Download Unit 2 : Astronomy A. Earth`s motion 1. rotation – turning or spinning

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Unit 2 : Astronomy
A. Earth’s motion
1. rotation – turning or spinning
of a body on its axis
2. Earth’s rotation around the sun
= 24 hours
a. rotation results in day and night
3. revolution - motion of earth along
a path around some point in space
4. Earth revolves around the sun
a. revolution results in seasons
b. Earth revolves around sun
once per year
5. the moon revolves around the Earth
6. Earth’s orbit around the sun is in an
elliptical shape with an average speed of
107,000 km/hr
7. Earth is the third planet from the sun
8. Earth is tilted at a 23.5 degree angle
B. Origin of the Galaxy - Big Bang Theory (just one of many)
1. at one time, the entire universe was confined to a dense, hot, super massive
2. 13.7 billion years ago, a violent explosion occurred
3. this caused the hurling of material in all directions which created all matter and
4. several thousand years later, the universe was cool enough for atoms to form
C. 3 Laws of Planetary Motion
1. The path of each planet around the sun is an ellipse.
2. Each planet revolves so that an imaginary line connecting it to the sun sweeps
over equal areas in equal time interval (a planet must travel more rapidly
when it is near the sun and more slowly when it is farther away from the
3. T2 = d3, where T is time it takes to orbit the sun, and d is distance to the sun
D. Hierarchy of Organization
1. universe is made up of galaxies
2. galaxies are made up of many stars
3. some stars have planetary systems
4. Earth is a satellite planet of one star (the Sun)
5. the moon is a satellite to the earth (because it revolves around the Earth)
E. Galaxy
1. Our solar system is located on the Orion arm of the Milky Way Galaxy
2. Our solar system revolves around the center of the Milky way in an up and
down motion
3. Galaxies move away from each other as the universe continues to expand
F. Precession
1. Precession – precession of Earth is the slight change in direction over a period
of 26,000 years
2. Earth’s axis maintains the same angle of tilt, but the direction of the axis points
changes slightly over a long period of time
3. Currently the Earth is pointing to the star Polaris but eventually it will point to
another star Vega
4. Will not affect the seasons because the 23.5 degree tilt will be the same
G. Nutation
1. Nutation – wobbling around the
precessional axis
2. This is a change in the angle – ½ degree
one way or the other
3. This occurs over an 18 year period
4. Nutation is caused by the moon
5. This would cause slight changes in
the seasons
H. Barycenter
1. Barycenter – the point between two objects where they balance each other
2. it is the center of mass where two or more celestial bodies orbit each other
3. For example – the moon does not orbit the exact center of the Earth, but a
point on a line between the Earth and the Moon approximately 1,710 km
below the surface of the Earth where their respective masses balance
4. This is the point (barycenter) about which the Earth and Moon orbit as they
travel around the Sun
I. Summer
1. When the Earth’s axis points towards the sun, it is summer for that hemisphere
2. July 4th the Earth is farthest from the sun
3. During summer solstice (June 21st or 22nd) the sun appears 23.5 degrees north
of the equator
4. When the sun is overhead, the light is falling straight on you, and so more light
(and more heat) hit each square centimeter of the ground
J. Winter
1. When the Earth’s axis points away from the
sun, it is winter for that hemisphere
2. Jan 3rd the Earth is closest to the sun
3. During the winter solstice (Dec. 21st or 22nd)
the sun appears 23.5 degrees south of
the equator
4. When the sun is lower in the sky, the light
gets more spread out over the surface
of the earth, and less heat (per square cm)
can be absorbed
K. Tides
1. Tides are daily changes in the elevation of the ocean’s surface
2. Ocean tides result from the gravitational attraction exerted upon the Earth by
the moon and, to a lesser extent, the sun
3. Gravity and inertia (resisting movement) are the forces that cause tidal changes
4. Spring tide – occurs during full and new moon (sun and moon pulling in the
same direction)
5. Neap tide – occurs during first and last quarter moon (sun and moon pulling in
perpendicular directions)
L. Shape of the Earth
1. Shape of the earth is not a true sphere – but rather bulging at the equator
2. Caused by the planets rotation and gravity
3. Gravity pulls all materials as close as possible to the core of the earth
4. Because earth rotates, the sphere is distorted by centripetal force which is
greatest at the equator causing a slight outward bulge