LUSTROUS MIDNIGHT.

Star (Christchurch), Issue 9319, 20 August 1908, Page 2

LUSTROUS MIDNIGHT.

— -♦ NIGHT TURNED INTO DAY. Tho astronomical correspondent of the Glasgow "Herald," writing on Friday, July 3, said : — The glorious midnight sky of Tuesday last, when night was almost turned into day and small print could bo read at the darkest hour, attracted, and fittingly, widespread attention. It is very mre indeed for a display of its kind so brilliant to bo witnessed. For a long time- both before and after midnight the lower northern sky seemed flooded with a vivid greenish light, which in places took on almost an electric hue. When reflected in a sheet of water, indeed, the aspect of the reflection closely resembled that of the light of an arc lamp. In the early hours of Wednesday morning, July 1, when the twilight began naturally to grow stronger, though the vividness of the greenish light paled, the beauty of the spectacle was enhanced by the apparition of tints of russet and gold nearer the horizon. The tints of the greenish lustre were, at times, almost auroral — but there was nothing auroral about the origin of the apparition. As, however, it seems to have been assumed in some quarters that the display was essentially "~au- ! roral " (perhaps < because there is a fine sun-spot at present visible), some points may be indicated. There were at least four matters observable which were inconsistent with an auroral origin. The light, when examined in detail, revealed a distinctly "cirrus structure." The light was seen towards the true north, and not towards the magnetic, as it would have beenN had it •been auroral. The luminous area, moreover, moved eastwards, and its boundary sank lower for a time as the night progressed — both facts inconsistent with auroral origin, though indicative of origin in solar light reflected. The magnificent display may be said to have been a consequence of the magnificent weather we have been having. It was, in fact, due to the formation in abnormal quantity and aggregation of a species of cloud which occasionally forms in Very warm weather, This is a species of cirrus — or " mares-tail" cloud, to give it perhaps the commonest of the names "ordinarily applied to clouds of that class — of an exceptionally delicate structure, irregularly branching in form, and glistening -more than other species. Its peculiarity, besides its extreme delicacy of structure, is the great height at which it is formed. Mr A. W. Clayden, F.R.A.S., the eminent authority on clouds, determined one example of it to have an altitude of rather over seventeen miles above the surface. He called it "cirrus excelsus," or Lofty Cirrus, on account of its characteristically great altitude. Of course, being suspended at so j;reat a height in -the air, it can catc!i the rays of the sun when well sunk beneath the horizon, and when its cloudlets are massed— as on Tuesday night (June 30) —in battalions they can, create a brilliant twilight of their own by acting as an accumulation of little mirrors. Mirrors of ice, however, not of silver, despite their aspect, for all "cirrus" clouds are composed of ic© particles. Tlfo gazer on Tuesday night was looking at a great gathering of these icy cloudlets, many miles above the surface, and co placed that the full splendour of their vivid reflection was received in the district where he stood. It is not likely that the display involved any reappearance- of the mysterious " luminous clouds " which aroused so rauoh interest, alike by their vivid light and almost unearthly aspect and beauty, a number of years ago. Clement Ley, the foremost authority < estimated their height at about fifty-eight miles above the surface. They reappeared during a, series of years, and then slowly vanished, as Ley had predicted they most probably would. They have never certainly returned. Mr Clayden, already mentioned, seems disposed to think they were an exaggerated and specially lofty form of the " cirrus excelsus," spoken of above as the cause of Tuesday's phenomenon. But this is doubtful, and som© have thought that their formation had some exceptional cause, such as the encountering by the earth, of a, cloud of meteoric dust of tho Krakatoa eruption. The- writer, who remembers the "luminous clouds" very well, saw on Tuesday only one strand of cloud which recalled them, and that even but slightly, and much more in tint than in structure. It may be added that the aspect of these " luminous clouds " suggested self-luminosity, not that they were not in truth selfluminous. Ley wrote that one might compare their " appearance to the mirrored volcano gleam often mistaken for, flame in the dust cloud hanging at night over the crater of a burning mountain.*' (This simile admirably illustrates Tuesday night's phenomenon.) Also, it was not shown that they had any association with auroral phenomena or sunspots. On Wednesday evening there was a repetition of th© phenomenon on a minor scale, but in consequence of haze it was not so conspicuous. Professor Becker, of Glasgow University, was communicated with, and suggested an explanation which x>roves to be in complete accord with that given by the astronomical correspondent. Professor Becker was of opinion that the phenomenon was probably due to sunlight reflected by cirrus clouds placed at a very high altitude. The meteorological observations made at tho Observatory at 8, 9 and 10 p.m. were in favour of this explanation ; notonly were such clouds observed at these hours on Tuesday evening, but the atmosphere in the lower strata was so free from haze and so trails-; parent that the hills near Crianlarich were plainly visible from Glasgow Observatory. Cirrus clouds are not frequently observed in Glasgow owing to the prevalent conditions of the atmosphere. : A striking phenomenon was witnessed in Lochab&r during the early hours of Thursday, July 2, and created the liveliest interest amongst those who happened to be abroad at the time. Atmidnight the sky was beautiful with banks of cumulus clouds varying in tint from deep orange and saffron to the most delicate and roseate pink, and the scene resembled more than anything else a delightful autumn sunset. Between 12 and 1 a.m. , the light was w> strong that one had not the slightest difficulty in reading tho smallest print, and moving objects were visible at a distance of several miles. An absolute calm prevailed. There was practically no night dividing Wednesday and Thursday, as at any time between dusk on the former and dawn on the latter day no difficulty wae experienced in either writing or reading in the open. From various parts of the country the weather reoorta contained allusions to the remarkable fact that the brightness of noonday prevailed at midnight on ' Wednesday. , j