Solar cycle 10
Solar cycle 10 was the tenth solar cycle since 1755, when recording of solar sunspot activity began. The solar cycle lasted 11.3 years, beginning in December 1855 and ending in March 1867. The maximum smoothed sunspot number (monthly number of sunspots averaged over a twelve-month period) observed during the solar cycle was 97.3, and the minimum was 5.2. There were a total of approximately 406 days with no sunspots during this cycle.
Solar storm of 1859
On September 1–2, 1859, the largest recorded geomagnetic storm on Earth occurred, known as the Carrington Event.  Aurorae were seen around the world, even over the Caribbean; those over the Rocky Mountains were so bright that their glow awoke gold miners, who began preparing breakfast because they thought it was morning.
Telegraph systems all over Europe and North America failed. Telegraph pylons threw sparks and telegraph paper spontaneously caught fire. Some telegraph systems appeared to continue to send and receive messages despite having been disconnected from their power supplies.
From August 28, 1859 until September 2, numerous sunspots and solar flares were observed on the sun. Just before noon on September 1, the British astronomer Richard Carrington observed the largest flare, which caused a massive coronal mass ejection (CME) to travel directly toward Earth, taking 18 hours. This is remarkable because such a journey normally takes three to four days. It moved so quickly because an earlier CME had cleared its way.
- Kane, R.P. (2002). "Some Implications Using the Group Sunspot Number Reconstruction". Solar Physics 205(2), 383-401.
- "The Sun: Did You Say the Sun Has Spots?". Space Today Online. Retrieved 12 August 2010.
- SIDC Monthly Smoothed Sunspot Number. ""
- Spotless Days. ""
- What's Wrong with the Sun? (Nothing) more information: Spotless Days. ""
- Solaemon's Spotless Days Page. ""
- "NASA — Severe Space Weather".
- "Bracing the Satellite Infrastructure for a Solar Superstorm".
- "Timeline: The 1859 Solar Superstorm".
- "The Great Storm: Solar Tempest of 1859 Revealed".
- "Bracing the Satellite Infrastructure for a Solar Superstorm", slide #2.