The Earth and the Solar System

STD: VI

Knowing about the universe• All the objects we see

in the sky are called heavenly bodies or celestial bodies.

• They include the stars, planets, satellites, asteroids, meteors and comets.

The UniverseUniverse means everything that exists in space.Nobody knows how universe was formed.Most scientist believe that 2000 crore years ago

universe was formed by the Big Bang.Universe is very vast.No ordinary units can measure the distance

between two heavenly bodies. Thus, astronomers have come up with a special unit called the light year (The distance travelled by

light in one year).

GalaxiesUniverse has countless galaxies.Galaxy means a collection of billion stars, gas and

dust.Each galaxy vary in size, shape and brightness.

The sun & all stars belong to a galaxy known as the Milky Way or the Akash Ganga.

It has about 10,000 crore stars.

StarsThese are huge celestial bodies

made up of very hot gases.

They twinkle as they have their own heat & light.

They are far and appear small.

Stars

They are formed from the clouds of gas & dust in space called nebula

StarsThe Sun is also a star. It looks big as it is closer to

the earth.The other nearest star to the earth is Proxima

CentauriIt is more than 4.24 light years away.

Members of the Solar SystemThe word ‘solar’ comes from the Latin word ‘sol’ meaning ‘Sun’.

Family of the Sun is called as the solar system.It consist of the Sun, eight planets and their satellites, numerous asteroids, meteors & comets.

The SunLargest member of the solar system.Located in the center..A huge ball of gases.It is the main source of light & heat on the Earth.Is about 15 crore km away.Temperature 6000 *C.Light from the Sun takes about 8 minutes & 20 seconds to reach the Earth.

The PlanetsThe word planet means wanderer.All the planets revolve around the Sun in ‘elliptical’ paths called orbits.While revolving around the Sun they also rotate on their axes. Each planet takes its own time to complete 1 revolution & 1 rotation. Planets do not have their own heat & light.They shine as they reflect the light of the Sun.

The PlanetsThere are eight planets.Increasing distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus & Neptune.Decreasing size: Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars & Mercury. The inner planets (terrestrial) & the outer planets(gas giants).

MercuryIt is named after the

messenger of the Roman gods.

Temperature:Day: about 400 *CNight: about -170 *C

Venus

Named after Roman god of love & beauty.Its almost the same size as the Earth known as Earth’s twin.It shines brightly & is seen before sunrise as Morning star & after sunset as the evening star.

Earth

It is the only planet to support life.Also called as the Blue planet.

It is the largest among the inner planets.

Mars

It is named after the Roman god of war.It is known as the Red planet.It is about half the size of earth.Its rotational period is same as the Earth.

JupiterIt is named after the ruler of the Roman gods.Jupiter, with its moons, is described as a mini solar system by NASA.

SaturnIt is named after Jupiter’s father in Roman mythology.It has bright rings around its equator.

Uranus

It is named after the Greek god of sky.

It also has rings around its equator.

NeptuneIt is named after the Roman god of the sea.It is similar to Uranus in size & structure.The two are called twin giants.

Satellites

It means an attendant or a companion.They revolve around the planets from west to east.They do not have their light & reflect the light of the sun.Until 1610, moon is the only satellite.Today, there are more than 150 known satellite.Mercury & Venus do not have any satellite.

The MoonIt is the closest celestial body to the Earth.The Sun & the Moon appear to be of the same size, although the Sun is much bigger.The Moon is closer. It is about 3,84,400km away from the Earth.No life exist there because it neither has water nor an atmosphere.

Phases of the MoonMoon reflects the light of the sun thus, the visible shape of the Moon changes from night to night.

The waxing & waning of the Moon is known as the phases of the Moon.

Phases of the MoonIn its journey from full moon to new moon, its visibility decreases and the Moon is said to wane.

From new moon to full moon, the visible portion increases and the Moon is said to wax.

Phases of the MoonThe Moon is always half dark & half bright.The angle of view from the Earth keeps changing.

On the new moon day the dark hemisphere of the Moon faces the Earth & on the full moon day the bright hemisphere is visible to us.

AsteroidsThese are small planet like objects also called as

planetoids or minor planets.

Each asteroid follows its own orbit around the Sun.

Billions of asteroids between Mars & Jupiter.

It is believed that asteroids are some broken pieces of some planets, which exploded soon after their birth.

CometsComets are huge lumps of snow &

rocky dust.Revolve around the Sun in large

elliptical orbits.When it reaches close to the Sun its

starts glowing & develops a long tail.

The most famous comet- Halley’s comet.

It comes near the Earth every 76 years.

MeteorsMeteors are also known as shooting stars.These are small pieces of rocks and dust revolving

around the Sun.Their presence is known only when they enter the

Earth’s atmosphere.Most of them burn up & disappear as gases. Some are big & thus they do not burn up

completely.

They strike the Earth & are known as meteorites.