Lars Lindberg Christensen

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Hidden | Universe
Lars Lindberg Christensen

Robert Fosbury

Robert Hurt

WILEY-CPH logo — IAU logo — IYA logo

Figure 1: Multiwavelength view of Cassiopeia A (inside front cover)

This stunningly colourful picture shows off the many sides rich structure of the supernova remnant Cassiopeia A. It is made upcomposed of images using three different wavebands of light. Infrared data from the Spitzer Space Telescope are coloured red; visible data from the Hubble Space Telescope are yellow; and X-ray data from the Chandra X-ray Observatory are green and blue. Located 10,000 light-years away in the constellation Cassiopeia, Cassiopeia A is the remnant of a once massive star that died in a violent supernova explosion that would have been seen from Earth some 325 years ago had it not been behind clouds of obscuring dust. It consists of a dead star, called a neutron star, and a surrounding shell of material that was blasted off as the star diedimploded.

Foreword by Riccardo Giacconi 5

Preface 6

About the book 6

Acknowledgements 7

1. Light and Vision (Robert) 8

The eye and evolution 9

Human colour theory 10

What is light? 12

The electromagnetic spectrum 14

Seeing invisible light 15

Producing light 16

Blackbody radiation 16

Spectral line radiation 18

Non-thermal radiation 19

2. The View from the Ground 20

Atmospheric obstacles 20

Types of ground-based telescopes 23

Future ground-based observatories 23

3. Space observatories (Lars) 25

Reliability 27

What is inside? 27

Future space observatories 31

4. The Visible Universe (Lars) 32

The colours of the stars 34

Spectral lines — atomic fingerprints 37

Stellar evolution 38

Are the colours real? 38

Where the invisible becomes visible and the visible invisible 39

5. The Infrared Universe (Robert) 42

History 44

Visible-light technologies for infrared light 47

Sources of infrared light 48

Dust becomes transparent 54

6. The Ultraviolet Universe (Robert) 61

Overview 61

History 63

Sources of ultraviolet 64

Blackbody 64

Spectral lines 64

Ultraviolet telescopes 65

Ultraviolet science 66

Sun and planets 68

Star formation 69

7. The Radio Universe (Bob) 73

Bremsstrahlung 78

Radio gas 79

Cool stuff 81

Cosmic Microwave Background 82


Images/figures 84

8. The X-Ray and High Energy Universe (Bob) 85

Sources of X-rays 86

Thermal X-rays 86

Spectral line X-rays 87

Non-thermal processes 87

Observing X-rays 88

X-ray sources 89

White dwarfs, neutron stars and black holes... 89

Active galaxies 90

Clusters of galaxies 92

The Solar System 95

Pushing the limits: Gamma rays 97

Gamma-ray bursts 99

The X-ray/high energy revolution 100

9. The Multi-wavelength Universe (Lars) 103

Centaurus A in visible light 104

Centaurus A in the infrared 105

Centaurus A in the ultraviolet 107

Centaurus A in radio 108

Centaurus A in X-rays 109

A multi-wavelength view of Centaurus A 111

Post script 113

Glossary 123

Further reading 124

Index 125

Back 126

______ Ready for editing

______ Edited once and proofread once
____ _ Being worked on outside — DO NOT EDIT

Figure 2: Messier 81

This image of Messier 81 combines data from the Hubble Space Telescope, the Spitzer Space Telescope and the Galaxy Evolution Explorer (GALEX) missions. The GALEX ultraviolet data were from the far-UV portion of the spectrum. The Spitzer infrared data were taken with the IRAC detector. The Hubble data were taken at the blue portion of the spectrum. Also see the infrared and ultraviolet images of this object in Figure 38 and Figure 47.

Foreword by Riccardo Giacconi

Washington DC, 15 June 2008

Riccardo Giacconi

Recipient of the Nobel Prize in Physics, 2002

Figure 3:The Orion Nebula in infrared and visible light

Images from the Spitzer and Hubble Space Telescopes have been combined to a striking infrared and visible-light composite. Swirls of green in Hubble's ultraviolet and visible-light view reveal hydrogen and sulphur gas that have been heated and ionized by intense ultraviolet radiation. Spitzer's infrared view exposes carbon-rich molecules called polycyclic aromatic hydrocarbons in the cloud. These organic molecules are shown as wisps of red and orange.
Orion Vis/IR:


Until 400 years ago when Galileo first turned his telescope towards the heavens, our perception of the Universe was limited by our eyes and the thoughts that sprung from considering what they could see. The huge leap in capability that even such a simple instrument could realise set us on the path of creating ever more powerful instruments to satisfy our voracious appetite for knowledge.
Nonetheless, until the mid-20th century our knowledge of the Universe was limited almost entirely to the narrow band of light that could penetrate the Earth’s atmosphere and was visible to our eyes or to sensitive photographic plates loaded at the focus of increasingly large telescopes. With these resources alone, the discoveries were still stupendous: the mapping of our Solar System, the identification of the mechanism that makes stars shine and determines how long they live, the realisation that there are a multitude of galaxies like our own Milky Way and that they constitute an expanding Universe. The profound revolution in physics during the first half of the century brought with it the understanding of how light is emitted and how to read the subtle messages it carries concerning the physical state and chemical composition of stars and nebulae.
Stimulated by the development of radar for military use, the first major expansion of our view was the result of the development of radio astronomy, leading to the realisation that the Universe could look very different to us when seen through new “eyes” tuned to a different radiation.
The launch of Sputnik in 1957 paved the way for astronomy’s escape from the absorbing and distorting effects of the Earth’s atmosphere. With truly clear skies, generations of exploratory spacecraft and orbiting observatories have produced a wondrous and often breathtakingly beautiful view of a Universe whose richness could not have been imagined. A string of new discoveries has come from this fleet of new space-based instruments and observatories, and each new insight has been firmly placed into the existing framework of understanding by astronomers. Meanwhile the impressive arsenal of today's ground-based facilities bears witness to the continuing success of the modern large and highly evolved versions of the traditional telescope.

This book will enable you to peer through these exotic new telescopes and see some of the more spectacular images that have become the icons of modern astronomy. By expanding your vision beyond the visible into an array of “colours” that span the full spectrum of light, you will be able to gain a more complete picture of the Universe than has ever been possible before in human history. These images are truly a legacy to be appreciated by everyone. Obtained using facilities built by governments and public institutions across the globe, they allow us all to better understand our place in a spectacular Universe, once hidden, but now revealed.

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