126:
288:. As for the principal mechanism of the phenomenon, measurements indicate that the opposition effect exhibits only a small wavelength dependence: the surge is 3-4% larger at 0.41 μm than at 1.00 μm. This result suggests that the principal cause of the lunar opposition surge is shadow-hiding rather than coherent backscatter.
31:
151:
As the phase angle of an object lit by the Sun decreases, the object's brightness rapidly increases. This is mainly due to the increased area lit, but is also partly due to the intrinsic brightness of the part that is sunlit. This is affected by such factors as the angle at which light reflected from
169:
from the viewpoint of the observer), this intrinsic brightness is usually close to its maximum. At a phase angle of zero degrees, all shadows disappear and the object is fully illuminated. When phase angles approach zero, there is a sudden increase in apparent brightness, and this sudden increase is
211:
A theory for an additional effect that increases brightness during opposition is that of coherent backscatter. In the case of coherent backscatter, the reflected light is enhanced at narrow angles if the size of the scatterers in the surface of the body is comparable to the wavelength of light and
147:
The phase angle is defined as the angle between the observer, the observed object and the source of light. In the case of the Solar System, the light source is the Sun, and the observer is generally on Earth. At zero phase angle, the Sun is directly behind the observer and the object is directly
181:. The usual major cause of the effect is that a surface's small pores and pits that would otherwise be in shadow at other incidence angles become lit up when the observer is almost in the same line as the source of illumination. The effect is usually only visible for a very small range of
269:. Gehrels' later studies showed that the same effect could be shown in the moon's brightness. He coined the term "opposition effect" for the phenomenon, but the more intuitive "opposition surge" is now more widely used.
283:
have suggested that its brightness increases by some 40% between a phase angle of 4° and one of 0°, and that this increase is greater for the rougher-surfaced highland areas than for the relatively smooth
152:
the object is observed. For this reason, a full moon is more than twice as bright as the moon at first or third quarter, even though the visible area illuminated appears to be exactly twice as large.
185:
near zero. For bodies whose reflectance properties have been quantitatively studied, details of the opposition effect – its strength and angular extent – are described by two of the
581:
272:
Since
Gehrels' early studies, an opposition surge has been noted for most airless solar system bodies. No such surge has been reported for bodies with significant atmospheres.
212:
the distance between scattering particles is greater than a wavelength. The increase in brightness is due to the reflected light combining coherently with the emitted light.
338:
Hameen-Anttila, K.A.; Pyykko, S. (July 1972). "Photometric behaviour of Saturn's rings as a function of the saturnocentric latitudes of the Earth and the Sun".
165:
When the angle of reflection is close to the angle at which the light's rays hit the surface (that is, when the Sun and the object are close to
532:
193:), an opposition surge is due to the uncovering of shadows on the ring particles. This explanation was first proposed by
117:. Two physical mechanisms have been proposed for this observational phenomenon: shadow hiding and coherent backscatter.
302:
310:, the apparently enormous and magnified shadow of an observer cast upon the upper surfaces of clouds opposite the Sun
139:
spacecraft at phase angles of 0°, 7° and 33°. The left image at 0° phase angle shows the brightness surge due to the
571:
223:
have shown that a strong coherent backscatter effect is required to explain the high albedos at radar wavelengths.
17:
556:
566:
340:
250:
236:
367:
von
Seeliger, H. (1887). "Zur Theorie der Beleuchtung der grossen Planeten insbesondere des Saturn".
206:
182:
98:
387:
Coherent
Backscatter: An Explanation for the Unusual Radar Properties of Outer Planet Satellites
561:
166:
114:
110:
353:
418:
349:
285:
130:
8:
576:
541:
220:
422:
523:, "Atmospheric optics" website. Includes a picture of the opposition surge on the moon
453:
Photometric
Studies of Asteroids. V: The Light-Curve and Phase Function of 20 Massalia
77:, when illuminated from directly behind the observer. The term is most widely used in
515:
434:
194:
135:
81:, where generally it refers to the sudden noticeable increase in the brightness of a
492:
472:
452:
386:
101:
of observation approaches zero. It is so named because the reflected light from the
529:, "Atmospheric optics" website. Diagrammatic representation of the opposition surge
426:
318:
186:
430:
307:
242:
190:
35:
526:
520:
246:
232:
82:
50:
537:
550:
438:
178:
30:
125:
313:
262:
42:
38:
78:
46:
406:
266:
219:. In particular, recent observations of Titan at 2.2 cm with
174:
74:
241:
On Earth, water droplets can also create bright spots around the
73:) is the brightening of a rough surface, or an object with many
297:
261:
The existence of the opposition surge was described in 1956 by
86:
473:
Wavelength dependence of polarization. III. The lunar surface
216:
94:
215:
Coherent backscatter phenomena have also been observed with
276:
106:
102:
90:
516:
Hayabusa observes the opposition surge of
Asteroid Itokawa
491:
Burrati, B. J.; Hillier, J. K.; & Wang, M. (1996) "
109:
appear significantly brighter than predicted by simple
582:
Scattering, absorption and radiative transfer (optics)
493:
The Lunar
Opposition Surge: Observations by Clementine
337:
471:
Gehrels, T.; Coffeen, T.; & Owings, D. (1964) "
407:"Anomalous radar backscatter from Titan's surface?"
404:
548:
265:during his study of the reflected light from an
405:Janssen, M.A.; Le Gall, A.; Wye, L.C. (2011).
256:
331:
245:in various situations. For more details, see
366:
533:"The-moon wikispaces" opposition surge page
369:Abh. Bayer. Akad. Wiss. Math. Naturwiss. Kl
398:
360:
189:. In the case of planetary rings (such as
173:The effect is particularly pronounced on
124:
29:
200:
14:
549:
155:
170:referred to as the opposition surge.
538:Opposition surge on Saturn's B Ring
24:
303:Bidirectional reflectance function
177:surfaces of airless bodies in the
25:
593:
509:
226:
160:
485:
465:
445:
379:
13:
1:
324:
431:10.1016/j.icarus.2010.11.026
7:
527:opposition effect mechanism
291:
257:Throughout the Solar System
120:
10:
598:
341:Astronomy and Astrophysics
251:Glory (optical phenomenon)
237:Glory (optical phenomenon)
230:
204:
148:ahead, fully illuminated.
41:brightens the area around
34:Opposition surge from the
61:(sometimes known as the
572:Observational astronomy
354:1972A&A....19..235H
207:Coherent backscattering
115:astronomical opposition
144:
111:Lambertian reflectance
54:
457:Astrophysical Journal
128:
33:
451:Gehrels, T. (1956) "
201:Coherent backscatter
557:Astronomical events
423:2011Icar..212..321J
275:In the case of the
156:Physical mechanisms
145:
55:
567:Optical phenomena
521:opposition effect
195:Hugo von Seeliger
141:opposition effect
63:opposition effect
45:'s shadow during
16:(Redirected from
589:
503:
489:
483:
469:
463:
449:
443:
442:
402:
396:
383:
377:
376:
364:
358:
357:
335:
319:Geometric albedo
279:, B. J. Buratti
187:Hapke parameters
133:, imaged by the
67:opposition spike
59:opposition surge
21:
597:
596:
592:
591:
590:
588:
587:
586:
547:
546:
542:Cassini–Huygens
512:
507:
506:
490:
486:
470:
466:
450:
446:
403:
399:
384:
380:
365:
361:
336:
332:
327:
308:Brocken spectre
294:
259:
243:antisolar point
239:
231:Main articles:
229:
209:
203:
163:
158:
123:
71:Seeliger effect
36:retroreflective
28:
23:
22:
18:Seeliger effect
15:
12:
11:
5:
595:
585:
584:
579:
574:
569:
564:
559:
545:
544:
535:
530:
524:
518:
511:
510:External links
508:
505:
504:
484:
464:
444:
417:(1): 321–328.
397:
378:
359:
348:(2): 235–247.
329:
328:
326:
323:
322:
321:
316:
311:
305:
300:
293:
290:
258:
255:
247:Heiligenschein
233:Heiligenschein
228:
227:Water droplets
225:
205:Main article:
202:
199:
162:
159:
157:
154:
122:
119:
83:celestial body
51:Neil Armstrong
27:Optical effect
26:
9:
6:
4:
3:
2:
594:
583:
580:
578:
575:
573:
570:
568:
565:
563:
562:Lunar science
560:
558:
555:
554:
552:
543:
539:
536:
534:
531:
528:
525:
522:
519:
517:
514:
513:
501:
498:
494:
488:
481:
478:
474:
468:
461:
458:
454:
448:
440:
436:
432:
428:
424:
420:
416:
412:
408:
401:
394:
391:
388:
382:
374:
370:
363:
355:
351:
347:
343:
342:
334:
330:
320:
317:
315:
312:
309:
306:
304:
301:
299:
296:
295:
289:
287:
282:
278:
273:
270:
268:
264:
254:
252:
248:
244:
238:
234:
224:
222:
218:
213:
208:
198:
196:
192:
188:
184:
180:
176:
171:
168:
161:Shadow hiding
153:
149:
142:
138:
137:
132:
129:Dwarf planet
127:
118:
116:
112:
108:
104:
100:
96:
92:
88:
84:
80:
76:
72:
68:
64:
60:
52:
48:
44:
40:
37:
32:
19:
499:
496:
487:
479:
476:
467:
459:
456:
447:
414:
410:
400:
392:
389:
381:
372:
368:
362:
345:
339:
333:
280:
274:
271:
260:
240:
214:
210:
183:phase angles
179:Solar System
172:
164:
150:
146:
140:
134:
70:
66:
62:
58:
56:
540:as seen by
314:Gegenschein
263:Tom Gehrels
99:phase angle
43:Buzz Aldrin
577:Radiometry
551:Categories
502:: 490-499.
482:: 826-852.
477:Astron. J.
462:: 331-338.
395:: 407:417.
385:Hapke, B.
375:: 405–516.
325:References
167:opposition
85:such as a
49:(photo by
39:lunar soil
439:0019-1035
197:in 1887.
79:astronomy
75:particles
47:Apollo 11
292:See also
267:asteroid
191:Saturn's
175:regolith
121:Overview
113:when at
419:Bibcode
350:Bibcode
221:Cassini
97:as its
497:Icarus
437:
411:Icarus
390:Icarus
298:Albedo
281:et al.
87:planet
286:maria
217:radar
131:Ceres
95:comet
93:, or
435:ISSN
277:Moon
249:and
235:and
136:Dawn
107:Mars
105:and
103:Moon
91:moon
57:The
500:124
495:".
475:".
460:195
455:".
427:doi
415:212
69:or
553::
480:69
433:.
425:.
413:.
409:.
393:88
373:16
371:.
346:19
344:.
253:.
89:,
65:,
53:).
441:.
429::
421::
356:.
352::
143:.
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
