What defines a spring tide?

A spring tide is defined by the alignment of the Earth, moon, and sun. This alignment enhances the gravitational pull exerted by these celestial bodies on the Earth's oceans, leading to higher high tides and lower low tides. The phenomenon occurs during both full moons and new moons when the sun and the moon are directly aligned with the Earth, resulting in the largest tidal variations.

The choice mentioning the perpendicular arrangement of the moon to the Earth does not influence the tidal range in the same significant way. Atmospheric pressure affects sea level but does not define spring tides. Additionally, the occurrence of spring tides is not limited to full moons; they also happen during new moons due to the same alignment of the Earth, moon, and sun. Hence, the alignment is the crucial factor that defines spring tides, making this choice the correct answer.