I. Choose the correct option.
1.
Ans: (a)
Our solar system belongs to the Milky Way galaxy.
2.
Ans: (b)
Venus is the hottest planet in the solar system due to its atmosphere trapping heat.
3.
Ans: (b)
Saturn is the planet with rings made of ice and rock around it.
4.
Ans: (b)
Mars is often referred to as the Red Planet.
5.
Ans: (c)
Earth rotates on its axis from west to east.
6.
Ans: (c)
Chandrayaan 1 was India's first mission to the Moon.
7.
Ans: (a)
When the Moon's shape appears to be growing, it is called the waxing period.
8.
Ans: (b)
Asteroids as small, rocky, airless fragments that orbit the Sun.
9.
Ans: (c)
Meteoroids as chunks of rocky and metal debris orbiting the Sun.
10.
Ans: (a)
Light year is the unit used to measure distance in space.
II. State whether the following statements are true or false. Rewrite the statements to correct them.
1.
Ans: False
2.
Ans: False
3.
Ans: True
4.
Ans: True
5.
Ans: False
III. Answer the following questions In brief.
1.
Ans: A galaxy is a vast system of stars, stellar remnants, interstellar gas, dust, and dark matter, all bound together by gravity. Our solar system is part of the Milky Way galaxy.
2.
Ans: A star is a self-luminous celestial object that produces its own light and heat through nuclear fusion. A planet, on the other hand, does not produce its own light and shines by reflecting the light it receives from a star, such as the Sun. Planets orbit stars.
3.
Ans: We use a light year to measure the vast distances in space because it provides a more convenient unit of measurement. A light year is the distance that light travels in one year, which is approximately 9.46 trillion kilometers. It helps us express astronomical distances in more manageable terms.
4.
Ans: Comets are celestial objects composed of dust, gas, and ice particles. They have elongated orbits around the Sun. When a comet approaches the Sun, the heat causes the ice particles to vaporize, creating a visible tail of gas and dust. Halley's Comet is a famous example.
5.
Ans: Meteoroids are chunks of rocky and metal debris that travel through space. They are smaller than asteroids and can vary in size from tiny particles to several meters in diameter. When a meteoroid enters Earth's atmosphere, it is called a meteor.
6.
Ans: A meteor, commonly known as a shooting star, is the visible streak of light produced when a meteoroid enters Earth's atmosphere and burns up due to friction. It is the bright flash of light that we see in the sky.
IV. Answer the following questions in detail.
1.
Ans: Our solar system formed about 4.6 billion years ago from a large cloud of gas and dust in space. This cloud, called a solar nebula, collapsed under its own gravity. The center of the collapsing nebula became the Sun, and the remaining material formed a rotating disk. Within this disk, small particles began to collide and stick together, eventually forming planetesimals. These planetesimals further collided and accreted to form planets, moons, and other celestial bodies in our solar system.
2.
Ans: Earth is considered a unique planet because it is the only known celestial body in the universe where life exists. It has a combination of conditions that support life, including a suitable atmosphere, moderate temperatures, liquid water, and a diverse range of ecosystems. Additionally, Earth has a stable climate and a protective magnetic field, which helps shield it from harmful solar radiation. These factors make Earth distinct and special among the planets in our solar system.
3.
Ans: Satellites are celestial bodies that orbit around planets. They can be natural, like moons, or artificial, like human-made objects placed into orbit around a planet. India has an active satellite program. It launched its first satellite, Aryabhata, in 1975. Since then, India has made significant advancements in satellite technology. The Indian Space Research Organisation (ISRO) has launched various satellites for purposes such as communication, weather forecasting, navigation, remote sensing, and scientific research. Notable examples include INSAT series for communication and meteorological purposes, NavIC for regional navigation, and the Chandrayaan missions for lunar exploration.
4.
Ans: The waxing period of the Moon refers to the phase when the Moon appears to be growing larger in the sky. This occurs as the illuminated portion of the Moon that is visible from Earth increases. It starts with the New Moon and progresses through the First Quarter to the Full Moon phase.
The waning period of the Moon, on the other hand, refers to the phase when the Moon appears to be getting smaller in the sky. This happens as the illuminated portion of the Moon that is visible from Earth decreases. It starts with the Full Moon and progresses through the Last Quarter to the New Moon phase.
5.
Ans: Meteoroids are chunks of rocky and metal debris that travel through space. They are smaller than asteroids and can range from tiny particles to several meters in diameter. When a meteoroid enters Earth's atmosphere and produces a visible streak of light, it is called a meteor or a shooting star.
If a meteoroid survives the journey through the atmosphere and reaches the Earth's surface, it is referred to as a meteorite. Meteorites can be found on Earth and provide valuable information about the composition of celestial bodies beyond our planet. They can be made of rock, metal, or a combination of both.
