Why Does the Solar Plane Sweep a Belt out of the Sky?
The Solar Plane Appears to Change Tilt
The image below shows a hyperbolic representation of the belt in the sky. Because the earth is tilted relative to the plane and is also rotating, the plane sweeps a belt across the sky. None of the planets or the sun will ever leave this imaginary belt. Pluto has a crazy orbit and if you could see it with the naked eye it would eventually stray out of the belt a little bit - but it's the only exception for this discussion.
So why do I have two planes represented here? Actually, I don't. It's the same plane that has just shifted tilt throughout the day and/or seasons. The plane that is labeled a) in the picture is what the plane looks like at sunrise during the deep winter. The plane labeled b) is what the plane looks like at sunset during the deep winter. It will shift by the season also: Plane A will also be what the solar plane will look like at sunset in the summer, B will be what it looks like at sunrise in the summer.
The image is a tad misleading. The upper belt limit should actually dip below the east-west line - at least for someone at 45 degrees north latitude such as myself. If you were in the southern hemisphere, it would be the lower limit that would be above that line. But for the sake of clarity, I don't want to clutter my images by having too many lines in such a small area. This image is most accurate for people that are looking at the sky from the equator. Another point of inaccuracy is that I'm trying to represent a hemisphere on a two-dimensional computer screen. A more accurate way to represent this would be to draw a circle with the cardinal directions labeled on it, but that would be way too confusing for this discussion.
Change of Tilt in Slow Motion
Now the tilt of the plane will look slightly different every day of the year and every time throughout the day. I like to use landmark events on the calendar and clock - dates like the equinoxes and solstices as well as sunrise, noon, sunset, and midnight. Consider the images below as a bit of time-lapse imagery of the solar plane on the shortest day of the year.
Equinoxes
Consider the image below. Plane a) is the solar plane at midnight in March as well as at noon in September. Plane b) is the solar plane at midnight in September and noon in March. Plane c) is the solar plane at sunrise and sunset for both equinoxes.
- The Sky
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