4 December 2007
SOHO – keeping an eye on the Sun for 12 years
The Solar and Heliospheric Observatory (SOHO) celebrated its twelfth launch
anniversary on 2 December 2007. The satellite has witnessed the Sun change
through almost a complete solar cycle – from quiet to stormy, and back
The solar cycle normally lasts about 11 years. In late 1996, shortly after
its launch, SOHO was able to observe the last minimum of the 11-year
activity cycle. The minimum was followed by a rapid rise in solar activity,
peaking 2001 and 2002.
Activity levels have slowly declined since then, but we haven’t reached
solar minimum yet, despite passing 11.1 years since the last minimum – the
average length of a solar cycle.
One way of measuring the solar cycle, is to observe sunspots on the Sun.
Sunspots are areas of very high magnetic fields on the Sun’s surface, their
numbers vary with the cycle. The sunspot cycles measured since the mid-18th
century vary in length from 9.0 to 13.5 years.
While a team of experts has attempted to predict when the next solar minimum
will be, we won’t really know until we get there. In fact, the experts were
sharply divided about the time of the next minimum and the intensity of the
next maximum, which should arrive at about 2012 or 2013.
Whenever the next cycle begins, SOHO will be there to observe it.
Notes for editors:
The official NOAA, NASA, and ISES Solar Cycle 24 prediction was released by
the Solar Cycle 24 Prediction Panel on April 25, 2007. The prediction panel
consisted of a team of international experts.
[NOTE: Images supporting this release are available at