Understanding The Differences Between Sidereal And Tropical Astrology

There is an ongoing debate about the validity of the two astrological calendar systems, sidereal and tropical. Both are widely used, sometimes in tandem, by novice and professional astrologers. I switched from tropical to sidereal because I feel more aligned — emotionally, mentally, and spiritually— with sidereal’s planetary transits.

Sidereal Versus Tropical

Both calendar systems are based on the circular ecliptic divided into 12 zodiac signs with thirty degrees in each sign, totaling 360 degrees. Sidereal is based on the location of “fixed stars” that move one degree every 72 years.

Tropical further divides the same ecliptic into four equal parts: vernal (spring) equinox, summer solstice, autumn equinox, and winter solstice. Western tropical astrologers use the same vernal point for the sun’s transit, located at 0 degrees of Aries each year.

The difference is based on how the systems address the precession of the equinoxes, or the relationship between speed of rotation of the earth with the speed of rotation of the galaxy.

Differences In Zodiac Signs

The dates for tropical astrology do not change because they always start with 0 degrees Aries. Sidereal dates shift between one or two days because of precession, so the equinoxes and solstices may differ by a day each year.

Below are the dates of the sun’s transits in the constellations for the sidereal and tropical calendar systems.





15 April – 15 May

21 March – 19 April


16 May – 15 June

20 April – 20 May


16 June – 16 July

21 May – 21 June


17 July – 16 August

22 June – 22 July


17 August – 16 September

23 July – 23 August


17 September – 17 October

24 August – 22 September


18 October – 16 November

23 September – 23 October


17 November – 16 December

24 October – 22 November


17 December – 15 January

23 November – 22 December


16 January – 14 February

23 December – 20 January


15 February – 15 March

21 January – 18 February


16 March – 14 April

19 February – 20 March

In tropical a person may be a Gemini sun, but Taurus in sidereal. The ascendant (rising sign) and moon sign will also differ by 23 degrees, sometimes an entire sign behind, with the sidereal system. This, too, is because of the sidereal calendar recognizing the shifts in the universe.

Aligning With The Stars

The debate between sidereal and tropical often leaves people using both calendar systems and experimenting with different house systems — equal, whole, or Placidus — and the various types of precessional systems (ayanamsa) to understand their natal chart. None of this is wrong.

I decided to follow the lunar calendar of sidereal and tropical to see which resonated with me. Studying the different astrology traditions, perspectives, and systems (there are many) allowed me to understand what I experienced.

The sidereal calendar using the whole sign system and Lahiri ayanamsa made logical and spiritual sense based on what I experienced. There are Western sidereal and Vedic astrologers who use the same combinations.

Astrological Beliefs And Experiences

The moon is our mind, mental perspective, and emotional side. We are in alignment with the moon. Our ancestors used the moon, sun, and stars to determine festivals, harvests, and events. The moon, in particular, was used to connect with intuition regarding how and where to migrate.

Tracking your own emotional, mental, and spiritual changes with the lunar cycles is one way of learning how the moon affects your mood, mental clarity, and intuition. Further, living in alignment with the lunar cycle helps you live in alignment with your soul, or sun sign. 

Regardless of whichever calendar system you use, sidereal or tropical, you will notice changes in your life as other planets transit.


Here is a free downloadable Vedic astrology calendar from Science of Light. Visit Astrologie-info for a free online calendar, sidereal and tropical.

NOTE: Vedic astrologers use the sidereal system. Not all sidereal astrologers use Vedic principles.

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