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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Similar to how geophysicists learn more about Earth’s interior by studying waves created by earthquakes, astronomers study the waves of the Sun and other stars. The speed of sound through a medium carries information about that medium and also about the object in which the sound bounces around.
Sound waves are pressure waves, and their speed is influenced by the temperature and density of the gas through which they propagate. You may have experienced this yourself: when taking a breath of helium from a balloon, your voice produces a funny high-pitched version of itself as the sound waves travel through a lighter gas in your lungs.
The brightness variations of stars inform scientists about their internal workings. And by linking this information to computer models mimicking stars, scientists can deduce general properties like their mass, radius and age.