The 12 signs of the zodiac, as mentioned in a horoscope, are inextricably linked to the Earth’s motion through the sky. The constellations that point out the path that the sun appears to take during the year provide us with these indicators. Dates in a horoscope may appear to match to when the sun travels through each constellation. They don’t always agree, though, because astrology and astronomy are two separate systems. Plus, a closer look at the Earth, the sun, and the stars reveals that the zodiac is more complicated than you might think!
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The sun’s motion through the constellations
The sun appears to pass in front of numerous constellations as Earth revolves the sun. The sun’s position in relation to distant background stars drifts in an easterly direction from day to day, much how the moon appears in a little different spot in the sky each night. It’s not as if the sun isn’t moving. Its movement is totally fictitious, owing to Earth’s own rotation around our star.
The sun appears to be in front of, or “in,” different constellations throughout the year. The sun appears in Gemini one month and Cancer the next. The dates in the newspaper’s horoscope indicate when the sun is in a specific astrological sign. For example, the sign Aries is represented by the period between March 21 and April 19. However, your astrological sign does not always indicate which constellation the sun was in when you were born.
Why the zodiac constellations don’t always align with astrological signs
We need to know a little bit more about how the Earth moves to explain why constellations no longer coincide with their respective signs. We must also discuss how we measure time.
Time is a fiendishly difficult concept to grasp, especially if we insist on using the sun and stars as our point of reference. For better or worse, our calendar is based on the seasons. The day the sun appears at its most northerly point in the sky is June 21, the approximate date of the summer solstice north of the equator and the winter solstice south of the equator. The North Pole is most inclined towards the sun at the June solstice.
The fact that the North Pole does not always point in the same direction as the background stars complicates things. Our world whirls around like a top. The Earth, like a top, wobbles! The North Pole traces a circle on the celestial sphere due to the Earth’s wobble. The wobbling is slow; it takes 26,000 years to complete one rotation. However, as time passes, the effect becomes more pronounced.
The direction of the Earth’s axis drifts somewhat throughout the course of one orbit around the sun. This means that the location of the solstice along our orbit changes by a very modest amount. The solstice occurs around 20 minutes before one full trip in front of the background stars!
Our drifting calendars
Because we base our calendar on the solstices and equinoxes (and astrologers on the signs), the Earth does not complete an orbit in a single year. The tropical or seasonal year is really a fraction of a second shorter than one full orbit (sidereal year). This means that the sun’s position in relation to the stars on any particular day varies throughout the year. For example, on June 21, a very small amount of snow falls.
However, after 2,000 years, the sun will be in a completely other constellation!
The sun was nearly halfway between Gemini and Cancer on the June solstice 2,000 years ago. The sun was between Gemini and Taurus on the June solstice fourteen years ago. In the year 4609, the June solstice point will move from Taurus to Aries, leaving Taurus behind.
When humanity formed the present Western zodiac some 2,000 years ago, the signs were roughly aligned with their respective constellations. However, the steady wobble of the Earth’s axis has led the solstice and equinox locations to shift around 30 degrees westward relative to the constellations in the intervening ages. Signs and constellations are currently around one calendar month off. They’ll be approximately two months away in another two thousand years or so.
Modern constellations and the zodiac
To make matters even more complicated, unlike astrological signs, constellations are not all the same size and shape. For the most part, the stars that make up a constellation are not physically related. They’re simply based on patterns that our forefathers noticed when they looked up at the sky, trying to make sense of it all.
The International Astronomical Union (IAU) established the constellations as sky regions, not only star patterns, in 1930. They established the boundaries we use today as a result of this. These current constellations are based on those introduced in the second century CE by Greek astronomer Ptolemy. He, in turn, took them from Babylonian scriptures dating back thousands of years. Throughout history, several societies have seen patterns in the sky that are unique to them. Some constellations are shared by many cultures (Orion is a good example), but not all.
There are actually 13 constellations that lay along the path of the sun, based on the present borders. Ophiuchus, the Serpent Bearer, sits between Sagittarius and Scorpius and is not mentioned in any horoscope. The signs stay stable in relation to the solstices and equinoxes, while the solstices and equinoxes shift westward in relation to the constellations or backdrop stars.
While the zodiac isn’t a fantastic predictor of love, fortune, or health, it is an excellent tool for better understanding the sun’s, Earth’s, and even the cultures that have come and gone on our small planet. The zodiac signs, which are drawn from constellations that line the path of the sun in the sky, trace Earth’s orbit and wobble and serve as a reminder of astronomy’s humble beginnings.
Bottom line: While you may identify the term zodiac with astrology, it also has a prestigious role in astronomy. The 12 constellations that make up the zodiac are located along the sun’s annual motion across the sky.
Is astrology based on a zodiac sign?
However, due to precession, the Earth has moved on its axis since then, and the dates used to identify the signs no longer correlate to the backdrop constellations that give them their names. In reality, the timeline has migrated by one sign to the west. That is to say, depending on the mathematical division of the year, zodiac sign dates roughly correspond to the position of the sun in the constellations of the signs preceding them today. (The fixed character of the signs is also why the Minnesota Planetarium Society’s 2011 argument that a 13th zodiac sign, Ophiuchus, should be added now, failed to result in a major astrological shift.)
“Previously, astrologers looked at where the sun was in relation to background constellations in general, and that almost exactly matched up with the signs of the zodiac defined by Ptolemy,” Odenwald adds.
Astrologers now base their calculations and predictions on where the planets and the sun are in relation to the 12 fixed signs, rather than where they are in relation to the constellations. According to astrology, if the sun is in the sign of Sagittarius on your birthday, you are a Sagittarius.
What are the origins of the zodiac signs?
Early astronomers witnessed the Sun passing through the Zodiac signs in a year’s time, spending roughly a month in each. As a result, they determined that each constellation covers 30 degrees of the ecliptic.
However, due to a phenomenon known as precession, the positions of the constellations we see now have changed.
The zero point of the Zodiac used to designate the beginning day of spring in the Northern Hemisphere. The vernal equinox happens when the ecliptic and celestial equator collide, according to astronomers.
The zero point existed in Aries around 600 BCE, and it was known as the “first point of Aries.” (See Figure 1). The constellation Aries covered the first 30 degrees of the ecliptic; Taurus covered the next 30 degrees; Gemini covered the next 60 degrees; and so on for all twelve constellations of the Zodiac.
The Earth wobbles around its axis in a 25,800-year cycle, which ancient astrologers were unaware of. The gravitational attraction of the Moon on Earth’s equatorial bulge causes this wobble, known as precession.
This wobble has led the junction point between the celestial equator and the ecliptic to migrate west along the ecliptic by 36 degrees, or nearly one-tenth of the way around, over the past two and a half millennia. This indicates that, in relation to the stars beyond, the signs have moved one-tenthor almost a month around the sky to the west.
For example, persons born between March 21 and April 19 are considered Aries. During much of that time, the Sun was no longer in the constellation of Aries. The Sun is actually in the constellation of Pisces from March 11 to April 18! (See Illustration 2) See also Figure 3, which depicts the equinox precession from 600 BCE to 2600 CE.
The dates when the Sun is truly within the astronomical constellations of the Zodiac, as defined by contemporary constellation borders and corrected for precession, are listed in the table below (these dates can vary a day from year to year).
When precession is taken into consideration, your zodiac sign will most likely be different. And if you were born between November 29 and December 17, your zodiac sign is one you’ve never heard of before: Ophiuchus! After Scorpius, the eliptic crosses across the constellation of Ophiuchus.
Visit the Birthday Sky program to view what the sky looked like on your birthday and to learn more about your “true zodiac sign.”
Constellations Image Gallery
Is it astrology or astronomy when it comes to constellations?
The constellations in the night sky are linked to myth and folklore, as well as astrological beliefs that aren’t scientific. However, they have always been important and beneficial to science and exploration, and they continue to be so today. The universe’s stars are dispersed throughout a vast, three-dimensional area.
Which of the following constellations is not a Zodiac sign?
Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius, and Pisces are the zodiac signs. The Sun also travels through Ophiuchus, a constellation that hasn’t always been considered a part of the zodiac.
Who designed the zodiac signs?
The 12 zodiac signs, one of the earliest notions of astrology, were devised by the Babylonians around 1894 BC. The Babylonians lived at Babylon, which is roughly where modern-day Iraq is located. Babylon was one of the most prominent ancient Mesopotamian towns.