Does the Market Really Reverse on Perihelion and Aphelion? We Checked 76 Years of Data
“I've looked at those dates going over the last 10 years, and there's always been market reversals on those days alone.” We heard this claim in a trading community last week — and with aphelion falling this Monday, it seemed like the right time to test it properly. The short answer: the pattern is real, and it means nothing.
The Claim
Perihelion is the point in Earth's orbit closest to the Sun. It arrives every year between January 2 and January 5. Aphelion is the farthest point, arriving between July 3 and July 6. The idea circulating in astro-trading circles is simple: these two astronomical extremes mark market turning points, and if you look back over the last decade you will find a reversal on every single one.
This is exactly the kind of claim we like, because it is checkable. It names specific dates, a specific market behavior, and a specific lookback window. So we checked it — not just for the last 10 years, but for all 76 years of daily S&P 500 history from 1950 to 2026.
One methodological note up front: we did not assume perihelion is “always January 4.” The exact date drifts from year to year, so we computed the true Earth–Sun distance minimum and maximum for every year from an ephemeris, then snapped each one to the nearest S&P 500 trading day. That matters more than you would think — aphelion has a habit of landing on July 4th, when the market is closed.
Test 1: The Claim as Stated — and It Passes
First we tested the claim the way its proponents likely check it: call it a reversal if the market puts in a local swing high or swing low (the highest or lowest close of a ±3-day window) within two trading days of the event.
By that standard, the last decade looks stunning. Perihelion “hit” in 10 of 11 years. Aphelion hit in 9 of 10. If you scrolled through charts checking these dates by eye, you would walk away a believer.
10 / 11
Perihelion years with a nearby swing, 2016–2026
9 / 10
Aphelion years with a nearby swing, 2016–2025
So the observation is honest. Anyone who looked at those dates would genuinely see reversals on almost all of them. The problem is not the observation — it is the control group nobody ran.
The base rate: 73.7% of ALL days pass the same test
On the S&P 500, a ±3-day swing high or low occurs roughly every five trading days. Ask the same question of any randomly chosen trading day— “is there a swing point within two days?” — and the answer is yes 73.7% of the time. Getting 9 or 10 hits out of 10 draws from a 74% deck is unremarkable: the binomial probability of doing at least that well by pure chance is 17–22%. Your birthday would pass this test too.
The Full 76-Year Record
Extending the same loose test across every year from 1950 gives the events far more chances to prove themselves. They don't.
| Test (swing within ±2 days) | Hit rate | Any-day base rate | p-value |
|---|---|---|---|
| Perihelion, 1950–2026 | 62/76 (81.6%) | 73.7% | 0.07 |
| Aphelion, 1950–2025 | 60/76 (78.9%) | 73.7% | 0.18 |
| Aphelion, exact day, strict ±5-day swing | 7/76 (9.2%) | 11.4% | 0.78 |
Nothing here clears any conventional significance threshold. The mild perihelion lean (81.6% vs. 73.7%, p = 0.07) is the most interesting number in the table, and even it has a mundane explanation we will get to below. Meanwhile, on the exact astronomical day with a stricter swing definition, aphelion performs worse than a random date.
Test 2: Require the Reversal to Mean Something
A reversal nobody could trade is not a reversal worth predicting. So we tightened the definition: a pivot only counts if price moved at least 2% into it and then reversed at least 2% away from it — a standard zigzag pivot. On the S&P 500 these occur about once every 12–13 trading days: 1,525 of them across the full 76 years.
With a definition that actually filters, the claim collapses entirely.
| Window | Any-day base rate | Perihelion | Aphelion |
|---|---|---|---|
| Exact day | 7.9% | 6.5% | 6.6% |
| ±1 day | 22.4% | 28.6% | 22.4% |
| ±2 days | 34.3% | 35.1% | 35.5% |
| ±3 days | 43.9% | 41.6% | 39.5% |
Every cell is statistically indistinguishable from the base rate (all p-values ≥ 0.12). On the exact day and at ±3 days, both events sit below chance.
And the last decade — the window the claim was actually made about — is where it fails hardest:
Perihelion, 2016–2026
2 / 11
Only January 2019 (a low after the Q4 2018 selloff) and January 2022 (the pre-bear-market top) had a 2%+ pivot within two trading days. In January 2024 the nearest such pivot was more than 40 trading days away.
Aphelion, 2016–2025
1 / 10
Only July 2022 qualified. In every other year the nearest 2%+ pivot was 4 to 24 trading days away from the event.
Why the Claim Feels So True
1. The base-rate illusion
Minor swing points occur about every five trading days. Checking whether “a reversal happened near date X” without asking how often one happens near anydate is the core error. Nearly three out of four random days pass the loose version of this test. Any fixed annual date — a solstice, a holiday, your wedding anniversary — will rack up an impressive-looking streak.
2. One unforgettable hit
The S&P 500's all-time high of January 3–4, 2022 — the exact top before a year-long bear market — landed on perihelion. A single spectacular coincidence like that anchors the belief, and confirmation bias fills in the rest of the years with whatever small wiggle is nearby.
3. Perihelion borrows the turn-of-year effect
Perihelion always falls January 2–5, a stretch already crowded with real calendar effects: tax-driven flows, January rebalancing, the first trading days of the year. The mild 81.6%-vs-73.7% lean in the loose test is far more plausibly ordinary turn-of-year seasonality than Earth–Sun distance. The distance itself barely changes — the orbit is 98.3% circular — and there is no proposed mechanism for why a 1.7% variation would time equity pivots.
4. Aphelion hides behind a market holiday
Aphelion regularly lands on or next to July 4th, when U.S. markets are closed. The “reversal” then gets credited to a trading day one or two days away — silently widening the window and making loose matches even easier to find.
The Checklist for Any “Always Reverses On” Claim
This study took an afternoon, and the recipe generalizes to every date-based market claim you will ever hear:
Pin down the dates. Compute them precisely (we used an ephemeris for the exact Earth–Sun distance extremes) instead of assuming a fixed calendar day.
Define “reversal” before looking. A definition you can't code is a definition that will stretch to fit whatever the chart shows.
Measure the base rate. Whatever you count near the special dates, count it near every other date too. This single step dissolves most calendar folklore on contact.
Use all the data. “The last 10 years” is 10 coin flips. We had 76 years available — the claim had every chance to show up, and didn't.
We build and test astronomical timing models for a living — some survive this kind of scrutiny and become strategies on our platform. This one doesn't. That distinction, between patterns that survive a base-rate test and patterns that only survive eyeballing, is the entire game.
Frequently Asked Questions
What are perihelion and aphelion?
Perihelion is the point in Earth's orbit closest to the Sun, arriving every year around January 2–5. Aphelion is the farthest point, around July 3–6. The exact date drifts by a day or two from year to year.
Does the stock market reverse on those dates?
Not beyond chance. Requiring a 2%+ reversal, perihelion and aphelion hit within two trading days in about 35% of years — against a 34.3% base rate for any random day. On the exact day, both sit slightly below the random-day rate.
Why does the claim look true on a chart?
Because small swing highs and lows occur roughly every five trading days, 73.7% of all trading days have one within two days. Any date “always” has a reversal nearby if you count wiggles. The streak is a property of markets, not of orbital mechanics.
Wasn't the January 2022 top exactly on perihelion?
Yes — and it is one of only two perihelion dates in the last 11 years that coincided with a 2%+ pivot. One spectacular hit is exactly what anchors beliefs like this; 76 years of data is what tests them.
Patterns That Survive the Base-Rate Test
Seasonal Edge backtests every calendar and cycle pattern against decades of data — win rates, profit factors, and regime filters included — so you can see which recurring dates actually held up historically and which are folklore.
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