The phases are created by the day-night spin of Moon, with respect
to sunlight. This period is is nearly two fortnights. As seen from the
Earth, the lighted surface of the its satellite moon appears to
grow and wane, alternately, within one lunar month. This causes
phases called new-crescent-gibbous-full -gibbous-crescent-new
cycle of phases.
In the Sun-Moon-Earth alignment, it is New Moon.
In the Sun_Earth- Moon alignment, it is Full Moon.
Earth orbits Sun in a plane called ecliptic.Moon orbits Earth as a
satellite in a plane inclined to ecliptic by about
In almost perfect alignments of the centers of this triad, New Moon
hides Sun for Solar Eclipse and Earth hides sunlight to Moon on
New Moon and creates Lunar Eclipse..
Each space body that attracts towards near and far other space
bodies (including you and me ) attracts by a force
the distance between the two.
The force is more on close by bodies.
For the water bodies of the Earth that includes seas, the resultant
attraction of (greater ) lunar force and ( smaller ) force from the Sun
is a maximum around Full Moon Sun-Moon-Earth alignment and a
minimum around New Moon Sun-Earth-Moon alignment. And this
causes Spring (maximum wave ) tides and Neap ( minimum wave )
tides, respectively. Owing to this rise and fall, seawater enters and
recedes, alternately, in river mouths, bays and estuaries.