Help with precession

[kik4adog]

Hi,
I'm new to these forums and I've turned to this site out of desperation. My college Earth, Space, & Science class has a project due that I am a part of and I am having a difficult time understanding 3 of the questions that deal with precession of the Earth's axis. I understand the basis of precession in that the axis itself rotates in addition to the rotation and orbit of the Earth but I guess I don't understand it well enough because these 3 questions have me totally stumped. Even Google searchs, which usually help, have left me clueless.

Here's what I'm working with:

Question 1.Refer to the image below to add the path for precession to the Earth’s axis. Include Polaris, Deneb, Vega, and Alpha Draconis.

I have NO IDEA what is being asked of me here. Any thoughts?

 

Question 2. Now make a sketch of the Earth’s axis pointing to Alpha Draconis. If you are having difficulty picturing this image, make a model. You can use a small ball with a toothpick for the Earth’s axis and a candle for the Sun. Place the Earth in the January position, and move the Earth in its orbital path until the Earth’s axis is directly facing the Sun. What is the month? This is the summer solstice for the Earth 10 million years from now.

 

Again, I'm not exactly sure how to predict what month the Earth's axis will be directly facing the sun in 10 million years by going through thre processing of visualizing its orbit.

Question 3. Based on precession, fill in the table below about seasons on your continent 10 million years from now. Compare and contrast these seasons with the current seasons.

 

Winter Solstice-Month this season begins=

Spring equinox-Month this season begins=

Summer Soltice-Month this season begin=

Fall equinox-Month this season begins=

 

I guess the idea is that in 10 millions years, due to precession, the solstices and equinoxes will be at much different times of year than they currently are and I'm supposed to find out when they will be.

 

I understand the purpose of this site isn't to provide the answer for homework assignments. I'm wondering if there's some kind of formula or something that I'm just not understanding which will help me predict the position of the Earth in 10 million years due to precession. I'll admit that I don't have a great grasp of how precession works. I just know that the axis moves ever so slightly like a top along with the Earth's rotation and orbit. If anyone can help I'd appreciate it.

 

Thanks

[MonDie]

 

 

Question One: Well, it looks like the path of Earth's axis is already there in the image, but I'll explain the underlying concepts anyway.

As the earth goes through its daily rotation, a given point in the sky will move parallel to the equator. However, this doesn't apply to a star that is directly above a pole (i.e. a star with a declination of +90 or -90 degrees); such a star will remain at that same point in the sky throughout the day. Currently, the star directly above the north pole is Polaris, the declination of Polaris is nearly 90 degrees. (Get it? Pole-aris, hehe). However, as the Earth's axis precesses, a different star will be on above the pole, and Polaris will have a lower declination.

 

I proclaim open use and/or alteration of this image without accreditation requirements. It's not copyrighted anyway.

I have attached an image, so there should be an image in my post. The yellow line represents the orbit of the earth around the sun. Alternatively, you can look at the yellow as the ecliptic, the annual (yearly) path of the sun through Earth's sky.

The red lines show Earth's equator and poles.

 

Question Two: Are you sure it's not 10 thousand years from now? I am going to assume it is's actually 10,000 even though this contradicts the direction of the arrow in the image given.

The precession cycle is approximately 26,000 years. 10,000 divided by 26,000 is 0.384615385. 12 times 0.384615385 is 4.61538462. That's a summer solstice 4.6 months ahead of the normal summer solstice.

If it actually is 10 million years, I would suggest finding a more precise number for the length of the precession cycle, but I'll use the rough approximation of 26,000 years. Divide 10,000,000 by 26,000. That comes out to 384.615384615 precession cycles. You just need the decimal place to determine how far it is into its current cycle. 12 times 0.615384615 is 7.38461538. That's a summer solstice 7.4 months ahead of the normal summer solstice.

 

This should be enough info for you to figure it out, so I'll leave you hanging.

 

Note To Self: Don't drink coffee when the western horizon is nearing the sun! You won't get any sleep!

Edited April 26, 2013 by Mondays Assignment: Die

[MonDie]

Correction, I think the solstices would actually be 4.6 (or 7.4) months behind their normal spots in the year, but I'm not sure of this.

Edited April 26, 2013 by Mondays Assignment: Die