Download Days and Years

Astronomy: The Earth, Sun, and Moon: Rotation, Axis, Revolution, Orbit, and timing
The ancient Egyptians were among the first people to
study stars. The study of the moon, stars, and other
objects in space is called
astronomy.
Ancient astronomers also studied the movements
of the sun and moon as they appeared to travel across
the sky. It seemed to them as though Earth was standing
still and the sun and moon were moving around it.
Actually, the sun and moon seem to move across the sky
each day mainly because Earth is rotating on its axis.
The imaginary line that passes through the Earth’s
center and the North and South poles is called Earth’s axis.
The north end of the axis currently points toward a point
in space near Polaris, the North star. Earth’s spinning on
its axis is called its rotation. A point on the equator
rotates at about 1,600 kilometers per hour. Even most
commercial jets can’t fly this fast!
As Earth rotates eastward, the sun appears to move
westward across the sky. It is day on the side of Earth
facing the sun. As Earth continues to turn to the east,
the sun appears to set in the west. Sunlight can’t reach
the side of the Earth facing away from the sun, so it is
night there. It takes Earth about 24 hours to rotate once
on its axis. As you know, each 24-houtr cycle of day
and night is called a day. It is Earth’s rotation on its
axis that cause day and night.
In addition to rotating in its axis, Earth travels
around the sun. The movement of one object around
another object is called revolution. One complete
revolution around the sun is called a year. Earth’s
path as it revolves around the sun is called an orbit.
As it travels around the sun, Earth’s orbit is not quite
a circle. It is an elliptical shape, a curved slightly flattened
circle, or oval shape.
Definitions
Astronomy: The study of the
moon, stars, and other objects in
space.
Rotations: The Earth or moon
spinning movement one entire
time on its axis.
Axis: The imaginary line that
passes through the Earth’s or
moon’s center and through North
and South poles.
Revolution: The movement of
one object around another object
one entire time.
Orbit: The path an object takes
around another object. Earth
around sun or moon around
Earth.
Elliptical: The curved slightly
flattened shape or oval.
The moon is Earth’s closest neighbor in space—much closer than
any planet. In fact, the average distance from Earth to
the moon is only about 30 times Earth’s diameter.
How much time?
Even so, it is quite far away. On an average, the
moon is 384,400 kilometers from Earth. If there
One revolution for Earth around the
were a highway to the moon you could travel
sun = approx. 365 days
at 100 kilometer per hour, it would take you
more than five months to get there.
One rotation of the Earth on its axis
= 24 hour period
The moon moves in space just as Earth does.
As the moon revolves around the Earth and
Earth revolves around the sun, the relative
positions of the moon, Earth, and sun change.
The positions of the moon, Earth, and sun cause
the phases of the moon, eclipses, and tides.
One revolution of the moon around
Earth = approx. 27.3 days about
one month
Motion of the Moon
The moon revolves around the Earth and rotates on
its own axis. It takes the moon about 27.3 days to
revolve around the Earth. Like Earth’s orbit around
the sun, the moon’s orbit around Earth is a flattened
circle or oval shape. The moon rotates slowly on its own
axis every 27.3 days, a “day” and a “year” on the moon are the same
length. As you study the moon, you will find that the “near side” always
faces the Earth. The “far side” of the moon always faces away from the
Earth, so you never see it from Earth.