A Short Timeline of Discoveries

In 1676, Ole Rømer used the moons of Jupiter to show that light takes time to travel. In 1912, Henrietta Leavitt published her rule for pulsing stars. In 1915, Albert Einstein completed his theory of gravity, and in 1917 he used it to describe a universe that stays the same size. In 1920, astronomers argued in public about whether the spiral nebulae were inside the Milky Way or far outside it.

In 1922, Alexander Friedmann showed that Einstein's theory allows a universe that grows. In 1923 and 1924, Edwin Hubble found pulsing stars in the Andromeda nebula and showed that it is a separate galaxy far beyond our own. In 1927, Georges Lemaître connected the moving galaxies with a growing universe, and in 1929 Hubble showed that more distant galaxies move away faster. In 1931, Lemaître suggested that the universe began from a "primeval atom".

Meanwhile, in 1925, Cecilia Payne found that stars are made mostly of hydrogen and helium. In 1933, Fritz Zwicky saw that a cluster of galaxies held far more matter than could be seen. In 1939, Hans Bethe explained how fusion makes the Sun shine. In 1948, George Gamow, Ralph Alpher and Robert Herman worked on the first minutes, and Alpher and Herman predicted a faint, cold light left over from the early universe. In 1949, Fred Hoyle used the name "Big Bang" in a radio talk.

In 1957, Margaret Burbidge, Geoffrey Burbidge, William Fowler and Fred Hoyle described how stars build the elements. In 1965, two radio engineers found the oldest light. In the 1970s, Vera Rubin showed that stars at the edges of galaxies move too fast for the matter we can see. In 1990, the Hubble Space Telescope was launched. In 1992, a satellite launched in 1989 found tiny differences in the oldest light, the seeds of later galaxies.

In 1998, two teams found that the expansion of the universe is speeding up. In 2017, astronomers saw two neutron stars collide and found signs of heavy elements such as gold. In December 2021, the James Webb Space Telescope was launched, and it has since found galaxies from when the universe was only a few hundred million years old.

About the Information in This Book

This book explains the widely accepted knowledge of astronomy and of how the universe began in plain words for readers without a science background. Numbers are rounded and dates are given as they are usually given in textbooks. Where scientists do not yet know something, or where there are several ideas and no clear answer, the book says so.

Scientific understanding grows all the time. New telescopes and new measurements may change some of the details in this book, and some of the open questions described here may be answered in the future. If you would like to learn more, public science museums, planetariums, libraries and the public pages of observatories are good places to continue.

Noor, Sami, Tomás, Ade and the space station in this book are imagined. Their daily life is based on the general life of astronauts in low orbit, but they are not real people, and any resemblance to real people is not intended. The scientists of the past who are named in the book were real people, and their work is described as it is usually told in the history of astronomy.