The other day I stumbled across a question on twitter. “How do astronomers know all of this”, in response to a post showing the scale of the universe and different objects within it. I replied with a simple explanation about how we use large telescopes to observe various objects and simulations to understand the physics, but I thought I would write a longer blog post on this topic. With the South African government investing heavily on some of these large telescopes, it is even more important for people to understand why this undertaking is so important.

There are two main types of astronomers or astrophysicists. On the one side the theoreticians: the ones that mainly work through complicated mathematical equations and creating mind-blowing simulations; but what I am going to talk about here is observational astrophysics, which I focus on, and where South Africa has shown great interest with the development of the Square Kilometer Array and the successful Southern African Large Telescope.

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Image of spiral galaxy M101 in four X-ray, Optical, Ultraviolet and Infrared Light taken using different telescopes

What exactly do we do?

Observational astronomers use telescopes (like MeerKAT, the Southern African Large Telescope, and several others) to study the night sky. These telescopes function as “light buckets” and collect information in the form of optical (visual) or radio light. Most land-based telescopes operate in optical or radio light because the atmosphere prevents any other light from reaching the earth, but space-based telescopes (like the famous Hubble Space Telescope) can detect X-rays, Infrared, and ultraviolet light.

This light can be used in a few different ways. We can take a picture of distant objects like galaxies to study things like their shape, structure, size and position. We can track how the light in an object like a star changes with time – which is how planets around distant stars are often discovered. Or, we can break the light up into a spectrum, which allows us to probe deeper into the chemical makeup of an object. Different types of light reveal different aspects of astronomical objects. While optical light is really good at detecting stars, the faint gas that fuels galaxies is only visible in radio wavelengths and hot, energetic events pop up as X-rays or gamma rays.

Bigger telescopes allow us to observe objects that are fainter and further away. This allows us to see further back in time, to understand the universe at earlier stages of its evolution. The further away an object is (and often the fainter an object is), the longer it takes for light to reach us here on Earth. Therefore, the light we collect with our telescopes essentially lets us look back in time to when the universe was much younger and smaller than it is today.   

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MeerKAT telescope dishes. Credit: SARAO.

Why does this matter?

Aside from being able to detect asteroids that might crash into Earth, astronomy has many benefits. Studying objects in space allows us to work on answers to some of the mysteries of physics. Gravity – something we all interact with on a daily basis (unless you are reading this from the International Space Station) – is something physicists thought we understood since Isaac Newton’s days. Until some astronomers looked at the motions of galaxies and realised that there was something invisible causing these galaxies to move in unexpected ways. This led to the discovery of dark matter – which we are still trying to figure out!

Just two years ago, the groundbreaking observation of a neutron star merger (which our very own SALT contributed to) revealed where heavy elements like gold are originally created. This event, which was detected through gravitational waves and various wavelengths of light simultaneously, was one of the most important discoveries of this decade.

Astronomy teaches us about how the universe works. Although not every discovery will have implications for our everyday life, we have a natural curiosity about the universe we live. Many people experience a sense of appreciation and wonder when they look up at the night sky, especially in the absence of city lights, and wonder what’s out there. Astronomy allows us to explore that curiosity and appreciate our universe.

(At the very least, astronomy gives us a bountiful amount of pretty pictures. You can find a new one every day on the Astronomy Picture of the Day website.)

If you are curious to learn more about how specific fields in astronomy contribute to scientific questions, I have a post on Medium that goes into much more detail! You can also learn more about astronomy through Crash Course: Astronomy and by following NASA on social media.

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