DAV Class 8 Science Solution Chapter 17 Stars and Solar Systems
DAV School Books Class 8 Science Solution Chapter 17 Stars and Solar Systems all Question Answer. DAV Class 8 17th Chapter Stars and Solar Systems full Chapter explanation by expert teacher.
DAV School Books Class 8 Science Solution Chapter 17 Stars and Solar Systems
A.) Fill in the blanks.
1.) The spiral shaped galaxy, in which our solar system is located, is known as the ___________.
2.) The various shapes, of the bright part of the moon, as seen by us during the month, are called ___________ of the moon.
3.) The temperature on moon ranges from ___________ at ‘noon’ to ___________ at ‘night’.
4.) The planet, known to have the largest number of natural satellites, as at present, is ___________.
5.) The comet, which ‘visits’ the earth every 76 years, is the ___________.
6.) Asteroids are found between the orbits of ___________ and ___________.
Answer: (1) Milky way (2) phases (3) 100°C, -173°C (4) Saturn (5) Halley’s Comet (6) Mars, Jupiter.
B.) Match the following.
1. Star nearest to earth | a. orion |
2. Brightest star in the night sky | b. sun |
3.star which appear stationary from earth | c. ceres |
4. constellation | d. Pole star |
5. The largest asteroid | e. Geo-stationary satellite |
6. Global communication | f. sirius |
Answer: (1) b (2) f (3) d (4) a (5) c (6) e.
C.) Tick the correct option.
1.) A star is twenty light years away from the earth. Suppose it brightens up suddenly today. After how much time shall we see this change?
Answer: 20 years
2.) Three stars A, B and C are observed in the night sky. The colours of these stars are: Star A: Blue colour, Star B: Red colour, Star C: White colour. The correct sequence, in terms of the increasing order of their surface temperature, is-
Answer: Star B < Star C < Star A
3.) Stars, like the Sun, appear to move from east to west around the earth. This means that earth rotates from-
Answer: west to east
4.) Phases of moon are observed because-
Answer: it is only sunlight, reflected by some parts of the moon that reaches the earth.
5.) The change in seasons on the earth occurs because-
Answer: the axis of rotation of the earth is tilted with respect to its orbit.
6.) The diagram shows the various positions of a comet in its orbit. In which position will the tail of the comet will appear to be longest?
Answer: position A
D.) Answer the following questions in brief.
1.) Name the first two stars closest to us.
Answer: Sun and Alpha Centauri.
2.) Name the brightest star in the sky,
(a) during day time.
Answer: Sun is the brightest star in the sky during day time.
(b) during night.
Answer: Sirius is the brightest star in the sky during night.
3.) Identify the planet with the help of the given clue.
(a) largest planet
Answer: Jupiter
(b) closest to the sun
Answer: Mercury
(c) this planet has two moons named, Phobos and Deimos
Answer: Mars
(d) red planet
Answer: Mars
(e) has a unique and special system of rings
Answer: Saturn
(f) has the largest number of moons
Answer: Saturn
(g) often known as morning or evening star
Answer: Venus
(h) named after the Roman Sea god
Answer: Neptune
4.) Define the following.
(a) Milky way
Answer: The spiral galaxy that houses our solar system is known as the Milky Way.
(b) Celestial objects
Answer: Celestial objects are the things that are in space.
(c) Pole star
Answer: A star that, when observed from Earth, appears to be immobile is referred to as a “pole star.”
(d) Constellation
Answer: A constellation is a collection of stars in the nighttime sky that exhibits recognisable patterns or formations.
(e) Asteroids
Answer: Among Mars and Jupiter’s orbits, there are tiny planets called asteroids that revolve around the sun.
(f) Geo-stationary Satellites
Answer: Geo-stationary satellites orbit the earth with an orbital speed of almost 24 hours, which is the equivalent of the time it takes for the earth to rotate.
(g) Comets
Answer: A tiny, ice object that orbits the sun and, when it approaches the star, emits a long, brilliant gas tail.
(h) Light year
Answer: A Light year is the amount of distance that light travels in a calendar year.
(i) Meteors
Answer:a piece of rock or metal that falls into Earth’s atmosphere and burns and shines brightly in the sky.
(j) Meteorites
Answer: Meteorites are small pieces of rock or metal that occasionally fall to the ground from space.
5.) Name the visible layer of the sun. Give an estimate of its temperature?
Answer: The photosphere is the name for the solar surface. The layer in which the sun’s energy is released as radiation and heat is the sun’s outermost layer, which is visible to the human eye. Around 5,500 K is the temperature of the photosphere.
E.) Answer the following questions.
1.) How is Pole Star located in the sky? Explain with a diagram.
Answer:The Pole Star, sometimes referred to as the North Star and Polaris, is a star that may be found in the sky near the North Pole of the planet. It is the brightest star in the Little Dipper constellation of Ursa Minor, which lies close to the “tail” of Ursa Major, popularly known as the Big Dipper. The Pole Star is situated extremely near the celestial north pole at a nearly fixed position in the night sky. The North Celestial Pole, or the location in the sky which is directly above the North Pole of the Earth, is 1 degree away from where it is located.
2.) Differentiate between the following, giving examples:
(a) stars and constellations
Answer: A star is a single celestial object, whereas a constellation is a collection of stars that make up an observable pattern. This is the major distinction between stars and constellations. The stars that make up a constellation may be physically unrelated and positioned at significantly different distances from the Earth; they only look close in the sky from the viewpoint of the observer.
(b) stars and planets
Answer: The primary distinction between stars and planets is that although planets are non-luminous objects that revolve around stars and reflect the star’s light, stars are luminous objects that produce energy through nuclear fusion. The size and mass of stars are also substantially greater than those of planets.
(c) terrestrial planets and Jovian planets
Answer: Terrestrial planets include those with a solid surface and are generally made of rock or metal. The terrestrial planets Mercury, Venus, Earth, as well as Mars are a few examples.
Jovian planets, commonly referred to as gas giants, lack a solid surface and are mostly made of gases like hydrogen and helium. Saturn, Uranus, Neptune, and Jupiter are a few examples of Jovian planets.
(d) artificial and natural satellite
Answer: A man-made structure that is launched into orbit around the planet or another heavenly bodies is called an artificial satellite. These satellites are often used for communications, navigational, or scientific study. The International Space Station, GPS stations, including weather satellites are a few examples of artificial satellites.
A celestial object that revolves around with a planet as well as other celestial entity is called a natural satellites, also referred to as a moon. Earth’s natural satellite is the moon. Titan, which orbits Saturn, and Ganymede, which orbits Jupiter, are more examples of natural satellites.
3.) Identify, and name the constellations X, Y and Z and answer the following questions.
Answer: Constellations X is Orion; Constellations Y is Big Dipper and Constellations Z is Cassiopeia.
(a) Name the constellation that can be used to locate star Sirius?
Answer: Orion.
(b) Name the constellation that can be used to locate the Pole Star.
Answer: Big Dipper
(c) Name the constellations visible during the-
(i) spring season
Answer: Ursa Major.
(ii) winter season
Answer: Cassiopeia.
(d) Name the stars A and B in the constellation marked as ‘X’
Answer: A is Betelgeuse and B is Riget.
4.) Give reasons for the following.
(a) Uranus is observed to have a ‘blue-green’ colour.
Answer: Methane gas found in Uranus’ atmosphere is responsible for the planet’s apparent “blue-green” hue. The planet appears this colour because methane reflects blue-green light while absorbing red light. The blue-green hue of the planet is further accentuated by the methane clouds’ reflection of sunlight.
(b) Venus is the hottest planet even though Mercury is closest to the sun.
Answer: Venus’s dense atmosphere, which is mostly made of carbon dioxide, makes it the warmest planet even though Mercury is closest to the sun. The surface temperature is substantially higher than that of Mercury because of the atmosphere’s ability to trap heat and produce a greenhouse effect. One side of Venus is exposed to the sunlight for a longer duration of time than the other due to Venus’ sluggish rotation on its axis. This aggravates the dense atmosphere’s heating effect even more. On the other hand, Mercury has a weak atmosphere, a barren surface, and few or no substantial heat-trapping gases, allowing heat to readily escape.
(c) The shape and size of bright side of moon appears to change (gradually) every day.
Answer: Due to the process of lunar phases, the bright part of the moon seems to shift in size and shape every day. The moon’s eccentric orbit around the Planet means that sunlight rays hit the moon’s surface at different angles as it moves through space. As a result, the lighted area of the moon that can be seen from Earth appears to fluctuate in size and shape. The moon’s movement on its axis and orbit around the Earth are also in time with one another, which adds to the brilliant side of the moon’s dynamic look.
(d) A star appears to rise four minutes earlier in the sky everyday than the previous day.
Answer: Due to the Earth’s revolution on its axis, a star appears to emerge in the sky every day four minutes earlier than it did the day before. The stars appear to move throughout the sky because the Earth finish one rotation of its axis every 24 hours. The “apparent motion” of the stars is the name given to this phenomena.
(e) Comets become visible only when they are near the sun.
Answer: Since comets are composed of ice, dust, as well as other flammable substances that sublimate, or transform from a solid to a gas, when warmed by the sun’s radiation, comets are only observable when they are close to the sun. A brilliant coma—a cloud of gases and dust surrounding the comet’s nucleus—is produced as the comet approaches the sun because the increasing temperatures causes a greater amount of ice and particles to sublimate. We can see the comet because of its coma and the tail that develops behind it.
5.) State, in brief, how artificial satellites are used in transmitting television programmes over large distances.
Answer: Through a technology known as satellite television, television broadcasts are sent across great distances using artificial satellites. A transponder aboard a geostationary satellite receives a television signal, amplifies it, and then delivers the signal back to Earth. A dish antenna, that is frequently found on the rooftop of a structure or residence, subsequently takes in the signal. After being decoded by a set-top box, the data is then delivered to the television to be viewed.