Chapter 12- Earth, Moon, and Sun
CUE WORDS or QUESTIONS
What is astronomy?
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What is the difference between
rotation & revolution?
NOTES WRITTEN
Astronomy- study of the moon, stars, and other objects in space
Earth moves through space in two main ways: rotation and revolution
Rotation – spinning of Earth on its axis (earth takes about 24 hours to rotate)
once
 Axis – imaginary line that passes through Earth’s center
(from North pole to South pole)
Revolution – the movement of Earth in orbit around the sun
(Earth takes about 365 days to complete one revolution)
 Orbit – path earth follows as it revolves around the sun…
slightly elongated circle (ellipse)
Sunlight directly hits the equator and so it is warmer
What causes the seasons?
Near earth’s poles the same amount of sunlight is spread out and is cooler
Earth has seasons because its axis is tilted as it revolves around the sun
 Earth is tilted at a 23° angle
X
As Earth revolves around the sun, this tilt causes one hemisphere to be
toward the sun and the other to be away from the sun
Solstice – two days a year when the sun is directly overhead at 23.5 degrees
(June and December 21st)
Equinox – two days a year when the sun is directly over the equator
 Vernal Equinox – around March 21st
 Autumnal Equinox – around September 23rd
What keeps planets in orbit?
Gravity– attracts all objects toward each other
Law of universal gravitation – every object in the universe attracts every
other object
The strength of the force of gravity between two objects depends on two
factors: the masses of the objects and the distance between them
 Mass – amount of matter in an object
 Weight – force of gravity on an object
Earth and all planets remain in orbit because of inertia and gravity
 Inertia – tendency of an object to resist a change in motion
SUMMARY
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CUE WORDS or QUESTIONS
What are the phases of the
moon?
X
NOTES WRITTEN
The phase of the moon you see depends on how much of the sunlit
side of the moon faces Earth (takes to 29.5 days complete its cycle)
Moon cycle: new moon- waxing crescent- 1st quarter- waxing gibbous– waning gibbous- 3rd quarter- waning crescent- new moon
full moon–
 The moon takes 27.3 days to revolve around the Earth
 The moon rotates on its axis once every 27.3 days
 The same side of the moon always faces Earth (the man side)
What is the difference between
solar and lunar eclipse?
Eclipse- when the moon’s shadow hits Earth (solar eclipse) or Earth’s
shadow occurs hits the moon (lunar eclipse)
Solar eclipse – occurs when the moon passes directly between Earth
and the sun, blocking sunlight from Earth
 Umbra – cone-shaped shadow (darkest part) from the moon on
Earth’s surface
 Penumbra – larger part of the shadow, part of the sun is visible
from Earth
Lunar eclipse – occurs at a full moon when Earth is directly between
the moon and sun
How does the moon cause
X the tides?
The moon’s gravity pulls water in the oceans toward the moon
Tides occur mainly because of differences in how much the moon
(and the sun) pulls on different parts of Earth
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What are the three features of
the moon?
There is a high and low tide on opposite sides of Earth
Tide Cycle – two high tides and two low tides every 25 hours
Spring tide- earth, sun, & the moon are in a straight line (highest)
Neap tide- moon is at a right angle to the sun (lowest)
Features on the moon’s surface include maria, craters and highlands
Maria – dark, flat areas formed from huge lava flows (thought to be oceans)
Craters – large round pits from meteoroid impacts
Highlands – peaks on the surface of the moon
Moon is 3,476 km in diameter – a little less than the distance across the US
 Moon has 1/18 the mass as Earth, temp. from 130°C to -180°C
How was the moon formed?
SUMMARY
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Scientists theorize that a planet-sized object collided with Earth and
the ejected material from the earth formed the moon