`21st century astrophysics' - Eds. S K Saha and V K Rastogi, 2005, Anita Publications, B-28, Second Floor, Sarvodaya Enclave, Mehrauli Road, New Delhi - 110 017, India (Contact person: vk_rastogi@rediffmail.com).

In the year 1905, Albert Einstein published four landmark papers, concerning (i) photo-electric effect for which he was awarded Nobel prize, (ii) Brownian motion, (iii) special theory of relativity that revolutionized physics, and (iv) the most famous equation of all time, E = mc^2. These papers, which appeared in Ann. der Physik, provided the basis for fundamental developments of 20th century physics and of astrophysics in particular. They have also found practical applications in Brownian ratchets, photocells, relativistic microchips, petawatt lasers, Bose-Einstein condensates etc, inspiring 21st century technology.

His first paper entitled, `On a heuristic point of view concerning the production and transformation of light' (17, 132-148), defines `photon' based on the idea that light might be made up of discrete packets or quanta, following Planck's suggestion (made to explain the black body radiation spectrum). The photon concept helped him to obtain his photo-electric equation and led to the conclusion that the number of electrons released would be proportional to the intensity of the incident light.

The second paper, `On the motion of small particles suspended in liquids at rest required by the molecular-kinetic theory of gaseous heat' (17, 549-560) described the determination of molecular dimensions, making use of current hydrodynamic theory to determine size of molecules suspended in a viscous liquid.

Einstein's third paper, `On the electrodynamics of moving bodies' (17, 891-921), dealt with motion of small particles suspended in liquids, as required by molecular kinetic theory of heat. He explained Brownian motion and showed that, by measuring the mean squared displacement, Avogadro's number could be determined. This provided definite proof for existence of atoms. It is this paper that also introduced the special theory of relativity. He extended and perfected Maxwell's theory by modifying the foundations of classical mechanics to remove the apparent contradictions between mechanics and electrodynamics.

The equation, E = mc^2, came from a paper called, `Does the inertia of a body depend on its energy content?' (18, 639-641), a corollary to his previous relativity paper, in which he wrote that energy and mass were descriptions of the same thing. He realized that the only way to explain the varying speeds of an object emitting radiation was to consider the kinetic energy of the object as adding to its effective mass.

The year 2005 has been declared the `World Physics Year' by UNESCO, the United Nations, and many national scientific and government organizations. It marks the centenary of these seminal papers. In this opportune moment, a book entitled, `21st Century Astrophysics' has been released. This book may serve as an interface between the physicists and astrophysicists. A set of articles encompassing the fields of (i) relativistic astrophysics, (ii) stellar and galactic astronomy, (iii) Sun and solar systems, and (iv) observational techniques are available in this book.

CONTENTS

1. Relativistic astrophysics

Dark matter: past, present, and future - Virginia Trimble

The cosmological constant as a unifying link - C Sivaram

Black hole accretion as black hole analogue - Tapas Kumar Das

Theory of the thermonuclear supernovae - Peter Hoflich

2. Stellar and galactic astronomy

The coming of age of X-ray astronomy - K P Singh

X-ray studies of active galactic nuclei - Poshak Gandhi

Asymmetries in powerful extragalactic radio sources - Gopal-Krishna and Paul J Witta

Spatio-kinematic studies of galactic planetary nebulae - B G Anandarao

Recent results from the Be prototype star gamma Cas - Ph Stee

3. Sun and solar systems

Helioseismology - Eric Fossat

Intense magnetic fields in the atmosphere of the sun - S S Hasan

Hall-magnetohydrodynamic turbulence - V Krishan and S M Mahajan

Magnetohydrodynamic waves in the solar corona - A Satya Narayanan and R Ramesh

Comets and scientific method - Peter B Fellgett

4. Observational techniques

From interferometers to hypertelescopes - Antoine Labeyrie

100 years of photon-counting: the quest for the perfect eye - Sebastien Morel and Swapan K Saha