It is a matter of common knowledge that in processes of genesis and evolution of many solar phenomena participate magnetic fields of sunspots. Usage of long-term observations of these fields is of a great importance for solving of many important problems of solar physics. In variety of observatories large material of daily sunspot magnetic fields observations is collected, which contains great potential possibilities for future investigation in solar physics.

As a basis for formation of the database we take data on magnetic fields, collected by set of observatories during many years of observations. Now the longest period of time (1957-1997) are presented by data, obtained by Pulkovo observatory observations which are presented in Pulkovo database of sunspot magnetic fields (its creation in 1998-2000 was supported by Russian Fund for Basic Researches, grant #98-07-9037). In 2001 to the combined database data of another observatories of former USSR were added, which were collected in periods of 1957-1961 and 1968-1972 years. This work was also supported by RFBR (grant #01-07-90289). Names of the included observatories and types of corresponding data are presented on the main page.

The frame of the database consists of values of maximal strength and polarity of sunspots, determined by Zeemann splitting of some lines of the solar spectrum.

Depending on type of information, the data of the database are arranged in structured sections. Information in the sections are presented separately for every observatory. Section "Magnetic field data" contains data of magnetic field observation for separate sunspots, presented in standard text format (ASCII). Every file of the section contains data for one year, with number in the filename corresponding to number of the year. Section "Statistics by days" includes files, containing sums of magnetic fields' strength of corresponding polarity for every day of observation and number of sunspots, from which it was calculated. Description of structure of these files is presented here. Files with data of these two sections are also available as zip-archives here.

The third section contains images of the Sun for given day as graphic files of GIF-format. These images are drawings of photographs of sunspots, including measured for them strengths of magnetic field. Dates, corresponding to the year, month and day of the observation is included in the name of the graphic file. Unfortunately, not all pictures have good quality. Nevertheless, this quality is enough for identification of sunspots with their numbers and corresponding strengths of magnetic fields.

Two methods of work with the database are possible. First of them implies direct view of the data by common HTML-interface. The second one is realized as CGI-script, which supplies access to interactive search mechanism, allowing searching and selection of magnetic field data by various criteria, specified by user. Here one can specify or/and select options of need: name of observatory, time ranges, as well as ranges of magnetic field strength and polarity of interest. Moreover, one can obtain information either as data of separate sunspots observations, or as summed daily values. Therefore, some possibilities, which usually are intrinsic only for relational databases, are realized. These features of the database essentially increase effectiveness of extraction and further using of the information.