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How do we know how many galaxies are in our universe?

According to the best estimates of astronomers there are at least one hundred billion galaxies in the observable universe. They’ve counted the galaxies in a particular region, and multiplied this up to estimate the number for the whole universe.

Astronomers get to travel to some of the most remote places on Earth to use huge optical telescopes far away from light pollution in order to make observations. Optical telescopes have been used for astronomical observation since the time of Galileo, but the technology has moved on significantly since then.

Twinkle twinkle

Twinkling stars may be pretty and romantic, but this distortion of the starlight by changes in temperature and wind speed as it travels through the atmosphere has been the bane of astronomers’ lives. Fortunately, adaptive optics can now compensate for the twinkles. By shining a laser in to the night sky, the path the star light takes to reach the telescope can be found more accurately. And a rapidly tilting mirror to adjust the light coming into the telescope makes the image much clearer.

Telescopes in space

A simpler way to overcome the atmospheric distortions is to put your telescope above the atmosphere. The Hubble Space Telescope orbits 600 km above the Earth and has been sending back the most amazing images of our universe since 1993.

In 2013, NASA, the European Space Agency and the Canadian Space Agency are due to launch the James Webb Space Telescope (JWST) to replace Hubble. The JWST will look at how the universe began and how galaxies are formed, but in order to do this it won’t use visible light to produce images. Unlike Hubble it will use infrared light.

By being sensitive to infrared light, the JWST will be able to detect objects hidden behind dust clouds and galaxies that are moving away from us at such speeds that their light has been red-shifted out of the visible region of the electromagnetic spectrum.

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