SELF-LUMINOUS NIGHT HAZE. 



By E. E. BARNARD. 



(Read April Ji, iqiiA 



There is one phase of the night skies which does not seem to have 

 received much or any attention. It is the occasional presence of 

 self-luminous haze. This matter does not seem to be similar to tfie 

 luminous night clouds, " die leuchtenden Nachtvvolken." which were 

 observed by O. Jesse and others some twenty-five or thirty years 

 ago, and which were found to be clouds at such great altitudes above 

 the earth's surface (upwards of fifty miles high) that they received 

 the sunlight long after or before the ordinary clouds. The observa- 

 tions of O. Jesse were printed in the Astronoinische Nachrichtcn, 

 Bd. 121, pp. JT,, III ; Bd. 130. p. 425; Bd. 133, p. 131 ; Bd. 140. p. 

 161. In A. N., Bd. 140 (No. 3347), he gives a long list of altitudes, 

 determined by photograph}-, which range from 81 km. to 87 km. 

 The mean value given by the observations from 1885 to 1891 was 

 82 km. (52 miles). These clouds were seen in the northern hemi- 

 sphere onlv near the time of the summer solstice. In the southern 

 hemisphere they were seen at the opposite season. From his papers 

 it is clear that these sunlit clouds were in no way related to the 

 present subject, and I onl}- mention them to forestall any suggestion 

 that they were similar to the ones seen by me. The objects to be 

 described here were apparently at the altitude of the ordinary higher 

 clouds. They have been seen in all parts of the sky and at all hours 

 of the night. In a paper on the aurora^ I have previously called 

 attention to the frequent luminous condition of the sky at night. 

 This feature long ago impressed itself upon me. Indeed any one 

 who has spent much time under the open sky hunting comets, etc.. 

 will have been forcibly impressed with this peculiarity. In most 

 cases this illumination has been due evidently to a diffusion of the 



^ " Astrophysical Journal, 31, April, 1910. 



246 



