I’m a Libra.
What does that mean? If you’re an evidence-based thinker, none of that means anything. But if you believe in astrology, that means I was born at a time when the influence of the sun on me (unidentified, uncertain and inexplicable) was ruled by the “Sun sign” of Libra. I will. Libra’s relationship to actual zodiac signs is murky at best. If you believe in astrology, you and I both have something to say.
But what does it mean that the Sun is “in” Libra? Why would we value that sign rather than, say, Orion, which is objectively cooler in almost every way?
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It boils down to two things. Our solar system is flat, meaning motion is relative.
Let’s tackle the “relative motion” part first. For example, consider our familiar Earth. Our planet revolves around the sun once a year. From our perspective on Earth, the sun appears to be rotating. us once a year. Not physically, but perceptually. Heliocentric theory aside, this is why we still say “the sun sets” in heliocentric terms, rather than “the rotation of the Earth such that the horizon rises and blocks the sun.” Of course, we don’t intuitively sense that the Earth rotates once a day or orbits the Sun at 100,000 kilometers per hour.
Other stars are much further away than the Sun, so they appear fixed in the sky relative to each other. Our meaning-seeking brains naturally interpret these “fixed” star patterns as recognizable shapes we call constellations (literally, “star clusters”). Well, they are generally Orion does look human and Scorpio does look like a scorpion, but Libra is made up of just four major stars in a strange diamond shape.
As the Earth rotates, we see these stars rise and set every day. If the Earth were fixed in space relative to the Sun, we would see the same constellations in the sky every night of the year. Instead, as the Earth moves around the stars, from our perspective the Sun is constantly moving through a background of constellations, and it takes one full circle to circle the sky and return to where it started. It takes years.
This is where the flatness of our solar system becomes important. Like all other major planets, Earth revolves around the Sun in a flat, nearly circular ellipse. Therefore, the apparent movement of the Sun relative to the stars traces a line around the sky. The earth is in the center. This path is called the ecliptic.
The movement does not change much from year to year and from century to century. The Sun follows the same well-worn path through the same constellations. The names are familiar: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio (not “Scorpio”), Sagittarius, Capricorn, Aquarius, I’m Pisces. Many of these constellations represent animals, and the ancient Greeks collectively called them Zodiacos Kyklos, or “Animal Ring”. From there, we call it the zodiac.
Movement of the Sun through the Zodiac (pronounced zo)dye-a-kul) The constellations generate a kind of calendar. For example, our stars overlap in Pisces in late March. This is further complicated in the long run by the wobble of the Earth’s rotation, called precession, caused by the gravitational pull of the Moon and Sun. Over thousands of years, the timing of the sun’s position in certain zodiacal signs has been thrown off, creating a discrepancy between what astrologers call a “sun sign” and the actual zodiac sign. 3000 years ago, when the ancient Greeks first used the sign, the Sun was indeed in Libra in late September. But due to precession, that changed, and when I was born, our star was actually in Virgo.
It is important to understand that the constellations we perceive are not natural, but the product of random star alignments filtered through the human brain’s pattern recognition tendencies. Although different cultures may exhibit different patterns, it just so happens that many modern societies use roughly the same patterns as ancient Greece. But still, its origins are a bit vague. For example, the Greeks thought of Libra as part of the constellation Scorpio, especially its claws, while the Babylonians thought of Libra as the scales without the scorpion, or the set of scales.
This means that the ancient Greeks thought there were only 11 zodiacal constellations, not 12, and Libra was introduced much later to combine them into an even number of 12 constellations. is.
But things get even worse. The actual orbit of the sun, the ecliptic, does not only pass through these 12 constellations. Ophiuchus (“Serpent Bearer”) lies between Sagittarius and Scorpio, and the Sun actually spends about 20 days, or most of the month, within its boundaries. That’s more time than the Sun spends in Scorpio! Therefore, Ophiuchus probably deserves to belong to the zodiac more than the poisonous arthropods, but it happens to contain fainter stars with a darker pattern, so it is excluded.
The solar system is flat, but not completely flat, so we’re not done yet. In other words, other planets mainly revolve around the Sun in the same plane as Earth, which is not the case. that’s right. Jupiter’s orbit around the sun is tilted by just over 1 degree relative to Earth’s orbit. Venus is tilted more than 3 degrees. The moon’s orbit is tilted more than 5 degrees! This means that moons and planets can appear far north or south of the ecliptic, and sometimes even within the boundaries of other constellations outside of the standard 12 zodiacal constellations. There are a dozen more constellations that the moon and planets can pass through, including Canis Minor, Pegasus, and even our old friend Orion.
So, no matter how you slice it, the zodiac is made up of everything from its constituent constellations to the meanings that our pattern-projecting brains assign to particular groups of stars.
This does not mean that the zodiac is not a useful construct. that’s right! Like other constellations, the zodiac provides a framework that we can use to navigate our way through the sky. For astronomers with some knowledge of the sky, knowing that Jupiter is in Taurus (as I am, for example, as I write this) means that this giant planet is visible after sunset in the fall and winter. means. It can be easily observed in the Northern Hemisphere. If you want to know more, there are any number of coordinate systems you can use to zero in on a specific location, but if you just want to be outside and under the night sky, the zodiacal constellations provide a “good enough” set. Masu. Direction of celestial bodies. Additionally, many of them contain bright stars in obvious patterns that are easy to spot and identify, making them fun to observe.
And it’s not Taurus.