The stars, the planets, moons and many other objects which are present in the sky are known as celestial objects.
THE MOON
The different shapes of bright part of the moon visible during months are called phases of the moon.
Different Phase of Moon
- Full moon day: the day on which the whole disc of the moon is visible.
- New Moon day: After the full moon day, the moon appears to become thinner and thinner. On the fifteenth day the moon is not visible. This day is known as the new moon day.
- Crescent moon: on the fifteenth day, only a small portion of moon is visible.
Moon has different phases because-
- Moon does not produce its own light and reflects the light coming from sun which is responsible for various phases.
- After new moon day, the visibility size of illuminated part of moon seen from Earth keeps increasing and after full moon day it keeps decreasing.
Moon is visible due to reflected sunlight Positions of the moon in its orbit and its corresponding phases.
The Moon’s Surface
- The Moon’s surface is dusty and barren
- There are many different sizes craters on it. Moreover, there are many high and small mountains.
- The Moon has no atmosphere and water.
THE STARS
- These are objects which twinkle in the sky at night.
- There is large number of stars in the sky.
- Sun is the nearest star to our planet which is approx 150 million km away from Earth.
- The distance of the Sun from the Earth may be said to be about 8 light minutes.
Light Year
it is defined as the distance travelled by light in one year. And it is the unit to measure large distances. The speed of light is about 300,000 km per second.
The star which is situated in the direction of the earth’s axis is known as pole star.
CONSTELLATIONS
The stars forming a group that has a recognisable shape is known as a constellation.
Some constellations in the night sky are-
- Ursa Major
(i) This constellation consists of seven stars.
(ii) It looks like a big ladle or a question mark. There are three stars in the handle of the ladle and four in its bowl.
(iii) It is also known as Big Dipper, the Great Bear or the
- Orion
(i) It is another well known constellation visible during late evenings in winter.
(ii) It also consists of seven or eight bright stars. The three middle stars in Orion represent the belt of the hunter and the remaining four bright stars are arranged in the form of a quadrilateral.
(iii) Orion is also called the Hunter.
- Sirius
(i) It is the brightest star in the sky.
(ii) To find the location of Sirius, imagine a straight line passing through the belt of three middle stars of Orion.
- 4. Cassiopeia
(i) It is another popular constellation in the northern sky. It is visible during winter in the early part of the night. It looks like a distorted letter W or M.
THE SOLAR SYSTEM
The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being smaller objects, such as dwarf planets and small Solar System bodies.
The eight planets in their order of distance from the Sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
- The Sun-The Sun is the nearest star amongst all the stars present in the universe.
It is the main source of heat and light for all the planets specially Earth.
- The Planets:
- The planets look like stars, but they do not have light of their own.
- They merely reflect the sunlight that falls on them.
- The planets keep changing their positions with respect to the stars.
These are the objects revolving around the sun in fixed path.
- This fixed path is termed as an orbit.
Period of revolution:It is the time taken by planet to complete full revolution around the sun.
2. Period of rotation: It is the time taken by planet to complete one rotation around its own axis.
3. Satellite: These are the celestial bodies present around other celestial body. Example Moon is a satellite of the Earth.
4. Artificial satellite: These are the man-made satellite present around the Earth.
Planets Revolving Around the Sun:
- Mercury (Budh)
- Nearest planet to the Sun and the smallest planet present in our solar system.
- It is very difficult to observe it, as most of the time it is hidden in the glare of the Sun.
- Mercury has no satellite of its own.
- Venus (Shukra)
- It is nearest planet to Earth.
- It is the brightest planet visible in the night sky.
- It is also called a morning or an evening star, because it appears in the western sky just after sunset.
- Venus rotates on its axis from east to west.
- Venus show phases just like the moon.
- Venus has no moon or satellite of its own.
- The Earth
- It is the only planet in the solar system on which life exists.
- Earth appears blue green due to the reflection of light from water and landmass on its surface.
- The axis of rotation of the Earth is not perpendicular to the plane of its orbit. The tilt is responsible for the change of seasons on the Earth.
- It has only one moon or satellite of its own.
- Mars (Mangal)
- It looks somewhat reddish and, so, it is also known as the red planet.
- Mars has two small natural satellites.
- Jupiter (Brihaspati)
- It is the largest planet of the solar system. It rotates very rapidly on its axis.
- Jupiter has a large number of satellites. And also has faint rings around it.
- It is about 1300 times larger than that of earth and its mass about 318 times than that of our Earth
- Saturn (Shani)
- It is yellowish colored planet.
- There are beautiful rings around this planet, which are not observed in any other planets.
- It is the least dense among all the planets. Its density is less than that of water.
- Uranus
- It is the one of outermost planet of the solar system.
- The most distinctive feature of Uranus is that it has highly tilted rotational axis.
- Neptune
- It is the outermost planet of the solar system.
- The outer planets have large number of moon.
SOME OTHER CELESTIAL MEMBERS OF THE SOLAR SYSTEM
- ASTEROIDS
- The small rocks like substances that are orbiting around the Sun are called asteroids.
- It is found in large gap between the orbits of Mars and Jupiter.
- They are visible only through large telescopes.
- COMETS
- They revolve around the Sun in highly elliptical or circular orbits.
- It looks like as if it has a bright head with a long tail and it is been seen that the tail keeps growing in size as it keeps approaching the sun.
- METEORS
- These are small objects that sometimes enter the Earth’s atmosphere.
- It occasionally enters the earth’s atmosphere with very high speed. Due to friction of earth's atmosphere, It glows then evaporates quickly. That is why the bright steak lasts for a very short time.
- METEORITE
- These are the leftover object that reaches the Earth.
- Meteorites help scientists in investigating the nature of the material from which the solar system was formed
- ARTIFICIAL SATELLITES
- Man-made satellites that revolve around the Earth.
- Aryabhatta was the first Indian satellite.
- Some other Indian satellites are INSAT, IRS, Kalpana-1, EDUSAT,
- Used for weather forecasting, transmitting television and radio signals. They are also used for telecommunication and remote sensing.