Last weekend I gave a talk on Solar Returns to the Mid-Hudson NCGR group in New York state. We had a lively discussion, and the meeting left me wondering about several aspects of solar returns which seemed worth investigating further. One of these was the issue of when the sun in reality completes a full annual cycle. This post will explore that topic in more depth.
In the scientific world, we view the Earth as revolving around the Sun. According to Kepler’s model, the two celestial bodies actually revolve around each other in a giant elliptical pattern that approximates a circle.
The scientific preference is to view this elliptical orbit from the point of view of the Sun, but astrologers on Earth prefer to view matters from their vantage point on Earth because it accords with their day-to-day experience. Thus, astrologers construct their charts with the Earth at the center and speak of the Sun revolving around the Earth. Obviously, astrologers are aware of the scientific model and accept Kepler’s first law that the planets travel around the Sun in elliptical (but nearly circular) orbits with the center of the Sun as one of the foci of the ellipse.
In any case, whether we adopt the frame of reference of the Sun revolving around the Earth, or the Earth revolving around the Sun, the question remains: how long is a year? We measure our lives in years, by which we mean the amount of time it takes, speaking geocentrically, for the Sun to reach the same point in its orbit around the Earth that it traversed at the moment of our birth — the so-called Solar Return — and we all hope to have many happy Returns.
You might think it’s an easy matter to measure a year, but in reality it turns out to be quite a complicated matter. First, there is the issue of what reference system (tropical or sidereal) we will use to measure the solar year.
Do we choose to measure movement in the solar system against the backdrop of the fixed stars, that is, using the sidereal zodiac? In the short term this system is fairly reliable, but in the long term the positions of the fixed stars are changing due to the expansion of the universe and the revolution of our solar system around the center of the Milky Way galaxy in which we reside.
Is the tropical zodiac any more reliable as a reference system for measuring the length of the year? Probably not. As you probably know, the tropical zodiac begins its measurement of 0 Aries at the spring equinox, that is, at the exact moment when the path of the Sun crosses the Earth’s equator (which is what gives us equal amounts of daylight and night, at the “equi-nox” or equal night). Scientists have measured the mean or average tropical year very precisely and found that it has a length of 365 days, 5 hours, 48 minutes, and 46 seconds, or 365.242189 days.
The problem is that, like the Moon’s Nodes, there are two types of tropical years: mean years and true years. It seems that reality does not precisely follow the abstract mathematical model. One issue it that the Earth wobbles on its axis (precession), like a spinning top, so that the Earth’s axis makes a complete circle about every 26,000 years. That may seem like a long time but the practical effect is that the Earth wobbles a teeny bit every year, enough so that the Earth’s Equator shifts a tiny bit, causing about a 20 minute difference in the exact moment of the spring equinox (used to measure 0 Aries) every year.
The Earth’s wobble affects the start of the tropical zodiac
In an article about this topic, Sarah Kaplan explains that “the consequence of all this wobbling is that a tropical year ends about 20 minutes before Earth actually completes an orbit of the sun.” The effect is that at the moment the Sun completes one tropical year to return to its birth location, the start of Aries has gradually shifted backward by 20 minutes (as measured against the fixed stars) so that the reference system used to measure the sun’s motion has changed. To correct for this ongoing change in the reference system, some astrologers prefer to use “precession-corrected” solar returns, which adjust the return for the 20-minute annual change in the position of 0 Aries in the tropical zodiac.
An analogy might be helpful here. Suppose you enter a 100-meter race. The Start Line is marked “0 meters” and the Finish Line, “100 meters.” During the race, the referee decides to move the start line backward so that it is one meter earlier than its original position. When you have run 100 meters in the original system, the distance measured from the new Start Line indicates that you have run 101 meters because it has undergone a form of precession. This is what happens with solar returns; at the moment the sun (or earth) completes one full orbit, the start line of the tropical zodiac (0 Aries) has shifted backward a tiny bit and you are 20 minutes into a new tropical year.
Planetary gravity alters the space-time continuum within our solar system
Another issue is that the orbiting planets all exert gravitational effects on the sun and on the other planets of the solar system, thus, as Einstein explained, distorting the space-time continuum in which we live. As a result, the duration of the planetary orbits varies slightly from one cycle to the next. In fact, even though the mean tropical year has been measured carefully to be 365.242189 days long (365 days, 5 hours, 48 minute, 45 seconds), the exact length of a true tropical year can vary up to 30 minutes from this figure. For astrologers, this means that the exact moment of your solar return, as measured by the mean or average tropical solar year, may in reality be as much as 30 minutes earlier or later, depending on the gravitational patterns of the other planets in the solar system for the year in question.
If you are interested in how long your true tropical year is for any date between 1900 and the year 2100, fortunately there is a table that gives this data at https://www.timeanddate.com/astronomy/tropicalyearlength.html.
Here is an excerpt from a table of the length of true tropical years for the current period. This table is based on the definition that “the length of a tropical year is the time it takes the Earth to complete a full orbit around the Sun, but it varies from year to year.”
|March 2016 – March 2017||365 days||5 hours||58 minutes||36 seconds|
|March 2017 – March 2018||365||5||46||41|
|March 2018 – March 2019||365||5||43||12|
|March 2019 – March 2020||365||5||51||4|
|March 2020 – March 2021||365||5||47||55|
I don’t know if astrological software adjusts for these differences in the length of the true tropical year from one year to the next. If not, we may have to be content with computer programs that use the mean tropical year and give average solar returns which may be off by a full 30 minutes from the true return of the sun to its birth location. This variability in the length of the tropical year would also affect many predictive measure that we use in astrology (progressions, directions, etc., especially those for which 4 minutes = 1 degree = 1 year of life). In some cases a 30-minute difference can radically alter the solar return chart by changing the Angles and house cusps which are essential to interpretation, so the next time your solar return interpretations completely miss the mark, you can blame the distortion of the space-time continuum by the other planets in our solar system.
ADDENDUM & CORRECTION (21 August 2018):
I am grateful to Bernd who wrote in response to the original post (see comments section below):
“Today tropical solar return calculation is done with computers using a simple formula:
Birthtime + Mean Tropical Year * X = Approximal Solar Return Time
After that a loop is done until the Exact Solar Return Time is found:
Approximal Solar Return Time +- Minutes / Seconds = Exact Solar Return Time
Where Exact Solar Return Time is the time the Sun reaches the same exact place on the ecliptic as it was at time of birth.
So there’s no need to know the exact Tropical Year length.”
According to Bernd, our astrological software does adjust for the variable length of the true tropical year to locate the sun each year at the same point on its path which it occupied in the birth chart. Thus, we don’t need to concern ourselves with variable-length tropical years when we use our computers to calculate the solar return.
I assume, however, that the position of the sun’s return is measured in the tropical zodiac so that there still remains the issue of correcting for precession because the start of the tropical zodiac is constantly shifting backward as the tilt of the Earth’s axis is constantly changing with respect to the Sun.