• The stars occur in clusters described as galaxies or nebulas.
• Each galaxy contain as many as 100 million stars.
• The Earth‟s own galaxy is the milky way.
• A ray of light from the sun takes about 8 minutes to reach the earth.
• Light takes only a second to reach us from the moon.
• All the planets revolve round the sun in elliptical orbits.
• The earth shines by the reflected light of the sun.
• The Sun has a surface temperature of 6,000 degree Celsius.
• Mercury is the smallest and closest to the sun. A year in Mercury is only 88 days.
• Venus is often considered as Earth‟s twin because of their close proximity in size, mass and density.
• The Earth has a natural satellite, the moon, 2,38,900 miles away, that revolves eastward around the earth once in every 27 days.
• Jupiter is the largest planet in the solar system. Jupiter is distinguished from other planets by its circular light and dark bands, and the twelve satellites circle round it.
• Saturn has three rings and nine satellites around it. Saturn is the second largest planet.
• Unlike other planets, Uranus orbits around the sun in a clock wise direction from east to west with five satellites revolving around it.
• Earth is not a perfect sphere. It is a little flattened at both ends. The shape of the Earth is called Geoid.
Evidence of Earth‟s sphericity:
1. Circum navigation of the earth: The first voyage around the world by Ferdinand Magellan from 1519 to 1522 proved that the earth is spherical. They had not encountered any abrupt edge over which they would fall
2. 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 in shape.
3. Ship‟s Visibilty: When a ship appears over the distant horizon, the top of the mast is seen first before the hull.
4. Sunrise and Sunset: As the earth rotates from west to east, places in the east see the sun earlier than those in the west.
5. The Lunar Eclipse: The shadow cast by the earth on moon during the lunar eclipse is always circular.
6. Aerial photographs: Pictures taken from high altitudes by rockets and satellites show clearly the curved edge of the earth.
• When the earth revolves round the sun, it spins on an elliptical orbit at a speed of 18.5 miles per second.
• The axis of the earth is inclined to the plane of elliptic at an angle of 66 ½ degrees, giving rise to different seasons and varying lengths of day and night.
• At the Arctic circle, the sun never rises and there is darkness for the whole day in mid-winter on 22 December. During mid-summer (21 June) the sun never sets and there is complete 24 hour period of continuous daylight.
• In summer the region north of the Arctic circle is popularly referred to as “ Land of the midnight Sun”.
• Mid-Summer at the north pole will be mid-winter at the south pole.
• The sun is vertically overhead at the equator on two days each year. These are usually 21 March and 21 september. These two days are termed equinoxes meaning equal nights because on these two days all parts of the world will have equal days and nights.
• June or Summer Solstice: The sun is vertically overhead at the tropic of cancer (23 ½ degree North). This is on June 21.
• Winter Solstice: The sun will be overhead at the Tropic of Capricorn (23 ½ degree South).
• The summer is usually associated with much heat and brightness because –
• In Summer the sun is higher in the sky. When the sun is overhead its rays fall almost vertically on the earth.
• Days are longer and nights are shorter in summer. More heat is received during longer daylight.
• The brief period between sunrise and full daylight is called Dawn.
• The brief period between sunset and complete darkness is termed twilight.
• The lines drawn on the globe that runs east and west parallel to the equator are called lines of latitude.
• The lines drawn on the globe that runs north and south passing through the poles are called lines of longitude.
• The most important lines of latitude are
i. The equator
ii. The tropic of cancer
iii. The tropic of Capricorn
iv. The arctic circle
v. The Antarctic circle
• On globe longitude is shown as a series of semi circles that run from pole to pole passing through the equator. Such lines are also called Meridians.
• The Royal Astronomical Observatory at Greenwich, near London represents zero degree meridian or the Prime meridian.
• India has accepted the meridian of 82.5 degree east for the standard time which is 5 hours 30 minutes ahead of Greenwich Mean Time.
• Both Canada and the USA have 5 time zones – the atlantic, Eastern, central, Mountain and pacific time zones.
• 180 degree meridian is the International date line where the date changes exactly by one day when it is crossed.