Astronomy | Astrophysics Answers

3.
a) Discuss Jeans criterion for the formation of stars and obtain an expression for Jeans mass
and Jeans length.

b) A supernova explosion takes place at the distance of 4 pc. If the absolute magnitude of
the supernova is −25, calculate its apparent magnitude. Will the supernova be brighter
than the Sun? Justify your answer.

c) What is the qualitative difference between a main sequence star and a compact star?
Show that, as the mass of the white dwarf increases, its radius decreases. Briefly discuss
the consequences of this result.

2.
a) List different layers of the Sun’s atmosphere. Explain why the temperature in the
chromosphere increases with height. What gives rise to solar wind?

b) If the pressure in the solar atmosphere is 104 Pa, calculate the strength of the magnetic
field required to balance it (pressure).

c) What is the basis of classifying the planets in the solar system as terrestrial and jovian?
State nebular hypothesis. Explain briefly (in not more that 150 words) the formation of
solar system as per the nebular model.

1.
a) Express the distance of the star Proxima Centauri from the star Sirius B and the planet
Earth in light years.

b) Draw the celestial sphere and show the observer’s meridian, zenith, celestial equator and
the horizon for an observer at latitude 30°N. Show the horizon coordinates of a star X on
the celestial sphere for this observer. Would these coordinates be the same at latitude 60°
N?

c) Which telescope, optical or X-ray, would have higher resolving power for the same
aperture? Calculate the magnitude of the faintest object that a 20 m optical telescope can
detect.

d) The average temperature of the interior of a sun-like star is of the order 108 K. Estimate
the mass of the star in terms of the solar mass if it has a radius of order 1010 cm.

A binary system has a period of about 100 years and an average separation of 50 A.U. Its combined is about _______ solar masses

A)1000
B) 2197
C) 13
D) 14
E) 169