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Introduction to
Astronomy
I- Earth Motions, Time, and Seasons.
A- Earth’s Rotation: Causes the apparent
motion of the sun, moon, and stars.
1- Earth rotates from west to east or
counterclockwise.
2- Earth rotates on its axis {imaginary rod}
a-Rotation causes day and night.
b-Poles experience several weeks of day
and night
3- Speed of rotation is 24 hours.
B- Daily Time:
1- Earth completes one rotation each day.
2- Earth rotates 3600 on around it axis in 24
hours.
a- If we divide 3600 by 24 hours we find that the
Earth rotates 150 per hour.
b- Longitude lines are based on this 150 and
represents a difference of one hour of Earth
time.
C- Earth’s Revolution:
1- Earth’s motion around the sun.
2- Earth’s path around the sun is its orbit.
3- Earth’s revolution has two major effects.
a- Time it takes Earth to go around the sun is one
year.
~ 365 ¼ days converted to 365 days, we add one
day every four years = Leap Year
b- Earths revolution plus the tilt of the Earth
causes the changing of the seasons
~Earth is always tilted in the same direction
towards the north star.
D- Yearly Seasonal Time:
1- If we divide 3600 by 12 months, we find that
Earth revolves about 300 per month.
E- Seasonal Changes:
1- The changes in the seasons are caused by the
tilt of the Earth on it’s axis as the planet
revolve around the sun.
~ On June 21st the Northern Hemisphere is tilted towards the
sun and the sun’s vertical rays reach 23.50 north of the equator.
~ On December 21 the Northern Hemisphere is tilted away
from the sun, and the sun’s vertical rays reach 23.50 south of
the equator.
~ On March 21st and September 23rd neither hemisphere is
really tilted towards the sun. The suns vertical rays strike the
equator, and all areas of Earth have equal periods of day and
night. {Equinox}
II- Our Solar System:
A- Consists of the Sun, and all the objects
that revolve around it (nine/eight planets,
asteroids, comets, moons, and meteoroids).
1- The Sun is a star. Light from the sun
takes 8 minutes and 20 seconds to
reach the earth.
2- Planets each has it’s own special
characteristics.
3- The Moon is a ball of rock that revolves
around the Earth.
a- Motions and Phases of the Moon:
~ The moon takes 29 ½ days, one month to revolve
around the Earth.
~ The moon completes one rotation in the same
amount of time it takes to orbit the Earth so we see
the same side of the moon all the time.
~ The moon reflects light from the sun.
~ Phases of the moon are the apparent changes in the
shape of it as it appears from Earth.
~ New Moon Phase the moon is between Earth and
the Sun.
~ Full Moon Phase the Earth is between the moon and
the Sun.
4- Eclipses:
~ Lunar eclipse when the moon passes through
Earth’s shadow. (only when the moon is full)
~ Solar eclipse when the moon cast it’s shadow on the
Earth. (only when the moon is new)
~ Total eclipse when sun is completely blocked by the
moon last a few minutes.
5- The Moon and Earth’s Tides:
~ Tides are the regular rise and fall in the level of the
ocean that take place twice a day.
~ Tides are caused by the gravitational pull of the moon,
and sun. {the moon has a greater effect because it is closer to
the Earth}
~ The moon’s pull causes the oceans to bulge on the
side facing the moon and on the other side. This is
high tide.
~ Between the bulges is low tide.
~ When the earth is between the sun and moon we get
higher high tides and lower low tides. {Because of the
extra gravitational pull of the sun}
6- Asteroids, Comets, and Meteoroids
~ Asteroids: Rock fragments of different sizes and
shapes many found in the asteroid belt, between Mars
and Jupiter.
~ Comets: Mass of rock, ice and dust the tail away
faces away from the sun
~ Meteoroid a fragment of rock that travels through
space.
* Meteor is a “shooting star” Burns up before it
reaches the earth’s surface
* Meteorite does not burn up before it hits the earth’s
surface.
The Barringer Crater in Arizona is
1.2 kilometers wide