# PHE-15 English Medium Solved Assignment 2018

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Assignment Code: PHE-15/TMA/2018

Medium: English

Category:

## Description

PHE-15 Solved Assignment For IGNOU B.Sc

Course Code: PHE-15

Course Name: Astronomy and Astrophysics

Assignment Code: PHE-15/TMA/2018

Medium: English

#### Questions Solved In Assignment

1. a) Compare the brightness of the stars Sirius B and Sun using the data given in Table 1.3 of Unit 1.
b) Express the distances of the stars Sirius A and Antares from the Earth in light years.
2. a) The zenith distance of a star at latitude 60o N is 25o. Calculate its declination.
b) Explain the horizon coordinate system with the help of a diagram.
c) The local time at Allahabad is 5 PM. Calculate the local time at New Delhi at that time.
3. a) Explain the nebular model of the solar system.
4. a) The absolute visual magnitude of a star is 6.5 and for its temperature, the bolometric correction
is –0.3. Calculate the absolute bolometric magnitude and the luminosity of the star.
b) What is H-R diagram? Discuss the characteristic features of stars located in any two distinct regions
of the H-R diagram.
5. a) i Explain triple ɑ-reaction. Also discuss its significance in respect of the formation of heavier
elements.
ii Why does the synthesis of elements stop at iron?
b) The estimated lifetime of the Sun on the main sequence is ~ 10^10 years. Calculate the main sequence
lifetime of stars of masses i 5 Μʘ and ii 0.2 Μʘ .
6. a) Show that the pressure of a degenerate gas is independent of its temperature.
b) What is the Chandrasekhar limit? Discuss the fate of stars whose masses are beyond the Chandrasekhar
limit.
c) What causes emission of pulses from a rotating neutron star?
7. a) Explain how Cepheid variables can be used to measure astronomical distances.
b) Give arguments to support the Big Bang theory instead of the steady state theory.
8. a) State Hubble’s law. How can this be used to get an estimate of the age of the universe?
b) Explain the need to postulate the existence of dark matter in the universe.

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