Download Precession of Earth

Precession of Earth: Spinning on the Axis
Environmental Science
Name: ____________________________________________Period:__________ Date: ___________
Essential Question: Why is earth’s axis wobbling? Een 1.1.1
Instructions: Study the selection and answer the questions.
Just like a toy top that wobbles before it falls, the Earth wobbles as it
rotates on its axis, the imaginary line that extends through the poles.
This wobbling motion is due to the slight bulge at the equator. If you
traced the Earth's axis out into space, you would see the extension of
the axis slowly tracing a cone shape. The wobble is very slow; it takes
the Earth 26,000 years to trace one complete conical shape. This
wobbling motion of Earth on its axis is called precession. Because of
precession, Polaris and Vega alternate as the North Star every 13,000
years.
Polaris: The Current North Star
Today the Earth's axis points within one degree of Polaris, the
brightest star in the constellation Ursa Minor (also called the Little
Bear or the Little Dipper). Polaris appears to be in a fixed position in
the sky throughout the year. All other stars and constellations seem to revolve around the North Star.
Why isn't the North Star Fixed?
Over the course of time, the North Star changes. Right now Polaris is within one degree of true north,
but at other times the North Star has been and will again be Thuban (the brightest star in the
constellation Draco), Vega (the brightest star in the constellation Lyra), and Alpha Cephei (the brightest
star in the constellation Cepheus).
The North Star changes over time because the direction of the earth's axis changes slowly over time, this
is the result of Precession. Since by definition the North Star is the star most closely aligned with the
earth's axis, as the axis moves the nearest star changes too.
Precession is the change in the direction of the axis, but without any change in tilt;
changes the stars near the Pole; It does not affect the seasons.
Nutation is the wobbling during precession; 1/2° one way or the other; period of 18
years; due to the Moon; It slightly effects seasons.
This type of axis movement is similar to that of a spinning top. As the top slows, the axis of rotation
changes as the top draws out each rotation; that is to say that the stem of the top itself traces out a circular
pattern rather than pointing at a single spot or staying mostly still. If you draw an imaginary line of the
earth's axis and continue it up to the sky, it will make a similar path. This type of axis rotation is called
precession.
In the case of the earth, precession is caused by the gravitational pull of the sun and the moon. The earth's
axis makes one complete rotation over the course of approximately 26,000 years. If you trace the path of
the axis in the sky, you will find that Polaris, Vega, Thuban, and Alpha Cephei all fall on or very close to
it. So when the earth's axis is at a point on the path near Vega, Vega becomes the North Star while
Thuban is the North Star when the axis is near it on the path.
Five thousand years ago, Thuban was the North Star. Five thousand years from now, the North Star will
be Alpha Cephei. Seven thousand years after that, it will be Vega. Nine thousand years after that, Thuban
will be the North Star again. At these dates, the various stars will be at the closest to absolute north. For
some time before, the relevant star will be approaching due north and it will be receding for some time
after the time listed. In these interim times, the North Star is whichever star is closest to north.
Answer the following questions
1. What is earth’s axis?
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2. What is precession?
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3. How long does it take for earth’s axis to wobble into a complete conical shape?
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4. What two stars alternate every 13,000 years as earth’s northern star?
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5. What is earth’s current northern star?
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6. What is the brightest star in the constellation Ursa Minor?
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7. What is the brightest star in the constellation Draco?
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8. What is the brightest star in the constellation Lyra?
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9. What is the brightest star in the constellation Cepheus?
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10. Why do earth’s northern star change over time?
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11. What is precession and what causes it?
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12. What are the four stars that can become earth’s northern star?
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13. What was earth’s northern star before Polaris?
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14. What will be earth’s northern star five thousand years from now?
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15. Which do we consider as our northern star and why is our northern star changing?
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16. What is the difference between precession and nutation? Think! (15 pts.)
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http://www.education.com/reference/article/precession-earth/
http://www.essortment.com/north-star-61725.html
Precession and Nutation
Environmental Science
Name: ____________________________________________Period:__________ Date: ___________
Essential Question: Why is Polaris fixed on its position throughout the year?
What is the difference between precession and nutation?
Instructions: Encircle and label the constellations where Polaris, Vega, Thuban, and Alpha Cephei are
found.
Polaris, the brightest star in the
constellation Ursa Minor (also called the
Little Bear or the Little Dipper). Polaris
appears to be in a fixed position in the sky
throughout the year. All other stars and
constellations seem to revolve around the
North Star. Thuban (the brightest star in
the constellation Draco), Vega (the
brightest star in the constellation Lyra),
and Alpha Cephei (the brightest star in the
constellation Cepheus).
Sirius, also known as the Dog Star
or Sirius A, is the brightest star in
Earth's night sky. The name means
"glowing" in Greek.
http://www.msnucleus.org/membership/html/jh/earth/stars/lesson4/stars04c.html
Identification:
_________________is the brightest star in the constellation Ursa Minor.
_________________is the brightest star in the constellation Draco.
_________________is the brightest star in the constellation Lyra
_________________is the brightest star in the constellation Cepheus
________________ is the brightest star in Earth's night sky.
Come up with your Hypothesis: How come Polaris seems to be stationary in the sky throughout the year
while the others stars in their constellations seem to revolve around it?
Hypothesis:
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Precession
change in the direction of the axis, but without any change in tilt; changes the stars
near the Pole; does not affect the seasons.
Nutation
wobbling around the precessional axis; 1/2° one way or the other; period of 18 years;
due to the Moon; slightly effects seasons.
Try this out!
1. Stand directly below anything that you can consider as your northern star, you
represent Earth’s axis. Directly above you is your north, your right side is your east, down
is south, and your left side is your west.
2. Look around and observe anything that you can consider as markers ( like ceiling fan,
light bulb, air vent, spot on the ceiling etc. ) and consider them as the other stars.
3. Slowly turn around 360 degrees from west to east direction while looking at your
northern star. Did your northern star move to another direction in reference to your
position ( N-E-S-W)? Explain.
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4. Again, slowly turn around 360 degrees from West to East direction while looking at your
other star markers. Did your other stars move to another direction in reference to your
position? ( N-E-S-W)? Explain.
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5. Why is the northern star stationary and the rest of the stars seemingly
rotating around it? Explain.
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Nutation is, in astronomy, a small irregularity in the precession of the equinoxes.
Nutation (Latin nutare, "to nod"). Nutation is the wobbling around the
precessional axis by 1/2° one way or the other. It slightly effects the seasons due
to the ½ degree change in Earth’s tilt.
6. How are we affected by Nutation? Think! ( 20 pts.)
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The cause of nutation lies chiefly in the fact that the plane
of the Moon's orbit around the Earth is tilted by about 5
degrees from the plane of the Earth's orbit around the
Sun. The Moon's orbital plane precesses around the Earth's
in 18.6 years, and the effect of the Moon on the precession
of the equinoxes varies with this same period.
7. Describe what causes Nutation.
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Rotation (R), Precession (P) and Nutation, jagged line (N) of the Earth. http://www.bristol.k12.ct.us/page.cfm?p=7105
http://en.wikipedia.org/wiki/Nutation http://nutation.org
R. E. Angat
precession
change in the direction of the axis, but without any change in tilt; changes the stars
near the Pole; does not affect the seasons
galaxy
A huge group of single stars, star systems, star clusters, dust, and gas bound together
by gravity
solar system
sun, planets, and all the other objects that revolve around the sun
universe
All space and the matter space contains; made of galaxies which are made of many
stars
planetary system
a system of planets revolving around a star
Kepler's laws
describe the motion of planets (consequence of Newton's law of gravitation)
Kepler's first law
The orbit of each planet around the Sun is an ellipse with the Sun at one focus.
Kepler's Second Law
A line joining a planet and the sun sweeps out equal areas in equal intervals of time
Law of Equal Area
Kepler's 2nd law: speed of planets is constantly changing, faster they are the closer to
the sun they are
Kepler's Third Law
The square of the orbital period is directly proportional to the cube of the average
distance of the planet from the sun.
orbital motion
motion of an object in an orbit around a fixed point
rotation
A transformation that turns a figure about a fixed point at a given angle and a given
direction. day/night
revolution
Earth's yearlong elliptical orbit around the sun
Earth's tilt
23.5°; it effects which areas of it's surface get sunlight which makes earth's seasons
vary in each hemisphere.
Play audio for this term
nutation
wobbling around the precessional axis; 1/2° one way or the other; period of 18 years;
due to the Moon; slightly effects seasons
barycenter
the point between 2 objects where they balance each other; the Moon doesn't orbit
around the exact center of the Earth but around a point where the 2 masses balance
out each other; think clay masses on a stick
Solar System's barycenter
our Sun is not stationary; it moves as the planets tug on it, causing it to orbit the solar
system's barycenter; the Sun never strays too far from the solar system barycenter
sidereal day
The length of time which passes between a given "fixed" star in the sky crossing a given
projected meridian (line of longitude). The sidereal day is 23 h 56 m 4.1 s.
mean solar day
from noon til noon
geocentric solar model
model of the Solar System with the Earth as the center; geo-earth; centric - center
heliocentric solar model
model of the Solar System with the Sun as the center; helio-sun; centric - cente
aphelion
the point in the orbit of a planet or comet where it is farthest from the Sun
perihelion
the point in the orbit of a planet, asteroid or comet where it is nearest to the sun
http://quizlet.com/30710267/earths-motion-through-space-quiz-on-dec-13-2013-flashcards/