The Sun provides light and heat, making life on Earth possible. The Sun also determines the spatial environment of the planets, comets and other bodies of the solar system. Many phenomena continuously modify our environment and create visible effects like aurora, shooting stars or sunspots. Other events are less visible, but determining for space missions, our atmosphere and climate. All the interactions between the Sun and the Earth are crucial for our life and the biosphere. This university course aims to summarize the main physical mechanisms active in the space environment of the Earth. It has been written for the master students in physics or in climatology at UCLouvain for the course Physics of upper atmosphere and space, and may also interests the wide public. That is why some parts are more descriptive, to be accessible to any reader who would like to know more about space physics, stars, solar wind, comets, cosmic rays, polar aurora, climate changes, space weather, atmospheric chemistry, etc. Some parts are more specialized and provide the physics equations allowing us to better understand the observations.