The Bradley Siderograph: A Complete Guide to Planetary Market Timing

Donald Bradley published Stock Market Prediction in 1948. The book introduced a composite index derived from planetary declinations and geocentric aspect angles, which he called the siderograph, and claimed it corresponded to turning points in the Dow Jones Industrial Average.

Seventy-five years later, the siderograph is still used by cycle analysts. It has been subjected to rigorous statistical testing. The results are less clear-cut than Bradley's original claims, but the index retains a following among researchers who take astronomical cycle analysis seriously. This guide explains what it is, how the calculation works, and what the evidence actually shows.

What Donald Bradley was trying to do

Bradley wasn't claiming that the planets cause stock market moves. His argument was more careful than that. He observed that certain planetary configurations, specific aspect angles, changes in declination, appeared to correlate with price turning points in historical data. Whether the correlation implied causation, or reflected some shared underlying driver, he left open.

This distinction matters. Dismissing the siderograph as "astrology" misunderstands what Bradley was actually proposing. He was a statistician and mathematician by training. His claim was empirical: the index correlates with turning points more often than chance would predict. He invited people to test it.

How the calculation works

The siderograph combines two components:

1. Declination sum Bradley calculated the sum of declinations for all visible planets (Mercury through Saturn) in both geocentric and heliocentric coordinates. When outer planets are at high northern or southern declinations, moving toward or away from the celestial equator, this contributes to the composite score.

2. Aspect angles Certain geocentric angles between planet pairs, the major aspects in traditional astronomical/astrological usage (0°, 60°, 90°, 120°, 180°), are weighted and added to the total. Harmonious aspects (60°, 120°) add positive value; dissonant aspects (90°, 180°) subtract.

The resulting time series is the siderograph. It rises and falls over weeks and months, producing a curve with local maxima and minima. Bradley's claim was that these extrema corresponded to major turning points in the stock market, not necessarily at the exact date, but within a few days.

The inversion problem This is the critical caveat that any serious user of the siderograph acknowledges: the polarity can invert. A siderograph high can correspond to either a price high or a price low. Bradley himself was explicit about this, the siderograph indicates when a turn will occur, not which direction.

This makes the siderograph a timing tool, not a directional signal. You still need other analysis to determine whether a siderograph extreme marks a top or a bottom.

Statistical testing: what does the evidence show?

Several researchers have tested the Bradley siderograph systematically since 1948.

The honest summary is: the evidence is mixed, but not uniformly negative. Studies using the S&P 500 from the 1950s through the 1990s found that siderograph extremes tended to fall within a few days of significant turning points at a rate above chance, not dramatically above chance, but measurably. Other studies found no reliable signal.

The methodological problem is consistency. Researchers define "turning point" differently, use different windows for what counts as a coincidence, and apply different corrections for data snooping. Published results depend heavily on these choices.

What the research does not support is using the siderograph alone for trading decisions. What it does support, or at least, doesn't contradict, is using it as one input in a multi-factor analysis where other timing tools provide corroboration.

How cycle analysts use it today

In practice, traders and cycle analysts who use the siderograph do so as a confluence filter:

• When a siderograph extreme coincides with a Gann time cycle, a round-number price level, and a Bartels-significant short-term cycle, that convergence gets attention
• When the siderograph is flat or in a non-extreme phase, other signals get weighted more heavily

The Gann Square of Nine provides independent time and price targets that can be checked against siderograph turning points. Where the two methods agree, conviction is higher.

The siderograph is also used as part of multi-year cycle frameworks. At longer timescales, quarterly or annual turning points, the inversion problem is less severe because the analyst can observe the longer trend and determine polarity empirically.

Practical access and tools

Computing the siderograph requires planetary ephemeris data and the Bradley algorithm. Crohamhurst.app calculates the current and forward siderograph as part of its astronomical cycle toolkit.

For comparison, commercial tools like Galactic Trader and Solar Fire include Bradley siderograph modules, we cover those in our alternatives guide.

What to do with a siderograph turning point

When the siderograph reaches an extreme:

1. Note the date and the direction of the turn (from high to low, or low to high)
2. Look at price context, is the market near a significant support or resistance level?
3. Check whether any Gann time cycles land near the same date
4. Determine polarity from recent trend, the siderograph doesn't tell you this; you have to read the market
5. If the confluence is strong, treat it as a timing alert, not a trade signal

The inversion ambiguity means you're looking for confirmation from price behaviour. A siderograph high near a major resistance level with the market showing distribution is readable. The same siderograph high with the market in strong uptrend suggests you wait and see whether the polarity has inverted.

Backtesting the siderograph

If you want to test Bradley's claims rigorously yourself, our backtesting primer walks through a systematic methodology for evaluating cycle-based market timing signals. The same framework applies to the siderograph.

The honest conclusion, after working with this tool seriously, is that the siderograph is neither the magic timing tool that enthusiasts claim nor the worthless noise that sceptics dismiss. It's a well-constructed index with a partial empirical basis that works best in combination with other methods.

Related: Gann Square of Nine 2026 Guide | Backtesting Cycle Methods: A Primer | Galactic Trader and Solar Fire Alternatives