麻豆传媒

EARTH鈥檚 atmosphere is pretty wonderful. As well as being a scientific curiosity, it is also the reason that life on our planet thrives in the way that it does. I am thankful for this, but as someone who studies the sky, the atmosphere also presents me with a problem: it blocks out some of the light frequencies that I want to use to study the incredible objects that populate the universe. It can also distort the light that isn鈥檛 blocked, creating disadvantages for doing astronomy using telescopes based on Earth.

That is why the atmosphere is the primary reason we send telescopes into space. You might think we do it to get closer to the action in space, but largely it is just to get further from the action in the atmosphere. Because of a unique (to our solar system anyway) mix of nitrogen, oxygen and notable smidgens of other gases, the atmosphere both allows us to breathe and absorbs particles of light called photons.

Millennials like me are probably most familiar with this phenomenon from discussions during a significant part of our childhood about a hole in the ozone layer of the atmosphere, which specifically blocks out some frequencies of ultraviolet (UV) radiation. The term UV radiation is just another way of talking about light that is in the UV part of the spectrum. The human eye isn鈥檛 sensitive to UV light, so it is invisible to us. In fact, our eyes are actually only sensitive to a limited part of the electromagnetic spectrum, what is called the
visible or optical part.

The difference between visible light and other parts of the spectrum is energy levels. Visible light frequencies, which we experience as the different colours in a rainbow, are associated with energies. Blue, the colour closest to the UV part of the spectrum, is more energetic than red. UV light and everything more energetic than it is mostly blocked by the atmosphere. We care about this missing light because some of the most interesting information about astrophysical phenomena like black holes, neutron stars and even the Milky Way comes at these energetic frequencies.

We first realised this when we launched X-ray detectors into space, which spotted light that turned out to be from far away sources. Since then, we have launched a great many telescopes that do observations in the high energy 鈥� X-ray and gamma ray 鈥� regime. The two best known in the US are the NASA Chandra X-ray Observatory and the NASA Fermi Gamma-ray Space Telescope.

鈥淚mages from Hubble, which is a UV and optical telescope, have become ubiquitous in pop culture鈥�

Over the past two decades, both instruments have helped to revolutionise our understanding of the universe, including our own galaxy. My friend Tracy Slatyer, a dark matter expert at the Massachusetts Institute of Technology, made headlines as a PhD student by using Fermi to co-discover a gamma-ray source at the centre of the Milky Way, now known as the Fermi Bubbles. We still don鈥檛 know what they are.

High-energy astrophysics isn鈥檛 the only area that has benefited from space-based instruments. As regular readers know, I am a big Star Trek fan, and one of my favourite things about rewatching old episodes of The Next Generation and Voyager is seeing the impact of the Hubble Space Telescope on set design. Look closely and you will notice that brilliant images of space phenomena started to appear in the background as time goes on.

Images from Hubble, which is a UV and optical telescope, have become ubiquitous in pop culture. I have always thought that Hubble changed the world immeasurably and I am glad that the late NASA scientist Nancy Grace Roman led the charge to get it built, earning her the name Mother of Hubble.

Of course, we can see visible light from the ground, but that doesn鈥檛 mean that sending Hubble into space was a mistake. This is partly because, as described above, Hubble is a UV instrument and much UV light is blocked by the atmosphere. But even in the visible, the atmosphere鈥檚 distortions to light mean that the pictures we get from Hubble are much crisper.

On top of that, we now have to contend with commercial phenomena blighting the sky: the ubiquity of SpaceX鈥檚 Starlink internet satellites makes looking at the universe from the ground increasingly difficult. One of the main barriers between Hubble and what we want to see is our technological prowess.

On the other hand, famously, when Hubble was first launched, it had a serious problem that made the images it sent back quite low quality. It had to be repaired by astronauts in what was a risky mission. Updating it is also difficult because it is in space. A ground-based telescope, like the Vera C. Rubin Observatory that is under construction in the Chilean Atacama desert, can be updated continuously. After all, it is easier to get things to the Atacama than into low Earth orbit.