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
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