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The Carrington Event of 1859

What happened in the September 1859 solar storm, how big it was by modern estimates, what remains uncertain, and how it compares with later extreme events. Primary sources linked.

What was observed

On 1 September 1859, Richard Carrington and, independently, Richard Hodgson saw an intense white-light brightening on the Sun while they were watching a large sunspot group. It was the first solar flare ever recorded. Both reported it in the Monthly Notices of the Royal Astronomical Society. [1] [2]

Within about a day, a severe geomagnetic storm began. Later analyses describe very low-latitude aurora and large magnetometer disturbances, including the record from Colaba (Bombay), India. [3] [4]

How big was it?

Tsurutani et al. (2003) used the Colaba magnetometer record and empirical relations between CME speed and magnetic field to estimate a Dst of about −1760 nT. That would make it the most intense storm in the historical record. They also argued that the flare and CME were extreme but not unique, so a storm this strong could happen again. [3]

Cliver & Svalgaard (2004) ranked events since 1859 by several measures: flare-related magnetic effects, energetic-particle fluence, Sun-to-Earth transit time, storm intensity and how far toward the equator the aurora reached. On each measure 1859 had close rivals or was beaten, but it was the only event near the top of every list. [4]

Single-number estimates like the Dst value rest on sparse 19th-century data and assumptions, so later studies continue to revise them. Read the papers for the ranges and caveats.

Could it happen again?

On 23 July 2012 a very fast CME, estimated at 2,500 ± 500 km/s, erupted from a region facing away from Earth, and the STEREO-A spacecraft measured it in situ. Baker et al. (2013) modelled it as if it had been aimed at Earth and found it would have produced a storm comparable to the largest of the 20th century. [5]

The effects on today's power grids would be very different from the effects on 1859 telegraphs. See our guide to solar storms and the power grid.

Sources

1. Carrington, R. C. (1859). Description of a Singular Appearance seen in the Sun on September 1, 1859. Monthly Notices of the Royal Astronomical Society. doi:10.1093/mnras/20.1.13
2. Hodgson, R. (1859). On a curious Appearance seen in the Sun. Monthly Notices of the Royal Astronomical Society. doi:10.1093/mnras/20.1.15a
3. Tsurutani, B. T. et al. (2003). The extreme magnetic storm of 1–2 September 1859. Journal of Geophysical Research: Space Physics. doi:10.1029/2002JA009504
4. Cliver, E. W. & Svalgaard, L. (2004). The 1859 Solar–Terrestrial Disturbance and the Current Limits of Extreme Space Weather Activity. Solar Physics. doi:10.1007/s11207-005-4980-z
5. Baker, D. N. et al. (2013). A major solar eruptive event in July 2012: Defining extreme space weather scenarios. Space Weather. doi:10.1002/swe.20097

Sources were checked on 2026-10-21. Text on this page is original. Quoted figures are attributed and linked to the source. General education only, not for safety or operational decisions. Disclaimer.