Monthly Sunspot Data, from 1749 to "Present"

Description

Monthly numbers of sunspots, as from the World Data Center, aka SIDC. sunspot.month is the version of the data that will occasionally be updated when new counts become available (or the numbers are recalibrated). Note that around 2014–2015 there has been an international effort to recalibrate the sunspots numbers; since R 4.5.0 (2025), the recalibrated series is used.
The version in (too long) use from 2014 to 2024 is provided as sunspot.m2014 for historical and reproducibility reasons. For strict reproducibility, hence use that, or sunspots instead of sunspot.month.

Usage

sunspot.month
sunspot.m2014

Format

The univariate time series sunspot.year, sunspot.m2014 and sunspot.month contain 289, 3177, and currently 3310 observations, respectively, where the latter will increase over time. The objects are of class "ts".

Author(s)

R Core Team.

Source

WDC-SILSO, Solar Influences Data Analysis Center (SIDC), Royal Observatory of Belgium, Av. Circulaire, 3, B-1180 BRUSSELS Currently at https://www.sidc.be/SILSO/datafiles

From around 2015, expert astronomers decided to recalibrate historical sunspot numbers, see the ‘References’. This is not yet visible in current sunspot.month but may well change by the next release of R.

References

Clette, Frédéric and Lefèvre, Laure (2016) The New Sunspot Number: Assembling All Corrections. Solar Physics 291, 2629–2651. doi:10.1007/s11207-016-1014-y

Clette, F., Lefèvre, L., Chatzistergos, T. et al. (2023) Recalibration of the Sunspot-Number: Status Report. Solar Physics 298: 44. doi:10.1007/s11207-023-02136-3

See Also

sunspot.month is a more up-to-date and hence also longer version of sunspots; the latter runs until 1983 and is kept fixed (for reproducibility as example dataset).

Examples

require(stats); require(graphics)
## Compare the monthly series
plot (sunspot.month,
      main="sunspot.month & sunspots [package 'datasets']", col=2)
lines(sunspots) # -> clear recalibration (to *larger* values)
at. <- seq(1750, 2030, by=10)
atyr <- at.[at. %% 50 != 0] #%
Axis(time(sunspot.month), at = atyr, side = 1,
     tck= -1/100, padj = -1.5, cex.axis = 3/4)

## Now look at the difference :
all(tsp(sunspots)     [c(1,3)] ==
    tsp(sunspot.month)[c(1,3)]) ## Start & Periodicity are the same
n1 <- length(sunspots)
table(eq <- sunspots == sunspot.m2014[1:n1]) #>  143  are different !
i <- which(!eq)
rug(time(eq)[i])
s1 <- sunspots[i] ; s2 <- sunspot.m2014[i]
cbind(i = i, time = time(sunspots)[i], sunspots = s1, ss.month = s2,
      perc.diff = round(100*2*abs(s1-s2)/(s1+s2), 1))

## How to recreate the "old" sunspot.month (R <= 3.0.3) =: sunspot.month.0
.sunspot.diff <- cbind(
    i = c(1202L, 1256L, 1258L, 1301L, 1407L, 1429L, 1452L, 1455L,
          1663L, 2151L, 2329L, 2498L, 2594L, 2694L, 2819L),
    res10 = c(1L, 1L, 1L, -1L, -1L, -1L, 1L, -1L,
          1L, 1L, 1L, 1L, 1L, 20L, 1L))
ssm0 <- sunspot.m2014[1:2988]
with(as.data.frame(.sunspot.diff), ssm0[i] <<- ssm0[i] - res10/10)
sunspot.month.0 <- ts(ssm0, start = 1749, frequency = 12)
stopifnot(length(sunspot.month.0) == 2988)