PHE-15 ASSIGNMENT BOOKLET
Bachelor's Degree Programme Astronomy and Astrophysics (PHE-15)
Please send this assignment to:
Prof. Vijayshri Course Coordinator, PHE-15 School of Sciences, IGNOU, Room No. 128, Block D, New Academic Complex NEW DELHI 110068
School of Sciences Indira Gandhi National Open University Maidan Garhi, New Delhi-110068 2005-06 Dear Student,
We hope you are familiar with the system of evaluation to be followed for the Bachelor’s Degree Programme. At this stage you may probably like to re-read the section on assignments for Elective Courses in the Programme Guide that we sent you after your enrolment. A weightage of 30 per cent, as you are aware, has been earmarked for continuous evaluation which would consist of two tutor-marked assignments (TMA) for this course.
Instructions for Formatting your Assignments
Before attempting the assignment please read the following instructions carefully:
1) On top of the first page of your TMA answer sheet, please write the details exactly in the following format:
ENROLMENT NO.:……………………………………………
NAME :……………………………………………
ADDRESS :……………………………………………
……………………………………………
…………………………………………… COURSE CODE: ……………………………. COURSE TITLE : ……………………………. ASSIGNMENT NO. ………………………….… STUDY CENTRE: ………………………..….. DATE:.…………………………………...
PLEASE FOLLOW THE ABOVE FORMAT STRICTLY TO FACILITATE EVALUATION AND TO AVOID DELAY. 2) Use only foolscap size writing paper (but not of very thin variety) for writing your answers. 3) Leave 4 cm margin on the left, top and bottom of your answer sheet. 4) Your answers should be precise. 5) While solving problems, clearly indicate the question number along with the part being solved. Be precise. Write units at each step of your calculations as done in the text because marks will be deducted for such mistakes. Take care of significant digits in your work. Recheck your work before submitting it. 6) This assignment will remain valid for one year. We strongly feel that you should retain a copy of your assignment response to avoid any unforeseen situation and append, if possible, a photocopy of this booklet with your response.
We wish you good luck.
2 Tutor Marked Assignment 1 Astronomy and Astrophysics (PHE-15)
Course Code : PHE-15 Assignment Code : PHE-15/TMA-1/2005-06 Max. Marks : 100
Note: This assignment is based on Blocks 1 and 2. You must write answers in your own words. DO NOT reproduce from your study material.
1. (a) Express the distances of the stars Sirius A and Antares in light years. (5) (b) Compare the brightness of the stars Sirius B and Sirius A using the data given in Table 1.3. (5)
2. (a) The zenith distance of a star at latitude 60 N is 20. Calculate its declination. (5) (b) Explain the horizon coordinate system with the help of a diagram. What are its shortcomings?
(5)
3. (a) The local time at Chennai is 4 p.m. Calculate the local time at New Delhi at that time. (5) (b) Calculate the declination of a star which is circumpolar at latitude 60 N. (2) (c) Explain why northern and southern stars are equally visible for 12 hours for an observer on the equator. (3) 4. (a) Compare the resolving powers of a 1 m telescope at 550 nm and a radio telescope at 10 cm.
(5) (b) Calculate the magnitude of the faintest object that the 10 m Keck telescope can detect. (5)
5. (a) Explain the significance of the virial theorem in the study of the universe. (5) (b) What do you understand by local thermodynamic equilibrium? (5)
6. (a) Discuss different layers of the Sun's atmosphere. (5) (b) What is a sunspot? Is the temperature of the sunspot lower than its surroundings? If yes, explain why it is so. (5) (c) The temperature inside a sunspot is 300 K and that of its surface is 6000 K. Calculate the strength of the magnetic field inside the sunspot which will balance the pressure inside and outside. (5) 7. (a) Explain the nebular model of the solar system. (5) (b) Show that the magnitude of the tidal force experienced on the Earth due to the Moon depends on the latitude. (10) 8. (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. (5) (b) What is H-R diagram? Discuss the characteristic features of stars located in any two distinct regions of the H-R diagram. (5) 9. (a) Show that the radiative transport of energy gives rise to the temperature gradient in stars. (5)
3 (b) Explain how fusion reactions are made possible in the stars. (5)
Tutor Marked Assignment 2 Astronomy and Astrophysics (PHE-15) Course Code : PHE-15 Assignment Code : PHE-15/TMA-2/2005-06 Max. Marks : 100
Note: This assignment is based on Blocks 3 and 4. You must write answers in your own words; DO NOT reproduce from your study materials. 1. (a) What is the difference between the HII region and HI region of the interstellar medium? Explain the process involved in the detection of HI region in the ISM. (5) (b) What do you understand by Jeans criterion? Explain its role in the fragmentation of a collapsing cloud. (5) (c) A collapsing cloud is made of neutral hydrogen (HI) only. Calculate its Jeans mass taking its temperature as 40K and its number density as 1100 m3. (5)
2. (a) (i) Explain triple -reaction. Also discuss its significance in respect of the formation of heavier elements. (3) (ii) Why does the synthesis of elements stop at iron? (2) (b) The estimated lifetime of the Sun on the main sequence is ~ 1010 years. Calculate the main
sequence lifetime of a star of mass (i) 5 M and (ii) 0.2 M. (3 + 2)
3. (a) Show that the pressure of a degenerate gas is independent of its temperature. (6) (b) What is the Chandrasekhar limit? Discuss the fate of stars whose masses are beyond the Chandrasekhar limit. (5) (c) What causes emission of pulses from a rotating neutron star? (4)
4. (a) Discuss the characteristic features of the main components of the Milky Way Galaxy. (5) (b) The average energy of particles in the early phase of the universe, when it was very hot, was approximately 10 GeV. Calculate the corresponding temperature. (5)
5. (a) Explain Hubble’s scheme of galaxy classification. Why has this scheme proved enduring? What class has been assigned to the Milky Way Galaxy? (5) (b) Explain in your own words why older galaxies should be redder. (5)
6. (a) Define an active galaxy. What is the source of its activity? (5) (b) Is de Vaucouleurs law obeyed by elliptical galaxies? Explain. (5)
7. (a) Calculate the half-width of a spectral line of wavelength = 550 nm when the temperature of the gas is 6 105 K. Assume H atoms to be emitters. (5) (b) Explain the unified scheme for understanding active galactic nuclei. (5)
8. (a) Explain how Cepheid variables can be used to measure astronomical distances. (5) (b) Give arguments to support the hot Big Bang theory instead of the steady state theory. (5)
9. (a) State Hubble’s law. How can this be used to get an estimate of the age of the universe? (7)
4 (b) Explain the need to postulate the existence of dark matter in the universe. (3)
5