Direction, Speed and Effect of Revolution
- Rotation and revolution are the two primary motions of the earth. The amount of heat received from the Sun also depends on these movements.
- Rotation is the turning around of the earth on its own axis from west to east.
- Revolution is the movement of earth around the Sun.
- The time taken by the earth to complete one revolution is called a year and is 365 days approximately.
- The path along which the earth travels round the Sun is called Orbit.
- Perihelion is the time when the earth is closest to the Sun. This happens on January 3.
- Aphelion is the time when the earth is farthest to the Sun. This happens on July 4.
- The main effects of revolution are cycle of seasons, apparent migration of the Sun, and temperature zones.
- Seasons are caused due to combined effect of revolution of the earth and the tilt of the earth’s axis.
- Seasons of one hemisphere are opposite to that of the other hemisphere.
- Earth on its elliptical orbit has some specific days.
- On June 21st, rays of the Sun fall vertically over the Tropic of Cancer. This day is known as Summer Solstice. Northern Hemisphere has the longest day and shortest night on this day.
- On December 22nd, rays of the Sun fall vertically over the Tropic of Capricorn. This day is known as Winter Solstice. Northern Hemisphere has the shortest day and longest night on this day.
- On September 23rd, rays of the Sun fall vertically over the equator. This day is known as Autumnal Equinox. All the places have equal days and nights on this day.
- On March 21st, rays of the Sun fall vertically over the equator. This day is known as Vernal Equinox. All the places have equal days and nights on this day.
- It appears to us as if the Sun is moving. This is known as apparent migration of the Sun. However, the Sun does not move; it is the earth, which moves.
- The earth has three temperature zones, depending on the amount of heat received. These are Torrid Zone, temperate zone and Frigid Zone.
- Time is one of the most fundamental qualities of the physical world. The basis of measurement of time is the motion of the Sun across the sky.
- Day is the average time taken by the earth to rotate once on its axis.
- A month originally was the time taken by the moon to complete one revolution around the earth.
- In modern calendars, a month consists of 30 or 31 days normally with the exception of February, which has 28 or 29 days.
- There are various calendars, which are used in different parts of the world. Some of the major calendars are Julian Calendar, Gregorian Calendar, Hindu Calendar, Islamic Calendar, and Jewish Calendar
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Almost every part of the Earth’s surface comes before the Sun at least once a day as the Earth rotates from -Marks:1
West to east
The Earth rotates West to East. That's why the Sun seems to move East to West each day. "East" and "West" do not depend on the observer's viewpoint.
The imaginary line that demarcates light from darkness, day and night-Marks:1
Circle of illumination
The circle of illumination is the division between day and night over the earth. The circle of illumination bisects (cuts in half) all latitudes on the spring and autumnal equinoxes. At this time, all places have equal day length (12 hours). The circle of illumination always bisects the equator (0 degrees latitude).
The total hour taken by the Earth to rotates on its own imaginary axis is about –Marks:1
The earth rotates about an imaginary line that passes through the North and South Poles of the planet. This line is called the axis of rotation. Earth rotates about this axis once each day (approximately 24 hours).
The path along which the Earth revolves round the Sun is called-Marks:1
Earth's orbit is the trajectory along which Earth travels around the Sun. The average distance between the Earth and the Sun is 149.60 million km, and one complete orbit takes 365.256 days, during which time Earth has traveled 940 million km.
The period taken for one rotation is called-Marks:1
Earth rotates once in about 24 hours with respect to the sun and once every 23 hours, 56 minutes and 4 seconds with respect to the stars.