The discovery of the chemical composition of every type of astronomical body, from our planet Earth, through planets, stars and interstellar gas, to distant galaxies is a major occupation of astrophysicists in our own time. Since nuclear science realized the dream of the alchemist, to transmute the elements from one to another, we have come to understand how the everyday materials that we take for granted have not always existed as such. The chemical elements are largely the by-products of nuclear reactions in stars, galaxies, and the early Universe. Nuclear astrophysicists apply the knowledge of the physics of nuclear reactions to fit together the data on the distribution of the elements to form a unified picture of the origin and evolution of the constituents of the Universe. Attempts are made to answer the questions: what was the composition of the Universe when it was first created ? What chain of events has resulted in the variety of chemical elements (92 natural ones) that can combine into almost an infinity of com¬pound materials, and the complexity of life that can speculate on its own earliest beginnings ? It is not, perhaps, widely appreciated that scientists can now be reasonably sure that all the atoms on Earth, for example, had to be created inside a generation of stars that evolved before the birth of the Sun and planets. The elucidation of the processes by which elements were and are created in the cosmic environment will stand in history as one of the great advances of the physical sciences in the twentieth century.

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