The Sun
Eight planets which revolves around the Sun- Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune
Satellites which revolve around their respective planets
Thousands of Comets and billions of meteoroids.

Planet is a celestial body
It orbits around the Sun
Has sufficient mass for self- gravity to overcome rigid body forces to assume a hydrostatic equilibrium (nearly round) shape
Has a clear orbital path

Planets have no light of their own.
All the planets except Venus and Uranus Rotate upon their axis from west to east. Venus and Uranus Rotate upon their axis from east to west.
The direction of the planets in their Revolution around the Sun is west to east.
Planets have satellites revolving around them. Earth has only one satellite (Moon), Jupiter has as many as 60, while Mercury and Venus have none.
Asteroids or Planetoids are very small planets or fragments of planets revolving around the Sun between the orbits of Mars and Jupiter.

Mercury and Venus which are closer to the sun than the earth are called Inferior planets while planets beyond the Earth are called Superior planets.
Mercury, Venus, Earth and Mars are called the Inner planets while Jupiter, Saturn, Uranus and Neptune are called the Outer planets.
Venus is the brightest among the planets, Mercury is the smallest while the Jupiter is the largest.
Mars is called the Red Planet and Earth is called the living or the Blue Planet.

Earth is not a perfect sphere but a spheroid which is compressed at the poles and bulges slightly along the equator.
It can also be called an oblate spheroid or an oblate ellipsoid.
The equatorial diameter of the earth is about 12,757 km (7,927 miles).
The polar diameter is about 12,715 km (7,901 miles).

Age: 4.6 billion years.
Mass: 5.976 x 1024 kg.
Volume: 1.083 x 1024 litres.
Mean Density: 5.518 kg/litre.
Shape: An Oblate Spheroid/Geoid.

Polar diameter- 12715.43 km; Equatorial diameter 12756.32 km.
Polar circumference 40,005 km and Equatorial Circumference 40,077 km.
Area
Total surface area 509.700.000 sq km.
Land area about 148.400.000 km (about 29% of the total area)
Water area about 361.300,000 sq. km (about 71% of the total surface area)

Rotation (spinning motion on its polar axis) once every 23 hours 56 minutes and 4.09 seconds.
Revolution (around the sun) once every 365 days 6 hours 9 minutes and 9.54 seconds.
Surface Features:
Highest point on land Mt. Everest is 8.850 metres above sea level.
Lowest area on landshore of Dead Sea is 399 metres below sea level . Mean height of land 756 metres.
Ocean Depths: Deepest area is Mariana Trench in Pacific Ocean southwest of Guam is 11.033 metres below sea surface.

Oxygen 46.6 %
Silicon 27.7%
Aluminium 8%
Iron 5.0%
Calcium 3.6%
Sodium 2.8%
Potassium 2.6%
Magnesium 2.0%
Other elements 1.6%

Mean Surface temperature: 14 deg C.
Highest temperature 58 deg C. Al Aziziyah, Libya.
Lowest temperature89.6 deg. C. at Vostok Station in Antarctica.
Inclination of the Polar Axis to the Orbital Plane : 66 deg 33 min 1 second.
Orbital Speed about the Sun: 29.8 km/second .
Mean Distance from the Sun : 149.598.500 km (one astronomical unit).

Geography is a spatial science and geographical study involving references to areas and locations. The location of a place or an area can be stated either in relative or absolute terms.
Relative Term- The location of a place or an area is expressed in relation to some known area or point. eg, Nepal is situated to the north of India.
Absolute Term- Location is stated in terms of Latitude and Longitude of a place or latitudinal and longitudinal extent of an area.

Latitude of a place is defined as its distance north or south of the equator, measured as an angle.
It is the angle subtended by a line drawn from a point on the surface of the earth to its center, with respect to the equatorial plane of the earth.
If all places having the same latitude are joined by a line or a smooth curve, the line thus produced will be parallel to the equator which is at 0 deg and they are counted up to 90 deg north and south, the two poles.
The lines of latitude are called Parallels.

Longitudes show the distance of a point east or west of the prime meridian which is at 0 deg and passes through Greenwich village near London in England.
There are 360 longitudes and all the longitudinal lines converge at the poles.
The longitude of a place is its distance east or west of the meridian of Greenwich, measured as an angle.
Lines joining all places situated at the same longitude are called Meridians.

The parallel (or latitude) of 0 deg is called the Equator. It is the line of reference for all latitudes. It divides the earth into Two hemispheres, The Northern and The Southern
Parallels of 23.2 deg North is known as the Tropics of Cancer.
Parallels of 23.2 deg South is called the Tropic of Capricorn.
Parallels of 66.2 deg North is known as the Arctic Circle
Parallels of 66.2 deg South is known as Antarctic Circle.

The two tropics, mark the limits of the zone in which the sunrays can be vertical at one time or the other.
In fact all places in this zone, except for the two tropics, experience vertical rays of the sun twice a year.
The sun is exactly overhead on the tropics only once a year at Tropic of Cancer on summer solstice and at the Tropic of Capricorn on winter solstice.
The Arctic and the Antarctic circles enclose the polar zones where one can experience a continuous day or night for or more than 24 hours. Outside these polar zones the day or night can never be as long as 24 hours or more.

Among the longitudes, the 0 deg or the meridian of Greenwich is known as the Prime Meridian and like equator in case of latitudes, it is the reference line for measuring longitude of various places.
The plane of prime meridian also divides the earth into two hemispheres, the eastern and the western hemispheres.
Area extending to its east up to 180 deg E is called the Eastern Hemisphere while that extending to its west up to 180 deg W is called the Western Hemisphere.

The line just opposite the Prime Meridian on the globe at the 180 deg longitude, is called the International Date Line.
It passes through Central Pacific and it is not a straight line as it avoids passing through major land mass or a single group of island.
The lntemational Date Line is the basis for keeping date and the date changes as one crosses this line.
The date in the Eastern Hemisphere is ahead of that in the Western Hemisphere. Therefore as one crosses this line one loses or gains a day depending upon whether the lnternational Date Line is crossed from west to east or vice-versa.

A great circle is a circle on the surface of the earth which divides the earth into two equal parts or hemispheres.
A great circle is the largest circle that can be drawn on the globe. Among the parallels of latitude only the equator is a great circle.
Small circle is the surface of the earth plane which does not pass through the center of the earth thus divides the earth into two unequal parts.
Among the meridians of longitude, all are great circles.
A great circle can be infinite in number and it need not follow particular latitude or longitude.
The arc of a great circle on the surface of the earth marks the shortest distance between two points on the earth. The navigators follow great circle routes to minimize the distance of their journeys.

Rotation
The earth has two motions namely Daily Rotation and Annual Revolution.
Rotation is the spinning movement of the earth on its axis and the earth completes one rotation in about 24 hours.
Due to this movement of the earth, each place on the surface of the earth faces the sun once in 24 hours. Hence we have day and night.
Revolution
The earth also revolves around the sun and completes one revolution in about 365.25 days. This is called its annual motion.
The annual revolution is responsible for the change of seasons.
The path of the earth around the sun (orbit) is Elliptical and consequently the distance between the earth and the sun keeps changing. It is minimum (147,000,000 km) around January 3, when the earth is in Perihelion, and is maximum (152,000,000 km) around July 4, when the earth is in Aplelion.

The Earths axis of rotation (the Polar Axis) is not vertical but inclined at an angle of 66 1/2 deg while the path of the ecliptic is tilted at 23 1/2 deg to form a line perpendicular to the plane of ecliptic.
The plane of ecliptic is imagined to be horizontal and passing through the center of the globe. The inclination of the axis of the earth and its orbit and the vertical sunrays which keeps changing from time to time results in difference in the energy received. This causes change of season.
When the angle of incidence of sunrays at a place is vertical or nearly vertical, more energy reaches the earth surface and there is summer season. When the sunrays at that place are slanting, it receives lesser energy from the sun and hence the winters.
Thus the change of season on the earth occurs due to the combined effect of the revolution of the earth around the sun and the inclination of its axis.

Due to the inclination of its axis, the Earth attains four critical positions in respect of the sun during its revolution around the sun. These are the Equinoxes and the Solstices.
Solstices
On June 21, the Earth is so located in its orbit, that the north polar end of its axis leans at the maximum angle of 23 1/2 deg toward the sun and the Tropic of Cancer receives the vertical rays of the sun. This condition is known as Summer Solstice (the longest day in the northern hemisphere). At this time the North Pole experiences a continuous day and the South Pole has a continuous night.
On December 22, the Earth is at an equivalent but opposite position in its orbit i.e., the Tropic of Capricorn receives the vertical rays of the sun. This condition is the Winter Solstice (the longest day in the southern hemisphere). At this time the North Pole experiences a continuous night and the South Pole has the continuous day.
During the Winter Solstice the Sun is not visible to a person on the North Pole and during the Summer Solstice, the Sun is not visible to a person on the South Pole.

Midway between the two Solstices occur the Equinoxes when the Earths axis makes a 90 deg angle with a line drawn to the sun i.e. the Equator receives the vertical rays of the sun and day and night are equal all over the world.
The Vernal or the Spring Equinox occurs on March 21.
The Autumnal Equinox on September 23.
When the sunrays are vertical in the Northern Hemisphere in the month of June they are highly slanting in the Southern Hemisphere. Likewise when the Sun is vertical over the Tropic of Capricorn in the Southem Hemisphere the sunrays are slanting in the Northern Hemisphere.
The seasons in the two hemispheres are therefore reverse of each other. When it is summer in the Northern Hemisphere, it is winter in the southern and vice-versa.

This quiz has been prepared with questions related to Solar System. These question were asked in various competitive exams across India. You can practice these questions to gain more knowledge.

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