Solar physics is one of the most interesting subjects in the field of astronomy. The Sun is the closest star to Earth, and it is easily observed. It is the only star that we can observe active events, surface variations, and atmosphere with very high temporal, and spatial resolution. All the observed time-dependent phenomena are called solar activity and are seen in different wavelengths as the Sun changes its appearance. Solar physicists have tried to quantify the variation of solar activity with time, beginning with Wolf’s classical formula for the relative number of sunspots. Attempts have been made to develop theories that would help to explain the physical mechanisms underlying these changes in solar activity. The variations observed on the Sun (solar activity) hugely affect the Earth and near-space environment. Thus, solar activity is strongly related to space weather phenomena such as ionosphere, magnetosphere, geomagnetic activity, etc. Therefore, to protect the Earth and near-space environment, solar activity predictions have fundamental importance.

Investigation of temporal and cyclic variations of solar activity will help to better understand its short and long-term behaviors. It will also increase our understanding of solar activity prediction, which is currently one of the most challenging topics of solar physics due to the non-existence of an exact prediction. Some powerful and explosive events observed on the Sun, such as coronal mass ejections and solar flares, can lead to a worldwide disturbance of the geomagnetic field, associated ionospheric, and thermospheric disturbances. Space weather examines the Sun’s physical conditions, parameters, associations, and interactions with the neighboring terrestrial bodies. This subject is particularly discussed between researchers nowadays, thus it is a very popular topic not only for astronomers but also for space weather researchers and geophysicists.

The aim of this Special Issue is to collate original research articles, as well as review articles, highlighting emerging research in these fields. We highly encourage submissions focusing on the beginning of a new solar cycle, the prediction of all kinds of solar, and geomagnetic activities. We hope that this Special Issue will bring new ideas into the existing research topics.

Potential topics include but are not limited to the following:

• Solar activity
• Sunspot groups and their evolution
• Solar flares
• Coronal mass ejections
• Solar wind
• Solar activity indices
• Cyclic variations
• Geomagnetic activity
• Solar and geomagnetic activity relationship
• Solar activity predictions
• Geomagnetic activity predictions
• Solar activity effects on the ionosphere and magnetosphere