article_snippet.sent: A previously unknown seasonal change on The sun is occurring every two years, according to a new study.
article_snippet.sent: a new study was already known that The sun goes through a solar cycle of 11 years, during which The sun activity increases and decreases.
article_snippet.sent: But this shorter two-year season seems to also play a part in The sun's activity, on a similar scale to the 11-year cycle - despite being much quicker.
article_snippet.sent: The bands, which appear in each hemisphere of The sun, cause the 11-year solar cycle to actually become a longer cycle that lasts 22 years.
article_snippet.sent: the 11-year solar cycle sees a periodic change in the sun’s activity - such as the number of ejections - in addition to changes in the number of sunspots, flares and other visible differences.
article_snippet.sent: Their frequency varies from several a day, when The sun is particularly active, to less than one a week during quiet periods.
article_snippet.sent: However, the cause of the 11-year cycle is poorly understood.
article_snippet.sent: The bands  appear to take place separately in the northern and southern hemispheres, with activity peaking over 11 months, then dropping over another 11 months.
article_snippet.sent: The almost annual variations can be likened to regions on Earth that have two seasons, such as a rainy season and a dry season. '
article_snippet.sent: The 11-year solar cycle sees a periodic change in the sun’s activity - such as the number of ejections - in addition to changes in the number of sunspots, flares and other visible differences.
article_snippet.sent: The almost-annual variability can also help explain a cold-war era puzzle: why do powerful solar flares and CMEs often peak a year or more after the maximum number of sunspots?
article_snippet.sent: This lag is known as the Gnevyshev Gap, after the Soviet scientist who first reported This lag in the 1940s.
article_snippet.sent: The answer appears to be that seasonal changes may cause an upswing in solar disturbances long after the peak in the solar cycle.
highlights_snippet.sent: The sun was already known to have an 11-year solar cycle .
  