Question 1

The sun rises two hours earlier in Arunachal Pradesh as compared to Gujarat in the west. But the clocks show the same time. How does this happen?

Accepted Answer

The sun rises two hours earlier in Arunachal Pradesh as compared to Gujarat in the west. But the clocks show the same time this happens because:i) The longitudinal gap between Arunachal Pradesh and Gujarat is about 30.ii) Due to this, there is time lag of about two hours between these states.iii) Since Arunachal Pradesh is in the east, the sun rises earlier here compared to Gujarat.iv) The Indian Standard Time is taken from the time of Standard Meridian of India and hence, the watches show the same time in both the states.

Question 2

Why $\displaystyle { 82 }^{ \circ  }{ 30 }^{ \prime  }E$ has been selected as the Standard Meridian of India?

Accepted Answer

The Standard Meridian is situated in the centre of all longitudes and latitudes in which India is located. It passes through Allahabad in Uttar Pradesh. The Indian Standard Time is calculated on the basis of 82&#8728;30&#8242;E82&#8728;30&#8242;E has been selected as the Standard Time for the entire country.

Question 3

What is a constellation? Name any two constellations.

Accepted Answer

The stars forming a group that has a recognisable shape is called a constellation. It is usually visible with naked eyes. Some examples of constellations are Ursa Major, Orion and Cassiopeia.

Question 4

The change in seasons on the Earth occurs because

Accepted Answer

We have seasons because the Earth is tilted as it makes its yearly journey around the Sun.The Earth's axis is tilted at an angle of $23.5^o$. This means that the Earth is always pointing to one side as it goes around the Sun. So, sometimes the Sun is in the direction that the Earth is pointing, but not at other times. The varying amounts of sunlight around the Earth during the year, creates the seasons. The tilt of the Earth's axis is the most important reason why seasons occur.The tilt of the Earth means the Earth will lean towards the Sun (Summer) or lean away from the Sun (Winter) 6 months later. In between these, Spring and Autumn will occur.Hence, the seasons occurs because the axis of rotation of the Earth is tilted with respect to the plane of its orbit.

Question 5

Variations in the length of day time and night time from season to season are due to _______.

Accepted Answer

Variations in the length of day and night time from season to season on the earth's surface is due to the axial tilt of earth's rotation axis with respect to its orbital axis. This causes variations in the intensity of Sun's rays falling at a given place over the span of a year leading to variations in day and night time.

Question 6

Why is the distance between stars expressed in light years? What do you understand by the statement that a star is eight light years away from the Earth?

Accepted Answer

Distance between stars are very large in magnitude. Hence a new unit is required so that the value of distance is not too big and is sensible. A light year is defined as the distance travelled by light in one year. $1\ ly = 9.461 \times 10^{12}\ km$$8\ ly = 7.57 \times 10^{13}\ km$A star is eight light years away from earth means that light from the star takes 8 years to reach the earth's surface. As shown above, its approximate distance from the earth is $7.6 \times 10^{13}\ km$.

Question 7

Mark the following statements as true (T) or false (F):(a) Pole Star is a member of the solar system.                          ( )(b) Mercury is the smallest planet of the solar system.             ( )(c) Uranus if the farthest planet in the solar system.                 ( ) (d) INSAT is an artificial satellite.                                            ( )(e) There are nine planets in the solar system.                          ( )(f) Constellation Orion can be seen only with a telescope.       ( )

Accepted Answer

(a) FPole Star is a star in the galaxy and hence not a part of the solar system.(b) TMercury is the smallest planet in the solar system and Jupiter is the largest planet in the solar system.(c) TUranus is the farthest planet to the sun in the solar system and Mercury is the closest planet to the earth in the solar system.(d) T INSAT or Indian National Satellite System is a series of artificial Indian satellites used for telecommunications, meteorology and search and rescue  operations.(e) FThere are eight planets in the solar system. They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Note the pluto is considered as a dwarf planet.(f) FOrion can be seen with naked eyes. It is one of the most magnificent constellations in the sky. It has seven or eight bright stars. Orion is also called the Hunter.

Question 8

Why do we need a Standard Meridian for India?

Accepted Answer

India is a large country. It covers a long range of longitudes ($\displaystyle { 67 }^{ \circ  }E$ to $\displaystyle { 97 }^{ \circ  }E$). As we know that variation in time is caused by longitudinal difference, so the time difference between the westernmost and the easternmost longitudes of India should be very large. For example, the time of Arunachal Pradesh should be two hours ahead of Gujarat, but such a situation could cause inconvenience in the activities like transmission of information across different parts of the same country. To avoid this, we designate the $\displaystyle { 82 }^{ \circ  }{ 30 }^{ \prime  }E$ longitude as Standard Meridian. The time at this longitude is accepted all across India as the Indian Standard Time.

Question 9

State whether given statement is True or False.INSAT is a natural satellite.

Accepted Answer

INSAT is an artificial satellite. Moon is the natural satellite revolving around the Earth.

Question 10

Fill in the blanks:(a) The planet which is farthest from the Sun is _______.(b) The planet which appears reddish in colour is ______.(c) A group of stars that appear to form a pattern in the sky is known as _____.(d) A celestial body that revolves around a planet is known as ______.(e) Shooting stars are actually not ______.(f) Asteroids are found between the orbits of _____ and ______.

Accepted Answer

(a) The planet which is farthest from the Sun is Neptune.(b) The planet which appears reddish in colour is Mars.(c) A group of stars that appear to form a pattern in the sky is known as constellation.(d) A celestial body that revolves around a planet is known as satellite.(e) Shooting stars are actually not stars.(f) Asteroids are found between the orbits of Mars and Jupiter.