Which alignment of the Sun, Earth, and Moon leads to spring tides?

Spring tides occur when the Sun, Earth, and Moon are aligned in a straight line, which can happen during both the new moon and full moon phases. This alignment causes the gravitational forces from both the Sun and the Moon to work together, resulting in higher high tides and lower low tides. The combined gravitational pull leads to more extreme tidal variations, creating the phenomenon known as spring tides.

In contrast, when the Moon is at apogee (its farthest point from Earth), or at its perigee (its closest point), the gravitational effects are different and do not create the same extreme tidal variations as seen during spring tides. During the half-moon phases, known as the first and third quarters, the Moon, Earth, and Sun form a right angle, leading to lower high tides and higher low tides, known as neap tides. Thus, the straight-line alignment of all three celestial bodies is key to the occurrence of spring tides.