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Sunspot number and solar cycle peak markets

The Sun's activity rises and falls on a cycle of roughly 11 years, and the number of sunspots is the classic way to track it. Event contracts may ask whether the monthly sunspot number will exceed a level, or whether a cycle has already peaked. Both depend on a specific data series with built-in lags and revisions. This SoftCta guide explains how to read it.

The official series

The international sunspot number is compiled by SILSO, the Sunspot Index and Long-term Solar Observations service at the Royal Observatory of Belgium. It combines observations from a worldwide network of stations into daily, monthly and smoothed values. In 2015, SILSO recalibrated the full record back to the 1700s, creating Version 2 of the series. Values from Version 1, still quoted in some older sources, are about 40% lower, so a contract should name the current series.

NOAA's Space Weather Prediction Center republishes SILSO numbers on its solar cycle progression page alongside other measures, such as the 10.7 cm radio flux, which tracks activity independently of counting spots.

Monthly versus smoothed

Monthly averages are noisy. The 13-month smoothed sunspot number is a centred average that gives half weight to the first and last months. It is the standard way to define a cycle's minimum and maximum, but because it is centred, the smoothed value for a given month is available only about six months later. A contract on "the smoothed peak by a date" cannot resolve until well after that date. Our guide to rolling averages explains this lag.

Solar Cycle 25

Solar Cycle 25 began in December 2019. The official forecast panel originally predicted a modest maximum, and activity ran higher than expected. In October 2024, NASA and NOAA announced that the Sun had reached its solar maximum period, while noting that the precise peak would be identified only in hindsight. Readers should check the latest SILSO smoothed values rather than older forecasts. A second, higher peak in the smoothed series is possible during a maximum period, which is one reason peak-timing markets are tricky.

Provisional values and revisions

Daily and monthly numbers are first published as provisional and can be adjusted as more station reports are processed. Our guides on provisional versus final resolution and data revisions cover how contracts usually handle that.

Sunspots and space weather

More sunspots generally mean more flares and geomagnetic storms, but large storms can occur well after a maximum. Our space weather guide covers flare classes and the Kp index.

Wording checks

• Series: SILSO Version 2, daily, monthly or 13-month smoothed.
• Provisional or final: which release settles the contract.
• Peak definition: maximum of the smoothed series, confirmed by a named source.
• Timing: expect a lag of months for smoothed-value markets.

A reading habit

Check the latest SILSO monthly and smoothed values and the NOAA progression page before reacting to a quote. Convert prices with the implied probability tool and verify live prices on the venue.

Primary sources SoftCta readers open

• SILSO, Royal Observatory of Belgium international sunspot number series
• NOAA Space Weather Prediction Center solar cycle progression page
• NASA and NOAA solar cycle announcements
• Solar Cycle Prediction Panel statements

Reading the quote step by step

• Read the full title and rules, including the named settlement source and the time zone.
• Convert the Yes and No prices to implied probabilities and note the gap between them.
• Subtract fees and spread to see the effective price you would actually face.
• Write your own probability range and the evidence behind it, then compare.
• Check related and near-duplicate markets on other venues for consistency.

Closing SoftCta checklist

• Re-read the venue definition in your own words before reacting to a price.
• Convert prices with fee and spread awareness; verify live cents on the operator.
• Prefer primary settlement sources over secondary headlines and social summaries.
• Treat ChanceWire hubs, movers, and tools as orientation — not order entry.
• Confirm age, location, and product eligibility; SoftCta pages will not suggest location spoofing.
• If clarity is incomplete, watching is a complete SoftCta outcome — no pick-selling urgency required.

SoftCta habits

• Write your own probability range before checking the crowd price.
• Prefer dated primary sources over social summaries.
• Compare related markets when a single book looks extreme.
• Size curiosity with fees and depth in mind; substantial risk of loss.