August 7, 1884] 



NATURE 



347 



OBSERVATIONS ON A GREEN SUN, AND 

 ASSOCIA TED PHENOMENA 1 



THE rarity of the phenomenon of a green or blue sun makes 

 it desirable to record with the greatest accuracy and detail 

 the observations made during its appearance in India during 

 several days of September 1S83. 



The notes taken at Madras at the time of the appearance will 

 best illustrate the general features of the phenomena : — 



On September 9, the sun, before setting, assumed a peculiar sil- 

 very appearance, and its brightness was so much decreased that for 

 about half an hour before sunset it could be observed with the 

 naked eye. This was observed, I believe, though to a less 

 extent, on the two days preceding, but I did not myself see it 

 on these dayr,. On September 10, from 5 to 5.30 p.m., the 

 Hin could easily be looked at with the naked eye, yet the limbs 

 were sharply defined. At 5.30 the sun entered a low bank of 

 clouds, and did not fully appear again; but a narrow strip 

 seen through a rift in the cloud at 5.43 was coloured a bright 

 pea-green. Round Madras this colour had been seen in the 

 morning, but in Madras itself clouds concealed the sun till it 

 had risen to a considerable altitude. Of the morning of the I Ith 

 I have no record, but in the evening the green colour was bril- 

 liant, and was visible for more than half an hour, being pre- 

 . as on the former night, by the silvery white appearance of 

 the sun's disk. On this evening a large sunspot about 1' long 

 was so conspicuous an object that it attracted the attention of 

 even the most casual observers. 



September 12. — At 12.35 a - m - " ie moon, which was near 

 the horizon, appeared a pale green. Bright stars near the 

 horizon showed the same tint. From 5.15 to 5.30 the clouds 

 to the east were coloured reddish brown. At 5.55 the sun 

 rose with a yellowish green colour, but was almost instantly 

 losl in clouds. It reappeared at 6 '4, and was then of a bright 

 green colour : this colour rapidly got fainter, but was quite 

 1. able till 7 o'clock. In the afternoon the phenomena 

 of the previous nights were repeated, and, the horizon being 

 free from clouds, the actual sunset was observed. The entry 

 in my notes is: "6.3. — The sun set as a greenish yellow 

 lull ; cumulus, stratus, and nimbus clouds near the horizon, but 

 moon fairly clear ; some blue sky, but hazy." The change from 

 green to greenish yellow was evidently due to the great increase 

 in the strength of the low-sun-band close to the horizon, which 

 left the strip of yellow between that band and the rain- 

 band by far the most prominent feature in the spectrum. 



September 13. — In the early morning there was a good deal of 

 distant lightning. The sun rose of a bright, golden yellow 

 colour ; no green was seen. In the afternoon there were slight 

 showers. 



A most remarkable observation made this morning by Mr. 

 m seems very difficult to explain, except by some form of 

 auroral display. I give his notes in full : — 



" 1S83, September 12, 17I1. om. Madras mean time. — The 

 sky a most remarkably intense reddish yellow, unusually bright. 

 A dark cloud-bank from about east to south, and the vivid light 

 above uncommonly auroral in appearance, more so than any- 

 thing I have seen here before. 



"At 17I1. 10m. the red hue considerably diminished, and 

 bright orange yellow the prevailing tint. The light quite bright 

 enough to make notes by. 



" At 17I1. 20m. the dark blue-black stratum, now from about 

 north to east, and very near the horizon. Sky tolerably clear 

 to about 20° altitude, but of a rich red tint, with bright yellow 

 clouds above, beginning at about 30°, and covering the rest of 

 the sky. 



" At 17I1. 30m. all changed within the last four or five minutes, 

 and writing now difficult without a lamp ; a thick dark red 

 stratum over the sunrise point, and everywhere else a very 

 greenish yellow. 



"At 17I1. 40m. the low cloud stratum now sea-green. Light 

 only enough to write by with difficulty. 



"At I7h. 50m., sun rising a bright yellowish white, and other- 

 wise nothing extraordinary, all unusual tints having disappeared 

 with the sunrise." 



September 14. — Before sunrise the clouds were blue and gray, 

 with patches of red clouds of all sorts — cirrus, nimbus, stratus, 

 cumulus, and mares' tails. Two bright flashes of lightning about 

 5.30 a.m. In the evening there was a slight green tinge, and 



1 Abstract of a paper read before the Royal Society of Edinburgh, July 7, 

 <ly Prof. C. Michie Smith. 



after sunset the sky was golden red till 6.50, while Mercury, 

 seen through the red haze, was twinkling strongly. 



September 15. — The sun rose golden. In the evening the 

 sunset was very fine : in the west the colour was golden to orange- 

 yellow, in the east it was greenish ; red clouds remained till 7.5. 

 There were very brilliant red " rayons de crepuscnle." 



From September 15 to September 20 the sunrises and sun- 

 sets were very fine, with red and gold, for more than half an 

 hour before sunrise and after sunset. 



September 21. — Sunset normal. 



September 22. — The sun rose as a yellow ball, and showed 

 distinct greenish yellow afterwards. From ten minutes before 

 till sunset the sun was greenish yellow, but the sun was much 

 brighter than on the 10th and nth. 



September 23.— The sun rose very green. At 5.37 p.m. the 

 sun appeared from under clouds, very green ; strong absorption 

 in the red end of the spectrum to C ; low-sun-bands weak. 

 5.45.— Clouds grayish purple. There was only one bank of 

 clouds which was near the horizon ; above this was a peculiar 

 grayish haze. At 6 the clouds were of a marked purple colour ; 

 breaks near the horizon were reddish brown. During the night 

 there was a great deal of sheet-lightning in the south. 



September 24.— The sun rose bright yellow. The spectrum 

 showed complete absorption up to B ; the rain-band a and 3 

 were very thick, and the low-sun-bands less marked than usual. 

 There was lightning all night, beginning in the south, and 

 working round to the south-east. It consisted chiefly of sheet- 

 lightning, with occasional zig-zag flashes, but no thunder ; the 

 stars were fairly clear except near the horizon. Saturn and the 

 moon, when near the horizon, were both very dim. 



September 25.— Sunrise golden green. In the afternoon the 

 shadows cast on white paper were still quite pink, but the sunset 

 was bright yellow. 



September 26. — Much the same as yesterday. 



September 27. — Before sunrise C, 0, a, the rain-band and the 

 dry-air-band were very strong, but the dry-air-band was less 

 than half as dark as the rain-band. The sun rose golden red. 

 The spectrum showed signs of clearing up; glimpses of A 

 could be obtained. After dark there was very bright lightning 

 in the west. 



September 28. — Spectrum still showed great absorption. 

 Lightning at night. 



September 29.— Spectrum absorption still very strong. After 

 dark there was a display of luminous clouds specially towards 

 the east. After II p.m. there was very heavy rain with much 

 lightning and some thunder. 



September 30.— Sunrise golden. The spectrum on the sun 

 showed A clearly, a was very thick. 



October 2. — In the morning from about 7 to 9 there was ;> 

 thunderstorm, in which the thunder was almost continuous for 

 about an hour and a half, but although the storm was almost 

 vertically overhead, hardly any lightning was visible. . . . The 

 total rainfall for the day was 4 - 88 inches. 



Accounts were collected from trustworthy observers in various 

 parts of India. All describe the brilliant sunsets of the first week 

 of September, and record the appearance of a green sun on 

 several days. It was seen at Muttum in the south of Madras on 

 the 9th, and continued for several days both in the morning and 

 the evening. The green colour was then lost, but reappeared 

 from the 22nd to the 28th inclusive. 



At Bellary the sun was seen " emerald-green " at rising and 

 setting from the 10th to the 14th inclusive. The observations 

 were not carried on longer. 



At Coonoor on the Nilgiris the abundance of green tints in 

 the sunsets was noted, but the sun itself was merely described as 

 of a " shimmery " appearance. 



The observations at Ongole have been already noticed in 

 Nature. 



The Spectrum .—The spectrum of the sun when green was re- 

 peatedly observed and photographed with the large zodiacal-light 

 spectroscope, which is furnished with one large prism of dense 

 glass and a very long collimator permitting the use of a wide slit. 

 The main features of the spectrum taken on the sun when green 

 were — . 



1. A very strong general absorption in the red end. 



2. A great development of the rain-band and of all other lines 

 that are ascribed to the presence of water-vapour in the atmo- 

 sphere, more especially of the group Cj of a and of the band at 

 W.L. 504. . . 



The absorption in the red end was of very varying intensity. 



