STARS AND THE SOLAR SYSTEM

IMPORTANT TERMS

Astronomy                   The branch of science that deals with the study of celestial objects.

An Astronomer             A scientist, who studies matter in outer space or celestial objects such as Sun, moon, stars etc.

Orbit                            The path followed by an object revolving around another object.

Light Year                    Distance travelled by light in one year.

Satellite                       Small Solar system body that revolves around a planet and do not emit heat or light.

Constellation                A group of stars that seem to form a recognizable pattern in the night sky.

Galaxy                         A galaxy is a collection of billions of stars, dust and gases which are held together by gravity.

Waxing Moon               Growing in illumination; waxing moon goes from the new moon to the full    moon.

Waning Moon               Decreasing in illumination; waning moon goes from full moon to the new moon.

 

THE MOON

The moon is the only natural satellite of the Earth. It revolves around the Earth.

Moon is not a luminous body. i.e., it does not emit any light of its own. It only reflects the light of the Sun falling on it.

Moon does not have an atmosphere as it does not have enough gravity to hold onto a thick atmosphere like the Earth.

The changes in the shape of the moon as they appear from the Earth are known as phases of the moon.

The moon revolves around the Earth and the Earth along with moon revolves around the Sun. Due to the changes in the relative positions of the Earth and the moon, the phases of the moon occur.

The day on which the moon is not visible at all is known as the new moon day. On this day, the moon is positioned between the Earth and the sun. The face of the moon which receives the sunlight is away from the Earth and the side of the moon facing towards the Earth receives no direct sunlight, therefore, we do not see any moon at all.

The day on which a small portion of the moon becomes visible is called the crescent moon.

When more than half of the moon is visible, it is called the gibbous moon.

The day on which the moon appears as a complete disc is known as full moon day. The full moon can be seen when the Earth comes between the Sun and the Moon and the Moon is located 5 degree above or below the Earth.

STARS

  1. Stars are luminous bodies which emit light of their own.
  2. Sirius is the brightest star in the night sky.
  3. Pole Star is the only star which appears to be stationary from the Earth; this is because it is situated above the axis of rotation of the Earth
  4. The stars appear to move from east to west because of the Earth’s rotation.
  5. Milky Way is the galaxy to which we belong. It contains millions of stars.

CONSTELLATIONS

A constellation is a group of stars that seem to form a recognizable pattern in the night sky. Ursa Major, Ursa Minor, Cassiopeia, Orion and Scorpius are some well-known constellations.

Ursa Major can be seen during summer time in the early part of the night. It consists of seven stars. If we join these seven stars with an imaginary line, it forms the shape of a ladle or a dipper. It is also known as the Great Bear.

Ursa Minor is also called the Lesser Bear. The famous Pole star is present in this constellation. The arrangement of stars is similar to that of Ursa Major, but it is less bright than Ursa Major.

Cassiopeia is visible in the northern hemisphere during winters. The five prominent stars in the constellation make it look like the letter 'M' or 'W'.

Orion is the constellation which appears in the winter sky. It looks like a hunter with a bow therefore it is also known as ‘The Hunter’.

Scorpius constellation comprises some of the brightest stars in the night sky. The arrangement of stars in this constellation resembles a scorpion, with a long curving tail.

SOLAR SYSTEM

The Sun and the celestial bodies which revolve around the Sun form the Solar System. It consists of planets and small solar-system bodies.

All the planets revolve around the Sun in definite elliptical (oval) paths called orbits. They take different time to complete one revolution around the Sun.

SUN

The Sun is the nearest star to the Earth. The distance of the Sun from Earth is 8.3 light minutes, which means that the light from Sun takes 8.3 minutes to reach the Earth.

Sun is the major source of both heat and light for all the planets.

The Sun is mainly composed of hydrogen gas. By mass the composition of the sun is 75 percent hydrogen.

THE PLANETS

A planet is a celestial body that revolves around a star in an elliptical order. They do not emit light of their own but merely reflect the sunlight that falls on them.

Mercury, Venus, Earth and Mars are known as inner planets as they are much closer to the Sun than the other four planets and are mostly made of rocks and metal.

Jupiter, Saturn, Uranus and Neptune are known as outer planets. They are much larger and are mostly made of gases such as hydrogen and helium.

 

Planets

Time period of Revolution around the Sun

Time period of Rotation on Axis

Prominent Features

Mercury

88 days

59 days

Smallest planet and nearest to the Sun

Venus

225 days

243 days

Brightest and hottest planet

Earth

365 1/4 days or 1 year

24 hours

Blue Planet; only planet where life exists

Mars

1.9 years

 

Red Planet

Jupiter

 

12 years

9 hr 54 min.

Largest Planet

Saturn

29.5 years

10 hr 14 min.

Ringed Planet

Uranus

84 years

10 hr 49 min.

Highly tilted rotational axis

Neptune

165 years

15 hr

Appears blue in colour due to the presence of Methane gas.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DWARF PLANETS

Pluto

Pluto was earlier regarded as one of the planets of the solar system but according to the new definition it is no longer a planet. It has been degraded in the category of a dwarf planet.

Ceres

It is a dwarf planet which lies between the orbits of Mars and Jupiter.

SMALL SOLAR-SYSTEM BODIES

Asteroids

Asteroids are large pieces of rock or metal and rock, which orbit the sun between Mars and Jupiter. This region is known as the Asteroid Belt.

Comets

Comets are small chunks of ice and dust which revolve around the sun.They have a very long orbit and take a very long time to return. Halley's Comet appears once every 76 years.

Meteoroids, Meteors and Meteroites

Meteoroids are mainly chunks of rock or metals thrown around when a comet collides against asteroids.

When the Earth's orbit crosses the path of a meteoroid, it falls through the Earth's atmosphere. As it falls, it burns up due to the enormous heat generated. This produces a streak of light known as Meteor, also known as a "shooting star" or a "falling star".

Most of the meteoroids fully burn up before they reach the lower atmosphere but some of them reach the Earth as a solid piece. They are known as Meteorites.

ARTIFICIAL SATELLITES

Artificial satellites are man-made satellites revolving around the Earth.

Communication Satellites help in transmitting television and radio signals and internet messages.

Weather satellites send cloud pictures from above the Earth and are used for studying and forecasting weather.

The global positioning system (GPS) is a system of several satellites that can be used to locate positions anywhere on the earth. GPS satellites are now used for all kinds of navigation.

Remote-sensing satellites collect information from a distance using powerful cameras to scan the planet and send valuable data about mineral deposits, agricultural yields and other details.

Sputnik-1 was the first artificial satellite launched by Russia in 1957.

Aryabhatt was the first satellite launched by India in 1975.

Some other Indian satellites are EDUSAT, Rohini, Bhaskara-1 etc.

Bhaskara-1 was the first experimental remote sensing satellite built by India. It was launched on 7 June, 1979.

Rohini is the name given to a series of satellite launched by the Indian Space Research Organisation (ISRO). It was first launched in 1979.

Kalpana-1 is the first exclusive meteorological satellite launched by Indian Space Research Organisation in 2003.

EDUSAT is the first Indian satellite built exclusively for serving the educational sector and was launched successfully by Indian Space Research Organisation in 2004.

INTERESTING FACTS

 

  • Since the moon has no atmosphere, the shoe imprints left on the moon by the astronauts will remain for millions of years.
  • There are millions of galaxies which form the universe and there are approximately 200-400 billion stars in our Milky Way Galaxy alone.
  • The surface temperature of the Sun is around 5500 degrees Celsius.
  • The Great Red Spot is a giant storm seen for more than 300 years on Jupiter. It is more than twice the size of Earth. Winds inside this storm reach speeds of about 270 miles per hour.
  • The Greeks have given names to the constellations. These names came from their mythological heroes and legends.
  • The planets in the Solar System are given the names of Roman Gods or their attendants.
  • For thousands of years human beings were not aware of the Solar System and believed that Earth was at the center of the Universe.
  • When a meteoroid hits the atmosphere of the Earth, it can be travelling as fast as 130,000 mph (209,215 kmph).