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. 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.
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? ______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. What will be earth’s northern star twelve thousand years from now? ______16. Which do we consider as our northern star and why is our northern star changing? ______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).
http://www.msnucleus.org/membership/html/jh/earth/stars/lesson4/stars04c.html
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: ______
Try this out!
1. Stand directly below a smoke alarm or anything that you can consider as your northern star. 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 astronomy, a small irregularity in the precession of the equinoxes. Precession is the slow, top-like wobbling of the spinning Earth, with a period of about 26,000 years. Nutation (Latin nutare, "to nod").
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. The British astronomer James Bradley announced his discovery of nutation in 1748.
Have you noticed your head nodding as you turned around at 360 Rotation (R), Precession degrees? This can be compared to the earth’s nutation ( jagged line in the (P) and Nutation , figure). What caused your nutation was your movement but what is jagged line (N) of the causing earth’s nutation? ______Earth. ______http://en.wikipedia.org ______/wiki/Nutation http://nutation.org