The accompanying [diagram] will at once show the difference between the rising conditions we have now to consider. It deals with the summer solstice, as being the most precise case, in Lat. 59° N.

At this time the position of the sun, that is of the sun’s centre, as given in the “Nautical Almanac,” is represented by the double circle on the sea horizon.

[Larger diagram]

Fig. 36.—The Conditions of “Sunrise” at the Summer Solstice in Lat. 59° N.

Vertical axis from bottom: Altitudes SEA HORIZON, HILL 1⁄2° HIGH, HILL 1° HIGH, HILL 11⁄2° HIGH.

Horizontal axis from left: Azimuths N 37°-42° E.

The azimuth of this position is N. 39° 16′ E. This is the equivalent of the declination of a star, but it will be seen that the real azimuths we want are very different. The dotted circles represent the actual position of the sun with regard to the horizon, the continuous circles the apparent positions caused by the lifting-up effect of refraction. We have the positions in azimuth of the apparent sun as it appears on a sea horizon, and when the horizon is formed by hills up to 11⁄2° in vertical height.

To make this quite clear I give a table which has been computed by Mr. Rolston, of the Solar Physics Observatory, showing azimuths with hills up to 11⁄2° high for lat. 59° N., and 51° N. nearly the latitude of Stonehenge, of the sun’s upper limb for the summer solstice:—

Lat. 59°Lat. 51°
Summer
Solstice.		Rising N-E
or
Setting N-W.		Rising N-E
or
Setting N-W.
°′°′
Sun’s centre; uncorrected39165040
Sun’s upper limb; corrected for semi-diameter and refraction- sea horizon37 14920
hill 1⁄2°high38345016
„1°„40 85112
„11⁄2°„413052 4
Winter
Solstice.		Rising S-E
or
Setting S-W.		Rising S-E
or
Setting S-W.
°′°′
Sun’s centre; uncorrected39165040
Sun’s upper limb; corrected for semi-diameter and refraction- sea horizon412452 0
hill 1⁄2°high395451 4
„1°„382350 8
„11⁄2°„36544914