Study the first 3 graphics and then answer the questions that follow each. Once you are sure you understand how the lunar day, the position of the sun and the moon, and orbital variations affect the tides, then try to apply this knowledge, and Be the Captain.

Lunar Day

Position of the
Sun and Moon

Orbital Shape

Be the Captain

Knowing when and how much the tides will rise and fall each day is important to beachcombers, mariners, fishermen, and the people who operate seaside industrial and commercial facilities. Miscalculating the arrival and size of the tides can have expensive, even deadly, consequences.

Predicting the tides is complicated because the tides are affected by many factors. In this activity, you'll have a chance to consider some of the most important and universal influences, those due to the movements of the sun, the moon, and the earth. In reality, a number of local and transient factors, such as the shape of the coastline, the flow of currents, and the weather, must also be taken into account.

Play the animation below to see how the relative positions of the sun and the moon effect the tide, then answer the questions below.

Position of the Sun and Moon

The height of the tides varies over the course of a month. The highest highs and lowest lows, called spring tides, occur when the moon and the sun are aligned. Moderate highs and lows, called neap tides, happen when the sun and the moon are at 90o to one another.


  1. Explain how spring and neap tides are created.
    Check Answer
    The tides are created by the pull of the moon and the sun. When those bodies are aligned with one another, their gravitational forces act in the same direction and reinforce one another, creating the maximum possible tidal bulges, called the spring tides. When the sun and moon are at 90o from one another, relative to Earth, their tidal forces are also pulling in different directions, so the neap tides are minimized.
  2. How many spring and neap tides occur each month? Why?
    Check Answer
    There are 2 spring and 2 neap tides each month. The moon rotates around the earth once in a month, so in that time it will be aligned with the sun twice, and at 90o to the sun twice.