Stars and the Solar System

The stars the planets and many other objects in the sky are called celestial objects. For example: moon, nine planets, asteroids etc.

Just like Earth, half of the moon is lit by the sun, and half is in shadow at any given time. As the moon travels around the Earth, we see the moon from different angles, and thus can see different percentages of light and shadow. When the moon is full, the moon is on the opposite side of the Earth from the sun. As a result, we can see the whole of the lit side of the moon. At new moon, exactly the opposite alignment exists, with the moon being between the Earth and the sun. At that point, we can only observe the shadowed side of the moon. At first and third quarter moons, the moon is at a 90 degree angle from the Earth and sun.

Moon has no atmosphere and as we know sound cannot travel when there is no medium thus we cannot hear any kind of sound on the moon.

1. Moon: Moon is a celestial object that does not have its own sunlight; it is visible to us due to reflected sunlight. There is no atmosphere and water on the moon, its surface is dusty and barren. Moon revolves around the earth so it is also called the natural satellite of earth.
2. Stars: Stars are other celestial object that can be seen in the night sky. Sun is the nearest star from the Earth; the stars are millions of times farther than the sun, STARS are present in the sky during the day time also but because of the bright sunlight they are not visible to us. They appear to move from east to west in the sky.

A moon is simply a natural satellite that moves around a planet, tied gravitationally to its parent planet. But a star is a large mass of gas that generates energy due to the thermonuclear fusion reactions happening at their cores. They range in size from a few kilometres in diameter to several times larger than the solar system. They form large collections that make up star clusters and galaxies.

On July 21, 1969 the American astronaut, Neil Armstrong landed on the moon for the first time.

• Have their own light.
• Twinkles at night.
• Since the stars are very far away, the telescope can only make them look brighter but not larger
• A star has very high temperature.
• There are billions of stars in the celestial sphere

We are not able to see the stars during the day time because of the bright sunlight.

Earth rotates on its axis from west to east, thus stars appear to move from east to west.

Group of stars having a recognisable shape is called constellation. Constellation is an internationally defined area of celestial sphere. For example: Ursa Major, Orion etc.

1. Ursa Major: Ursa Major can be seen in the sky during summer time in the early part of the night, it is also known as Big Dipper or Saptarashi. There are seven prominent stars in this constellation; it appears like a big question mark or ladle.
2. Orion: Orion can be seen in the sky during winter in the late evenings. It has seven or eight stars. The brightest star Sirius is located close to the Orion.

Cassiopeia: Cassiopeia is a constellation that can be seen in the northern sky. It is visible during winter in the early part of night. It looks like distorted letter W or M.

Planets move in their own orbit, thus they do not collide while revolving around sun.

Any celestial body revolving around another celestial body is called its satellite. Aryabhatta, INSAT, IRS, EDUSAT, Kalpana- 1, etc. are some satellites.

Natural satellites are celestial body that orbits a planet or any other celestial body, they are found by nature. The most well-known natural satellite is the earth�s moon. The natural satellites are made up of natural materials like rocks, minerals, water, dust etc. The natural satellite cannot communicate on earth or with other planets. But artificial satellite is the device placed in orbit around the Earth, moon or other planet. They are man �made. The first artificial satellite was sputnik I. It can communicate with instruments on earth.

The artificial planet can communicate with instruments on earth. Artificial satellites have many uses, including relaying communication signals, making accurate surveys and inventories of the earth's surface and weather patterns, and carrying out scientific experiments.

1. Mercury: It is the nearest planet to the sun. It is the smallest planet of our solar system. It is very close to the sun so it is quite difficult to observe it. It has no satellite of its own.
2. Venus: It is the Earth's nearest planetary neighbour. It is the brightest planet in the night sky. Sometimes it appears in the eastern sky before the sunrise, and sometimes in western sky just after the sunset. Thus it is also called morning or evening star. It has no satellite of its own.

1. Jupiter: It is the largest planet of the solar system. It rotates very rapidly on its axis. It has a large number of satellites. It also has a faint ring around it.
2. Saturn: Saturn lies beyond Jupiter; it contains beautiful rings around it which is not visible with the naked eye. It has a large number of satellites. It is least dense among all planets.

Outermost planet of solar system includes planets like Jupiter, Saturn, Uranus and Neptune.

Jupiter: It is the largest planet of the solar system. It rotates very rapidly on its axis. It has a large number of satellites. It also has a faint ring around it.

Saturn: Saturn lies beyond Jupiter; it contains beautiful rings around it which is not visible with the naked eye. It has a large number of satellites. It is least dense among all planets.

Uranus: It can be seen via telescope only. In its orbital motion it appears to roll on its side. It rotates from west to east.

Neptune: It can be seen via telescope only. Neptune has a planetary ring system, though one much less substantial than that of Saturn.

Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones.

Small pieces of space debris (usually parts of comets or asteroids) that are on a collision course with the Earth are called meteoroids. When meteoroids enter the Earth's atmosphere they are called meteors. Most meteors burn up in the atmosphere, but if they survive the frictional heating strike the surface of the Earth and they are called meteorites.

Yes. Pole Star is located by Ursa Major. On a clear moonless sky during summer at 9.00 p.m. at the northern part of sky we can see Ursa Major. Imagine a straight line that passes through these stars and extend this line towards the northern side to a star that is not too bright. This is a Pole Star. This star does not move at all. Ursa Major moves east to west of this Pole Star.

Stars are very far from the earth, their distance if written in km will not be convenient to read and memorise, and thus large distances are expressed in light year. It is the distance travelled by light in one year.

Superstitious about comets is that comets are messengers of disasters, such as wars, epidemics and floods, but it is actually a myth as appearance of comets is a natural phenomenon.