The Orientation of Earth's Orbit in Our Galaxy

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The Orientation of Earth's Orbit in Our Galaxy

INTRODUCTION. The introduction to projects on the cosmos mentions that many things have been staring us in the face for thousands of years, and yet have escaped our abilities to explain them. One of those things pertains to how our earth is situated within the starry host. Previous sections bring you to see with your own unaided eyes that we are in a wing of a flattened galaxy, which has long been called the Milky Way. (Your dictionary will even tell you that the origin of the word 'galaxy' itself has to do with 'milk'!)

On a sunny day, stand in the middle of a large field and face south. Draw an imaginary line through the sky indicating where you remember that the sun passes during the day. This line is called the ecliptic. Now imagine that the line is not a straight line, but rather that you are looking at the edge of a huge circle that extends more than 180,000,000 miles across, and that the sun sits in the middle of the circle. That circle is 2-dimensional and flat. It can be imagined to have been drawn on a huge sheet of paper that extends far beyond the circle - far, far, far beyond. Maybe some of the other planets and the moon also sit on that plane, maybe in their own circles. But those ideas are subject of projects further down the list on the astronomy page. We shall call that flat surface the earth's orbital plane, and we want to know how that plane is oriented with respect to our galaxy's plane ("the galactic plane").

After 10 p.m. (at mid-latitudes)** on a clear, dark and moonless night* away from city and even small town lights, go out into a large field and again face south (a magnetic compass might help you to face the correct direction). Again imagine the ecliptic, but remember that you are now standing on that huge circle but facing away from the sun. Take note of the direction of the tilt of the galactic plane - how the Milky Way slants across the sky. Also take note of the time. Even with this one observation you can see how skewed the earth's orbit is away from that of the galactic plane. Can you draw a diagram depicting your conclusion?

To check yourself out, you will want to have some "looks" in other directions. Well, you could get up at 4 a.m. for a look 90° from your 10 p.m. observation. Or you could come back to the same place 3, 6 and 9 months later at the very same hour and look again and thusly have a total inspection in four different directions (explain how this can be!). Now draw all your conclusions together into a neat "theory" - make a "synthesis" of your thoughts into a grand, complete theory of the earth's orbit in relation to the galactic plane. You might even consider making a model of your grand theory! (Hint: You really understand what you are doing if you can tell which, if any, of the three figures on this page are not possible.)


*For those of you growing up in cities and towns, you are really missing a wondrous sight. Yes, you can see a few stars and the moon in a large city, but - well, it cannot be explained - you just have to escape all those lights and the light that reflects from the dust in the atmosphere ("sky-glow"), and get out into the dark countryside to behold a truly awesome sight. It is so awesome that even small children who have never seen it before quiet down in amazement! Alas, since the invention of the electric lightbulb, it is now a rare sight.

**It can be earlier for places nearer the equator, and later nearer the poles (alas, once across the arctic and antarctic circles you will have to skip the summer reading as the sun won't set at all to give you a dark sky.


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