Motions of the Earth - Long Answer Questions
Rotation and Revolution.
Rotation is the movement of the earth on its axis. It takes 24 hours.
The movement of the earth around the sun in a fixed path or orbit. It takes 365 1/4 days.
The axis of the earth (imaginary line) makes an angle of 66 1/2 degrees with its orbital plane. The plane formed by the orbit is known as the orbital plane.
The circle that divides the day from night on the globe. This circle does not coincide with the axis.
Earth takes 365 days and 6 hours to revolve. We ignore the 6 hours for convenience. In 4 years, these 6 hours add up to 24 hours (1 day). This surplus day is added to February.
The earth moves around the sun in an elliptical orbit (oval shape, not a perfect circle).
Seasons change due to the change in the position of the earth around the sun (Revolution) and the tilt of the axis.
Northern Hemisphere is tilted towards the sun. Rays fall directly on Tropic of Cancer. It is the longest day and shortest night in the Northern Hemisphere. This is the 'Summer Solstice'.
Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it. It is summer in the Southern Hemisphere. This is the 'Winter Solstice'.
On 21st March and 23rd September, direct rays of the sun fall on the equator. Neither of the poles is tilted towards the sun. The whole earth experiences equal days and equal nights.
Because of the tilt. When the North Pole is tilted towards the sun, places beyond the Arctic Circle experience continuous daylight for about 6 months.
The portion of the earth facing the sun would always experience day (hot). The other half would remain in darkness (freezing cold). Life would not be possible.
Because of the earth's tilt. When the North Pole is tilted away from the sun, the South Pole is tilted towards it.
It is Autumn (Equinox) in the Northern Hemisphere and Spring in the Southern Hemisphere.
Technically no, but on Venus (which spins backwards) it would appear to rise in the West.
Often defines the period of rotation (24 hours). It is the daily motion of the earth.
February has 29 days instead of 28 days every fourth year.
Because the hemisphere is tilted away from the sun, receiving slanting rays and less daylight hours.
A large portion of the Northern Hemisphere gets light. Heat is high in the Torrid Zone.
Motions of the Earth - Important Facts
Rotation causes Day and Night.
Revolution causes Seasons.
Earth's axis is tilted at 66 1/2 degrees to the orbital plane.
Earth's axis is tilted at 23 1/2 degrees to the vertical.
Circle of Illumination separates day and night.
One revolution takes 365 days and 6 hours.
A normal year has 365 days.
6 hours saved every year are added to make a Leap Year.
Leap year has 366 days.
Summer Solstice is on 21st June.
Longest day in North India is 21st June.
Winter Solstice is on 22nd December.
Christmas is celebrated in summer in Australia.
Equinox means 'Equal Night'.
Equinox dates: 21st March and 23rd September.
On Equinox, direct rays fall on the Equator.
Elliptical orbit means oval path.
Seasons: Summer, Winter, Spring, Autumn.
Change of seasons is due to the change in Earth's position.
At the poles, day and night last for 6 months each.
The sun never sets for 6 months at the North Pole in summer.
Aryabhata stated that earth is round and rotates on its axis.
Perigee: Point nearest to the sun.
Aphelion: Point farthest from the sun.
Morning and Evening are caused by rotation.
Slanting rays provide less heat.
Direct rays provide more heat.
Southern Hemisphere has reverse seasons to Northern.
21st March is Spring Equinox in the North.
23rd September is Autumn Equinox in the North.
Rotation speed is max at Equator.
Rotation speed is zero at Poles.
Revolution speed varies slightly in orbit.
We don't feel the motion because everything moves with us.
The axis points towards the Pole Star.
Ancient astronomers studied these motions.
Calendars are based on Revolution.
Day length varies due to the tilt.
If axis was vertical, days would be equal always.
If axis was vertical, there would be no seasons.
The bulb and ball experiment explains Day/Night.
Earth rotates from West to East.
Sunlight covers half the earth at any time.
Space photos show the terminator line (Circle of Illumination).
Seasonal changes affect plants and animals.
Migration of birds depends on seasons.
Harvest festivals are linked to seasons.
Solstice comes from Latin 'Solstitium' (Sun stands still).
Equinox comes from Latin 'Aequinoctium'.
The tilt is constant throughout the revolution.
Motions of the Earth - Important Dates/Coordinates
Summer Solstice
Winter Solstice
Equinox
Equinox