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
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Whole -sky map (ecliptic coordinates) of Lyman-alpha emission observed by Soho's SWAN instrument. Two areas were not covered for safety reasons, around the Sun (at left) and around the anti-solar direction (at right). The colour codes the intensity, in counts per second per pixel (one square degree). A number of UV hot stars can be identified, tracing the galactic plane. The rest of the ubiquitous emission is due to solar UV Lyman-alpha photons, backscattered by hydrogen atoms in the solar system. These H atoms came from interstellar space, and are approaching the Sun down to about 2 AU, in the direction of the incoming flow. A maximum of Lyman-alpha intensity surrounds this upwind direction. In the opposite direction, the emission is weaker by a factor of 3.5, because most atoms have been destroyed by charge-exchange with solar wind protons, creating a cavity void of hydrogen atoms in the downwind direction. A detailed comparison of such Lyman-alpha maps will allow determination of the solar wind mass flux at all ecliptic latitudes. [Image Date: 19-11-96] [96.11.003-002]