Days and nights on moon | Hindi | How and Why ?
Channel: Arvind Gupta
Date: 17/08/2015

The other night while it was full moon and I could see moon fully lit up, I started wondering what would happen if we lived on moon. Well as we continue to wreak havoc with our environment, pollute our cities who knows we might have to one day.
So anyways if end up living on moon will we have days and nights. Now days on earth happen when part of earth where live faces the sun. Since the earth is spinning this part of the earth shall face away from sun some time later and we will have nights. So we need to explore this little to see if moon is also actually spinning on its axis as the spin of moon would lead to days and nights on moon.
Well we have heard this old story of a lady spinning the wheel on the moon but whenever we see the moon we realize that moon shows the same face to us. In other words we can see only the some part of the moon. Part with spinning lady. What about the other side. Why don't we see that because moons do spin around the earth?
Consider moon tied to the earth as it spins around the earth. So the same part of moon is always facing the earth. This is the motion of our natural satellite as it moves around the earth. It is almost as if it is tied with a rope to earth. It is clear that moon is going around the earth. But do you think moon is spinning on its axis in this motion. Yes it is. 
Consider this position of moon when the white face is pointing towards you. Moons black spots or craters are on other side facing the earth. So people from earth can see these craters on moon. As the moon covers half the distance around the earth you can see these black spots spinning towards you. So people from earth can still see only these craters on moon. They spin back away from you after one full rotation of moon around the earth. So you can see the moon spinning as it goes around the earth such that from earth you can see only craters or black spots on moon.
So what is amazing about this motion is that moon spins on its axis and rotates around the earth in the same time. This is also called the synchronous motion and is the reason why there is a DARK SIDE OF MOON or why we can see only one side of moon.
The other equally important reason for the dark side of moon (which no one book talks about) is that moons axis is almost perpendicular to its moons plane of orbit around earth (1.6% tilt) unlike earth whose axis is tilted at 23.5 degrees wrt to earth’s orbit around sun. Consider a scenario where moons axis is tilted 90% in this scenario regardless of synchronous motion we will see other side of moon in 28 days.
So now we have seen that moon spins around its axis in 28 days so it will face the sun for 14 days and face away from sun for 14 days. So the moon will have days and night almost 14 day long ignoring the fact that moon's going around the sun in one year also causes one day. And. Except when earth comes between moon and sun and then we have the lunar eclipse. Well if we were living on loon we would have called it the solar eclipse and we would not be able to see the sun.
And why we don't have we don’t have eclipses every 28 days we will see in another video.
This work is supported by IUCAA and TATA Trust. TATA Trust: Education is one of the key focus areas for Tata Trusts, aiming towards enabling access of quality education to the underprivileged population in India. To facilitate quality in teaching and learning of Science education through workshops, capacity building and resource creation, Tata Trusts have been supporting Muktangan Vigyan Shodhika (MVS), IUCAA's Children’s Science Centre, since inception. To know more about other initiatives of Tata Trusts, please visit www.tatatrusts.org