Size wise, as you see, earth is the fifth one among the nine planets of the solar family. Though the Earth appears to be round in shape, it is flattened at its two poles. These are the upper and lower tips of the globe. At the Equator, the line along which the Earth can be halved, it is bulging outwards. This typical sphere-like shape is known as oblate spheroid. But whatever be the shape or size, it is so huge compared to our size that we have no idea about its shape. We do not even see that we are standing at a specific point on a curved surface. And while travel along the surface we move along the curvature. Just like an ant creeping along the surface of a very very large globe.
In a similar fashion, we do not feel earth's motion, though the Earth's rotation carries us along rapidly. It turns on from west to east around its axis. The axis, an imaginary line, passes along the diameter joining the two poles. As the Earth rotates, we are subject to two types of motion. The daily motion takes a whole day, or about 24 hours, to complete. This daily, or diurnal, motion is due to the Earth's rotation along its own axis. The other motion is annual. As the Earth turns on side wise, it moves forward along its orbital path. This path, shaped like an egg pointed at both ends, circles round the Sun. And this motion takes 365 days 5 hours 48 minutes and 45.51 seconds to complete one full lap around the Sun. The daily motion stretches over 24 hours, or, exactly, 23 hours 56 minutes 4.09 seconds, and causes the days and night. The annual rotation causes the seasons. This is because of a tilt in the Earth's axis. As the Earth goes round the Sun the Northern and Southern halves are alternately tilted. This tilt is one of main reasons that causes the seasons come and go one after another during the yearly motion.
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