Picture the earth in your mind, as if you are standing at a distance from it such that it appears as a large sphere, but can comfortably fit in your field of view. You can see it spinning slowly on its axis, the continents moving slowly across the side of the earth facing you before gradually disappearing behind it as the earth spins. Every day, the earth completes one rotation on its axis, approximately 24 hours long.
Now picture the earth’s axis. Imagine a thin pole extending through the earth’s north and south poles to help you visualize the earth’s axis. The earth’s axis is usually tilted at a small angle from the vertical axis. You can also see the equator running along the earth’s middle section, dividing it into two hemispheres.
Next, imagine we have a large sphere surrounding the earth. This sphere is extremely large and any heavenly body you can see, be it a planet or star, is easily accommodated by the sphere. Picture the sky as a movie being played on a spherical screen surrounding the earth, which is our imaginary sphere. This makes it such that the heavenly bodies are all suspended on an arbitrary sphere that corresponds with the earth’s sphere. The distance from each celestial body here doesn’t matter. What matters is what we observe. This arbitrary sphere is called the celestial sphere and just like the earth, it has a corresponding northern and southern celestial pole. It also has a celestial equator.
Remember that the earth’s axis is tilted a bit from the vertical plane. This tilt is around 23.5˚. There is also a plane on which the earth appears to lie on as it moves around the Sun. It’s like an invisible ground on which the earth is ‘walking’ as it moves around the Sun, only that this ‘ground’ is not beneath the earth, but passes through it. Like the earth is suspended on it. This is called the ecliptic plane.
Even the other planets all lie on or near this plane in their motion around the Sun. So if you’re standing on earth and staring at the sky for a prolonged period of time, you will observe that the Sun, Moon and planets appear to move along the same general path. Note that I said general path. This is because It’s only the Sun that lies exactly on the ecliptic. The Moon and other planets lie a few degrees above or below it on the celestial sphere. This difference is negligible and we take it that they all lie on the same general plane on the celestial sphere which we call the ecliptic.
For the Sun, it’s not really moving but due to the relative motion caused by earth moving around it, we observe that it is also ‘moving’ slowly through the celestial sphere along the ecliptic. Imagine how kids love to play this game where they wrap their hands around a pole and move around it in circles. If you’re that child, you’ll observe that everything is moving in circles around the pole while it’s really just you moving. Likewise, as the earth moves around the sun, since the background is fixed, we get the visual effect of the Sun moving along the heavenly background.
Since the earth is tilted on its axis, its equator (and therefore the celestial equator) is also tilted from the ecliptic at 23.5˚ just like the earth’s axis tilts from the vertical. Remember, the ecliptic is the plane on which the Sun, Moon and planets appear to lie as observed from the earth. On the celestial sphere, this is a thin belt on the section where the ecliptic plane is projected on the sphere. You can refer to the images attached to see it in your mind if you have trouble visualizing it.
I would also like to make a minor clarification here. The motion I am talking about is not the one you see on a daily basis when you look at the sky, like the sun rising in the east and setting in the west. This is due to the earth spinning on its axis which causes day and night. The motion I am talking about has to do with the earth moving around the Sun which causes the Sun to appear to move along the ecliptic slowly. As well as the Moon moving slowly around the earth (though relatively faster than other heavenly bodies as it takes just a month to complete a cycle) and the planets moving around the Sun in their own orbits. This is in case anyone mistakes what motion I am talking about in this lesson.
Going back to the topic, remember that all heavenly bodies, from constellations to planets, are all projected on the celestial sphere. The twelve zodiac constellations also lie along the ecliptic plane, encircling the celestial sphere along the same section. So in effect, as the planets, Sun and Moon make their journey along the ecliptic plane, they are observed to move along the background that is the zodiac constellations.
The celestial sphere is a very useful concept that dates back to ancient Greece and likely even more ancient times (Astrology and Astronomy are way more ancient than modern science acknowledges). Greek astronomers like Aristotle taught more sophisticated versions involving several spheres for each planet. This had deep occult meanings. But the celestial sphere as I have explained above is sufficient in understanding Astrology.
Even outside Astrology, the celestial sphere is very useful to Astronomers. Astronomers use the celestial sphere to map the position of any star. Like we use longitudes and latitudes to map any point on the earth’s surface, you assume the celestial sphere is like the earth and the stars can be on a point that you can map using a system similar to our co-ordinate system on earth. Astronomers use right ascension (corresponds with longitudes) and declination (corresponds with latitudes) to tell the position of a star on the celestial sphere.
In closing, you don’t need to delve into planetary spheres as taught by the ancient Greeks or how Astronomers map the sky. This was just a bit of extra information about the celestial sphere. All I have taught in the previous sections of this lesson is what is needed for you to understand Astrology. I will delve deeper into the celestial sphere in the next few lessons.
-Blackdragon666
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