The periodic comet is Halley's comet, as it appears after regular interval of time (76 years).

No, the nearest star alpha Centauri is at a distance 40000000000000 km from the Earth. So, they can be expressed in light year.

Largest planet of solar system is Jupiter and smallest planet is Mercury.

No, some are dim (yellow) while some are bright (white).

No, as there is a need of a medium for the propagation of sound. On the moon, there is no such medium. Thus, we cannot hear the sound on the moon.

You might have heard from your parents that there are nine planets in our solar system. This was true till 2006.Pluto was the farthest planet from the sun. The International Astronomical Union (1AU)at a meeting held on 24 August 2006 adopted a new definition of planet. Pluto does not fit in this definition. It is no more a planet of the solar system. So, the solar system now consists of only eight planets.

In fact, the stars are present in the sky during the day-time also. However, they are not visible because of the bright sunlight.

As moon does not produce its own light, we see the moon because the sunlight falling on it gets reflected towards us. We, therefore see only that part of the moon, from which the light of the sun is reflected towards us.

When sun is shifting towards the south, then it is called dakshnayan and when the sun shifts towards the south, it is called uttarayan. So, the Sun shifts towards the south from 21 st June and it starts shifting towards north from 22nd December.

The moment, the meteors enter the Earth's atmosphere, then due to the friction of air, they get heated up and become visible. Then, they seen as a bright streak of light flashing for a moment across the sky, so they usually burnt out completely before reaching the surface of the Earth.

We know that (time period)2  ∝ (radius of orbit)3
\({ T }_{ 1 }^{ 2 }={ Kr }_{ 1 }^{ 3 }\)                     . . . (i)
\({ T }_{ 1 }^{ 2 }={ Kr }_{ 2 }^{ 3 }\Rightarrow { T }_{ 2 }^{ 2 }=\left( \frac { { r }_{ 1 } }{ 2 } \right) ^{ 3 }\)          .... (ii) \(\left[ \because { r }_{ 2 }=\frac { { r }_{ 1 } }{ { r }_{ 2 } } \right] \)
\(\frac { { T }_{ 1 }^{ 2 } }{ { T }_{ 2 }^{ 2 } } =\frac { { r }_{ 1 }^{ 3 } }{ { r }_{ 1 }^{ 3 } } \times 8\)
⇒ \({ T }_{ 2 }^{ 2 }=\frac { { T }_{ 1 }^{ 2 } }{ 8 } \)
⇒ \({ T }_{ 2 }=\frac { 1 }{ 2\sqrt { 2 } } \)
It means that time period reduces by \(\left( \frac { 1 }{ 2\sqrt { 2 } } \right) \) factor.
So, the days in a year will be approx. 129 instead of 365 days.

(a) Constellation
(b) Great Bear or Ursa Major
(c) Pole star