What Is the Difference Between Astronomy and Astrology?

Astrology and astronomy are two sides of a similar coin. They share the prefix “astro,” meaning both relate to the stars, celestial bodies, or outer space in general. In this article, we look at how they are similar and just what the difference is between astronomy and astrology.

the Difference Between Astronomy and Astrology

Astronomy and Astrology From Ancient Times

Astronomy and astrology date back as far as 1000 B.C. when early Mesopotamian scholars looked to the stars for answers. These great astronomers wanted to look beyond the Earth in an attempt to understand the cosmos and its effect on humanity.

It wouldn’t be until the 17th or 18th century that the two schools of study finally began to diverge. The scientists of the day started to unlock answers that demonstrated how objects relate to each other on Earth and in space.

However, both share a knowledge of the zodiac that carries through to today.

Understanding the Ecliptic

Motion of Sun, Earth and Moon around the Milky Way
The motion of Sun, Earth and Moon around the Milky Way. (Image credit: Jim slater307 on Wikimedia Commons CC BY-SA 4.0)

To understand the zodiac, we must first understand the ecliptic. This imaginary line circles the Earth’s heavens and represents the Sun’s apparent path during a calendar year. It serves as a starting point for the celestial coordinate system and is used as a baseline for identifying the location of every other celestial object.

Since the Solar System is more or less a flat plane, all the planets and the Moon also appear close to this line. It’s named the ecliptic because the Sun and Moon have to both be right on the line for an eclipse to take place.

The 12 Constellations of the Zodiac

The zodiac in astronomy and astrology represents 12 constellations that sit on an imaginary belt that extends nine degrees above and below the ecliptic. As we travel on our never-ending journey around the Sun, our star appears to hang out in these constellations for approximately a month at a time.

Those 12 constellations are:

  • Capricornus, the goat
  • Aquarius, the water bearer
  • Pisces, the fish
  • Aries, the ram
  • Taurus, the bull
  • Gemini, the twins
  • Cancer, the crab
  • Leo, the lion
  • Virgo, the virgin
  • Libra, the scales
  • Scorpius, the scorpion
  • Sagittarius, the centaur
Zodiac Constellations
Astrophotos of the Zodiac’s twelve classical constellations. (Image credit: Till Credner on Wikimedia Commons CC BY-SA 4.0)

With these constellations in mind, let’s discover how they mean different things to astronomers and astrologers.

What is Astronomy?

Astronomy is a specific branch of science that encompasses the study of everything in the universe that exists beyond Earth’s atmosphere. This broad area includes stars, planets, galaxies, nebulae, black holes, and more, all the way down to the smallest particle in space. It also covers everything outside our atmosphere that we’ve yet to discover or understand.

Many faces of astronomy
A collage of astronomy’s various fields of study. (Image credit: NASA)

Because of its enormous scope, we often break the science into four subcategories:

  • Astrophysics involves the study and application of the laws of physics in space. Scientists in this field may work to understand how the universe began or how the laws of physics work in and around black holes.
  • Astrometry looks to the locations of celestial objects in an attempt to create an accurate map of the known universe. This subcategory of astronomy also studies how objects in space move and interact with each other.
  • Astrogeology works in the physical study and analysis of extraterrestrial rocks and terrain. At present, we’re limited to samples from the Moon, Mars, asteroids, meteorites, and comets.
  • Astrobiology is the constant search for life beyond the confines of our Earth. It also strives to understand how life originated and our place in the cosmos.

As you can see, the 12 constellations of the zodiac are one tiny part of astronomy as a whole.

What is Astrology?

A female astrologer determining her client ascendant
A female astrologer is determining her client ascendant.

On the other hand, astrology is the study of the influences celestial bodies have on humans based on their movements and positions. Such areas may involve a planet’s apparent direction in the sky as seen from Earth or which of the zodiac constellations the Sun is currently located in.

Today, those that still follow astrology often focus on horoscopes. A horoscope predicts future life events based upon the zodiac constellation the Sun was in on the day you were born. The dates currently used for assigning zodiac constellations to individuals date back as far as the Babylonians.

A horoscope globe
A horoscope globe.

Unfortunately, there isn’t any scientific proof to back up astrology or horoscopes. To further throw question to the validity of the field, the Sun’s location along the zodiac has changed considerably since these dates were established.

The dates the Sun actually passes through these constellations have shifted almost a month in the last 3,000 years. The basis for astrological findings is no longer accurate.

This is due to the fact that the Earth wobbles as it moves around the Sun. This subtle shift that we will never feel on terra firma slowly shifts the location of stars and constellations from our vantage point.

The Thirteenth Constellation of the Zodiac

Zodiac Sign Constellation Snake Charmers Ophiuchus
13th Zodiac Sign Constellation: Ophiuchus “The Snake Charmer.”

To make matters worse, astrology completely ignores the fact that the Sun spends around 25 days a year in the constellation Ophiuchus instead of any of the other 12. Astronomers make note of Ophiuchus and astrometers mark the Sun’s passing through it, but astrologers completely ignore this event.

The Farmer’s Almanac

If you ever find yourself reading a farmer’s almanac, you’ll notice it has two different listings for the Moon’s location in the sky. The almanac’s astronomical chart shows which constellation along the ecliptic the Moon is physically in front of on any given day. This chart includes the constellation Ophiuchus.

The astrological chart splits the sky into 12 equal slices and lists the Moon’s location based on astrological dates. This chart relies on a predetermined schedule to list the placement of the Moon and takes no consideration in its actual location.

What is the Farmer’s Almanac, and are its claims true?

Final Thoughts

The desire to better understand humanity led to astrology, which pushed astronomy along for thousands of years. It was only in the last few hundred years that astrology lost its place in the scientific world. Many people turn to the stars for answers, and astrology and astronomy show that people do this in unique ways.

About Noah Zelvis

Noah is a content writer who has had a love of all things astronomy for as long as he can remember.
When not reaching for the stars, you’ll likely find Noah traveling or running.