Effect of the Sun and Moon on Tides
As previously mentioned, tides that occur on Earth result from both
solar and lunar influences. When these two bodies are in line with
Earth, as shown in figure 7-1, their combined effect causes high tides to
be higher than average and low tides to be lower than average. These
types of tides are referred to as spring tides (and has nothing to do with
the season of the year).
Figure 7-1. Spring tides occur when influences of the
Sun and the Moon act together.
When the direction of the Sun and the Moon are 90° apart, as when the
Moon is in the first and last quarter, the gravitational effect of the Sun
counteracts that of the Moon enough that both high and low tides are
lower than normal. These types of tides are referred to as neap tides.
Figure 7-2. Relationship of terms used when measuring heights and