1、 - - CIE I 80 7006145 OOOOOOL 738 INTERNATIONAL ASTRONOMICAL UNION UNION ASTRONOMIQUE INTERNATIONALE COMMISSION INTERNATIONALE DE LCLAIRAGE INTERNATIONAL COMMISSION ON ILLUMINATION INTERNATIONALE BELEUCHTUNGSKOMMISSION Guide lines for minimizing Urban Sky Glow near Astronomical Observatories by R. C
2、ayrel and F.G. Smith (IAU) and A.J. Fisher and J.B. de Boer (CIE) Published with the financial assistance of UNESCO COPYRIGHT International Commission on IlluminationLicensed by Information Handling Services CIE L 80 7006345 0000002 b74 = COPYRIGHT International Commission on IlluminationLicensed by
3、 Information Handling ServicesCIE 3 80 sl 9006345 0000003 500 Guidelines for Minimizing Urban Sky Glow Near Astronomical Observatories Joint CIE/IAU publication The extremely rapid increase of outdoor lighting in most urban areas over recent decades has resulted in levels of sky glow which seriously
4、 affected several astronomical observatories and which are threatening others, even where they have been purposely located at more than 100 km from large cities. The International Astronomical Union (IAU) and the CIE have worked together to prepare these guidelines to promote collective action to mi
5、nimize the degradation of the environment of astronomical observing sites. The problem and its solutions are stated in a manner that provides a basis for understanding, cooperation, and action by astronomers, lighting engineers and public authorities. The report explains the effect of man-made sky g
6、low, the degree of glow likely to be produced by lighting near an observatory, the level above which sky glow should not be allowed to rise, and how it can be contained by good lighting practice and public ordinances. Richtlinien zur Minimierung stdtischer Himmelsaufhellung in der Nahe astronomische
7、r Observatorien Gemeinsame Publikation CIE/IAU Der rasche Anstieg der AuBenbeleuchtung in den meisten Stadtgebieten in den letzten Jahrzehnten verursachte eine Himmelsaufhellung, die einige astronimische Observatorien ernsthaft beeintrchtigte und andere gefhrdete, auch wenn diese absichtlich mehr al
8、s 100 km von groi3en Stdten entfernt errichtet wurden. Die International Astronomical Union (IAU) und die CIE bereiteten gemeinsam diese Richtlinien vor, um die gemeinsame Arbeit zur Minimisierung der Verschlechterung der Umweltbedingungen astronomischer Beobachtungsstationen zu frdern. Die Darstell
9、ung des Problems und seiner Lsung liefert eine Basis fr Verstndnis, Zusammenarbeit und Aktionen von Astronomen, Lichttechnikern und Behrden. Der Bericht erklrt die Wirkung der von Menschen verursachten Himmelsaufhellung, den Grad der Aufhellung, der von Beleuchtung in der Nhe eines Observatoriums ve
10、rursacht wird, den hchstzulssigen Grad der Himmelsaufhellung, und zeigt, wie sie durch gute Beleuchtungspraktiken und behrdliche Vorschriften eingedmmt werden kann. Guide pour minimiser la lueur du ciel urbain 5 proXimit6 des observatoires astronomiques Publication jointe CIE/IAU Laugmentation extrm
11、ement rapide de lclairage extrieur dans la plupart des sites urbains qui sest produit dans les dernires dcennies a provoqu un niveau de la lueur du ciel qui a srieusement affect quelques observatoires astronomiques et a menac dautres, mme sils ont t construits, intentionnellement, une distance de pl
12、us de 100 km de grandes villes. La IAU (International Astronomical COPYRIGHT International Commission on IlluminationLicensed by Information Handling Services- CIE L 80 900bL45 0000004 447 Union - Union Astronomique Internationale) et la CIE ont collabor pour prparer ce guide dans le but de promouvo
13、ir une action collective pour minimiser la dgradation de lenvironnement de sites dobservation astronomiques. Le problme et ses solutions sont prsents de manire fournir une base pour la comprhension, la coopration et laction des astronomes, des ingnieurs dclairage et des autorits publiques. Le rappor
14、t explique leffet de la lueur du ciel produite par lhomme, le degr de lueur provoque par lclairage proximit dun observatoire, le seuil admissible maximum de la lueur du ciel, et une faon de la limiter par une bonne pratique de lclairage et par des ordonnances publiques. COPYRIGHT International Commi
15、ssion on IlluminationLicensed by Information Handling ServicesCIE II 80 9006345 0000005 383 TABLE OF CONTENTS 1. INTRODUCTION 2. NATURAL AND ARTIFICIAL SKY GLOW 2.1 Natural sky glow 2.2 Limitations on astronomical observations caused by sky glow 2.3 Mechanism of artificial sky glow 2.4 Estimate of s
16、ky glow resulting from urban lighting 2.5 Spectral composition of sky glow 3. METHODS FOR MINIMIZING ARTIFICIAL SKY GLOW 3.1 Sources of artificial sky glow 3.2 Techniques for minimizing sky glow 3.3 Applications of techniques to lighting situations 4. MEANS TAKEN BY LOCAL AUTHORITIES IN ORDER TO CON
17、TROL THE GROWTH OF MAN-MADE SKY GLOW 4.1 General 4.2 The Tucson ordinance 4.3 Other ordinances 4.4 Recommendations concerning future ordinances 4.5 Other means of action 5. CONCLUSION REFERENCES APPENDIX 1: Report and recommendations of Commission 50 I Introduction II The acceptable levels of artifi
18、cial lighting IV Absorption due to atmospheric pollution VI Recommendations III The acceptable levels of radiofrequency interference V Interference from aircraft VI1 Practical application of the Recommendations APPENDIX 2: CIE Statement concerning protection of sites for astronomical observatories A
19、PPENDIX 3 : Ordinance No. 3840 relating to “outdoor lighting“ amending chapter 3 of the Tucson Code by adding article 6, outdoor light fixtures Page 1 2 6 10 14 15 16 21 22 COPYRIGHT International Commission on IlluminationLicensed by Information Handling Services CIE I 80 9006345 0000006 2LT 1 1. I
20、NTRODUCTION Advances in astronomy depend heavily upon observations of very faint objects which can be detected only with large telescopes located on sites away from industrial pollution and city lights. For example, observations of cosmological interest deal with extremely remote sources, galaxies,
21、or quasars at such distances that the light has travelled several billions of years, sometimes twice the age of our solar system, before reaching us. Observations of such very faint extragalactic sources, and even of most galactic gaseous nebulae, can be done only during the dark moon, the sky backg
22、round being much too strong when moon light is present. Man-made lighting of the sky due to urban lighting has, unfortunately, the same adverse effect on sky background in limiting observations. The sky background is referred to from hereon as sky glow. Even where the location of large observatories
23、., built during or after the second world war, had been carefully selected, far from large cities, problems have arisen because of the remarkable growth of light output from urban areas. This has been as high as 20 per cent per year over a couple of decades (i) representing a 38-fold increase in art
24、ificial illumination of the sky in twenty years. A dramatic picture of the USA by night taken from a spacecraft clearly demonstrates the significance of the fact (Figure i). It was mainly for this reason that the IAU decided in 1973 to establish a permanent commission in charge of identification and
25、 protection of existing and potential observatory sites (Commission 50). At the 1976 General Assembly the International Astronomical Union adopted the following resolution: “The IAU notes with alarm the increasing levels of interference with astronomical observations resulting from artificial illumi
26、nation of the night sky, radio emission, atmospheric pollution, and the operation of aircraft above observatory sites. The IAU therefore urgently requests that the responsible civic authorities take action to preserve existing and planned observatories from such interference. To this end, the IAU un
27、dertakes to provide through Commission 50 information on acceptable levels of interference and possible means of control.“ The information on acceptable levels of interference and possible means of control was issued in 1977 and can be found in Appendix 1. contain other useful information. The pione
28、ering work (4) made at Kitt Peak Observatory by Boag and Peterson must also be mentioned here. aware of these problems (6, 7, 8, 12, 13). The reports of Commission 50 (2, 3) Lighting technologists have become Later, in June 1978, the CIE adopted a statement acknowledging the problems caused by uncon
29、trolled outdoor lighting near the best observatory sites and agreeing that all possible action should be taken to protect these sites from such interferences. statement is given in Appendix 2. discussions between Commission 50 of the IAU and Technical Committee 4.6 of the CIE. The CIE The present gu
30、idelines are the result of further The guidelines are concerned only with sky glow and are intended to give guidance to agencies which have funded large astronomical facilities; to lighting technologists responsible for or engaged in designing public lighting in the vicinity of astronomical observat
31、ories; and to public authorities concerned with a coherent use of public funds in districts encompassing astronomical observatories- Cooperation between these three parties is needed if the possibility that ground-based astronomy will be eventually untenable, because of a polluted environment, is to
32、 be avoided. The argument that space astronomy will make this problem obsolete is not correct: the largest telescopes are still and will continue to be ground-based for a long time because of cost. The experience of two decades of space astronomy is that space observations have renewed and triggered
33、 more programmes from the ground rather than making them obsolete. COPYRIGHT International Commission on IlluminationLicensed by Information Handling Services CIE 3 80 9006345 OOOOOO 156 D 2 GUIDE LINES FOP. MIKCMIZING URBAN SKY GLOW 2. NATURAL AND ARTIFICIAL SKY GLOW 2.1 Natural sky glow Most of th
34、e brightness of the night sky is due to: (i) intrinsic emission of the upper atmosphere (night glow) occurring both at the specific wavelengths of emission lines and in a continuum; unresolved star light when the angular resolution of the instrument is not very large; the zodiacal light, which is su
35、n light scattered by dust particles in the solar system outside the earths atmosphere; mentioned above; light scattered by the atmosphere coming from artificial lighting on earth. (ii) (iii) (iv) light scattered by the earths atmosphere coming from the sources (v) It is this last component which is
36、of concern and over which some control can be achieved. As long as it remains weak compared to the other ones it is acceptable. Thus, the natural background is the standard by which man-made sky glow is judged. The average natural brightness or luminance of the night sky, integrated over the visible
37、 range, is about 2 x square degree or to one star of magnitude 21.6 per square arc second (5). the value quoted in the IAU recommendations (Appendix 1). However, it should be noted that darker conditions can be expected under some circumstances, for the following reasons: cd.m-2, equivalent to 300 s
38、tars of magnitude 10 per This is (i) the unresolved starlight (stars fainter than magnitude IUTJ = 6.0) which is conventionally counted as part of the night sky, and accounting for about 25 per cent of it, should not be included in the background for observa- tion with large telescopes, since it is
39、actually resolved down to at least magnitude 20 by large telescopes; the zodiacal light, which can account for 35 per cent of the total background, varies with angular distance to the sun and to the ecliptic plane. target object. (ii) It may be larger or smaller according to the direction of the The
40、 combined effect of these factors gives the darkest background level as about 1.5 x per unit wavelength interval (nm), taking the effective bandwidth of eye sensitivity as about 100 nanometers. cd.mT2 when integrated over the visible range, or 1.5 x cd.m-2 2.2 Limitations on astronomical observation
41、s caused by sky glow Sky glow would not be a significant limiting factor if it could be subtracted with an unlimited accuracy from the total light signal, made up of light from the source of interest and from the sky glow. inescapable difficulty in this subtraction, which is the result of the photon
42、 nature of light. the statistical fluctuations in the total light rather than in the source alone. The sky glow must therefore be kept as low as possible. There is, however, a fundamental and The uncertainty in any measurement of light intensity is determined by The IAU recommends (Recommendation 1)
43、 that the man-made sky glow above the best observing sites be kept below 10 per cent of the natural level. For a very faint astronomical source, this is equivalent to saying that it is acceptable that man-made sky glow increases the observing time by 10 per cent to get the same signal/noise ratio as
44、 obtainable when only the natural sky background is present. the sky glow by man-made lighting means that the efficiency of the telescope is halved; for example, a 4-metre telescope becomes as slow as a 2.8-metre telescope, the 4-metre telescope having cost about two and a half times more. a very se
45、rious level of interference, both technically and economically. A doubling of This is already COPYRIGHT International Commission on IlluminationLicensed by Information Handling Services CIE 3 80 I 9006345 0000008 O92 I COPYRIGHT International Commission on IlluminationLicensed by Information Handlin
46、g ServicesCIE L 80 E 9OObLY5 0000009 T29 NATURAL AND ARTIFICIAL SKY GLOW 3 The 10 per cent recommended by the IAU is necessarily somewhat arbitrary, it is meant to characterize a degradation still one order of magnitude below the unavoidable degradation due to the natural sky glow. that if the artif
47、icial sky glow is f times the natural sky glow, the time needed to get the same quality of observation at the telescope is multiplied by 1 +f), or the telescope becomes slower by a factor (1 + f) . A difrerent situation exists at the specific wavelengths of the emission line A more general statement
48、 is of the natural sky glow. the continuum and are variable in intensity. In the visible, the emission is concentrated at the wavelengths 557.7, 630.0 and 636.4 m. (oxygen lines) and 569.0-589.6 nm. (D-lines of sodium). These lines emit much more energy per unit wavelength than Against this variable
49、 background the detectivity is no longer controlled by the photon statistics and the limitation on man-made sky glow can therefore be relaxed. The IAU recommends (Recommendation 2) that the artificial increase in sky brightness over the wavelength band 588.8 nm to 589.8 nm should not exceed the minimum natural level in this band, whereas Recommendation 1 requests that the increase be not more than 10 per cent at other wavelengths: This relaxation, by a factor of ten, compared with the continuum, suggest
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