This PSEB 8th Class Science Notes Chapter 17 Stars and the Solar System will help you in revision during exams.
PSEB 8th Class Science Notes Chapter 17 Stars and the Solar System
→ The sky is dotted with countless stars, some bright and some not so bright. Some of them twinkle, too.
→ Moon is the brightest object in the sky.
→ Moon, stars, planets, and other objects in sky are known as celestial objects.
→ On full moon day, the moon is fully round, while on new moon day, no moon is visible in the sky.
→ The moon changes its shape from crescent moon to full disc and then disc to no moon. This cycle goes on. These are phases of the moon.
→ The moon reflects the light of the Sun falling on it, as it has not had its own light.
→ The moon revolves around the earth and the earth along with the moon revolves around the Sun.
→ The moon completes one rotation on its axis, as it completes one revolution around the earth.
→ Moon’s surface is dusty, barren, and is full of craters of different sizes.
→ Moon has neither atmosphere nor water.
→ Neil Armstrong was the first human being to set foot on the moon on July 21, 1969.
→ The distance between Sun and the earth is about 150 million kilometers.
→ The nearest star to the earth (next to the Sun) is Alpha Centauri, nearly 40 billion kilometers away.
→ A light-year is a distance traveled by light in one year.
→ Time taken by light to reach from Sun to earth is 8 minutes.
→ Alpha Centauri is 4.3 light-years apart from the earth.
→ Stars are invisible in day time due to bright Sunlight.
→ Stars appear to move from east to west.
→ The movement of stars is due to the rotation of the earth from west to east about its axis.
→ Pole star appears to be stationary in the sky, as it is situated in direction of the earth’s axis.
→ A constellation is a group of stars having a recognizable shape.
→ Ursa major/Saptarishi/Big dipper/The Great Bear is a common constellation during summertime.
→ All stars in the sky revolve around the pole star.
→ Orion, Cassiopeia, etc. are other important constellations.
→ The sun and the celestial bodies (planets, asteroids, comets, meteors, meteorites, satellites) which revolve around the sun form a solar system.
→ Planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Pluto, and Neptune.
→ Sun is the biggest star which is continuously emitting heat and light.
→ Planets are like stars, but without their own light and they revolve around the sun in fixed orbits and rotate around their own axes, too.
→ Any celestial body revolving around another celestial body is called a satellite. Moon is a natural satellite of the earth.
→ Artificial satellites are man-made satellites, which revolve around the earth.
→ Mercury is the nearest planet to the sun. It has no satellites.
→ Venus is neighbour to the earth and shows phases just like the moon.
→ The earth is the only planet with the existence of life on it.
→ Jupiter is the largest planet having 318 times the mass that of earth.
→ Saturn is yellowish in colour. It is beautiful due to the presence of rings around it.
→ Saturn is less dense than other planets and has a large number of satellites.
→ Uranus and Neptune are outermost planets and can be seen only with large powerful telescopes.
→ Inner Planets include Mercury, Venus, Earth, Mars, which are near to the sun and are also known as terrestrial planets.
→ Outer Planets or Jovian planets are far from the Sun and include Jupiter.
→ Saturn, Uranus, Neptune.
→ The gap between the orbits of Mars and Jupiter is occupied by a large number of small objects called asteroids.
→ Comets revolve around the sun in elliptical orbits and their period of revolution around the sun is very large.
→ Halley’s Comet was seen in 1986. It will again appear after 76 years.
→ Shooting Star or a meteor is a small celestial body revolving around the sun and appears like a streak of light in the earth’s atmosphere.
→ Large meteors which do not evaporate completely in the earth’s atmosphere are meteorites.
→ Aryabhatta (the first), INSAT, IRS, Kalpana-1, EDUSAT are Indian artificial satellites.
→ Weather forecasting, television and radio transmission, communication and remote sensing, etc. are some practical applications of artificial satellites.
→ Artificial satellites that revolve around the earth are much closer than the moon.
→ Celestial Objects: The objects found in the sky such as stars, moons, planets, sun, etc are called celestial objects.
→ Light year: The distance travelled by light in one year is called a light year.
→ Satellites: The celestial bodies which revolve around another celestial body are called satellites.
→ Planets: Celestial body revolving around another celestial body.
→ Asteroids: Small objects lying between the orbits of Mars and Jupiter.
→ Constellation: A group of stars having a recognizable shape.