The thick green line in the graph above shows the accumulated (total number of) spotless days so far during the transit from solar cycle 24 to 25.
#Spotless show series
Only, when comparing sunspot numbers or spotless days statistics, this should be done within the time series from the respective networks. We’d like to emphasize there's no "wrong" here. A more meaningful index is the total number of spotless days over an entire cycle minimum, however those spotless days are grouped in contiguous intervals. Finding the longest spotless interval is more like a curio. In that case, one can expect large differences between independent time series, but those differences should not be considered as statistically meaningful to characterize the solar cycle.
So, the key point is that the duration of spotless time intervals is based on small-number statistics, as any rare single short-lived tiny spot can break a spotless interval. The differences that are observed in the spotless days streaks are linked to small sunspots (not easy to see when they are there) with a short lifetime (not observed the whole day) that were observed by our network and not noticed by its NOAA counterpart. The possible hours of observation are different from station to station and thus from one network to another, including the ones NOAA uses. Here at SILSO, we use our own network (mostly European-based). NOAA (their Solar Region Summaries (SRS) are at ). The reason for this is simply because we (SILSO) are using a different network than e.g. Please note that the number and stretches of spotless days may differ from those of other sources (e.g. This “Spotless Days page” will continue to provide you with a front-row seat on the current status of the solar cycle minimum and the number of spotless days. The previous minimum surprised scientists and solar observers by being the deepest in nearly 90 years, and also this minimum is -once again- a very deep one. This page contains graphs and tables on the accumulated number of spotless days, stretches of spotless days, and comparisons to other solar cycles – all supplemented with a word of explanation. In order to have an idea on the total number of spotless days during this minimum transit, and how these numbers compare to past solar cycles, the SILSO folks created a “Spotless Days page” back in 2016. As the new solar cycle 25 has started, several consecutive days and even weeks without sunspots will become less frequent. For example, during the previous minimum (around 2008), no less than 817 spotless days were recorded, whereas the minimum period leading into solar cycle 23 (around 1996) counted only 309 such blemishless days. The number of spotless days can vary significantly from one solar cycle transit to another. These spotless disks have become a familiar feature as the solar cycle is transiting through its minimum, which has taken place in December 2019 (see for more information). Regular solar observers have noticed that since mid-2016, the Sun has occasionally been devoid of sunspots.
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