It will now be of interest to consider the minor movements of
the sun and moon, as they also affect the tides by reason of
the alterations they cause in the attractive force. During the
revolution of the earth round the sun the successive positions
of the point on the earth which is nearest to the sun will form
a diagonal line across the equator. At the vernal equinox
(March 20) the equator is vertically under the sun, which then
declines to the south until the summer solstice (June 21), when
it reaches its maximum south declination. It then moves
northwards, passing vertically over the equator again at the
autumnal equinox (September 21), and reaches its maximum
northern declination on the winter solstice (December 21). The
declination varies from about 24 degrees above to 24 degrees
below the equator. The sun is nearest to the Southern Ocean,
where the tides are generated, when it is in its southern
declination, and furthest away when in the north, but the sun
is actually nearest to the earth on December 31 (perihelion)
and furthest away on July I (aphelion), the difference between
the maximum and minimum distance being one-thirtieth of the
whole.

The moon travels in a similar diagonal direction around the
earth, varying between 18-1/2 degrees and 28-1/2 degreed above
and below the equator. The change from north to south
declination takes place every fourteen days, but these changes
do not necessarily take place at the change in the phases of
the moon. When the moon is south of the equator, she is nearer
to the Southern Ocean, where the tides are generated. The new
moon is nearest to the sun, and crosses the meridian at midday,