Try This!
The sun creates tides, too

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The sun also pulls up tides on the earth. The solar tides are toward the sun and away from the sun. The total tide is the sum of the solar and lunar tides and depends on the alignment of the sun and the moon. Since each phase of the moon also depends on the alignment of the sun and the moon, the pattern of tides follows the moon’s phases.

Materials

• Model from "The tides get later" activity
• Earth with sun tides image

Assembly

• Print this page and cut out the drawing of the earth with sun tides (below).

• Remove the earth from the north pole image from your model and replace it with this one.

• Draw a sun on your piece of cardboard.

To Do and Notice

• Assemble your tide activity as shown below.


• Align the tides pulled up by the sun and the tides pulled up by the moon, and compare them. Notice that the sun tides are only half as high as the moon tides.

• Place the moon directly between the earth and the sun. Now it's a new moon. The high lunar and solar tides combine, causing a lunar-solar high tide known as a spring tide (spring as in "to leap up," not as in the season).

• Revolve the moon in its orbit counterclockwise 90 degrees without letting the sun tides revolve. (Viewing the page as a clock, if the sun is at 9 o'clock, the moon will be at 6 o'clock.) This is the first-quarter position. With the high tides produced by the sun and the moon at 90-degree angles, the solar high tide partly fills in the lunar low tide. These tides, which have the lowest change in height between high and low tides, are called neap tides.

• Move the moon opposite the sun with the earth between them, which is the full-moon position. Notice the addition of the tides when the moon is full.

• Finally, move the moon to the third-quarter position and notice that the tides fill in once more. You total tide cycle should look like this:

What's Going On?

The force of the sun on you as you stand on the surface of the earth is 180 times greater than the force of the moon on you. But what raises tides is the difference in the gravitational force from one side of the earth to the other. Although the force from the sun is greater, the sun is also much more distant. The difference in the force of the sun across the earth is only 0.0017 percent, while the moon's pull across the earth differs by 6.7 percent.