Space Observatories

Why then put telescopes on rockets? Why put spectrographs on satellites? Between the comfortable observatories of Haute-Provence or California and the thousand fires of the universe, the Earth's atmosphere scrambles communications. The air, opaque to so many kinds of radiation, seriously perturbs the few that it Iets through. The task ofthe imprisoned astronomer is a subtle detective game -decoding the message, reading between the spectral lines, inventing the invisible. How can the air (the popular expression, undiscerning as usual, is 'thin air'!) surrounding the Earth -that shallow layer of air only a few kilometers thickinßuence and even paralyze astronomical observations by its presence alone, forcing the imprisoned astronomer to escape? Weshall try to answer this question, first by describing the different layers of the \* J.-C. Pecker, Experimenta!Astronomy (transl. by Robert S. Kandel), D. Reidel Pub!. Co., Dordrecht, 1970. construction of the original Figures 3, 4, and 5 (Part I), and the calculations of Chapter III (Part II); and finally, Mademoiselle G. Drouin, who put the finishing touches on tbe manuscript with great competence and devotion. I am deeply indebted to my translator, Dr. Janet Rountree Lesh, who has not only made a fine translation, but also improved the original on several points, pointed out a few mistakes, and made it when possible up-to-date. CHAPTER I Le ciel est, par-dessus le toit, The sky is, up above the roof, Si bleu, si calme! So blue, so calm! Un arbre, par-dessus Je toit, A tree there, up above the roof, Berce sa palme. Waves leaves of palm. La cloche, dans le ciel qu'on voit, A church bell, in the sky I see, Doucement tinte. Softly tolls. Un oiseau, sur l'arbre qu'on voit, A bird, upon the tree I see, Chante sa plainte. Sadly calls. PAUL VERLAINE Like Verlaine, we are in prison. The prison is our Earth, "which is so pretty"; our atmosphere and its clouds, its "marvellous clouds". (You would think that Verlaine, Prevert and Baudelaire had been comparing notes!) The sky is up above the roof ... A tree there, up above the roof ... Stars in the sky, like birds ... their rays, like bells (and here we are with Apollinaire!) What we see opens the way to what we guess at; what we observe Ieads us towards the unobservable. A poem releases images, and the invisible grows big with reality. Astronomcrs are a little like poets (indirectly from the Greek 7tostco, make): they make the universe by interpreting messages, extrapolating spectra, and inventing 'models' of the cosmos or of stars - fictional constructions whose observable part constitutes only a small fraction of the whole, and which only the inductive logic of the theoretician allows us to consider as representing unique physical reality Front Matter....Pages I-XI Front Matter....Pages 1-1 The Structure of the Atmospheric Layers....Pages 3-7 The Opaque Wall of the Atmosphere....Pages 8-19 Atmospheric Diffusion: Extinction and the Blue of The Sky....Pages 20-30 The Inhomogeneity of the Earth’s Atmosphere: Clouds and Refraction....Pages 31-44 The Particle Barrier....Pages 45-47 The Fusion of Meteorites....Pages 48-50 Front Matter....Pages 51-52 Beyond Diffusion....Pages 53-61 Beyond Turbulence....Pages 62-66 Beyond Ultraviolet Opacity....Pages 67-83 Astronomy at Short Wavelengths....Pages 84-105 Beyond Infrared Opacity: Towards the Infrared by Balloon....Pages 106-108 Beyond The Ionosphere: Towards Very Long Wavelengths by Eccentric Satellite....Pages 109-113 A Prospective Conclusion of Limited Perspective....Pages 114-115 Conclusion....Pages 116-116 Back Matter....Pages 117-122