Introducing Astronomy

Astronomy is the science that investigates the universe around us. It is, arguably, the oldest of the sciences, for humankind must have been aware, long before written records began, of the Sun, Moon, stars and naked-eye planets and their movements in the sky. Gradually, sky watchers began to chart their positions, identify patterns in their behaviour, and use that information - on the one hand for practical purposes, to record the passage of time, the recurrence of the seasons, and as an aid to navigation - and on the other, with increasing sophistication over the centuries, to attempt to understand the nature of these objects and the scale of the universe in space and time.

For millennia, these studies were restricted to what could be seen directly by the unaided human eye. That changed, at the beginning of the seventeenth century, with the invention of the telescope, which enabled astronomers to see details on the surfaces of the Sun, Moon and planets, to detect objects far fainter than the eye alone could see and, therefore, to penetrate much deeper into space. Another key step, in the nineteenth century, was the invention of the spectroscope, a device that allowed astronomers to analyse in detail light arriving from distant objects, and to investigate their chemical and physical properties. In that same century, photography arrived on the scene, enabling astronomers to record permanent images and to detect objects that were too faint to be seen by the human eye even with telescopic aid. During the twentieth century and into the twenty-first, progressively larger telescopes, and advances such as electronic imaging, the computer analysis of data, and the ability to place telescopes in orbit beyond our atmosphere, and to send spacecraft to the planets and moons of our immediate cosmic neighbourhood, have utterly transformed the depth and breadth of the science.

But astronomy remains essentially an observational science. Whereas a chemist or physicist can set up an experiment in a laboratory, change the conditions and measure the outcome, astronomers cannot touch, or experiment directly with, stars or galaxies. Instead, they have to piece together their picture of the universe by detecting, measuring and analysing light and other forms of radiation that are coming our way from the depths of space..

Part of astronomy’s enduring fascination is that it grapples with fundamental questions concerning the origin, evolution and ultimate fate of planets, stars, galaxies and the universe as a whole, and touches on that most intriguing of conundrums: is life unique to the Earth or a widespread phenomenon? Another part of its great attraction is its accessibility: we can all go out and explore the beauty of the night sky for ourselves. This book outlines and explains what astronomy has to tell us about the nature of planets, stars, galaxies and the universe, and highlights some of the ways in which astronomers have arrived at this body of knowledge.

Contents

Introduction - the science of the universe

1 Our place in space



2 The changing sky

3 Planets and orbits

4 The Sun

5 The Sun’s domain

6 Stars - their properties and variety

7 Interstellar clouds and the birth, life and death of stars



8 Galaxies

9 The evolving universe

10 Exoplanets and the conditions for life

11 Tools of the trade