Ans. (a) All natural objects present in the sky outside the Earth’s atmosphere are called celestial objects. Examples: Sun, Moon, stars, planets, comets, asteroids (any four).

Ans. (b) During the power cut, the surroundings became darker. There was less artificial light, so light pollution reduced and the faint light from distant stars became more easily visible.

Ans. (c) During the day, bright sunlight is scattered in the atmosphere, making the sky bright. The faint light of distant stars is then not strong enough to be seen against this bright background.

Ans. (a) Stars are very far away and do have their own motion, but they do not revolve around the Earth. The apparent motion of stars across our sky is mainly due to the rotation of the Earth.

Ans. (b) The Earth rotates from west to east. Due to this rotation, stars appear to move in the opposite direction, that is from east to west, in the night sky.

Ans. (c) The nearest star to the Earth is the Sun.

Ans. (a) A constellation is a group of stars that appear to form a recognizable pattern or shape in the night sky.

Ans. (b) The seven bright stars forming a ladle are part of Ursa Major (Great Bear or Big Dipper). The hunter-like pattern with three stars in a line is Orion.

Ans. (c) Constellations help in locating stars like the Pole Star and were used in ancient times for navigation and making calendars. They also help sky-watchers identify regions of the night sky.

Ans. (a) They probably saw the constellation Ursa Major (Great Bear or Big Dipper).

Ans. (b) They should identify the two stars at the end of the “bowl” of Ursa Major (pointer stars), draw an imaginary line from the lower pointer through the upper one and extend it about five times the distance between them. The bright star on this line is the Pole Star.

Ans. (c) The Pole Star lies almost along the direction of the Earth’s axis of rotation. Therefore, as the Earth rotates, this star appears almost fixed in the sky while other stars seem to move around it.

Ans. (a) Stars are very far away and act as tiny point sources of light. When their light passes through Earth’s atmosphere, it is bent many times by moving air layers, causing the light to appear brighter and dimmer repeatedly. This gives the effect of twinkling.

Ans. (b) Planets are closer to the Earth and appear as small discs, not point sources. The atmospheric bending of light from different parts of the disc averages out, so planets usually shine steadily without twinkling much.

Ans. (c) Stars are much farther from the Earth than planets in our solar system, which is why they appear as points and twinkle, while planets do not.

Ans. (a) The solar system consists of the Sun and all celestial bodies that revolve around it, such as eight planets, their satellites, asteroids, comets and other small objects.

Ans. (b) The eight planets in order from the Sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Ans. (c) The fixed paths in which planets move around the Sun are called orbits.

Ans. (a) The first group is called inner planets (Mercury, Venus, Earth, Mars) because they are closer to the Sun and lie inside the asteroid belt.

Ans. (b) The second group is called outer planets (Jupiter, Saturn, Uranus, Neptune) because they are far from the Sun and lie beyond the asteroid belt.

Ans. (c) Inner planets are smaller and mainly rocky with few or no moons. Outer planets are very large, gaseous, often have rings and many satellites.

Ans. (a) Earth is called a unique planet because it is the only known planet where life exists.

Ans. (b) Two life-supporting conditions are: (i) Presence of liquid water. (ii) Suitable range of temperature (neither too hot nor too cold).

Ans. (c) The Earth’s atmosphere contains oxygen for breathing and carbon dioxide for photosynthesis. It also has an ozone layer that protects living beings from harmful ultraviolet rays of the Sun, making life possible.

Ans. (a) The phases of the Moon are the different shapes of the bright part of the Moon seen from the Earth at different times in a month.

Ans. (b) When the Moon is not visible, it is the New Moon phase. When it appears fully round, it is the Full Moon phase.

Ans. (c) Phases of the Moon occur because the Moon revolves around the Earth and we see different portions of its sunlit half, due to the changing positions of the Sun, Earth and Moon.

Ans. (a) The Moon’s surface is dusty and uneven with many craters, mountains and flat plains called “seas”, though they contain no water.

Ans. (b) The Moon has almost no atmosphere, so there is no air. Without air, there can be no winds, clouds or rain; hence there is no weather.

Ans. (c) Life is not possible on the Moon because: (i) There is no atmosphere containing oxygen. (ii) There is no liquid water and the temperature varies from extremely hot to extremely cold.

Ans. (a) The Moon takes about 27.3 days to complete one revolution around the Earth.

Ans. (b) It also takes about 27.3 days to rotate once on its own axis.

Ans. (c) Because the Moon’s rotation period and revolution period are almost equal, the same side of the Moon always faces the Earth and the other side always faces away from us.

Ans. (a) Asteroids are small rocky bodies that revolve around the Sun.

Ans. (b) Most asteroids are found in the asteroid belt between the orbits of Mars and Jupiter.

Ans. (c) Scientists believe that asteroids may be the remains of a large body or planet that could not form completely during the formation of the solar system and broke into small pieces.

Ans. (a) A comet is made mainly of ice, dust and gases.

Ans. (b) When a comet comes near the Sun, its ice and gases heat up and start evaporating, forming a bright head and a long glowing tail.

Ans. (c) The tail of a comet always points away from the Sun because solar radiation and solar wind push the gases and dust away from the Sun.

Ans. (a) They did not see real stars; they saw meteors, which are small stone-like objects entering the Earth’s atmosphere.

Ans. (b) As meteoroids enter the atmosphere at high speed, they rub against air and become hot. They burn and glow for a short time, producing bright streaks of light called meteors.

Ans. (c) If a meteor does not burn completely and its remaining part reaches the Earth’s surface, it is called a meteorite.

Ans. (a) A meteor shower is an event when a large number of meteors are seen in the sky in a short time.

Ans. (b) Meteor showers occur when the Earth passes through a region in space having many meteoroids, often the dusty path left behind by a comet.

Ans. (c) Most meteors burn up completely in the atmosphere and do not reach the ground, so meteor showers are generally not dangerous to people on Earth.

Ans. (a) An artificial satellite is a man-made object that is placed in orbit around the Earth or another planet using rockets.

Ans. (b) A powerful rocket carries the satellite to a certain height. At the required height and speed, the satellite is released in a direction tangential to its orbit so that it begins to revolve around the Earth.

Ans. (c) The Earth’s gravity pulls the satellite towards it, while the satellite’s forward motion tries to move it away. The balance of these two effects keeps the satellite in its orbit and it does not fall.

Ans. (a) Uses of artificial satellites include: communication (TV, telephone, internet), weather forecasting, remote sensing, navigation and scientific research.

Ans. (b) Weather satellites monitor clouds, storms and cyclones. They help in predicting severe weather and issuing warnings in advance, which saves lives and reduces damage.

Ans. (c) Remote sensing is the technique of collecting information about the Earth’s surface from a distance, usually from satellites, without direct contact.

Ans. (a) A natural satellite is a celestial body formed by nature which revolves around a planet. Example: Moon is the natural satellite of the Earth.

Ans. (b) An artificial satellite is a man-made object launched into space to revolve around the Earth or another planet. Example: INSAT.

Ans. (c) Natural satellites occur naturally and are irregular in shape, while artificial satellites are built by humans and have designed shapes. Natural satellites are studied mainly by scientists, while artificial satellites are used for communication, weather, remote sensing and research.

Ans. (a) The planet is closer to the Earth and appears as a small disc, so the atmospheric effects average out and it does not twinkle like distant stars.

Ans. (b) A comet moves around the Sun in a long orbit and appears for many days with a tail, whereas a meteor is a small body that quickly burns in the atmosphere and appears only for a moment as a shooting star.

Ans. (c) Both the planet and the comet are members of the solar system.

Ans. (a) Grouping planets as inner and outer helps remember their order, position and characteristics (rocky vs gaseous, smaller vs larger, few moons vs many moons) in a systematic way.

Ans. (b) Understanding phases of the Moon helps students clearly explain why the Moon’s shape seems to change, draw proper diagrams, and answer reasoning questions about New Moon and Full Moon in exams.

Ans. (c) Learning about artificial satellites is important because they are used for communication, weather forecasting, navigation and remote sensing, all of which are essential in modern life and national development.