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Sunspot Drawings


Archives structure (rel. zu web-root)

...annual subdirectory

YYYY... subdirectory according to the year of observation

Data format and file names


... scanned sunspot drawing in the format JPEG

YYYYMMDD_hhmm...date and time of the observation

The images are saved with 8-bit grey scales and have a size of about 140 kB. The file names correspond to the SOHO file name convention for synoptic data.

Data description

Sunspot Drawings

The daily Sunspot Drawings continue a long tradition of Solar Observation at Kanzelhöhe. Although looking superseded by imaging technologies they show their ability to give a quick overlook what is going on. The feature to inspect them without any displaying tool and the ease handling make them favourable for preselecting of periods to investigate but they are precise ennough to be also used for deriving proper motions of sunspots. Nevertheless they are still used for deriving the Sunspot Relative Numbers.
Doing a Sunspot Drawing is very simple. We use a refractor (d/f = 110/1650 mm) on our patrol instrument, a projection lens enlarges the primary image to 25 cm diameter and focuses it to an attached drawing desk. Due to the folding of the light path the drawing is side reversed (i. e. E-limb is to the right). The sheet is rotated for azimuth = 0 points to sky North. The alignment is checked by tracing a spot's movement across the sheet due to the Earth's rotation. Although the precision of the scanning devices is quite high we do not recommend to use the scanned images for any positional measurements. We encourage you to work on the original drawings which are accessible to guests of the observatory.


This online service began in February 2000 and is updated daily with the new drawing. The complete archives of sunspot drawings since 1944 were digitized. The Kanzelhöhe Observatory would like to thank Dr. Alfred Schroll and DI Franz Vogler for their commitment to do the scanning of the drawings. Austrian Academy of Sciences has given financial support for the hardware.


  1. Date and Time of Observation
  2. Observation Conditions (Seeing, weather, observer, X and Y give the diameters of the circle at time of observation - may change due to paper shrinking
  3. Physical Ephemeris of the sun and the correction angle DP
  4. Number of groups, spots...; as used for the Sunspot Relative Numbers
  5. Alignment markings (spot's trace)
  6. Markings of Solar N and S (Rotation Axis, corrected for the misalignment DP
  7. Markings of the Solar Limb
  8. Spot group with Zürich classification

Zürich classification

Class A: A single pore or group of pores showing no bipolar configuration
Class B: A group of pores showing bipolar configuration
Class C: A bipolar group, one spot of which possesses a penumbra
Class D: A bipolar group whose main spots possess penumbrae; at least one of the spots has a simple structure. the length of the group is generally < 10 deg.
Class E: A large bipolar group; the two main spots possess penumbrae, and have generally complex structure. Numerous smaller spots lie between the main spots. The length of the group is > 10 deg.
Class F: A very large bipolar or complex group; length > 15 deg.
Class G: A large bipolar group containing no small spots between the main spots; length > 10 deg.
Class H: A unipolar spot possessing a penumbra; diameter > 2.5 deg.
Class J: A unipolar spot possessing a penumbra; diameter < 2.5 deg.

Zürich Klassifikation

The Zürich Classification of sunspot groups. Four examples of each class are shown. The scale at the bottom indicates degrees of heliographic longitude. Details are given in e. g. Bray & Loughhead, Sunspots, Chapman and Hall, 1964.