Chart to be used in connection with text of booklet, “Orienting the
House”
In the first place, you see three broad, concentric circles, on the
outside of which the rising and setting sun is depicted for both
midsummer and midwinter day. The figures, 30°–50°, alongside of the sun
represent degrees of north latitude, wherever you may happen to live,
which, with the exception of most of Florida and southern Texas, cover
the United States. The short arrows show the direction of the sun’s
rays at sunrise and sunset.
[Illustration:
Garden Side of Residence, Westbury, L. I.
Peabody, Wilson & Brown, Architects]
The inner circle represents your horizon, and the degrees marked upon
it show the points of sunrise and sunset, north or south of the direct
east and west line. These angular distances, in terms of degrees, are
called amplitudes, north or south, and must not be confused with the
degrees of latitude on the earth’s surface, indicated by the numbers
along side of the sun, though intimately dependent upon them. The
amplitude of the horizon point, where the sun rises and sets from
time to time during the year, always depends upon the latitude on the
earth’s surface where you happen to live, as may be seen by following
with your eye the direction of the arrows of latitude through the
amplitude circle. Starting from the number indicating the latitude
where you live, trace the arrow until it touches the amplitude circle.
You can then read the degree on it which shows how far north or south
of the east and west line the sun rises or sets. We are indebted to
Professor Philip Fox, of the Dearborn Astronomical Observatory at
Evanston, Illinois, for determining these points.
The two outer circles are sun-dials for midsummer and midwinter day at
the 40th degree of north latitude; and, if you imagined them pivoted
on their rising and setting points and tipped up from the south to
represent the slanting path of the sun during the day, they show the
direction from which the sun is shining during successive hours of the
day (or night on the other side of the world). The shaded portions of
these circles represent night, which for all northern latitudes is
short in summer and long in winter, as the day is short in winter and
long in summer. If you examine the hour spaces on the winter dial of
your winter night, you will find them exactly like those on the summer
dial of your summer day. So also your winter day hours are spaced like
your summer night hours. South of the equator, people have precisely
the same experiences only in the reverse order. New Zealanders, we
fancy, wear straw hats in January and fur caps in July. If you liked
summer well enough and cared to move, you could live in a perpetual
summer on our little globe. It is probable, however, that, like most
people, you rather prefer the change of seasons, in spite of occasional
extremes.
The irregular hour spaces on the dials would make it appear that the
sun moves around the earth in a sort of jerky way. On the contrary, it
moves, or rather the earth rotates, at an absolutely uniform rate, but
the tilt of the sun’s path to your horizon line gives you at certain
points a fore-shortened view by which the sun seems to cover various
distances at various stages of its course.
The sun-dial time is used on our chart as it more universally applies
at different meridians on a given latitude, than does our standard time
which, for the sake of timepiece uniformity, is a compromise based on
mean solar time. As the earth’s orbit is such as to make the sun gain
a little or lose a little in crossing the meridian each day during
the year, the total _annual_ time of the sun is averaged into uniform
_daily_ periods, which in turn are divided into 24 uniform hours and
referred to certain meridians the world round, about an hour apart.
To show the exact position of the sun in strict agreement with these
standardized hours would require a special chart for every degree of
longitude, and then be of no especial value for our present purpose;
for while the astronomer must have exact time to the fraction of a
second, the differences between watch and sun-dial are not enough at
any time to affect essentially our problem. So that, if you do not
find the hours marked on our summer and winter sun-dials, at any time,
exactly agreeing with your watch, you may, nevertheless, trust them to
show you accurately enough from what direction the sun is shining at
different hours of the day.
[Illustration: