English subtitles for clip: File:Hubblecast 10 – Making the Universe come to life - behind the Hubble images (astronomical image processing explained).webm

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We live in a Universe of unimaginable scale and almost incomprehensible beauty.

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How is the light from stars, galaxies and nebulae fashioned into the spectacular images that have so inspired us over the years?

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This is the Hubblecast!

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News and Images from the NASA/ESA Hubble Space Telescope. Travelling through time and space with our host Doctor J a.k.a. Dr Joe Liske.

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Welcome to the Hubblecast!

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Do you ever look at these beautiful Hubble images and wonder how they were made?

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What exactly happens after the faint light from distant objects is detected by Hubble? 

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How are these cosmic photons captured in space transformed into the glorious colour images down here on your wall or on computer screen?

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On a clear night when we look up into the heavens we can see the light from thousands of stars.

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Our eyes are fantastic detectors but in reality are actually very limited.

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They aren’t sensitive enough to peer out very far into space.

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Also we can only see visible light, but not ultraviolet or infrared light like Hubble can.

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That’s why for professional astronomers the Hubble Space Telescope is such an exciting tool to probe the Universe

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Sitting at its vantage point 600 km above the Earth, Hubble is a window on the Universe.

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The journey to make a Hubble image begins when light from a distant object starts on its way towards us. 

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After travelling across the vast distances of space it is captured by Hubble with its 2.4 metre wide mirror.

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The light is then sent to one of Hubble’s several cameras where the photons are turned into an electrical charge by a CCD chip rather similar to the ones in digital cameras.

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The Advanced Camera for Surveys, for example, contains over 16 million picture elements or ‘pixels’.

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These act as miniature ‘buckets’ to collect the light.

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The camera then reads out how much light has been captured in each bucket (the charge within each of the pixels) and outputs an image.

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This readout is then beamed back to the Earth as a series of encoded numbers that are stored in archives in the US and Europe.

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Hubble’s cameras image the Universe through different filters – like this one. 

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These select specific wavelengths of light that are characteristic of different physical processes which may be going on in different parts of distant galaxies and nebulae.

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Each of the filters results in a single greyscale image which is then assigned a colour.

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This colour is usually chosen to more or less correspond to the actual colour of the filter, although this is not always true.

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Anywhere between two and six of these images are then combined to create the final colour image.

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Take this view of the colliding Antennae Galaxies.

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Hubble imaged this colliding pair through red, green and blue filters to reveal the different components inside the galaxies.

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For example the red light is coming from old stars and glowing hydrogen gas, while the blue light is showing the violent star formation triggered by the cosmic collision.

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The red, green and blue images are then combined to create the final multi-colour image.

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One of the challenges in making images is that there is a huge range of brightness in nature from faint to bright objects

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and astronomical images are so rich in information that our eyes and computer screens cannot show their full content. 

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Nature can be difficult to capture in a single photograph and most of us have encountered situations like the following. 

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Imagine you try to take a picture of a landscape.

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When you do so you can either capture the bright parts of the sky or the darker parts of the vegetation, but rarely both together. 

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The job of the image processing specialists is to compress this range of brightnesses together so that we can see all the nuances

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Image experts use the program FITS Liberator, pioneered by ESA, ESO and NASA to produce a magnificent rich image which can be interpreted by our eyes.

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But is this what we would see with our eyes if we could look through Hubble? Well not really.

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Look at this image of the Cigar Galaxy. This is what Hubble sees in visible light. 

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Our eyes aren’t actually sensitive enough to be able to detect the faint light from this distant object even when looking through a telescope.

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The reason why Hubble’s instruments can do it is because they can gather and add up the light over an extended period of time - which is something our eyes can’t do.

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Furthermore some telescopes can ‘see’ wavelengths that we can’t see with our eyes.

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This multi-wavelength view shows us much more than our eyes, or any one telescope, can see.

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Parts of the image were made with the Chandra X-ray Observatory in X-rays and part with the Spitzer Space Telescope in infrared light.

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In this episode we have seen how the images that have amazed and intrigued us are created.

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You too can have a go at making your own images, just Google for ‘FITS Liberator’.

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This is Dr J signing off for the Hubblecast.

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Once again nature has surprised us beyond our wildest imagination .

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Hubblecast is produced by ESA/Hubble at the European Southern Observatory in Germany.

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The Hubble mission is a project of international cooperation between NASA and the European Space Agency.