Self-Luminous Night Haze ¹

Abstract

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 the luminous night clouds, “die leuchtenden Nachtwolken,” which were observed by O. Jesse and others some twenty-five or thirty years ago, and were found to be clouds at such great altitudes above the earth's surface (upwards of 50 miles high) that they received the sunlight long after or before the ordinary clouds. The observations of O. Jesse were printed in the Astronomische Nachrichten, Bd. 121, pp. 73, 111; Bd. 130, p. 425; Bd. 133, p. 131; Bd. 140, p. 161. In Astronomische Nachrichten, Bd. 140 (No. 3347), he gives a long list of altitudes, determined by photography, 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 hemisphere only 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 only mention them to forestall any suggestion that they were similar to the ones seen by me.