Introduction to

Astronomy

I- Earth Motions, Time, and Seasons.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- II- Our Solar SystemOur 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