Book contents
- Frontmatter
- Contents
- Preface
- Dedication
- Note on some conventions
- 1 Introduction
- 2 Our Galaxy
- 3 The large-scale structure of the universe
- 4 Elementary particles – a preliminary look
- 5 Is the universe open or closed?
- 6 Three ways for a star to die
- 7 Black holes and quasars
- 8 Galactic and supergalactic black holes
- 9 A black hole is not forever
- 10 Slow and subtle changes
- 11 Future of life and civilization
- 12 A collapsing universe
- 13 The steady state theory
- 14 The stability of the proton
- 15 Epilogue
- Glossary
- Selected bibliography
- Index
- Frontmatter
- Contents
- Preface
- Dedication
- Note on some conventions
- 1 Introduction
- 2 Our Galaxy
- 3 The large-scale structure of the universe
- 4 Elementary particles – a preliminary look
- 5 Is the universe open or closed?
- 6 Three ways for a star to die
- 7 Black holes and quasars
- 8 Galactic and supergalactic black holes
- 9 A black hole is not forever
- 10 Slow and subtle changes
- 11 Future of life and civilization
- 12 A collapsing universe
- 13 The steady state theory
- 14 The stability of the proton
- 15 Epilogue
- Glossary
- Selected bibliography
- Index
Summary
In astronomy one uses distances and periods of time large compared to terrestrial ones. The word ‘astronomical’ has in the English language come to mean some very large quantity. When discussing the universe as a whole one uses even larger distances and periods of time than those used in ordinary astronomy. The convenient unit for measuring distances in astronomy is not the kilometer or the mile, but the light year, which is the distance traversed in a year by light moving at the speed of about 300,000 kilometers a second (km/s); a light year is approximately 9 × 1012 km or 9 million million km. To have some idea about the light year, let us consider some familiar distances and convert these to ‘light travel time’. The circumference of the Earth is about 40 000 km, so in one second light can travel round the Earth more than seven times. The distance to the Moon is 371 000 km, so it takes light between 1 and 1.5 seconds to travel from the Earth to the Moon. The mean distance of the Earth from the Sun is approximately 150 million km. This distance is covered by light in 8–8.5 minutes. The mean distance from the Sun to Pluto, the furthest planet in the solar system, is approximately 5900 million km, which distance is covered by light in about 5.5 hours.
- Type
- Chapter
- Information
- The Ultimate Fate of the Universe , pp. 8 - 12Publisher: Cambridge University PressPrint publication year: 1983