pagiven@drutx.UUCP (GivenP) (11/05/84)
- Thanks to all who replied to "Sunrise Phenomenon." Briefly, netters were asked if they could explain the "rosy fingers of dawn:" on a cloudless morning, shafts of alternating deep blue and orange light radiating from the horizon just before sunrise. Can it happen at sunset, too? Summary of responses: 1. Yes, it has been observed to happen at sunset by at least one respondent. 2. The orange light is caused by atmospheric refraction, as we observe at the usual sunrise or sunset. 3. The light appears in shafts because of either cloudmass or terrain irregularities that lie beyond the horizon and block some of the refracted red light. 4. Although the sky appears cloudless, it really has a thin haze of cirrus clouds that act as a "movie screen" upon which is projected shafts of light caused by sunrise over either irregular terrain or cumulus clouds. Perspective gives the illusion of radiating bars. 5. The blue light is there because the strongly refracted red light is blocked thereby letting the observer see the weakly refracted blue light. 6. The horizon must be far enough away from the observer to allow refracted light to reach, thus the phenomenon is never observed at sunset from Denver: the mountainous western hor- izon is too close. Nor is it observed if the cloudmass is above the horizon. The common thread in these explanations seems to be the requirement of irregular terrain or cloudmass just beyond the horizon. I am reminded of the solar eclipse phenomenon where sunlight peers through lunar surface asperity, is it called "Bailey's Beads?" However, none of the explanations deal with the *striking* regular- ity and even spacing of those bars of light! Random chance? or slipshod observing? Nor do the proffered explanations address the phenomenon's rarity. If unchanging irregular terrain and a clear sky are all that is required, why do we not see it more often? (at least for those of us foolish enough to be up at such a ridiculous hour :-)) ----------------------------------------------------------------- Paul Given {ihnp4, houxe, stcvax!ihnp4}!drutx!pagiven AT&T Information Systems Laboratories 11900 N. Pecos, Rm 1B04, Denver 80234 (303)-538-4058 -----------------------------------------------------------------