Fundamentals of SOI,AR ASTRONOMY WORLD SCIENTIFIC SERIES IN ASTRONOMY AND ASTROPHYSICS Editor: Jayant V. Narlikar Inter-University Centre for Astronomy and Astrophysics, Pune, India Published: Volume 1: Lectures on Cosmology and Action at a Distance Electrodynamics F. Hoyle and J. V. Narlikar Volume 2: Physics of Comets (2nd Ed.) K. S. Krishna Swamy Volume 3: Catastrophes and Comets* V. Clube and B. Napier Volume 4: From Black Clouds to Black Holes (2nd Ed.) J. V. Narlikar Volume 5: Solar and Interplanetary Disturbances S. K. Alurkar Forthcoming: The Universe: From Inflation to Structure Formation V. SahniandA. A. Starobinsky Dust in the Universe K. S. Krishna Swamy 'Publication cancelled. World Scientific Series in Astronomy and Astrophysics - Vol. 6 F u n d a m e n t a ls of SOIAR ASTRONOMY "The point of living is to study the Sun" -Anaxagoras (499-428 BC) Arvind Bhatnagar Udaipur Solar Observatory, India William Livingston National Solar Observatory, Arizona, USA World Scientific NEW JERSEY • LONDON • SINGAPORE • BEIJING • SHANGHAI • HONGKONG • TAIPEI • CHENNAI Published by World Scientific Publishing Co. Pte. Ltd. 5 Toh Tuck Link, Singapore 596224 USA office: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601 UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. Cover page: Displaying the icon of Surya — the Sun god; ancient emblem of the dynasty of Mewar (Udaipur, Rajasthan, India) kings, along with solar Coronal Mass Ejections and prominences. FUNDAMENTALS OF SOLAR ASTRONOMY Copyright © 2005 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the Publisher. For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher. ISBN 981-238-244-5 ISBN 981-256-357-1 (pbk) Printed in Singapore by Mainland Press Professor M. K. Vainu Bappu (1927- 1982) This book is dedicated to our friend and mentor Professor M. K. Vainu Bappu. Arvind Bhatnagar William Livingston V Preface The aim of this book is to inculcate, motivate and inspire readers to take up the study and observations of our nearest star - the Sun, and enjoy its beauty and glory. Our Sun is the only star in the Universe which presents its surface details, as there is no other star near enough to show features of the order of a few hundred kilometers. Extending from deep inside the Sun to the solar surface and beyond, the Sun manifests a variety of phenomena, ranging from a few hundred kilometers to thousands of kilometers in size, temperature ranging from a few thousands to several million degrees and in temporal domain from a few seconds to several decades and dynamical events with speeds from a few tenths of km/sec to thousands of km/sec. Thus why not make use of this unique celestial laboratory to study the physical characteristics of matter and to understand other celestial bodies in the Universe. The remarkable dynamical phenomena occurring on the Sun, such as mass ejections in the form of eruptive prominences, filaments, surges, sprays, Coronal Mass Ejections, transient events; like solar flares, ephemeral regions, sunspots, granulations etc., make the study of the Sun extremely fascinating and interesting. One can see various solar phenomena occurring right in front of one's eyes and follow them for hours and days. The purpose of this book is to present some of these fascinating phenomena, in their full glory to the readers through ample number of illustrations, sketches and photographs. This book is mainly addressed to those who are starting to study the Sun and want to pursue an advance course in solar physics, but lack the basic knowledge of solar astronomy. To encourage young people, especially the budding amateur solar astronomers, we have pointed out to vii viii Preface the high quality early visual solar observations made in the seventeenth and eighteenth centuries, through small telescopes by Father Secchi, Langley, Captain Tupman, Professor Fernley and many others of solar granulations, sunspots, prominences, spicules, solar corona etc. We have emphasized that keen, persistent and careful visual observation through small telescopes can, not only provide extremely useful scientific data, but also gives great joy and fun, and one can always think of serendipity discovery that is just awaiting to be made about the Sun. Thus people with limited means in terms of equipment need not be discouraged, but follow the example of early observers and take up observing the Sun and contribute to its global watch. From time immemorial Sun has occupied a central stage in all ancient cultures. It had been and still worshiped in many cultures, countries and civilizations. Our ancestors had considered the Sun as god and goddess, because it gave them light, warmth, seasons and the very existence of life on this planet. To perpetuate its glory and might, all the ancient cultures created mythological stories about the Sun, and interwoven them in their daily cultural life and rituals. To give an idea about these ancient myths, in Chapter 1 we have briefly described them, as these are not readily available in the standard texts on solar astronomy. The readers will note that actual solar observations during the year were very important activity in ancient times, to mark the solstices and equinoxes, which were part of the cultural, religious and agricultural life. For this purpose huge structures like the Stonehenge were built more than 5000 years ago. We have tried to keep to bare minimum the use and derivation of mathematical equations, only some basic knowledge of physics and mathematics is required to understand the text. There is some amount of repetition also, which to some extent it is intentional so that various Chapters could be read independently too. In Chapter 2, we have given a brief description of some of the operating solar optical and radio observatories, ranging from very small observatories with 10-15 cm aperture telescopes to the state-of-the-art observatories, such as the New Swedish Solar Observatory, the Dutch Open telescope, the German Vacuum Solar Observatory, the THEMIS and the National Solar Observatory at Kitt Peak, USA. It has been pointed out that even small observatories have and are significantly Preface ix contributing to synoptic solar observations, in spite of available highly sophisticated solar telescopes and space missions. A brief description of some of the operating and planned space solar missions has also been given. We feel guilty of the fact that in this list of solar observatories we have not been able to include the enormous contribution being made by amateur solar astronomers. In Chapter 3, some of the basics of solar structure, energy generation, transport, irradiance, solar rotation and the neutrino puzzle are discussed. Chapter 4 gives a description of the Quiet Sun, although the Sun is never quiet, it is in action all the time. In Chapter 5, we present the Active aspect of our Sun, covering activities in the photosphere, chromosphere and the corona. To appreciate and enjoy the Sun in Action, the readers are advised to see time lapse movies now available from Websites of several solar observatories. In Chapter 6, we have given methods and techniques to determine basic solar parameters, such as the Solar Parallax, mass, distance, temperature, heliographic coordinates of solar features. These may be found useful for those initiated in solar astronomy from other disciplines. Chapter 7 covers in some detail, description of solar optical instruments, especially the various types of light feeds (solar telescope), spectrographs, imaging equipment, like narrow band filters and spectroheliographs. In this Chapter we have gone to great length in discussing the principle and working of birefringent filters, this is essentially because narrow band filters are the heart of any solar observational investigation, and description of such filters is not readily available in standard textbooks. We hope that the discussion given on the birefringent filter will familiarize the readers enough, not to consider it as a 'black box'. The fascinating phenomenon of the total solar eclipse is discussed in Chapter 8, emphasizing the importance of eclipse observations, and what we have learnt and what more can be learnt. Since the early days in nineteenth century, enormous scientific data and results are now available, but still some unsolved problems persist. However, we urge the newcomers to this field, that there is nothing like watching the whole event of the total solar eclipse with naked eyes (of course after taking due care), and suggest the readers of this book to witness at least once,