Conside the following phenomena :
(1). Size of the sun at dusk
(2). Colour of the sun at dawn
(3). Moon being visible at dawn
(4). Twinkle of stars in the sky
(5). Polestar being visible in the sky
Which of the above are optical illusions?
Conside the following phenomena :
(1). Size of the sun at dusk
(2). Colour of the sun at dawn
(3). Moon being visible at dawn
(4). Twinkle of stars in the sky
(5). Polestar being visible in the sky
Which of the above are optical illusions?
(c)
Option-1( Size of the sun at dusk) is an optical illusion.
When the sun (or moon) is high in the sky there are no objects of
known size to compare the sun (or moon) to. But when the sun is
low in the sky we can see far off objects near the horizon that we
know are big and we imagine that the sun is even bigger.The
apparent change in size is an optical illusion.
Option-2( Colour of the sun at dawn) is an optical illusion.
Light is made up of lots of colors. And out of all those colors, red is
the one that travels the farthest.That means is that red is the last
color seen, when the sun sets. When the sun is setting, all of those
colors are slower-moving, and it is no longer bright outside,
because the colors are all moving at a separate pace. The other
colors start disappearing, and red (being the fastest), is what is last
seen.
Option-3( Moon being visible at dawn) is NOT an optical illusion.
The moon is visible somewhere in the sky at dawn during the
entire half of the cycle of phases from Full Moon to just before
New Moon.It is not an optical illusion.
Option-4( Twinkle of stars in the sky) is an optical illusion.
Stars continuously emit light. These light travels through various
layers of earth atmosphere before they reach our eyes. Now
refractive index decreases as we move from down through
atmosphere. So light keeps on getting bent towards normal at
each point of incidence. Practically there are infinite points of
incidence as refractive index keeps changing as we move down.
This happens in accordance and finally light reaches our eye. So we
see the star at B but actual position of star is at A. Further
atmospheric conditions keeps on changing. Hence light flux
reaching our eyes keeps varying and so star appears bright at
some time and it appears fade at other. So starts apparently
twinkles but practically they don’t.
Option-5( Polestar being visible in the sky) is NOT an optical
illusion.
The sky appears to rotate around points called the celestial poles
(one north pole and one south pole). These points represent the
directions where the Earth’s rotation axis points.Thus, for a fixed
observer on Earth, a celestial pole would always be in the same direction (due north or due south, depending where we are), and
its altitude over the horizon would be equal to our latitude.Polaris
is not exactly at the celestial pole; it is less than one degree from it
(so that it is hard to tell the difference without measuring) making
it a good indicator for the pole — that is why it is called the Pole
Star