Spring tides occur only when a. the Sun is near the vernal equinox. b. the Moon's phase is new or full. c. the Moon's phase is first quarter or third quarter. d. it is either spring or fall.

Gravitational forces play a crucial role in the occurrence of tides on Earth. The gravitational attractions of both the Moon and the Sun influence the movement of water in our oceans. While the Moon has a stronger effect due to its proximity, the Sun's gravity is also significant because of its large mass.
When the gravitational forces of the Moon and the Sun align, they create a stronger combined force that pulls more water towards the areas of alignment. This alignment leads to what we call spring tides, characterized by higher high tides and lower low tides.
Understanding the interplay of gravitational forces is fundamental to predicting tidal patterns and their effects on coastal areas.

The Moon goes through a cycle of phases approximately every 29.5 days. This cycle is defined by the changing positions of the Moon, Earth, and Sun and how they light up the Moon's surface as seen from Earth. These phases include new moon, first quarter, full moon, and third quarter.
Each phase has unique visual characteristics and impacts on Earth's environment. For example, the arrangement during a full moon or new moon leads to specific gravitational effects that significantly influence the tides. Spring tides occur during these phases when the gravitational forces of the Moon and the Sun are in alignment, causing more extreme tidal conditions.

A new moon occurs when the Moon is positioned between Earth and the Sun. At this time, the side of the Moon that is illuminated by the Sun is facing away from Earth, making the Moon appear invisible to us.
Despite its lack of visibility, the new moon phase is significant in the context of tides. During this phase, the gravitational forces of the Moon and the Sun work together synergistically. This alignment amplifies the gravitational pull on Earth's oceans, resulting in spring tides. These tides are characterized by higher high tides and lower low tides, having noticeable effects on coastal regions.

The full moon phase occurs when Earth is positioned between the Moon and the Sun. During this phase, the Sun fully illuminates the side of the Moon facing Earth, making the Moon appear completely round and bright in the night sky.
Like the new moon, the full moon phase also plays a crucial role in creating spring tides. When the Moon is full, the gravitational forces of the Moon and the Sun align in a way that enhances their collective pull on Earth's oceans. This alignment leads to more pronounced tidal movements, specifically higher high tides and lower low tides that define spring tides.