horizon.

The zenith distance of any point or celestial body is its angular
distance from the zenith of the observer.

The Ecliptic is the great circle representing the path in which the sun
appears to move in the celestial sphere. As a matter of fact, you know
that the earth moves around the sun, but as you observe the sun from
some spot on the earth, it appears to move around the earth. This
apparent track is called the Ecliptic as stated before, and in the
illustration the Ecliptic is represented by the curved line, C V T. The
plane of the Ecliptic is inclined to that of the Equinoctial at an angle
of 23 deg. 27-1/2', and this inclination is called the obliquity of the
Ecliptic.

The Equinoxes are those points at which the Ecliptic and Equinoctial
intersect, and when the sun occupies either of these two positions, the
days and nights are of equal length. The Vernal Equinox is that one
which the sun passes through or intersects in going from S to N
declination, and the Autumnal Equinox that which it passes through or
intersects in going from N to S declination. The Vernal Equinox (V in
the illustration) is also designated as the First Point of Aries which
is of use in reckoning star time and will be mentioned in more detail
later.

The Solstitial Points, or Solstices, are points of the Ecliptic at a
distance of 90 deg. from the Equinoxes, at which the sun attains its highest
declination in each hemisphere. They are called the Summer and Winter
Solstice according to the season in which the sun appears to pass these
points in its path.

To sum up: The way to find any point on the earth is to find the
distance of this point N or S of the equator (i.e., its Latitude) and
its distance E or W of the meridian at Greenwich (i.e., its longitude).
In the celestial sphere, the way to find the location of a point or
celestial body such as the sun is to find its declination (i.e.,
distance in arc N or S of the equator) and its hour angle. By hour
angle, I mean the distance in time from your meridian to the meridian of
the point or celestial body in question.

Assign for Night reading, Arts, in Bowditch:
270-271-272-273-274-275-277-278-279-280-282-283-284.

WEDNESDAY LECTURE

TIME BY THE SUN--MEAN TIME, SOLAR TIME, CONVERSION, ETC.

There is nothing more important in all Navigation than the subject of
Time. Every calculation for determining the position of your ship at sea
must take into consideration some kind