Two Astrologies

zodiac clock

I noticed that Elvis, David Bowie, and Stephen Hawking all share January 8 as their birthdays. Had they lived to see 2020, Hawking would have been 78, Bowie 73, and Elvis would have been 85. That coincidence made me wonder if this simultaneity had any connection to their zodiac signs. But that would also depend on which of two astrologies you want to follow.

The horoscopes you commonly see use a system called tropical astrology which is the most popular system in the U.S. and Europe.

I learned this when I was back in college because of ​a college girlfriend who was deeply into astrology while I was into astronomy. She did not believe in the tropical astrological signs or the general horoscopes you find in newspapers and online. She told me about another system called sidereal astrology.

I have never been a believer in astrology and horoscopes, but this sidereal version seemed a bit more scientific, so it appealed to me. The popular tropical version doesn’t use the actual constellations in the sky on any day, including the positions of the stars at the time you were born. Tropical astrology is based on the seasons.

Sidereal and tropical are astrological terms used to describe two different definitions of a year.  A tropical year (also known as a solar year) is the time that the Sun takes to return to the same position in the cycle of seasons, as seen from Earth. For example, you could measure the time from the vernal equinox to the vernal equinox, or from the summer solstice to the next summer solstice.

On the other hand, if you measure the time it takes Earth to complete one full orbit around the Sun as measured with respect to the fixed stars, you have a sidereal year.

Ancient stargazers of 2000 years ago saw constellations that matched with the seasons. For them, the Sun was always entering Aries during the Spring Equinox. But the stars have slowly changed location relative to Earth’s seasons. By now, there is a difference of up to two zodiac signs between the popular horoscope system and the actual constellations up there now.

I found a lot of information about all this at  which is a site by Athen Chimenti who is a “sidereal astrologer.” (see video below)

Both systems divide the ecliptic into twelve “signs.” That divides the 360 degrees into 12 slices of 30 degrees.

That old girlfriend, Catherine, did my natal chart based on the stars at the time of my birth. (She wasn’t thrilled that I didn’t know the actual hour of my birth.)  I’m not surprised that technology can now do your chart much faster and easier than Catherine.

I don’t think Stephen Hawking would have had any belief in astrology, but if he did I think the sidereal approach would be his preference because it was more exact. I imagine that Elvis and Bowie (Starman) might have had some interest in their astrological horoscopes.

Using a calculator on, I generated this natal chart for my birth day. I don’t have that old one that Catherine did, and I don’t have her here to explain what it means. Back in college, she did explain it and a lot of things made sense. Of course, she knew me, so I always wondered if she was just telling me what she knew was true. I wish I remembered what else she said that didn’t make sense to me then. Maybe over the years, they came to be true too.

natal chart

Here are the sidereal signs which are based on the midpoint between constellations. If you are within three days of another sign you are supposed to be a blend of both.

Hey, Catherine – I don’t know where you are now, but it turns out I might be a Virgo instead of a Libra!

Aries (Apr 21 — May 12)
Taurus: (May 13 — Jun 19)
Gemini (Jun 20 — Jul 16)
Cancer (Jul 17 — Aug 6)
Leo (Aug 7 — Sep 14)
Virgo (Sep 15 — Nov 3)
Libra (Nov 4 — Nov 22)
Scorpio (Nov 23 — Dec 6)
Ophiuchus (Dec 7 — Dec 18)
Sagittarius (Dec 19 — Jan 19)
Capricorn (Jan 20 — Feb 13)
Aquarius (Feb 14 — Mar 9)
Pisces (Mar 10 — Apr 20)

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Ken Ronkowitz

A lifelong educator on and off the Internet. Random by design and predictably irrational. It's turtles all the way down. Dolce far niente.

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