Final answer:
A rare proxigean spring tide is caused by the aligned gravitational pulls of the Moon and the Sun during perigee and perihelion, which results in exceptionally high tides.
Step-by-step explanation:
A rare proxigean spring tide occurs when the gravitational pulls of the Moon and the Sun reinforce each other at a time when the Moon is at its closest point to Earth (perigee) and the Earth is at its closest point to the Sun (perihelion). This aligns the three bodies in such a way that the gravitational effects are maximized, leading to exceptionally high tides, known as spring tides. When these factors combine with the Moon being at its perigee, the tides are even more pronounced, which is why we refer to them as rare proxigean spring tides.
The gravitational tidal forces are responsible for these tides, and these forces are amplified when the distances between the Earth, Moon, and Sun are smaller. While the Moon's gravitational pull has the most significant impact on the tides, the Sun's pull also contributes to the tidal forces, especially during spring tides when it aligns with the Moon and Earth.