THE EARTH AND THE UNIVERSE

1. Exploring the Universe

• The stars are far bigger than the earth.
• Some of the stars have been estimated to be many millions of times the size of the Earth.
• These stars are not dispersed regularly in space: they occur in clusters, better described as galaxies or nebulas.
• Each galaxy may contain as many as 100 million stars.
• It is believed that the earth’s galaxy (the Milky Way) alone contains as many as 100,000 million stars.
• The stars appear small to us, even through a telescope because they are far away from us.
• The light from the nearest star travels towards the earth at the speed of 186,000 miles per second. It will take four years to reach Earth.
• The light rays from the sun reach Earth in eight minutes.
• Light takes only one second to reach us from the moon.

2. The solar system

The solar system comprises the sun and nine planets. These have been developed from the condensation of gases and other lesser bodies. All the planets revolve around the sun in an elliptical orbit. Planets shine only the reflected light of the sun. The sun has a surface temperature of 6,000®C and increases to 20 million ®c in the interior. The surface is filled with fairy gases that leap up going flames like a volcano in eruption. The sun is 300,000 times as big as the Earth.

• Mercury is the smallest and closest to the sun, only 36 million miles away. Mercury revolves around the sun for only 88 days.
• Venus, twice the distance away from the sun, is the second closest planet.  It is considered 'Earth's twin because of its closeness in size, mass (weight) and density.
•  Earth has life and all the living things. Like many other planets, the Earth has a natural satellite, the Moon, The distance from the Earth to the Moon is 238,900 miles. The moon revolves eastward around the Earth once every 27 days.
• Mars is the fourth planet from the sun.  Mars has dark patches on its surface.  It is believed that it is the next planet after Earth to have the possibility of some plant life.
• Jupiter is the largest planet in the solar system.  Its surface is made up of many gases like hydrogen, helium, and methane.  It is well known from other planets for its circular light and dark bands, and the twelve satellites that circle it. The distance from the sun is more than 485 million miles. its surface is very cold, probably about 200°F. (-130°C.).
• Saturn has three rings and nine satellites on it. It is the second-largest planet and it takes 29 ½ years to complete its orbit.
• Uranus: The seventh planet is Uranus, which was discovered in the eighteenth century. It is fifty times larger and fifteen times heavier than the Earth. It orbits around the sun in a clockwise direction from east to west with five satellites revolving around it.
• Neptune and Pluto: The two outermost planets in the solar system are Neptune and Pluto.  Their discoveries were the result of mathematical calculations on their irregular gravitational effects on neighbouring planetary bodies. Neptune closely resembles Uranus except that it has only been known to satellites and is probably much colder.  Pluto is smaller than Earth, as the orbits of the planets are not circular but elliptical.  The distance of Pluto from the Sun during perihelion (i.e. when it is closest to the Sun) is 2,766 million miles, and at aphelion (i.e. when it is farthest from the Sun) is 4,566 million miles. A year in Pluto is no less than 247 years on Earth.  Due to their very recent discovery and their extreme remoteness from the Earth, very little is so far known about these last two planets.

3. The Shape of the Earth

Sailors feared journeying far into the distant ocean because they thought the earth was as flat as a table. They thought that when they reached the edge of the earth, they would slip down and fall into the huge ocean. From years of collected knowledge, experience and observations in different parts of the world. We know that the earth is round. Its accepted spherical shape is a fact, proved, and done by all. There has been so much research on earth science that its various dimensions have been specifically found. It has an equatorial conference circumference of 24,897 miles and- its polar circumference is less than 83 miles. Its equatorial shorter by is 267,926 miles and its polar diameter is shorter by 26 miles. Earth is not a perfect sphere. It is a little flattened like an orange. The shape of the earth is the geoid. The spherical shape of the earth is masked by the intervening highlands and oceans on its surface.

Evidence of the Earth’s Sphericity

There are many ways to prove that the earth is spherical. The following are some of them.

• Circum-navigation of the Earth: The first journey around the world by Ferdinand Magellan and his team, from 1519 to 1522 proved past doubt that the earth is spherical. No traveller going around the world by land or sea has ever encountered an abrupt edge, over which he would fall. Modern air routes and ocean navigation are based on the assumption that the earth is round
• The circular horizon: The distant horizon viewed from the deck of a ship at sea, or from a cliff on land is always and everywhere circular. This circular horizon widens with increasing altitude and can only be seen on a spherical body.
• Ship’s visibility: The ship appears over the distant horizon, the top of the mast seen in the first before the hull. In the same way when it leaves the harbour, its disappearance over the curved surface equally. If the earth was flat the entire ship was seen or obscured at once.
• Sunrise and sunset: The sun rises and sets at different times in different places.  As the earth rotates from west to east, places in the east see the sun earlier than those in the west. If the earth were flat, the whole world would have sun, i. e and sunset at the same time. But we know this is not so.
• The lunar eclipse: The shadow cast by the earth on the moon during the lunar eclipse is always circular. It takes the outline of an arc of a circle. Only a sphere can cast such a circular shadow.
• Planetary bodies are spherical: All observations from telescopes reveal the planetary body, the Sun. Moon, satellites and stars have circular outlines from whichever angle you see them. They are strictly spheres. Earth, by analogy, cannot be the only exception.
• Driving poles on level ground on a curved earth; Engineers when driving poles of equal length at regular intervals on the ground have found that they do not give a perfect horizontal level. The centre pole normally projects slightly above the poles at either end because of the curvature of the earth.
• Aerial photographs: Pictures taken from the high latitudes by the rockets and satellites show clearly the curved edge of the earth. It is proof of the earth’s sphericity.

4. The earth’s movements

The earth moves in two ways: It rotates on its axis from west to east once in 24 hours causing day and night and It also revolves around the sun in an orbit once in 365¼ days causing seasons and years.

Day and night: The earth rotates on its axis, one side of the earth is exposed to sun rays and experiences day and the remaining part of the darker side experiences night. Earth rotates from west to east.

The Earth’s revolution

The Earth revolves around the sun, in an elliptical orbit at a speed of 18.5 million per second or 66,000 m.p.h. Earth revolves around the sun for 365¼ days. It is impossible to show a quarter of the day in a calendar. A normal year is taken to be 365 days and the extra day is added for every four years as a leap year.

• Varying lengths of day and night: The axis of the earth is inclined to the plane of the ecliptic at an angle of 66½, giving rise to different seasons and varying lengths of day and night. If the axis is perpendicular to the plane the day and nights would be equal. In the northern hemisphere in the winter if we go northwards the nighttime will be more.  At the Arctic Circle [66½N] the sun never rises and there is darkness for the entire day in mid-winter on 22^nd December. Beyond the Arctic Circle, the number of days with complete darkness increases towards the North Pole. Half a year would remain in darkness. In summer the conditions are exactly reversed. Daylight increases when we go towards the polewards. In the Arctic Circle, the sun never sets. In mid-summer [21 June] complete 24 hours of daylight. It is popularly known as the ‘land of the midnight sun. At the North Pole, there will be continuous six months of daylight. In the southern hemisphere, the same conditions are taking place, except the conditions are reversed.
• The altitude of the midday sun: The sun is vertically overhead at the equator on 21 March and 21 September each year. These two are termed equinox. Because of these two days, the world has two equal days and nights. After the March equinox, the sun appears to move north and vertically overhead on the tropic of Cancer on about 21 June. This is called summer solicit.  The northern hemisphere will have its longest day and the shortest night. 22^nd December the sun will be overhead at the tropic of Capricorn is called the winter solicit. Beyond these, the sun is never overhead at any time of the year.
• Seasonal changes and their effects on temperature: Summer is usually with more heat and brightness and winter is with cold and darkness. In the summer the sun is higher in the sky than in winter. The sun is overhead and its rays fall almost vertically on the earth, concentrating its heat over a small area. In winter oblique rays of the sun fall faintly, thus little heat and the temperature is low. Shorter nights and longer nights in the winter season reverse effect.
• Dawn and twilight: The brief period between the sun's rise and fall of daylight is said to be dawn. The period between the sunset and the complete darkness is said to be twilight. This is caused because the earth receives diffused or refracted light from the sun. The sun rises and sets in the vertical path at the equator the refracted light received is short. But in temperate latitudes, the sun rises and sets in an oblique path and the period of refracted light is longer. It is much longer still at the poles so the winter darkness is only twilight most of the time.

5. Mathematical location of places on the globe

The earth’s surface is so vast that mathematical methods can be used. It is impossible to locate any places on it. Imaginary lines are drawn on the globe. The lines running east to west parallel to the equator are called latitudes. The lines running north to south towards the poles are called longitudes. The intersection of the latitudes and longitudes pinpoint at any of the earth’s surfaces.

• Latitude: It is the angular distance of a point on the earth’s surface. These lines are also known as the parallel of the latitude. For precise location on the map, each degree is divided into 60 minutes and each minute is divided into 60 seconds. The important lines of the latitudes are the equator the tropic of Cancer [23½ N] and the tropic of Capricorn [23½S], the Arctic Circle [66½N] and the Antarctica Circle [66½S]. The linear degree of the latitude is longer at the poles than at the equator. At the equator 68.704 miles, at 45° 69.054 miles and the poles, it is 69.407 miles. The average is 69 miles. For the calculating distance to any place. Bombay is 18.55° N. It is therefore 18.55 ×69 or 1280 miles from the equator.
• Longitudes: It is an angular distance measured along with the equator to the east or west towards the prime meridian. The semi-circles that run from pole to pole passing through the equator are called meridians. The prime meridian passes through the Royal Astronomical Observatory at Green witch near London. As the parallels of latitude become shorter polewards, the meridian of the longitudes converges at the poles. The local time of the Greenwich Mean Time is sometimes referred to as the world time.

6. Longitude and time 

• Local Time: The earth makes one complete revolution of 360° in one day or 24 hours.  It passes through 15° in one hour or 1° in 4 minutes. The earth rotates from west to east, so every 15° we go eastwards, local time is advanced by 1 hour.  If we go westwards, local time is retarded by 1 hour.
• Standard time and time zones: A system of standard time was adopted to avoid confusion while travelling to different places. Most countries adopt their own standard time based on their central meridian. India’s standard meridian is 82.30° E, which is 5 hours and 30 minutes ahead of Greenwich Mean Time. The world has 24 standard meridian times, which consists of 15° longitude or 1 hour in time. The USA, Canada and Russia have several time zones due to their larger extent.
• The International Date Line: The International Date Line is where the date changes exactly when it crosses. If a traveller crossing the dateline from east-west loses a day and if he crosses west-east he gains a day. The crew knew nothing about adding a day for the One Strait, Fiji, Tonga and other islands to prevent the confusion of the day and date in some of the island groups that are cut through by the meridian. Some of them keep Asiatic or New Zealand standard time; others follow- the American date and time.