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of : 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 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 to trace one complete conical shape. This wobbling motion of Earth on its axis is called precession. Because of precession, and alternate as the 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 Ursa Minor (also called the Little Bear or the Little Dipper). Polaris appears to be in a fixed position in the sky throughout the . All other and seem to revolve around the North Star.

Why isn't the North Star Fixed? Over the course of , the North Star changes. Right now Polaris is within one degree of , but at other the North Star has been and will again be (the brightest star in the constellation ), 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. is the wobbling during precession; 1/2° one way or the other; period of 18 years; due to the ; It slightly effects seasons.

This type of axis movement is similar to that of a spinning top. As the top slows, the axis of 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 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? ______2. What is precession? ______3. How long does it take for earth’s axis to wobble into a complete conical shape? ______4. What two stars alternate every 13,000 years as earth’s northern star? ______5. What is earth’s current northern star? ______6. What is the brightest star in the constellation Ursa Minor? ______7. What is the brightest star in the constellation Draco? ______8. What is the brightest star in the constellation Lyra? ______9. What is the brightest star in the constellation Cepheus? ______10. Why do earth’s northern star change over time? ______11. What is precession and what causes it? ______12. What are the four stars that can become earth’s northern star? ______13. What was earth’s northern star before Polaris? ______14. What will be earth’s northern star five thousand years from now? ______15. Which do we consider as our northern star and why is our northern star changing? ______16. What is the difference between precession and nutation? Think! (15 pts.) ______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: ______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. ______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. ______5. Why is the northern star stationary and the rest of the stars seemingly rotating around it? Explain. ______

Nutation is, in , a small irregularity in the precession of the . 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.) ______The cause of nutation lies chiefly in the fact that the plane of the Moon's 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. ______

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

A huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity

solar system sun, , and all the other objects that revolve around the sun

universe All space and the matter space contains; made of 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 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: of planets is constantly changing, faster they are the closer to the sun they are

Kepler's Third Law The square of the 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. /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.

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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 ). 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-flash- cards/