The Sun is our nearest star; it is a dynamic star, which changes with time. Solar variations have significant influence on Earth's space environment and climate through the Sun's magnetic field, irradiation and energetic particles. Long-term and reliable historical datasets of solar and stellar activity indices are crucial for understanding the variations and predicting the future solar cycle. IAU Symposium 340 brings together scientists from diverse, interdisciplinary areas to address the latest discoveries from these long-term datasets for the understanding of solar and stellar magnetic cycles. They make comparisons between different datasets and discuss how to make uniform databases. The proceedings of IAU S340 contain a selection of presentations and reviews from internationally renowned experts. They provide an up-to-date account of this field of importance to researchers and advanced students in solar, stellar, space and heliospheric physics.

Powerful solar explosions, such as flares and coronal mass ejections, greatly disturb the electromagnetic environment around the Earth and the atmosphere. They may even impact various social systems-communications, positioning, electric power supply, aviation and activities in space. Such variations in the space environment, which can influence human activities, are called "space weather." The space weather disaster caused by a solar explosion is a potential risk in modern society. To reduce and mitigate space weather impacts, it is essential to understand the structure and dynamics of the solar-terrestrial environment and to predict the variations. This book comprehensively describes space weather, from the basics of related sciences to the possible social impacts. It was compiled based on a national research project on solar-terrestrial environment prediction conducted in Japan recently. It consists of four parts: the linkage between space weather and society; the magnetosphere of the Earth and space weather prediction; solar storms and space weather prediction; and long-term prediction of solar cycle activity and climate impacts. Each chapter covers the basics and applications of each area, which helps readers gain a broad understanding of the subject matter throughout the book. In addition, readers are able to select and read the topics they are most interested in. It is especially valuable for undergraduate and graduate students and young researchers studying space weather and related topics, and is further helpful for experts in various industries related to space weather disasters. The translation was done with the help of artificial intelligence (machine translation by the service DeepL.com). The present version has been revised technically and linguistically by the authors in collaboration with a professional translator.