atmospheric refraction Flashcards
name a few phenomena in nature for atmospheric refraction, scattering of light and tyndall effec
atmospheric refraction
-twinkling of stars
-4 minutes of additional daylight everyday
-advanced sunirse
-delayed sunset
-sun appears oval and flat during sunset or sunrise but it is circiular at noon
scattering of light
-clear sky is blue in colour
- the sun is red during sunrise/sunset
-clouds are white
-colour of deep sea water
tyndall effect
-dust particles in the air scatter sunlight when it comes through a window
-the sunlight comes down through the clouds
-when headlight beams come through the fog/mist
-when the sunlight comes down through the canopy of dense forest
explain the phenomenon behind the random wavering and flickering of object when seen through hot air rising abv a fire or radiator
The air just above the fire becomes hotter than
the air further up. The hotter air is lighter (less dense) than the cooler air
above it, and has a refractive index slightly less than that of the cooler
air. Since the physical conditions of the refracting medium (air) are not
stationary, the apparent position of the object, as seen through the hot
air, fluctuates. This wavering is thus an effect of atmospheric refraction
(refraction of light by the earth’s atmosphere) on a small scale in our
local environment.
define atmospheric refraction
=when light rays pass through the atmosphere having layers of different densities and refractive indeces, it undergoes refraction. This refraction of light is valled atmospheric refraction
why do stars twinj=kle
The twinkling of a star is due to atmospheric refraction of
starlight. The starlight, on entering the earth’s atmosphere,
undergoes refraction continuously before it reaches the earth.
The atmospheric refraction occurs in a medium of gradually
changing refractive index. Since the atmosphere bends
starlight 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 (Fig. 11.9). Further, this apparent
position of the star is not stationary, but keeps on changing
slightly, since the physical conditions of the earth’s
atmosphere are not stationary, as was the case in the
previous paragraph. Since the stars are very distant, they
approximate point-sized sources of light. As the path of rays
of light coming from the star goes on varying slightly, the
apparent position of the star fluctuates and the amount of starlight entering the eye flickers – the star sometimes appears brighter,
and at some other time, fainter, which is the twinkling effect.
why dont planets twinkel
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 number of point-sized sources of light, the total
variation in the amount of light entering our eye from all the individual
point-sized sources will average out to zero, thereby
nullifying the twinkling effect.
what is the reason behind the advanced sunrise and delayed sunste
The Sun is visible to us about 2 minutes before the
actual sunrise, and about 2 minutes after the actual
sunset because of atmospheric refraction. By actual
sunrise, we mean the actual crossing of the horizon by
the Sun. Fig. 11.10 shows the actual and apparent
positions of the Sun with respect to the horizon. The
time difference between actual sunset and the apparent
sunset is about 2 minutes.
why is the sun oval in the sunset/sunrise and circular at noon
at the sunrise/sunet, the sun is near the horizon so the light rays coming from the upper and lower edge of the sun bend unequally while travelling through the atmosphere. thus the sun appears oval to the observer.
at noon the sun is overhead and the light rays fall normally (at 90 degrees), so they do not bend at all while passing through the atmosphere.therefore the sun appears circular.
what causes atmospheric refrcaion
the earth’s atmosphere consists of various layers with different densities of air. The layers close to the earth surface are more denser and are more optically denser, than the layers which are far away from the earth;s surface which are optically rarer because they have lesser density of air. there fore the light undergoes multiple times refraction.
