheric refraction becomes more sever when
there are strong temperature gradients, and refraction
and refraction is non uniform when the atmosphere is
inhomogeneous, as when there is unbalance in the air.
This is the cause of twinkling of stars and various
deformations of the shape of the sun at sunset and
sunrise. So atmospheric refraction of the light from a
star is zero in the zenith

4. Due to continuous atmospheric refraction of
starlight.
Since the atmosphere bends straight towards
the normal, the apparent position of the star is
slightly different from its actual position.
The star appears slightly higher (above) than its
actual position when viewed near the horizon.
This apparent position of the star is not
stationary, but keeps on changing slightly, since
the physical condition of the earth’s atmosphere
are not stationary.

5. The apparent position of the star fluctnotes and
the amount of star light entering the eye
flickers-the star appears brighter as the path of
rays of light coming from the star goes on
varying slightly
The planets are much closer to the earth, and
are thus seen as extended sources. If we consider
a planet as a collection of a large no of point-
sized sources of light. The phenomenon is
termed terrestrial scintillation.
Atmospheric twinkling is defined as variations
in illuminance only. Twinkling of stars is caused
by the passing of light through different layers of
a turbulent atmosphere.
Most scintillation effects are caused by

7. Planets do not Twinkle. Why ?
Planets are very close
to the earth as
compared to the stars.
The planets act as
extended sources of
light. So the intensity of
light we receive from
the planets is very large.
Therefore, the variation
in the brightness of the
planets is not detected.
Hence, planets do not
twinkle.

8. Sometimes the refraction of the light rays tend to
being into view, objects which are actually below the
horizon. This happens in the case of sun just before
sunrise and just after sunset.
Thus, we can see the sun about 2 minutes before the
sunrise and 2 minutes after the actual sunset
because of atmospheric refraction. The actual sun
rise takes pace when the sun is just above the
horizon.
 But due to refraction of sunlight caused by the
atmosphere, we can see rising sun about 2minutes
before it is actually above the horizon.
When the sun is slightly above the horizon then the
sunlight coming from less dense air to more dense air

9. Thus, the day would have been shorter by
about 4 minutes if the earth had no
atmosphere. The sun appears flattened at
sunrise and sun set. The sun appears
flattened at sunrise and sun set.
This apparent flattening of sun during
sunrise and sunset is also due to atmospheric
refraction.
It is also due to atmospheric refraction that
we can still see the sun for about 2 minutes
even after sun has set below the horizon. So,
the time from sunrise to sunset is lengthened
by 2+2=4 minutes because of atmospheric
refraction.
Because of this atmospheric refraction, the

10. Akash Mahanand
Akash A.S
Anandhu C.N
Aleena Suresh
Abhisha.R.Suresh