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Deep Field
29 September 2026 2518 stories tracked

Glossary · The Sun & Space Weather

The Parker spiral

Why the Sun's magnetic field reaches the planets as a spiral rather than a straight line.

The solar wind flows radially outward, but its magnetic field stays anchored to a Sun that rotates once every 27 days. The result is the shape a rotating garden sprinkler makes: each field line is dragged into an Archimedean spiral. Eugene Parker predicted it in 1958 and was widely disbelieved. It matters practically — it is why a particle storm from a flare on the Sun's western limb reaches Earth quickly, and one from the eastern limb often does not reach us at all.

Related terms

Coronal mass ejection A billion tonnes of solar atmosphere thrown into space, and the cause of most serious aurorae. Solar flare classes A, B, C, M, X — a logarithmic scale for how hard the Sun just flashed in X-rays. Kp index A 0–9 scale of how disturbed Earth's magnetic field is right now. The solar cycle An eleven-year rhythm in sunspots, flares and the Sun's entire magnetic field.

Questions

What is Parker spiral?

Why the Sun's magnetic field reaches the planets as a spiral rather than a straight line.

Why does it matter?

Eugene Parker predicted it in 1958 and was widely disbelieved. It matters practically — it is why a particle storm from a flare on the Sun's western limb reaches Earth quickly, and one from the eastern limb often does not reach us at all.

Written and computed by . Corrections and errors to hello@cantinalabs.dev.