THE EARTHChapter VII

The Motion of the Earth in Space

- The Earth revolves around the sun from west to east. The speed of the earth’s orbit is about 108,000 km/hr (30000 meter per second) during an orbit it travels 940 million km.

- The earth completes one revolution every 365.242199 mean solar day, almost 365 and ¼ days and that is 365 days, 5 hours, 48 minutes and 46 seconds.

• Perihelion - the earth is closet to the sun, happens during January 3 with a distance of 147,098,074 km

•Aphelion – The earth’s distance is farthest from the sun, happens during July 4 with a distance of 152,097,701 km

Earth moves very fast. It spins (rotates) at a speed of about 1,000 miles (1600 kilometers) per hour and orbits around the Sun at a speed of about 67,000 miles (107,000 kilometers) per hour. We do not feel any of this motion because these speeds are constant. The spinning and orbital speeds of Earth stay the same so we do not feel any acceleration or deceleration. You can only feel motion if your speed changes. For example, if you are in a car which is moving at a constant speed on a smooth surface, you will not feel much motion. However, when the car accelerates or when the brakes are applied, you do feel motion.

FYI

• Sidereal time - From a given observation point, a star found at one location in the sky will be found at nearly the same location on another night at the same sidereal time. This is similar to how the time kept by a sundial can be used to find the location of the Sun. 

• Sidereal day – is about 23 hours, 56 minutes, 4.0916 seconds. The time it takes to make a one rotation.

Precession - is a change in the orientation of the rotational axis of a rotating body. - The period of earth’s precession is every 26,000 yrs caused by the gravitational pull of the sun and moon.

VEGA (Brightest star in constellation of lyra) will be the next northern pole star

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