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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The twin galaxies NGC 4496A and NGC 4496B dominate the frame in this image from the NASA/ESA Hubble Space Telescope. Both galaxies lie in the constellation Virgo, but despite appearing side-by-side in this image they are at vastly different distances from both Earth and one another. NGC 4496A is 47 million light-years from Earth while NGC 4496B is 212 million light-years away. The enormous distances between the two galaxies mean that the two cannot interact, and they only appear to overlap owing to a chance alignment.
Chance galactic alignments such as this provide astronomers with the opportunity to delve into the distribution of dust in these galaxies. Galactic dust adds to the beauty of astronomical images — it can be seen in this image as the dark tendrils threading through both NGC 4496A and NGC 4496B — but it also complicates astronomers’ observations. Dust absorbs starlight, making stars seem dimmer and shifting their light towards longer wavelengths, a process that astronomers refer to as “reddening” (not the same thing as redshift). By carefully measuring how starlight from background galaxies is affected by dust in intervening galaxies, astronomers can map out where the dust is in the foreground galaxy’s spiral arms. The resulting “dust maps” help astronomers calibrate measurements of everything from cosmological distances to the types of stars populating galaxies.