Important points to remember :
- The universe includes innumerable galaxies, the space between them and also energy.
- The scientist Edwin Hubble showed that there exist many galaxies beyond our Milky Way. In 1990, NASA, the American space agency launched the ‘Hubble Telescope’ in the orbit of the earth.
- There are innumerable galaxies in the universe. Our solar system, various star clusters are part of the Milky Way. z Various types of stars like the sun can be seen in the Milky Way.
- Different planets in the solar system have peculiar characteristics. Some planets have satellites whereas others do not have any.
- Comets have a characteristic structure but their appearance keeps on changing.
Question 1 : Name these
a) Birth place of stars: Nebula
b) Biggest planet in the solar system: Jupiter
c) The galaxy which is our neighbour: Andromeda
d) Brightest planet in the solar system: Venus
e) Planet with largest number of satellites: Jupiter
f) Planets without a single satellite: Mercury and Venus
g) Planet with a rotation different from other planets: Venus and Uranus
h) A celestial body that carries a tail along: Comets.
Question 2 : Fill in the blank
a) The group of galaxies of which our Milky Way is a part is called ‘Local Group‘.
b) Comets are made of ice and dust particles.
c) The planet Uranus appears as if it is rolling along its orbit.
d) Jupiter is a stormy planet.
e) The Pole Star is the best example of a variable type of star.
Question 3: Say if the statements given below are right or wrong. Rewrite the statements after correcting them.
a) Venus is the planet closest to the sun.
Answer : No, the statement is incorrect. Mercury is the planet closest to the Sun.
b) Mercury is called a stormy planet.
Answer : No, the statement is incorrect. Jupiter is called a stormy planet.
c) Jupiter is the biggest planet.
Answer : Yes, Jupiter is the biggest planet.
Question 4: Answer the following.
a) What is a special characteristic of the planet Mars ?
Answer : Mars : It is the fourth planet in the solar system. As the soil on Mars contains iron, its colour is reddish. Hence Mars is also called the Red Planet. The highest and longest mountain in the solar system ‘Olympus Mons’ is located on Mars.
b) What are the types of galaxies ?
Answer : The most widely used classification scheme for galaxies is based on one devised by Edwin P. Hubble and further refined by astronomer Gerard de Vaucouleurs. It uses the three main types, and then further breaks them down by specific characteristics (openness of spirals, size and extent of bars, size of galactic bulges).
c) Which celestial bodies does a galaxy include ?
Answer : A galaxy includes celestial bodies like sun, star, moon, comets, meteorite, planets, satellite, etc
d) Name the different types of stars.
Answer : There are many different types of stars in the Universe, from Protostars to Red Supergiants. They can be categorized according to their mass, and temperature.
Sun-like stars : These stars can be slightly smaller or bigger than the sun. But there is a lot of difference in their temperatures. Examples : stars like Sirius, Alpha Centauri.
Red Giants : The temperature of these stars ranges between 3000°C and 4000°C. But their luminance can be 100 times that of the sun. Their diameter is 10 to 100 times that of the sun and they are red in colour.
Super Nova : These are even brighter and larger than the red giant stars. Their temperature is between 3000°C to 4000°C but their diameter can be more than a hundred times greater than that of the Sun.
Binary or Twin Stars : More than half of the stars in sky are binary stars. They consist of two stars that revolve around each other. At times, three or four stars that revolve around each other have also been located.
Variable Stars : The luminance and shape of these stars is not stable. They are constantly contracting or expanding. When a star expands, it emits less energy and at such times its brightness decreases. As against this, when a star contracts, its surface temperature increases and the star emits greater energy and appears brighter. For example, Polaris (Pole Star).
e) What are the types of comets and on what basis are they classified ?
Answer : Comets are sorted into four categories: periodic comets (e.g. Halley’s Comet), non-periodic comets (e.g. Comet Hale–Bopp), comets with no meaningful orbit (the Great Comet of 1106), and lost comets (5D/Brorsen), displayed as either P (periodic), C (non-periodic), X (no orbit), and D (lost).
f) What is the difference between meteors and meteorites ?
Answer : Like meteorites, meteors are objects that enter Earth’s atmosphere from space. But meteors which are typically pieces of comet dust no larger than a grain of rice burn up before reaching the ground. The term “meteorite” refers only to those bodies that survive the trip through the atmosphere and reach Earth’s surface.
g) What are the characteristics of the planet Neptune ?
Answer : Neptune : It is the eighth planet in the solar system. A season on Neptune lasts for about 41 years. On this planet winds blow with extremely high speed.
# Can you tell
1. Which celestial bodies form the solar system?
Answer : Our solar system is filled with a wide assortment of celestial bodies – the Sun itself, our eight planets, dwarf planets, and asteroids – and on Earth, life itself! The inner solar system is occasionally visited by comets that loop in from the outer reaches of the solar system on highly elliptical orbits.
2. What is the difference between stars and planets?
Answer : The celestial object that has a fixed path (orbit), in which it moves around the star, are known as Planets. Stars have their own light, whereas planets do not have their own light, they reflect the sunlight that falls on the planets. … The temperature of a star is very high, while that of a planet is low.
3. How many planets are there in our solar system?
Answer : There are eight planets in our Solar System.
4. What is to be found between Mars and Jupiter ?
Answer : The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars, that is occupied by a great many solid, irregularly shaped bodies, of many sizes but much smaller than planets, called asteroids or minor planets.
5. Why do we see only one side of
Answer : Only one side of the Moon is visible from Earth because the Moon rotates on its axis at the same rate that the Moon orbits the Earth – a situation known as synchronous rotation, or tidal locking. The Moon is directly illuminated by the Sun, and the cyclically varying viewing conditions cause the lunar phases.
6. Which planet has a day longer
than its year?
Answer : Venus has the longest day of any planet in our solar system. It completes one rotation every 243 Earth days. Its day lasts longer than its orbit. It orbits the Sun every 224.65 Earth days, so a day is nearly 20 Earth days longer than its year.
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