Sunspot areas and tilt angles for solar cycles 7-10

Abstract

Extending the knowledge about the properties of solar cycles into the past is essential for understanding the solar dynamo. This paper aims at estimating areas of sunspots observed by Schwabe in 1825-1867 and at calculating the tilt angles of sunspot groups. The sunspot sizes in Schwabe's drawings are not to scale and need to be converted into physical sunspot areas. We employed a statistical approach assuming that the area distribution of sunspots was the same in the 19th century as it was in the 20th century. Umbral areas for about 130,000 sunspots observed by Schwabe were obtained, as well as the tilt angles of sunspot groups assuming them to be bipolar. There is, of course, no polarity information in the observations. The annually averaged sunspot areas correlate reasonably with sunspot number. We derived an average tilt angle by attempting to exclude unipolar groups with a minimum separation of the two alleged polarities and an outlier rejection method which follows the evolution of each group and detects the moment it turns unipolar at its decay. As a result, the tilt angles, although displaying considerable scatter, place the leading polarity on average 5.85+-0.25 closer to the equator, in good agreement with tilt angles obtained from 20th-century data sets. Sources of uncertainties in the tilt angle determination are discussed and need to be addressed whenever different data sets are combined. The sunspot area and tilt angle data are provided online.

accepted for publication in Astron. & Astrophys

References in corpus (2)

• Re-examining Sunspot Tilt Angle to Include Anti-Hale Statistics
• The Properties of the Tilts of Bipolar Solar Regions

Cited by in corpus (20)

• Solar cycle prediction
• On-line Tools for Solar Data Compiled at the Debrecen Observatory and their Extensions with the Greenwich Sunspot Data
• Visualization of the challenges and limitations of the long-term sunspot number record
• Solar Cycle Variability Induced by Tilt Angle Scatter in a Babcock--Leighton Solar Dynamo Model
• Models for the long-term variations of solar activity
• Double-peaks of the solar cycle: An explanation from a dynamo model
• Sunspot positions, areas, and group tilt angles for 1611-1631 from observations by Christoph Scheiner
• Updated sunspot group number reconstruction for 1749-1996 using the active day fraction method
• Sunspot tilt angles revisited: Dependence on the solar cycle strength
• Christian Horrebow's Sunspot Observations -- II. Construction of a Record of Sunspot Positions
• Sunspot group tilt angle measurements from historical observations
• The effect of telescope aperture, scattered light, and human vision on early measurements of sunspot and group numbers
• Spatial-temporal forecasting the sunspot diagram
• Revisiting Kunitomo's Sunspot Drawings during 1835-1836 in Japan
• Towards an algebraic method of solar cycle prediction II. Reducing the need for detailed input data with ARDoR
• Scale Transfer in 1849 : Heinrich Schwabe to Rudolf Wolf
• Revisiting the Amplitude of Solar Cycle 9: The Case of Sunspot Observations by W.C. Bond
• On the use of naked-eye sunspot observations during the Maunder Minimum
• Detection of Solar Filaments using Suncharts from Kodaikanal Solar Observatory Archive Employing a Clustering Approach
• Sunspot Records by Antonio Colla just after the Dalton Minimum