1. Attempt any five parts

A star is brought from 40 pc to 5 pc. Calculate the change in its magnitude.

Discuss the characteristics of globular clusters.

If the estimated main sequence life-time of the Sun is 10^10 years, calculate the main sequence life-time of a star having mass 0·25M0·

Sketch the Milky Way galaxy and label its various components.

Compute the size of a star in terms of R0 if its temperature is 5000 K and absolute magnitude is -10.

Explain why the solar corona is observed only during total solar eclipse.

Sketch the coordinates of the Pole star in the horizon system.

Sketch the mass-radius relation for a white dwarf star and explain its importance.

2. Define luminosity and the radiant flux. Using
Stefan-Boltzmann law of radiation, obtain the ratio of radii R1 and R2 of two stars with surface temperatures T1 and T2 and of absolute magnitudes M1 and M2, respectively.
OR
What is meant by the resolving power of a telescope? Explain the Rayleigh criterion for resolution. Calculate the diffraction limit of resolution of a 3 m telescope for the wavelength of 600 nm.

3. What do you mean by a polytropic change Obtain expressions for pressure and central temperature for polytropic stellar model.
OR
State virial theorem. Starting with the equation of hydrostatic equilibrium

dP/dr

prove the theorem for the star made up of monoatomic gases.

4. State Jeans criterion for the collapse of a molecular cloud. Obtain an expression for Jeans mass.
OR
What is the basic difference between the first generation stars and the second generation stars? Write and discuss the nuclear chain reaction involved in the CN-cycle. Why are the stars, in which energy is generated by the CN-cycle, generally found in the upper region of the main sequence in the H-R diagram?

5. Explain how the Cepheid variables are used to estimate astronomical distances.
OR
What are active galaxies Explain the main
features of Seyfert galaxies.

Physical Constants:

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