In the previous section we discussed the basics of computing tides. We thereby focused on the effects caused by the Moon. Now we will factor in the tidal acceleration caused by the Sun. In reality the tidal forces acting on the earths surface are a combination of the tidal effects of the Moon and the tidal effect of the Sun. The computation of the latter one is done exactly like we did for the moon. Due to the greater distance of the Earth from the Sun the effects caused by it are a bit smaller despite its significantly larger mass. The following animation shows the two separate tidal bulges of the Moon and the Sun.
Please note that the Sun is not shown directly in the animation since it is too far away to be visualized in a meaningful manner. Instead light beams and shadows give a hint at the position of the Sun.
Neap Tides occur at half moon when the Sun, Earth and Moon are positioned at a 90 degree angle. Under these circumstances the gravitational bulges of Moon and Sun overlap destructively because the tidal forces of the Sun are acting against the tidal forces of the Moon. At neap tide difference between high tide and low tide are the least.
The opposite of neap tides are called spring tides. Spring tides occur when Sun, Earth and Moon line up. Such an arrangement happens at every full Moon and new Moon phase. Then the gravitational forces of Sun and Moon are forming a large tidal bulge. At spring tide the difference between high tide and low tide are at their maximum.
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