Motions of the Earth

The position of the earth when it is winter season in Northern Hemisphere and summer season in Southern Hemisphere is called Winter Solstice.

Because of the change in the position of the earth around the sun.

On 21st June, the Northern Hemisphere is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer. As a result this area receives more heat. Since a large portion of the Northern Hemisphere gets light from the sun, it is summer in the north regions of the Equator. The longest day and the shortest night at these places occur. At this time in the Southern Hemisphere all these conditions are reversed. It is winter there. The night is longer than the days. This position of the Earth is called the Summer Solstice.

When a year has 366 days instead of 365 days it is known as leap year. We say there are 365 days in the year and by this we mean that it takes the earth 365 days to make its annual trip around the sun. Actually, though, It takes the earth 365-1/4 days to make this trip. This means that every year we gain one-fourth of a day and every four years we gain one full day. If we did nothing about this, our calendar would move backward one full day every four years to keep this from happening, we add the extra day every four years and put it into February .

The Earth rotates on its axis from West to East and completes it in 24 hours. When the Earth rotates, the half portion facing the sun causes day and the other half remains in darkness causing night. Thus, day and night is a continuous phenomenon because of the rotation.

If the Earth did not revolve, then:
i) There would be no change in seasons.
ii) There would not be variety of flora and fauna on the earth.

Dusk: - Is that period of evening which has diffused light after the sunset.
Dawn: - It is that period of the morning, which has diffused light just before the sunrise.

On 22nd December, the Tropic of Capricorn receives direct sun rays due to the tilt of South Pole towards it. As the sun rays are vertical on it, hence it has summers. Therefore, Christmas which falls on 25th December is celebrated in summers in the Southern hemisphere.

The sun rays of the noon are hottest in comparison to the sunrays of the morning and evening. This is because the rays of the sun are almost vertical at noon. They fall over a small area and hence give a greater amount of heat that means the heat received at per unit area increases. The rays of the sun are slanting in the morning and in the evening. They spread over a wider area and hence they cover larger area but give less amount of heat. That is why it is hotter when the sunrays are vertical at a place.

The shadows are long in the morning and evening and short at noon. It is the effect of slanting and direct rays of the sun. When the rays of the sun are overhead in afternoon, the shadow is shortest. The rays of the sun are slanting during evening and morning hence the shadows are long.

Sun’s rays fall directly on the equator on 21st March.

The polar night occurs when the night lasts for more than 24 hours. This only occurs inside the polar circles. The opposite phenomenon, when the sun stays above the horizon for a long time is called the polar day or midnight sun.

On September 22nd or 23rd in the northern hemisphere, when night and day are nearly of the same length and Sun crosses the equator moving southward. And in the southern hemisphere on 20th or 21st March, Sun crosses the equator moving northward it is known as autumn equinox.

The seasons are caused due to the revolution of the earth. Due to the change in the position of the earth around the sun, we have different seasons.

During May, June and July, the northern hemisphere is exposed to more direct sunlight because the hemisphere faces the sun. The same is true of the southern hemisphere in November, December and January. This is due to the tilt of the Earth. So June, July and August are the hottest months in the northern hemisphere and December, January and February are the hottest months in the southern hemisphere.