What is the difference between sidereal and tropical astrology?


The difference between sidereal and tropical astrology lies in their approach to the zodiac, with sidereal astrology focusing on the actual positions of stars and tropical astrology aligning with the Earth’s seasons.

The Sidereal Zodiac Explained

Astrology began sidereally, as far as we know. When the ancients looked up into the sky and saw the reddish wandering star close to those two twin stars, they were seeing Mars in Gemini. If you look at any readily available Tropical ephemeris today (9/01) and find Mars in Gemini, then go outside and look at the fixed stars behind Mars, you will see the stars of the Constellation of Taurus (unless Mars is in the last 5 ½ degrees of tropical Gemini at the time). This will show you the visible difference between the Tropical and Sidereal zodiacs.

Sidereal astrology is the older of the two systems, tracing its roots back to ancient Babylonian and Vedic astrology. In sidereal astrology, the zodiac is based on the actual positions of the stars in the sky. The starting point for the sidereal zodiac is the fixed star Spica, which is the principal star in the constellation Virgo. The sidereal zodiac divides the ecliptic into 12 equal segments, each representing 30 degrees.

Key characteristics of sidereal astrology include:

  1. Precision: Sidereal astrology is known for its precision in calculating the positions of celestial objects, as it takes into account the precession of the equinoxes.
  2. Star-Based Zodiac: The sidereal zodiac is directly linked to the position of stars and constellations in the sky.
  3. Individualized Charts: Sidereal astrology aims to provide a more personalized and accurate interpretation of an individual’s birth chart based on the actual positions of celestial bodies at the time of birth.

As of 2001 the difference between the two zodiacs is about +/- 25 degrees. The sidereal longitude is about +/-25 degrees behind the tropical longitude.

This difference is caused by the precession of the equinoxes, the shifting of the equinoctial points against the celestial backdrop of the fixed stars.

What does this precessional shift mean to you in interpreting your natal chart? It means, basically, that in terms of the astrology of the ancients, you may not be a Taurus, with a “bull- in-the-china-shop” attitude; you might well look at yourself as a sidereal Aries, ruled by aggressive, competitive Mars. Or instead of being a “secretly aggressive” Mars-ruled Scorpio, you may be a peaceful, Venus-ruled Libra.

Think about how sign delineations are derived: one part is based on observing the characteristics and behavior of people born with the Sun or other point in a particular 30 degree division of the zodiac; another part is based on the theory that a sign is “ruled by” a planet, or has a particular affinity with the nature of one or more of the planets. In a delineation the “observed” part must fit or be made to fit the “theory” part.

Following is a list of approximate dates that the Sun is in each of the Sidereal Constellations:

Aries — April 14 – May 14
Taurus– May 15 – June 14
Gemini– June 15 – July 16
Cancer– July 17 – August 16
Leo — August 17 – September 16
Virgo — September 17 – October 16
Libra — October 17 – November 16
Scorpio- November 17 – December 16
Sagittarius — December 17 – January 13
Capricorn — January 14 – February 12
Aquarius — February 13 – March 1
Pisces — March 15 – April 13

Remember these days are approximate and may vary from year to year.

The Tropical Zodiac Explained

It’s all Hipparchus’ fault. He started it 2,000 years ago when he discovered the displacement of the Earth’s axis. At that time the first day of Spring happened to coincide with 0 degrees of the Constellation Aries, but of course, as you may have read on the Sidereal side – precession has moved things along some +/-25 degrees since that time. But to a Tropical astrologer none of that matters because we do not mark the position of the planets against the Constellations but against the Ecliptic, which is the band of sky which traces the apparent path of the Sun throughout the year.

Tropical astrology, on the other hand, is the more commonly used system in the Western world. It is based on the position of the Sun at the vernal equinox, where day and night are approximately of equal length. This point is also known as the First Point of Aries and marks the start of the tropical zodiac. The tropical zodiac divides the ecliptic into 12 equal segments, each representing 30 degrees, just like the sidereal zodiac.

Key characteristics of tropical astrology include:

  1. Fixed Seasons: The tropical zodiac is closely tied to the Earth’s seasons, making it easier for people to relate to the signs, as they correspond to specific times of the year.
  2. Symbolic Zodiac: Unlike sidereal astrology, which is based on actual star positions, tropical astrology’s zodiac signs are more symbolic representations of personality traits.
  3. Popularity: Tropical astrology is more widely practiced and popularized in Western cultures, and horoscopes in newspapers and online usually use this system.

There are twelve Signs in the Tropical Zodiac but they no longer coincide with the Constellations, even though the Signs are called by the same names (creating quite a bit of confusion to beginners). The 360 degrees of the Ecliptic are divided into twelve 30- degree sections, one section for each Sign.

The Ecliptic, is of course circular but you have to have a beginning somewhere, and so Tropicalists mark the beginning of this Zodiac at 0 degrees of Aries on the first day of Spring – the Vernal Equinox (in the Northern Hemisphere). The following 30 degree sections are named Taurus, Gemini, etc. When the Sun reaches 0 degrees of Cancer, we here on Earth are celebrating the Summer Solstice. The Autumnal Equinox occurs when the Sun enters the Sign of Libra, and finally when the Sun enters 0 degrees of Capricorn we are at the Winter Solstice.

So you see Tropicalists have tied their Zodiac to the seasons here on Earth. This is an entirely different principle, based on different assumptions than those used by the Siderealists.

But the important point to make is that both systems work, both are valid.

Following is a list of the approximate dates that the Sun is in each of the Tropical Signs:

Aries — March 21st – April 20th
Taurus –April 21st – May 20th
Gemini –May 21st – June 21st
Cancer –June 22nd – July 22nd
Leo — July 23rd – August 22nd
Virgo –August 23rd – September 22nd
Libra –September 23rd – October 23rd
Scorpio — October 24th – November 22nd
Sagittarius — November 23rd – December 21st
Capricorn — December 22nd – January 20th
Aquarius — January 21st – February 18th
Pisces — February 19th – March 20th

These dates may vary from year to year.

Differences in Zodiac Sign Dates

The fundamental difference between sidereal and tropical astrology lies in the fixed starting points of their zodiacs. This difference results in variations in the dates associated with each zodiac sign. For example, someone born under the sign of Aries in tropical astrology may be considered a Pisces in sidereal astrology, and so on.

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