Halo and Mock Suns

Abstract

THIS morning a very distinct halo accompanied by mock suns on either side was seen here. As the latter, owing to the altitude of the sun, were at a considerable distance outside the halo, I think the following details are worth putting on record. At 11h. 12m., Berne time, the sun's altitude being 48° 30′, the distance from the halo to the left-hand mock sun was 9° 15′. The parhelic circle was plainly visible, reaching from the sun slightly beyond the mock suns. Each of the latter consisted of a reddish patch shading off into white and then into blue on the side away from the sun. From the brightest red to the brightest blue was about 2°, and the measurement 9° 15′ was taken from half-way between these to the nearest point of the circle dividing the red from the blue of the halo. It is difficult or impossible to measure such faint objects with the sextant, So I held a pencil at both arms' length, and noted the length on the pencil corresponding to the desired angle. Holding the pencil with both hands gives it a very definite distance from the eye, provided the position of the body and the altitude of the object be not much altered. Paying attention to these points I measured the angle subtended at my eye by a certain length on the side of a house, both with the pencil and a sextant. The angle 9° 15′ was found thence by simple proportion. I think the error of this measurement can hardly exceed 30. The halo of course was the common one of 22°.