Thursday, 7 February 2019
Motions of the Earth << Learners Hobby
ROTATION
Like all other planets, the Earth also has two types of motions- Rotation and Revolution. The spinning of the Earth on its axis is known as rotation. The axis of Earth makes and angle of 23and1/2 degree with the perpendicular to the plane of the Earth's orbit. This tilt of the Earth causes days and nights of unequal duration beyond the line of Equator. If the Earth did not rotate, only the portion of the Earth facing the Sun would experience day and the other half would always remain in darkness.
If the Earth's axis were perpendicular to the orbital plane, then all places on Earth would have 12 hours day and 12 hours night each. Earth's orbit around the Sun is known as revolution.
CIRCLE OF ILLUMINATION
The part of the Earth that faces the sun is lighted. The circle which divides the Earth into lit-half and dark-half is known as circle of illumination.
ORBIT
The Earth's shape is described as Geoid. The elongated path of a planet around the Sun is called Orbit.
PERIHELION AND APHELION
When the Earth in its elliptical orbit reaches a point nearest to the Sun, it is known as Perihelion. When it is farthest from the Sun in its elliptical orbit, it is said to be at Aphelion.
DAYS AND NIGHT
The combined effect of elliptical orbit and tilt of the earth is:
(i) Unequal duration of days and nights at different latitudes.
(ii) Different seasons. Both the effects are similar to slanted and vertical rays of the sun. For different seasons, the revolution of the earth around sun explained subsequently is however greatly responsible. The effect also goes on increasing from Equator towards poles.
REVOLUTION
Earth revolves around the Sun in an inclined position while continuing to rotate. The path around the sun, known as orbit, is elliptical or egg-shaped. Earth completes one revolution around the sun in 365and1/4 Earth days. While 365 days make one year, 1/4 day is added to the month of February. As a result February has 29 days every four year. This year is known as leap year. A leap year is always divisible by 4.
SEQUENCE OF SEASONS
The combined effect of the earth's inclination is revolution and rotation as well as journey on elliptical path is felt on earth through the sequence of seasons. The direct and slanting rays of the sun are also responsible for this sequence. We have four distinct and extreme positions of the sun on 21st March, 21, June, 23rd September and 22nd December.
The sequence of seasons is relative to these four positions of the sun - Summer, Autumn, Winter and Spring.
At the equator, there is just one hot summer season. In the Tropics, summer and winter alternate each other and in the subtropical regions, three distinct seasons prevail. There are four seasons in the temperate region, and frigid zones have short summers and long winters.
SOLSTICES
In the orbital path when the Northern Hemisphere is inclined the maximum towards the sun, the sunrays reach their northernmost point on the Tropic of Cancer as on 21st June. As a result, the days become longer and nights shorter at the North Pole. At this time, the opposite happens in the Southern Hemisphere. On December 22nd, the Southern Hemisphere is inclined the maximum towards the sun and the sunrays reach their southernmost point on Tropic of Capricorn. Therefore, the days become longer and nights shorter at the South Pole. These two extreme positions are known as the summer and winter Solstices respectively. The duration of days and nights from equator to pole and from one part of the year to another varies in rhythmic precision.
EQUINOXES
Since the sunrays fall vertically on the equator, in equatorial regions days and nights are of almost equal duration. On March 21st and September 23rd, the sunrays fall straight on the equator causing days and nights of equal length not only on the equator but throughout the world. These two days are known as Equinoxes.
EFFECTS OF REVOLUTION
Seasons occur almost in rhythmic order because the revolution of the earth and its inclination are in a fixed direction. The seasons vary from equator to poles in both hemisphere.
Between 10degreeN and S and23degree N and S, there are two seasons of long summers and short winter. Between 23degree N and S and 66degree N and S seasons vary between three to four. The poles experience six months day and six months nights respectively. As such, summer seasons is mild but winters are cold and harsh.
CLIMATE CHANGE
Climate must be distinguished from weather. In a sense, climate is a particular weather condition over a long period of time say 35 years. The earth's mean temperature is rising. As a result, climate is changing. On account of this change known as Global Warming, temperature of ocean water is slightly warm and glaciers on high mountains as well as over the Antarctica are melting. These changes are likely to produce an effect on earth's inclination which will produce many other changes particularly climate and life forms.
Like all other planets, the Earth also has two types of motions- Rotation and Revolution. The spinning of the Earth on its axis is known as rotation. The axis of Earth makes and angle of 23and1/2 degree with the perpendicular to the plane of the Earth's orbit. This tilt of the Earth causes days and nights of unequal duration beyond the line of Equator. If the Earth did not rotate, only the portion of the Earth facing the Sun would experience day and the other half would always remain in darkness.
If the Earth's axis were perpendicular to the orbital plane, then all places on Earth would have 12 hours day and 12 hours night each. Earth's orbit around the Sun is known as revolution.
CIRCLE OF ILLUMINATION
The part of the Earth that faces the sun is lighted. The circle which divides the Earth into lit-half and dark-half is known as circle of illumination.
ORBIT
The Earth's shape is described as Geoid. The elongated path of a planet around the Sun is called Orbit.
PERIHELION AND APHELION
When the Earth in its elliptical orbit reaches a point nearest to the Sun, it is known as Perihelion. When it is farthest from the Sun in its elliptical orbit, it is said to be at Aphelion.
DAYS AND NIGHT
The combined effect of elliptical orbit and tilt of the earth is:
(i) Unequal duration of days and nights at different latitudes.
(ii) Different seasons. Both the effects are similar to slanted and vertical rays of the sun. For different seasons, the revolution of the earth around sun explained subsequently is however greatly responsible. The effect also goes on increasing from Equator towards poles.
REVOLUTION
Earth revolves around the Sun in an inclined position while continuing to rotate. The path around the sun, known as orbit, is elliptical or egg-shaped. Earth completes one revolution around the sun in 365and1/4 Earth days. While 365 days make one year, 1/4 day is added to the month of February. As a result February has 29 days every four year. This year is known as leap year. A leap year is always divisible by 4.
SEQUENCE OF SEASONS
The combined effect of the earth's inclination is revolution and rotation as well as journey on elliptical path is felt on earth through the sequence of seasons. The direct and slanting rays of the sun are also responsible for this sequence. We have four distinct and extreme positions of the sun on 21st March, 21, June, 23rd September and 22nd December.
The sequence of seasons is relative to these four positions of the sun - Summer, Autumn, Winter and Spring.
At the equator, there is just one hot summer season. In the Tropics, summer and winter alternate each other and in the subtropical regions, three distinct seasons prevail. There are four seasons in the temperate region, and frigid zones have short summers and long winters.
SOLSTICES
In the orbital path when the Northern Hemisphere is inclined the maximum towards the sun, the sunrays reach their northernmost point on the Tropic of Cancer as on 21st June. As a result, the days become longer and nights shorter at the North Pole. At this time, the opposite happens in the Southern Hemisphere. On December 22nd, the Southern Hemisphere is inclined the maximum towards the sun and the sunrays reach their southernmost point on Tropic of Capricorn. Therefore, the days become longer and nights shorter at the South Pole. These two extreme positions are known as the summer and winter Solstices respectively. The duration of days and nights from equator to pole and from one part of the year to another varies in rhythmic precision.
EQUINOXES
Since the sunrays fall vertically on the equator, in equatorial regions days and nights are of almost equal duration. On March 21st and September 23rd, the sunrays fall straight on the equator causing days and nights of equal length not only on the equator but throughout the world. These two days are known as Equinoxes.
EFFECTS OF REVOLUTION
Seasons occur almost in rhythmic order because the revolution of the earth and its inclination are in a fixed direction. The seasons vary from equator to poles in both hemisphere.
Between 10degreeN and S and23degree N and S, there are two seasons of long summers and short winter. Between 23degree N and S and 66degree N and S seasons vary between three to four. The poles experience six months day and six months nights respectively. As such, summer seasons is mild but winters are cold and harsh.
CLIMATE CHANGE
Climate must be distinguished from weather. In a sense, climate is a particular weather condition over a long period of time say 35 years. The earth's mean temperature is rising. As a result, climate is changing. On account of this change known as Global Warming, temperature of ocean water is slightly warm and glaciers on high mountains as well as over the Antarctica are melting. These changes are likely to produce an effect on earth's inclination which will produce many other changes particularly climate and life forms.
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