pratap nagar
nagpur.
28th april 09
article 2--
series.. SCIENCE IN OUR DAILY LIFE!
Dear all,
Today i am talking about rays.. as we know the part of light that come from sun,we call it rays..
but there are two types of rays..
crepuscular rays and anti crepuscular rays..
as rays appear to be coming from the sky thus passing through clouds. so reflection and scattering of light is an important
phenomena.as we know that light has to pass through various layers of atmosphere, defraction of light takes place.. so the light from the stars reach our eye and the stars appear to be twinkling. similarly the light of sun also defracts before it reaches our eyes.. scattering of light enables the light to spread everywhere in world..
you must have seen on cloudy days.. the rays from sun come from behind the clouds.. so we can see that the light comes from a single point. these rays are called crepuscular rays. the rays which appear to come from a single point are known as crepuscular rays.we find that they are almost parallel after some distance from the cloud. but it is apparent like that in case of convex mirror.in this case all the light appears to come from a single point.
Crepuscular rays are usually red or yellow in appearance because the path through the atmosphere at sunrise and sunset pass through up to 40 times as much air as rays from a high midday sun. Particles in the air scatter short wavelength light (blue and green) through Raleigh scattering much more strongly than longer wavelength yellow and red light.
similar origination is of the anticrepuscular rays but they appear in the opposite direction in the sky.i mean they r in the opposite direction to sun.. but as we know that the earth and its surrounding atmosphere is curved, the crepuscular rays travel all the way from one's sunrise and sunset point in the horizon.but their projections are in curvature and they are visible only at the sunrise or sunset points of the horizon.. so we see them coming from the opposite direction.Crepuscular rays are usually much brighter than anticrepuscular rays. This is because for crepuscular rays, seen on the same side of the sky as the sun, the atmospheric light scattering and making them visible is taking place at small angles
Although anticrepuscular rays appear to converge onto a point opposite the sun, the convergence is actually an illusion. The rays are in fact parallel, and the apparent convergence is to the vanishing point at infinity.the reason is the curvature of the earth;s surface.
LIKE YOU ARE STANDING ON A BEACH.IT IS CLEAR SUNNY DAY AND A SHIP IS APPROACHING FROM INFINITY. SO AS THE SURFACE IS CURVED,WE WILL SEE THE FIRST DECK OF SHIP FIRST AND THEN LATER WE WILL SEE THE ENTIRE SHIP.. WE CAN SEE SOME PART OF SHIP'S DECK FOR THE FIRST TIME WHEN THE SHIP JUST CROSSES THE FIELD LIMIT THAT IS 180 DEGREE FROM US IN THE ENTIRE SKY AND THE SURFACE..
THIS IS TWO TYPES OF RAYS.NEXT TIME WHEN YOU GET UP IN THE MORNING OR WHEN YOU ARE SEEING A SUNSET..DO REMEMBER IT.
Akshay Deoras
