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We live in a brightly coloured world

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even if it doesn't always seem that way

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But if you hold a prism up to the whitest of lights

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you get a rainbow

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For scientists, unweaving this rainbow

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tells them about the properties of the Universe

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Hubble's ability to study its colours

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Is at the heart of many of its most important discoveries

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Hubblecast episode 59: Unweaving the rainbow

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Presented by Dr J, aka Dr Joe Liske

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Hello and welcome to another episode of the Hubblecast

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Hubble is famous for its sharp and detailed images of the cosmos

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But to scientists, the orbiting observatory has another

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equally important function:

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decoding the light and probing the colours of the Universe

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Hubble’s images see a lot of detail

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But if you focus on any spot in the image

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the colour information is actually relatively limited

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The telescope’s cameras capture the brightness of only a handful of colours

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That’s also how our eyes perceive colour

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But to see the full story, scientists need to use something a lot like this prism

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to split up the light and study the brightness of the individual colours

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in the rainbow in more detail

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So, let’s say goodbye to Hubble’s pretty pictures...

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and hello to...

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rainbows?!

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Well... almost

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Scientists aren’t the most poetic folk, so they call them spectra instead of rainbows

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And instead of printing the pretty colours

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their scientific reports display their measurements as graphs

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But the graphs are simply a way of showing the brightness of the different colours 

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in the light coming from an object

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The subtle differences in brightness and darkness 

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darkness can reveal a huge range of information

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including the chemical composition, temperature, movement 

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and distance of the object

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Hubble has a couple of instruments onboard that do this kind of science

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They function a lot like high-tech versions of a prism 

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except they work even on the faintest galaxies

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and can take extremely precise measurements of brightness

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It is these measurements lie behind some of Hubble’s most fascinating discoveries

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such as the detection of different gases in the atmospheres of exoplanets

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As a star’s light passes through an exoplanet’s atmosphere

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the chemical signature of the atmosphere is imprinted on the light 

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as dark lines in its spectrum

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These lines tell scientists precisely what gases 

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are present in the planet’s atmosphere

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Another great example is Hubble’s work on very distant galaxies 

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which only appear as tiny blobs in images

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So here we have a Hubble image

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and it contains a range of objects of different brightnesses 

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and ultimately different distances

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But if we just focus on this image here

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the galaxy in the centre

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you can see how we add the spectroscopic information

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Now this direct colour image, but what we do is 

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to disperse the light of all those objects in the field into spectra

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which you can see in white here

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And so for this object here, we see the spectrum spread out on one side

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and from the distribution of light in that spectrum 

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we can learn a lot about this galaxy

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A distant galaxy’s spectrum reveals which elements it is made of

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Every substance affects or emits light in a particular way

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imprinting a series of bright or dark lines in the spectrum that betrays its presence

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And by looking at the way these lines are shifted towards red or blue in the spectrum

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Hubble sees whether they are moving towards or away from us

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In the case of really faraway objects

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the redshift also tells us how distant the galaxy is

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Spectra aren’t as immediate and attractive as pictures

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but they are an absolutely vital tool for astronomers

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to reveal the hidden properties of the Universe

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facts you just cannot discover even in the sharpest of images

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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

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www.spacetelescope.org

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Transcribed by ESA/Hubble. Translation: --