| Cycle Num: | 23 |
| Start Date: | August 1996 |
| End Date: | December 2008 |
| Duration: | 12.3 |
| Max Count: | 180.3 |
| Max Count Date: | November 2001 |
| Min Count: | 11.2 |
| Spotless Count: | 817 |
| Prev Name: | Solar cycle 22 |
| Next Name: | Solar cycle 24 |
| Prev Dates: | 1986–1996 |
| Next Dates: | 2008-late 2019 |
Solar cycle 23 was the 23rd solar cycle since 1755, when extensive recording of solar sunspot activity began.[1] The solar cycle lasted 12.6 years,[2] beginning in August 1996 and ending in December 2008. The maximum smoothed sunspot number observed during the solar cycle was 180.3 (November 2001), and the starting minimum was 11.2.[3] During the minimum transit from solar cycle 23 to 24, there were a total of 817 days with no sunspots.[4] [5] [6] Compared to the last several solar cycles, it was fairly average in terms of activity.
Large solar flares and coronal mass ejections (CMEs) occurred on 7 September 2005 (X17), 15 April 2001 (X14.4) and 29 October 2003 (X10), with auroras visible in mid-latitudes.
One of the first major aurora displays of solar cycle 23 occurred on 6 April 2000, with bright red auroras visible as far south as Florida and South Europe.[7] On 14 July 2000, the CME hurled by a X5.7 solar flare provoked an extreme (G5 level) geomagnetic storm the next day. Known as the Bastille Day event, this storm caused damage to GPS systems and some power systems.[8] Auroras were visible as far south as Texas.[9]
Another major aurora display was observed on 1 April 2001, due to a coronal mass ejection hitting the Earth's magnetosphere. Auroras were observed as far south as Mexico and South Europe. A large solar flare (the second-most powerful ever recorded) occurred on 2 April 2001, an X20-class, but the blast was directed away from Earth.
In late October 2003, a series of large solar flares occurred. A X17.2-class flare ejected on 28 October 2003 produced auroras visible as far south as Florida and Texas. A G5 level geomagnetic storm blasted the Earth's magnetosphere over the next two days.[10] A few days later, the largest solar flare ever measured with instruments occurred on 4 November; initially measured at X28, it was later upgraded to an X45-class.[11] [12] This flare was not Earth-oriented and thus only resulted in high-latitude auroras. The whole sequence of events that occurred from 28 October to 4 November is known as the Halloween Solar Storm.