@ attempto (Schauungen & Prophezeiungen)

Ulrich ⌂ @, Germering, Freitag, 12.07.2013, 18:59 (vor 3316 Tagen) @ attempto (21815 Aufrufe)

Hallo attempto,

Auch das Einbeziehen von Fachleuten (Kennt da jemand jemanden? Oder ist ein Mitleser kundig?) wäre meines Erachtens ratsam. Oder ist das schon erfolgt, und ich habe lediglich angesichts der Masse der Ergebnisse der Suchfunktion den entsprechenden Beitrag nicht gefunden? Vermutlich nicht. Sonst tappten wir bei der Finsternis nicht vollständig im dunkeln.

David A. J. Seargent:
Weird Weather: Tales of Astronomical and Atmospheric Anomalies. Springer, 2012.

Kapitel:
"Dark Days and Atmospheric Opacity" (S. 291-294)

"Believe me, one of the most unnerving experiences that we can have is to wake up to absolutely no light. Not even the faintest glimmer! Not long ago, this writer had just such an experience. Waking in the early morning hours, there was simply no light at all. I was on the western plains of New South Wales at the time, so the glare of streetlight and so forth was not expected, but even a cloudy night in a rural setting has some light; at least, that had always hitherto been my experience. And on a clear night, the combined illumination of a starry sky and airglow (to say nothing of even a slender Moon if it is present) throws a surprising amount of light onto the land. But on this night – nothing. For a few moments, I began wondering if I had gone blind in my sleep, and only a faithful flashlight next to my bed fully dismissed such a dismal thought.
From my location, the next day dawned relatively clear. Not so for Sydney and the coastal regions. There, residents awoke to a red glow suffusing everything. So strange was the light that some wag at one of the radio stations thought the song End of the World would be a suitable disk to spin.
It was not the end of the world of course, but it probably signaled the end of career for many country farmers. What had caused the deep darkness at my location and the weird redness at Sydney was a huge cloud of dust; topsoil blown from drought ravaged farms by strong winds and lofted far and wide by the prevailing westerly stream.
Dust storms like this, as well as smoke from large forest or prairie fires and volcanic eruptions have been responsible for many instances of dark days and strangely colored daylight. In times past (and not only in times past!) these have caused much fear. This is entirely understandable, as the apparent failure of sunlight speaks to some of our deepest fears. Yet, if these events are explained relatively simply by atmospheric opacity resulting from dust, smoke or volcanic ash, there is no real anomaly, no real mystery, here. We should be able to look back on records of dark days and find everything according with this explanation. The trouble is, we do not always find this. Many dark days fit perfectly, but some do not.
What, for example, can we make of the account from April 23–25, 1547 which the famous astronomer Kepler relates on the authority of Gemma that “the Sun appeared as though suffused with blood, and many stars were visible at noonday”? This was clearly not a solar eclipse, but if the dullness of the Sun and apparent darkness was caused by atmospheric opacity, how were stars visible at noonday?
That great compiler of anomalous reports, William Corliss, wondered why, if all dark days and similar events result from dust, volcanic ash and fires, there should be an apparent lack of any reports of these types of events coincident with some of the dark day reports. Where, for example, is there evidence of fires or the like at the time of the Washington dark day of September 12, 1902? Why is there seldom a mention of the smell of smoke or fall of ash in the accounts of many dark days? Certainly, some dark days can be traced to these events, but the causes of others are more doubtful. Some people have even speculated that at least a few might have resulted from the encounter between Earth and clouds of cosmic dust. This sounds a bit farfetched, but the universe that we inhabit is such a strange place that it cannot simply be dismissed on that ground alone.
In fact, there is one recorded instance of, if not a “dark day” in the full sense of the term, at least a day of odd sky effects and apparent atmospheric opacity of a milder degree, that almost certainly had an astronomical origin. This happened on June 30, 1861; a day on which peculiar sky effects were reported from widely separated regions of the planet.
In England, “Mr. Lowe of Highfield House” noted that the sky took on an odd yellowish tint late that afternoon, at which time the Sun also appeared unusually dull. Although stopping well short of a fully fledged dark day, there must have been a noticeable diminution of daylight as Lowe mentioned that the local vicar had the pulpit candles lit at 7 P.M., still well before sunset on that long summer’s day. Similar sky effects were also noted by others, including the well known astronomer J. R. Hind.
These sky anomalies did not stop at evening. Neither were they confined to the northern hemisphere. On the other side of the world, in New South Wales, astronomer John Tebbutt noted that the eastern horizon was illuminated that evening, as if the Moon were about to rise, although the Moon was then past last quarter and rising hours later than the time of this observation. Various reports of “aurora” (?) were also received from wide areas of the state at that time.
The odd daylight sky, apparent dimness of the Sun and nocturnal illuminations of that date almost certainly had an astronomical source. The culprit was a large comet discovered on May 13 by the same John Tebbutt who observed the luminous eastern sky of New South Wales. Initially a telescopic object, the comet passed close to Earth at the end of June and became bright enough to be visible in full daylight without the use of optical aid. On June 30 – coinciding with the strange sky phenomena – the Earth passed through its dusty tail. Now, we cannot prove with absolute certainty that this encounter with the tail gave rise to the nocturnal glows, sensation of dullness and so forth reported on that day, but it would be an enormous coincidence if the two were unrelated.
Which raises an interesting question. Were some other sky peculiarities – even genuine dark days – similarly caused by encounters with cometary debris?
The one which primarily stands out in this respect is an event recorded by Erman for February 12, 1106. According to this account, the Sun was darkened on that day and “meteors” appeared in the sky. On the face of it, the reference to “meteors” is especially suggestive of cometary debris, although the term was sometimes used to cover a broader range of atmospheric phenomena than its stricter usage of today.
In any case, at the time of this event, a bright comet with a very long tail was visible in the skies. Earlier that month, records show it to have been visible in the daytime close to the Sun – shades of Tebbutt’s Comet of 1861!
Before we can jump to any conclusions however, it is worth mentioning that, although no satisfactory orbit has been computed for this comet, it is widely believed to have been a member of the so-called Kreutz group of sungrazers. These comets pursue similar orbits that take them (as their name implies) very near the Sun. Some smaller ones have even hit it! But (and here’s the problem) if the 1106 comet truly was a Kreutz object, it could never have approached closely to Earth and the Earth/comet/Sun geometry would have precluded any possibility of Earth’s passing through its tail or, for that matter, encountering any other form of detritus from the comet. The daylight visibility, unlike the 1861 object, resulted from the comet’s very close encounter with the Sun, not with the Earth.
If the majority of astronomers are right about the 1106 comet, the dark event of February 12 must have had some other, unrelated, cause. Of course, it is possible for astronomers to be wrong sometimes, so it might be suggested that the comet was not a Kreutz sungrazer after all, that it did make a very close approach to our planet and that we did pass through the tail (or a cloud of debris) on February 12. The biggest difficulties with this, apart from the good agreement between the comet’s position and appearance and that of a large sungrazer appearing at that time of year, is the gap of over a week between the comet’s daylight showing and the dark day (unlike Tebbutt, where the two coincided as the comet passed almost between Earth and Sun) and the fact that the comet remained in the western evening sky through the date of the dark day. Because of the geometry necessary for an encounter between Earth and a comet’s tail, one would normally expect a comet to go from morning to evening sky (or vice versa) or from northern to southern hemispheres (once again, or vice versa) as the comet passed between Earth and Sun. In the 1106 instance, the comet simply became more prominent in the western sky as it drew away from the Sun. Had the dark event happened earlier or the daylight sighting later, there may have been a case to answer. As it is, the comet appears almost certainly innocent of causing the darkness recorded that year."

Das Buch von William Corliss, auf das sich Seargent bezieht, kann ich suchen, falls es interessiert. Es ist aber "nur" eine ratlose Sammlung von Einzelphänomenen, wenn ich recht erinnere, ohne jeden Erklärungsversuch.

Gruß,
Ulrich


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