Book contents
- Frontmatter
- Contents
- Foreword
- Preface
- Acknowledgements
- Notes about units
- 1 The Solar System
- 2 The Sun
- 3 The Moon
- 4 Mercury
- 5 Venus
- 6 Earth
- 7 Mars
- 8 Minor members of the Solar System
- 9 Jupiter
- 10 Saturn
- 11 Uranus
- 12 Neptune
- 13 Beyond Neptune: the Kuiper Belt
- 14 Comets
- 15 Meteors
- 16 Meteorites
- 17 Glows and atmospheric effects
- 18 The Stars
- 19 Stellar spectra and evolution
- 20 Extra-solar planets
- 21 Double stars
- 22 Variable stars
- 23 Stellar clusters
- 24 Nebulæ
- 25 The Milky Way Galaxy
- 26 Galaxies
- 27 Evolution of the universe
- 28 The constellations
- 29 The star catalogue
- 30 Telescopes and observatories
- 31 Non-optical astronomy
- 32 The history of astronomy
- 33 Astronomers
- 34 Glossary
- Index
14 - Comets
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Foreword
- Preface
- Acknowledgements
- Notes about units
- 1 The Solar System
- 2 The Sun
- 3 The Moon
- 4 Mercury
- 5 Venus
- 6 Earth
- 7 Mars
- 8 Minor members of the Solar System
- 9 Jupiter
- 10 Saturn
- 11 Uranus
- 12 Neptune
- 13 Beyond Neptune: the Kuiper Belt
- 14 Comets
- 15 Meteors
- 16 Meteorites
- 17 Glows and atmospheric effects
- 18 The Stars
- 19 Stellar spectra and evolution
- 20 Extra-solar planets
- 21 Double stars
- 22 Variable stars
- 23 Stellar clusters
- 24 Nebulæ
- 25 The Milky Way Galaxy
- 26 Galaxies
- 27 Evolution of the universe
- 28 The constellations
- 29 The star catalogue
- 30 Telescopes and observatories
- 31 Non-optical astronomy
- 32 The history of astronomy
- 33 Astronomers
- 34 Glossary
- Index
Summary
Comets are the most erratic members of the Solar System. They may sometimes look spectacular, but they are not nearly so important as they then seem, and by planetary standards their masses are very low indeed. In most cases, though not all, their orbits round the Sun are highly eccentric. A comet has been aptly described as a dirty ice-ball.
COMET PANICS
In earlier times comets were not classed as being celestial bodies, and were put down as atmospheric phenomena, although it is true that around 500 BC the Greek philosopher Anaxagoras regarded them as being due to clusters of faint stars. They were always regarded as unlucky. Recall the lines in Shakespeare's Julius Cæsar:
When beggars die, there are no comets seen:
The heavens themselves blaze forth the death of princes.
In 1578, the Lutheran bishop Andreas Calichus went further, and described comets as being ‘the thick smoke of human sins rising every day, every moment, full of stench and horror before the face of God’. However, his Hungarian contemporary, Andreas Dudith, sagely pointed out that in this case the sky would never be comet-free! The first proof that comets were extraterrestrial came from the Danish astronomer Tycho Brahe, who found that the comet of 1577 showed no diurnal parallax, and must therefore be at least six times as far away as the Moon (actually, of course, it was much more remote than that).
- Type
- Chapter
- Information
- Patrick Moore's Data Book of Astronomy , pp. 255 - 272Publisher: Cambridge University PressPrint publication year: 2011