All of us know that Earth revolves around the Sun. But most of us may still be having some doubts and random thoughts as to the process and out comes of these revolutions and variations in days. Even now we use words like Sun rises, Sun sets, etc. even though all of us know that it is not rising of Sun.
What happens is the Earth is slowly turning towards Sun and it is turning from west to east. As the Sun becomes visible we say Sun is Rising. And at evenings Earth is turning towards west from east side. So the portion of Earth that was in east now becomes slowly dark and there will be night as it turns towards west side. The portion that was in the west will now be getting towards east and facing Sun. So it will be day time for that portion of the world. That is how when it is day time in India it is night for U.S. and vice versa.
But why Sun is rising? How does it rise from below Earth to above and at mid-day appears on our heads? How is it possible? When Earth is turning towards Sun which is already there, it should appear in front of us and should remain there through out the. But the reality is Earth is turning towards Sun from west to east rolling in such a way that it appears as if Sun is rising upward whereas it is the Earth rolling upside to bottom wards. It is just like you revolve in a Giant Wheel. When you are in a giant wheel you can experience that while you are coming down, the objects in front of you appear to be moving upwards whereas it is not so. It is only you that are moving downward and all objects are intact at their own position. In this same manner, when you are at a point of the Earth and rotating upward to downward, you experience Sun to be rising in front of you.That is how Sun rises in our lay man’s view point.
When earth is rotating all the people, animals, birds and rivers and seas and everything on it are also turning and rotating along with it from east to west and west to east. How is it possible? It is because of the gravitational force of the Earth. There is a central gravitational point and magnetic field around the Earth which holds every thing in position during its rotations. So every thing remains in its own position during these rotations and nothing gets disturbed.
Now, one more thing. The Earth is not absolutely round in its shape. It is oblate spheroid in shape. Rotating on its own axis the Earth is revolving around the Sun also. To complete one such revolution around the Sun it takes 365. 25 days roughly. And when rotating around itself, Earth is not rotating perpendicularly. It is rotating at a tilted axis of 23.5 degrees roughly tilted towards celestial plane. Further it is revolving around Sun in an oval shaped orbit known as elliptical orbit. Due to this reason Earth is placed sometimes nearer to Sun and at other times farther.
These variations in distance of Earth from Sun and the tilted axial rotation of the Earth and its oval shaped revolution around Sun all contribute for the seasonal variations in any year. When Earth is nearer to the Sun and gets direct rays from Sun, it is Summer and when Earth is farther from Sun and the sun rays are falling slantly on Earth it is cold or Winter, and like wise. These same factors contribute for the differences in the lengths of days and nights and variations in seasonal changes also.
Note: Images copied from Google images