Astronomy and Celestial Phenomena

There are many craters of different sizes on the surface of the Moon.

The smallest part of visible moon is called crescent moon. It appears after and before the new moon day. This occurs because of continuous change in the shape of the bright part of the moon. This change is called phases of the moon.

For life to exist, water is very essential. However, there is no water as well as no atmosphere on the Moon. Hence, life cannot exist on Moon.

Moon revolves around the Earth from East to West. Along with the Earth it also revolves around the Sun. Moon does not have its own light. Hence, we can see only that part of the moon that is illuminated by the Sun. When the moon is in the East, it lies somewhere between the Earth and the Sun. Thus the illuminated part faces the Sun and the dark part faces the Earth. Thus we cannot see any moon in the sky. This is the new moon day. After this, gradually the Moon starts moving towards the West through North. As it moves in this path, the illuminated part of the Moon gradually faces the Earth and we see the phases of the Moon from new moon, to crescent moon. Then half moon, and finally the full moon, when it reaches the West, in the West, the entire illuminated part of the moon faces the Earth and it is the full moon day. Then moon gradually starts moving towards the east once again through south and the visible part of the moon goes on decreasing in the same manner until the new moon day and the cycle keeps repeating itself. Thus we see the phases of Moon. It takes 15 days for the moon from new moon day to full moon day and another 15 days from full moon day to new moon day.

The surface of the moon according to the astronauts is dusty and barren.

According to the astronauts the surface of the Moon is rough, dusty, barren and irregular. It has large craters on its surface and many steep and high mountains.

If new moon day is day $1$, then-

If new moon day is day $1$, then:

The summer solstice in the northern hemisphere occurs when the Sun is directly overhead at noon on the Tropic of Cancer. The summer solstice happens on 21 June. This day has the longest daylight time.

• The Earth experiences days and nights as a result of the planet spinning on its axis.
• As the planet spins, the part that is facing the sun experiences day, while it is a night for the part facing away from the sun.
• The alternation between day and night is caused by the rotation of the Earth on its axis.
• If the Earth did not rotate as it does, the day/night cycle would be very different or possibly even nonexistent. 

• The winter solstice falls on 22nd December during which there is continuous daylight on the South pole and continuous darkness at the North pole. Hence option D is correct.
• During summer solstice i.e. 21st June, there is continuous daylight at the North pole.
• Equinox refers to an equal period of darkness and daylight.

After 22nd March, other parallels between the equator and the Tropic of Cancer in the northern hemisphere start receiving perpendicular rays sequentially. Only on 21st June and 22nd December the sunrays become perpendicular on the Tropic of Cancer and Tropic of Capricorn respectively.These two days are called Solstice days.

Sunrays are never perpendicular to any of the parallels between Tropic of Cancer and the North Pole or between Tropic of Capricorn and the South Pole. 22nd December marks the longest day and the shortest night in the southern hemisphere.

The movement of the sun towards the north or south in a year is called the apparent movement of the sun. The revolution of the earth around the sun and the tilted axis of the earth are the two factors responsible for the apparent movement of the sun. Seasons occur only with reference to the northern and the southern hemispheres.

In the northern hemisphere , 21st March is called spring or vernal equinox whereas 23rd September is called autumnal equinox. The equinox or solstice dates can vary by a day or so.