The European Space Agency (ESA) is Europe’s gateway to space. Its mission is to shape the development of Europe’s space capability and ensure that investment in space continues to deliver benefits to the citizens of Europe and the world.
Find out more about space activities in our 23 Member States, and understand how ESA works together with their national agencies, institutions and organisations.
Exploring our Solar System and unlocking the secrets of the Universe
Go to topicProtecting life and infrastructure on Earth and in orbit
Go to topicUsing space to benefit citizens and meet future challenges on Earth
Go to topicMaking space accessible and developing the technologies for the future
Go to topicSOHO's SWAN instrument sees 'Lyman-alpha' emissions, caused by ultraviolet rays interacting with hydrogen atoms, sweeping like a lighthouse beam across interplanetary gas beyond the Sun.
The Sun takes roughly four weeks to turn completely around on its axis, but active regions can appear and grow in only a few days. So until two years ago, no one had any way of telling when an active region might come 'around the corner' - perhaps blazing away with eruptions as soon as it appeared. If an active region can be detected in the middle of the far side it will appear on the eastern (left-hand) side of the visible disk about seven days later.