LOW-SUN PHENOMENA IN LUZON 
By Willard J. Fisher 
Assistant Professor in Physics, University of the Philippines 
TWO TEXT FIGURES 
I. ZENITH OBSERVATIONS OF DAWN, MANILA, 1918-1919 
By “low-sun phenomena” I mean those aspects of the sky and 
the atmosphere which are seen during the period of oblique or 
nearly horizontal illumination within a short time before and 
after sunrise or sunset ; as the Zodiacal Light, dawn and twilight, 
crepuscular rays and shadows, colors of sky and clouds, and 
the color and form of the low sun itself. Related to these, though 
not all exactly solar in the origin of their light, are the phenom- 
ena of moonrise and moonset, of low stars, of the eclipsed moon, 
the Gegenschein, and atmospheric refraction at low altitudes — 
particularly horizontal refraction at sea level, when the rays of 
light are parallel to the ocean surface. 
For the study of low-sun phenomena Luzon possesses certain 
advantages. It is subject to steady and well-studied tropical 
oceanic conditions of pressure and temperature ; it is not so large 
but that the horizon, seen toward east or west from heights that 
are small compared with the air depths, would be a sea horizon ; 
it has good roads and railway communications ; it has been geo- 
detically and topographically surveyed and mapped; there is a 
good meteorological and telegraphic standard time service cen- 
tering in the Manila Observatory; many of its mountain peaks 
are considerably above the hazy low altitudes which extend to 
the strato-cumulus level, and some are reached by good trails — in 
one case, Santo Tomas, Benguet, there is a modest summit hotel. 
The observations following were made mostly in Manila; 
where the point of observation was elsewhere, it is noted. This 
city, being the center of civilization and government, with ex- 
cellent scientific libraries, has advantages in some ways over any 
other point in the Philippines ; the open sea is only about forty 
miles away east or west, though the physical horizon east or 
west is mountainous ; the sun, however, during a few weeks about 
the winter solstice sets in the water between Corregidor Island 
and Bataan Province; most stars of declinations between south 
151 
