Ans: Light year is a unit of distance .one light year is a distance covered by light in 1 year.
1 light year = 9.46 x 10^12 Km
A2.What is the source of stars energy?
Ans: The source of stars energy is nuclear fusion in which hydrogen atoms split up into helium atoms and large amount of energy is librated.
A3.What gives galaxies different shapes? Name a few common shapes of galaxies.
Ans: The arrangement of stars gives galaxies different shapes of galaxies. About 100 billians galaxies in the universe some of them are in shape of spiral, ring like or elliptical.
A4.What is the big Dipper?
Ans: The seven brightest stars in between the month of February and may form a shape of dipper in northern sky. This constellation is called Big deeper or Saptarshi.
A5. Why are Mercury venues, and Mars called terrestrial planets?
Ans: This is because they are closest to sun and rocky like earth.
A 6. Name the planet which have ring around them?
Ans: Saturn, Jupiter , Uranus and Neptune
A7. What is the huge spot on Jupiter?
Ans: This spots are actually a huge storm, which has been ranging on Jupiter for more than 300 years
A8. Name two dwarf planets?
Ans: Ceres and Eris
A9. How do dwarf planets different from other planets?
Ans: dwarf planets are not able to pull in the object (gravitational force) near its orbit at the time of its formation
A10.Why do scientists think that Mars had liquid water in the past?
Ans: Scientists think that Mars had liquid water in the past as the channels visible on its surfaces.
B1. What re the difference between stars and planets?
Stars are: a. luminous b. Stationary
Planets are : a. Non luminous b. Movable
B2. What re the difference between galaxy and constellation?
Ans: (i) The first difference is that a galaxy is a collection of billions of stars whereas a constellation is a collection of only a very few stars.
(ii) The second difference is that a galaxy does not form a definite pattern which resembles the shape of an animal or a human being but a constellation appears to resemble an animal or human being in its shape
B3. What are the asteroids?
Answer: There is a large gap in between the orbits of the Mars and Jupiter. This gap is occupied by a large number of small bodies that revolve around the sun. These are called asteroids
B.4.What is meteorites? In which bodies are meteorites craters more commonly found and why?
Ans: meteorites are rocky bodies revolving around the sun. Large meteors when hit the surface of planet create craters. Meteorites craters more commonly found on those planets and moon which have no or little atmosphere to burn off the falling rocks. E.g. Moon and mercury.
B5. What is comet? How is its tail formed?
Ans: Comet is small body of ice and dust revolving around the sun in its elongated orbit. When comet approaches the sun, it heats up and leaves behind a stream of hot glowing gases and dust particles. We see it as a tail.
B6. Why does geostationary satellite seem fixed above a point on the earth?
Ans: A satellite placed at about 3600 km above the equator completes one revolution around the sun in 24 hrs . This makes its position fixed above a point on the earth
B.7. why do other stars appear to move from east to west whereas the pole star appear to be stationary?
Ans: Pole star lies exactly above axis of the rotation of earth while other star does not. Therefore when earth rotates from west to east the star will appear to move from east to west to an observer on the earth but pole star appear stationary to same observer.
This property of pole star makes it useful to the sailors as they can locate north with the help of pole star
B.8. Why Venus is hotter than mercury even if it is far away from the Sun?
Ans: Venus has highest percentage of CO2 in its atmosphere that result into greenhouse effect.
B.9. why is mercury so hot during the day and cold at night?
Ans: Being close to sun, mercury turns extremely hot about 400 degree centigrade during day. As gravitational force is not enough to support hot atmosphere the temperature drops to - 200 degree centigrade.
B. 10. How far away is earth from the sun if sunlight takes 8.3 minutes to reach earth?
Ans: Time taken by sunlight to reach earth = 8.3 min = 498 sec
Speed of light = 3 x 10^8 m/s
Distance b/w earth and sun = 3 x 10^8 m/s x 498 sec = 1494 x 10^8 m
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