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The tides we experience here on Earth owe their existence to the concept of gravitational forces. Essentially, gravity is the invisible pull that celestial bodies exert on one another. Take the Moon for example; it exerts a force on Earth that pulls the planet's water towards it, creating what we call a 'tidal bulge.' This is why the side of Earth nearest to the Moon experiences high tide. On the opposite side, inertia causes water to bulge outward as well, resulting in another high tide, while the areas at 90 degrees to these points experience low tides.

But the Moon isn't the only player in this cosmic dance. The Sun, despite being 390 times farther from Earth than the Moon, also has its own tangible effect on our tides due to its massive size. When these two celestial bodies align their gravitational forces—either they're on the same side of Earth or on opposite sides—their combined pull creates what we call spring tides, which boast the highest high tides and the lowest low tides.

When discussing tides, the term 'tidal range' frequently comes into play. It refers to the vertical difference between the high tide and the subsequent low tide. It's this measurement that can tell us how drastic the change between tides will be--a large tidal range means a significant difference in water levels, leading to more pronounced tides.

Normally, the tidal range varies from place to place and from day to day. However, during spring tides, the tidal range is at its maximum. Why is that? Well, it's because the gravitational forces of the Moon and the Sun are working in unison, which amplifies the effect on Earth's waters. This phenomenon leads to higher than normal high tides and lower than usual low tides, making the tidal range during spring tides the 'star of the show' when it comes to dramatic seashore changes.

The Moon goes through a cycle of phases based on its position relative to Earth and the Sun. Two of these phases, the new moon and the full moon, play pivotal roles in the story of spring tides. During the new moon, the Moon is positioned between Earth and the Sun. This means that the Sun, Moon, and Earth all line up, with the Sun and Moon being on the same side of our planet. Conversely, during the full moon phase, the Earth lies between the Sun and the Moon, with the three again forming a straight line, but this time with Earth in the middle.

It's during these particular alignments that the gravitational pull of the Moon and the Sun can combine in their most powerful form, reinforcing each other's influence on Earth's waters. The result is extreme tides, known as spring tides, that occur roughly twice a lunar month, coinciding with the full and new moon phases. This is why fishers, sailors, and coastal residents pay especially close attention to the lunar calendar—it helps them prepare for the notable shifting of tides that these phases bring.