SILSO data/image, Royal Observatory of Belgium, Brussels

Daily total sunspot number
---------------------------

Time range: 1/1/1818 - 31/05/2015

Data description: 

Daily total sunspot number derived by the formula: R= 0.6 (Ns + 10 * Ng), 
with Ns the number of spots and Ng the number of groups counted over 
the entire solar disk. The 0.6 scaling factor was determined to bring 
the modern counts to the scale of the original sunspot index derived 
by Rudolph Wolf in the mid-19th century. 
By definition, the index cannot take values between 0 (no spots) and 7 
(single solitary spot, R=0.6*11). 
No daily data are provided before 1818 because daily observations become 
too sparse in earlier years. Therefore, R. Wolf only compiled monthly means 
and yearly means for all years before 1818.

Filename: dayssn.dat
Format: plain ASCII text

Contents:
Column 1: Gregorian calendar date
Column 2: Date in fraction of year
Column 3: Daily total sunspot number. A '?' symbol replaces the value 
                                      when none is available for that day.
Column 4: Definitive/provisional marker. A blank indicates that the value is definitive. 
                                      A '*' symbol indicates that the value is still 
                                      provisional and is subject to a possible revision 
                                      (Usually the last 3  to 6 months)

Line format [character position]:
 - [1-4]   Year
 - [5-6]   Month
 - [7-8]   Day
 - [11-18] Decimal date
 - [20-22] Daily sunspot number
 - [24]    Definitive/provisional indicator