The Cycle of the Seasons
The Earth revolves around the sun. This means that it travels or orbits in a set path
around the sun. The revolution of the Earth takes 365 days, or one year. It also takes
one year to complete a cycle of seasons: winter, spring, summer, and fall.
The seasons change because the Earth’s axis is tilted or at an angle. Because of this, the
Northern Hemisphere is tilted towards the sun for part of the year. This is summer, when
we have long, hot days with lots of bright sunlight. At the same time, the Southern
Hemisphere points away from the sun. This half of the globe gets less sunlight and it is
winter. Winter occurs in the Northern Hemisphere when this part tilts away from the sun
and receives less light and heat. The seasons change as the Earth revolves around the
sun each year, but we have 4 seasons because of the tilt of the Earth’s axis.
Day and Night
The Earth rotates or spins on its axis. The Earth’s axis is an imaginary line that runs
through the center of our planet, from the North Pole to the South Pole. It takes 24 hours
for the Earth to spin around its axis.
We have day and night on Earth because our planet rotates. When it is day, our part of
the Earth is facing the sun. The other part of the Earth is in darkness because it is facing
away from the sun. It may look like the sun travels around the Earth, but it does not.
The sun appears to move across the sky from east to west because our planet is rotating.
As the Earth spins, we go from day to night again and again.
The Phases of the Moon
The moon makes no light of its own. The moonlight that we see is actually sunlight,
reflecting off the surface of the moon. The sun shines on half of the moon, and this part
is illuminated. The other half is dark because it faces away from the sun.
Because the moon orbits around the Earth, we see different parts of the shining half of
the moon each night. The size and shape of the lit portion of the moon changes as the
moon travels around the Earth. After the new moon (when we cannot see the moon at
all), more and more of the shining surface of the moon becomes visible. We say that the
moon is waxing or growing. During a full moon, we can see the entire illuminated part of
the moon. Then the moon wanes or shrinks until it disappears from sight. It is a new
moon, and the cycle starts again.
The Cycle of High Tide and Low Tide
The moon orbits around the Earth. As the moon follows its path around our planet, the
moon’s gravity pulls on the oceans that cover three-fourths of the planet’s surface.
The pull of the moon’s gravity causes the ocean to rise or get higher in some places. This
is called high tide. During high tide, the ocean covers more of a beach as water levels
rise. High tide is like a bulge in the oceans. This results in lower water levels in other
places, called low tide. The ocean seems to recede from the shore during a low tide.
The tides go up and down twice in a little more than 24 hours: low, high, low, high.
There is about six hours between each high tide and each low tide.