We live in a brightly coloured world
even if it doesn't always seem that way
But if you hold a prism up to the whitest of lights
you get a rainbow
For scientists, unweaving this rainbow
tells them about the properties of the Universe
Hubble's ability to study its colours
Is at the heart of many of its most important discoveries
Hubblecast episode 59: Unweaving the rainbow
Presented by Dr J, aka Dr Joe Liske
Hello and welcome to another episode of the Hubblecast
Hubble is famous for its sharp and detailed images of the cosmos
But to scientists, the orbiting observatory has another
equally important function:
decoding the light and probing the colours of the Universe
Hubble’s images see a lot of detail
But if you focus on any spot in the image
the colour information is actually relatively limited
The telescope’s cameras capture the brightness of only a handful of colours
That’s also how our eyes perceive colour
But to see the full story, scientists need to use something a lot like this prism
to split up the light and study the brightness of the individual colours
in the rainbow in more detail
So, let’s say goodbye to Hubble’s pretty pictures...
and hello to...
rainbows?!
Well... almost
Scientists aren’t the most poetic folk, so they call them spectra instead of rainbows
And instead of printing the pretty colours
their scientific reports display their measurements as graphs
But the graphs are simply a way of showing the brightness of the different colours
in the light coming from an object
The subtle differences in brightness and darkness
darkness can reveal a huge range of information
including the chemical composition, temperature, movement
and distance of the object
Hubble has a couple of instruments onboard that do this kind of science
They function a lot like high-tech versions of a prism
except they work even on the faintest galaxies
and can take extremely precise measurements of brightness
It is these measurements lie behind some of Hubble’s most fascinating discoveries
such as the detection of different gases in the atmospheres of exoplanets
As a star’s light passes through an exoplanet’s atmosphere
the chemical signature of the atmosphere is imprinted on the light
as dark lines in its spectrum
These lines tell scientists precisely what gases
are present in the planet’s atmosphere
Another great example is Hubble’s work on very distant galaxies
which only appear as tiny blobs in images
So here we have a Hubble image
and it contains a range of objects of different brightnesses
and ultimately different distances
But if we just focus on this image here
the galaxy in the centre
you can see how we add the spectroscopic information
Now this direct colour image, but what we do is
to disperse the light of all those objects in the field into spectra
which you can see in white here
And so for this object here, we see the spectrum spread out on one side
and from the distribution of light in that spectrum
we can learn a lot about this galaxy
A distant galaxy’s spectrum reveals which elements it is made of
Every substance affects or emits light in a particular way
imprinting a series of bright or dark lines in the spectrum that betrays its presence
And by looking at the way these lines are shifted towards red or blue in the spectrum
Hubble sees whether they are moving towards or away from us
In the case of really faraway objects
the redshift also tells us how distant the galaxy is
Spectra aren’t as immediate and attractive as pictures
but they are an absolutely vital tool for astronomers
to reveal the hidden properties of the Universe
facts you just cannot discover even in the sharpest of images
This is Dr J signing off for the Hubblecast
Once again, nature has surprised us beyond our wildest imagination
Hubblecast is produced by ESA/Hubble at the European Southern Observatory in Germany
The Hubble mission is a project of international cooperation between NASA and the European Space Agency
www.spacetelescope.org
Transcribed by ESA/Hubble. Translation: --