Go to a website that will show you the times for high and low tides; for example, http://saltwatertides.com. Pick a location and bring up the tide table for today and the next 14 days. Why are there two high tides and two low tides every day? What is the difference in the height of the water between high and low tides? In the last few columns of the table, the times of moonrise and moonset are indicated, as well as the percent of lunar illumination. Does the time of the high tide lead or follow the highest position of the Moon in the sky? Compare with Figure \(4.12 \mathrm{c}:\) what phases of the Moon have the greatest differences in the height of high and low tides?

The gravitational pull of celestial bodies plays a critical role in the formation of tides. The Moon's gravitational force is the primary driver behind tidal movements. This is because the Moon is much closer to Earth compared to the Sun, making its gravitational influence stronger despite its smaller size. When the Moon's gravity pulls on Earth's oceans, it creates bulges of water on the side of Earth nearest to the Moon and on the opposite side.
Besides, the Sun also contributes to tidal forces, although to a lesser extent. When the Sun and Moon align during new moon and full moon phases, their combined gravitational pulls create more pronounced tides known as spring tides. Conversely, when the Sun and Moon are at right angles during the first and third quarters of the moon, their gravitational forces partially cancel each other out, resulting in weaker tides called neap tides.

Each day, we experience two high tides and two low tides. This happens due to the Earth's rotation and the gravitational pull from the Moon. As Earth rotates, different areas move through the bulges of ocean water created by the Moon's gravity. This rotation results in the cyclical rise and fall of sea levels.
The timing of high and low tides depends on the position of the Moon. High tides usually occur when the Moon is directly overhead or on the opposite side of the planet. Low tides, conversely, happen when the Moon is at the horizon. Therefore, we have two high tides and two low tides within approximately a 24-hour period.
The difference in water height between these tides is known as the tidal range, and it varies depending on geographical location and lunar phases.

The different phases of the Moon impact the tidal range. During a new moon or full moon, the Earth, Moon, and Sun are aligned. This alignment enhances the gravitational pull, leading to higher high tides and lower low tides—known as spring tides.
Conversely, during the first and third quarters of the lunar cycle, the Moon and Sun are at right angles to each other relative to Earth. This configuration causes their gravitational forces to interfere partially with each other, resulting in lower high tides and higher low tides—known as neap tides.
By looking at a tide table, you can often observe these patterns coinciding with the moon phases. This is why sailors and fishers frequently consult both tide tables and lunar calendars to plan their activities.

The tidal range is the vertical difference between the high tide and the low tide. This range varies daily based on the relative positions of the Earth, Moon, and Sun.
During spring tides—which occur during new and full moons—the tidal range is the greatest. You will see very high high tides and very low low tides. During neap tides, which occur during the first and third quarters of the moon, the tidal range is much smaller, resulting in moderate high and low tides.
Several factors influence the tidal range at different locations around the world, including the shape of the coastline and the depth of the ocean floor. Narrow bays and inlets typically experience larger tidal ranges, while more open areas have smaller ranges.

Lunar illumination is the portion of the Moon's surface that is lit by the Sun and visible from Earth. The level of illumination varies as the Moon goes through its phases, affecting the timing and magnitude of tides.
During a full moon, the entire face of the Moon is illuminated, and during a new moon, none of it is visible to us. These phases have the greatest impact on tides—resulting in larger tidal ranges. Conversely, during the first and third quarters, roughly half of the Moon is illuminated, leading to smaller tidal ranges.
By observing lunar illumination, you can better understand when to expect higher or lower tides. Tide tables often include lunar phase information to help in predicting tidal patterns more accurately.