6E3BD Atmosphere, Water Cycle, Waves, and Currents
Earth and Space
Ocean Tides
Lexile 960L
1 The gritty sand oozes between your toes as you
stroll along the beach. The gentle lapping of the
waves lulls you into a peaceful state. The ocean
water appears to stretch its cool fingers farther up
onto the shore than it did earlier in the day. Is it
your imagination or is the water level rising?
2 Well, you may feel better knowing that it is not your
mind playing tricks on you. Throughout each day,
the ocean water rises and falls at different times.
This movement of water is known as a tide. A tide
is a change in water level at the shoreline; it is being caused by the pull of gravity between
Earth and the Moon and Earth and the Sun. During each 24-hour period, the beach will
experience two high tides and two low tides in most places around the world. Periodically,
the beach will also experience a spring tide and a neap tide.
3 How does the gravity between the Moon and Earth cause a tide? Each day, the beach can
expect a high tide, a low tide, another high tide, and then another low tide. Between each of
these tides is approximately six hours. This is important to know because each quarter turn
of Earth takes six hours. Earth will make four quarter turns in a 24-hour period. With each
turn, the Earth and the Moon will be in different positions. These positions determine if it is a
high or low tide. These tides are a direct effect of the Moon's gravity tugging on the water on
Earth.
4 The Moon's gravity has a powerful effect on Earth's waters. In fact, it is far more powerful
than the Sun's effect. Why, you ask? It is because the Moon is closer to Earth than the Sun.
The Moon pulls the water that is on the side of Earth facing the Moon toward itself in a big
bulge. At the exact same time, on the side of Earth that is facing away from the Moon,
another bulge is forming. These two places will experience high tides. The opposite places
on Earth, which are not facing toward or away from the Moon, will experience low tides. As
Earth keeps making quarter turns, the tides change from high to low and low to high.
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6E3BD Atmosphere, Water Cycle, Waves, and Currents
Earth and Space
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How does the Sun affect the ocean tides? As mentioned before, the Sun has less of an
effect on the tides. However, the gravitational tug of the Sun can increase a high tide by
making it rise higher than normal. This is known as a spring tide. A spring tide has
absolutely nothing to do with the season spring. A spring tide happens when the Moon is
either in its new moon or full moon phase. The Moon, Sun, and Earth line up perfectly with
one another. This allows their gravitational pull on the ocean to work together making the
high tide rise higher.
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A neap tide is the opposite of a spring tide. A neap tide is a lower than normal high tide. At
the same time, there is also a higher than normal low tide. This happens as the Moon
enters a first and last quarter moon phase. At this time, the Sun and the Moon are in
positions that form a right angle to one another. The gravitational pull of the Sun pulls
water away from the bulge formed by the Moon at high tide. The water moves toward the
places that are having low tides. This results in a low high tide and a high low tide.
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In a 24-hour period, a beach will have two high tides and two low tides. When the Moon is
new or full, it will line up with the Sun and Earth causing a spring tide. When the Moon and
the Sun form a right angle to one another, there will be a neap tide. The next time you visit
a beach, pay attention to the water level on the shoreline. You might just experience a high
or low tide yourself. As you do, remember that the gravitational pull of the Moon is what is
causing the ocean tides.
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6E3BD Atmosphere, Water Cycle, Waves, and Currents
Earth and Space
1
2
Which statement best describes what an ocean tide is?
A
A change in water level that makes a high tide higher
B
A change in water level at the shoreline that is being caused by the
gravitational pull of the Moon
C
A change in water level at the shoreline that is being caused by the
gravitational pull of the Sun
D
A change in water level that makes a low tide lower
What effect does the Sun have on the ocean tides?
A
The Sun does not have an effect on the ocean tides because it is too far
away.
B
The Sun warms the water causing it to rise.
C
The gravitational pull of the Sun causes spring and neap tides.
D
The gravitational pull of the Sun's gravity is more powerful than the Moon's.
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6E3BD Atmosphere, Water Cycle, Waves, and Currents
Earth and Space
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4
During a spring tide, the Moon is either in its new moon or full moon phase. What
effect does this have on an ocean tide?
A
The Moon, Sun, and Earth line up perfectly with one another, allowing their
gravitational pulls to work together and making the high tide rise higher.
B
The Moon and Sun are positioned at a right angle to one another causing a
lower than normal high tide. The Sun warms the water causing it to rise.
C
In most places, the beach will experience two high tides and two low tides.
D
A spring tide only happens during the springtime.
How does the gravity between the Moon and Earth cause the tides to rise and
fall?
A
The position of the Sun interferes with the Moon's gravity.
B
During each quarter turn that Earth makes, the Moon and Earth line up in
different positions allowing for the high and low tides.
C
Earth makes four quarter turns each day causing spring and neap tides.
D
The gravity of the Moon is stronger at night than during the day.
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6E3BD Atmosphere, Water Cycle, Waves, and Currents
Earth and Space
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What is the main point of paragraph 3?
A
Solar flares affect the tides.
B
Tides are not affected by the Moon's orbit.
C
The neap tide is the opposite of the spring tide.
D
Gravity between the Moon and Earth causes different tide levels.
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