Space – with its solar systems, galaxies, stars, and planets – is something breathtaking in its vastness and its complexity. With so much there to be known – and with such a sense among us that we know so little – the fascination is totally understandable.

What is a black hole? What exactly caused the Big Bang? How exactly do gravitational forces work? Will galactic travel ever be possible? All of these questions that you ask yourself as a kid don’t actually become much clearer as you get older. Indeed, the greatest minds in science – astronomers and physics experts – wouldn’t necessarily have an answer for you either.

That’s because, really, we’re fairly new to the game of investigating the universe. Sure, we think we have some pretty good telescopes, we know a bit about star formation, and we’ve just observed gravitational waves. But, anyone who knows anything about this stuff will tell you we are only just scratching the surface. There’s a lot more to know.

And this is why the space industry is so busy – and why there are more jobs in space studies and research than you might have realised.

Here, we’re going to take a look at three of the main disciplines in the study of space: cosmology, astronomy, and astrophysics. Because, whilst the three roles overlap and take inspiration from each other, they are actually slightly different. And any space enthusiast should know what the differences are.

Let’s take a look.

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milky way from earth
Get out of the city and it is easy to see the Milky Way

What are the Main Differences Between Cosmology, Astronomy, and Astrophysics?

The three major disciplines that involve the study of space are astronomy, astrophysics, and cosmology. And, as we said, whilst they are profoundly symbiotic – in the sense that a cosmologist couldn’t do her job without the data provided by an astrophysicist – the differences between the three disciplines are important.

Imagine a philosopher. Maybe he primarily writes political theory. However, to come to his theories, he has to observe the world around him – what’s going on where and by whom – and he has to look at the hidden mechanics behind these political trends. What is the effect of economics on these politics? Or of climate change? Or of religion?

A similar analysis can be made of the study of space.

Cosmologists study the origins and development of the universe – from the Big Bang to the universe’s eternal expansion.

However, they get much of their data from the astronomists. Astronomists use observational techniques to identify, categorise, and describe celestial bodies – stars and planetary objects.

And they will also get their data from astrophysicists too. If astronomy is based on the study of space in general, astrophysics seeks to explain the processes that make the universe as it is. Astrophysics is pretty much a subcategory of astronomy – yet, where astronomers might look at the chemical character of a planet, astrophysicists will look exclusively at the physics of space.

Just like the analogous political philosopher, someone studying space does not limit themselves to one of these three disciplines. Rather, cosmology, astrophysics, and astronomy are what people do, rather than being something that they are as such.

Now let’s take each of these disciplines one at a time.

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What is Astronomy?

Let’s start with astronomy. This is probably the broadest of the disciplines, as in many ways it is the umbrella term that includes the others. Astrophysics is fundamentally astronomical, whilst cosmology combines astronomical knowledge of our solar system, our galaxy, and our universe with philosophy.

We’ve Been Doing Astronomy Since Humans Began.

Astronomy is ancient; there is evidence that it has been practised for as long as humans have been alive. Because you don’t need a massive space telescope to be an astronomer. Nor do you need one to observe the Milky Way, celestial objects like comets and asteroids, and planetary systems and their orbits.

Because these are the things that are the object of an astronomer’s study. And the methodology of observation is still the method that astronomers use – just in a much more sophisticated way.

The Ancient Greeks were excellent at astronomy. Aristarchus of Samos, back in the third century BC, for example, had already worked out that the Earth travels around the Sun – something that scientists didn’t confirm until the seventeenth century. Meanwhile, Eratosthenes used shadows to measure the size of the Earth – something he did with incredible accuracy.

And whilst we all know about the Greeks, the oldest calendar we know has been found in Aberdeenshire, Scotland. Known as the Warren Field calendar, it is made of twelve pits that correlate to the phases of the moon. It’s thought to be ten thousand years old.

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calendar astronomy
This banal thing is based on astronomy.

Astronomy Today.

In this sense, any investigation into the planets and universe – including stargazing and any studies that are ground-based – counts as astronomy.

These days, we just have better instruments with which to conduct such investigations. We are continuing to discover new planets, stars, and even galaxies, whilst the Voyager 1 became, in 2013, the first shuttle to pass Neptune and journey off into the interstellar medium beyond our solar system.

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What is Astrophysics?

We’ve seen that astronomy is the broadest discipline when it comes to studies of space. Astrophysics is a subdiscipline of astronomy, essentially, which combines – you’ve guessed it – physics and astronomy.

If astronomy maps the positions and movements of astronomical objects, astrophysics uses the laws of physics to describe and to explain their nature.

Using Physics to Understand Space.

You know what physics is and what the major concerns are of that subject: thermodynamics, atomic and molecular physics, relativity, quantum physics, nuclear behaviour – and a whole lot more.

Sure, these are all things that are relevant to the Earth and that were developed through study and knowledge of the nature of the Earth and its physical properties. But space offers a larger arena in which to study them – as well as a whole lot of other things besides.

By looking at black holes, we push further our knowledge of gravity. By looking at dark matter and dark energy, we need to apply our knowledge of subatomic particles and particle physics.

But there is so much that we don’t understand about space that astrophysics is often highly theoretical. Dark matter in itself, will quite famous as a phenomenon, is entirely speculative: we have not actually found any evidence that it exists at all.

When Did Astrophysics Kick Off?

Whilst astronomy has been around since the beginning of human civilisation, this is not quite true of astrophysics.

Because this discipline only actually was named as such in the mid-nineteenth century, when Joseph von Fraunhofer began to use spectroscopy – the study of spectra – to draw conclusions about the material nature of stars.

Since then, the study of the astrophysical came increasingly distinct from astronomy, with the majority of new discoveries about space occurring in astrophysics.

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And Cosmology?

So, where does that leave cosmology? If astronomy focuses on describing the positions and movements of space, and astrophysics on explaining its nature, what can be properly described as the cosmological?

NASA describes cosmology as the study of the ‘large scale properties of the universe as a whole’ – as opposed to astronomy that looks specifically at the objects in space specifically.

However, this definition does not really give a full sense of everything that cosmology is and has been. Because cosmology has often overlapped with and been propelled by speculations in philosophy and metaphysics too – about the nature of the universe and its origins.

a galaxy - astronomy, astrophysics, cosmology
The Milky Way!

Cosmology through the Ages.

The earliest philosophers, religions, and thinkers all proposed their own image of the universe – their own cosmology.

Take that which is known as the Hindu cosmology, which was proposed in the second millennium BC. It was believed here that the universe was infinite and cyclical, and that each world or cosmos would last eight billion years.

Meanwhile, the cosmology of Ptolemy, the Greek thinker, described a universe with the Earth at the middle.

Science and Physical Cosmology.

Yet, with the scientific epistemology that developed in the west over the last five hundred years, the metaphysical nature of cosmology has decreased.

Cosmology these days is more concerned with testing hypotheses regarding the origin, development, and future of the universe. Fairly predictably, one of its major concerns is the Big Bang – as well as the expansion of the universe and the nature of the early universe.

Given that, these days, cosmology is a science, it takes its data from astronomy and from astrophysics – as it needs observed material upon which to base its hypotheses.

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A student by trade, Daniel spends most of his time working on that essay that's due in a couple of days' time. When he's not working, he can be found working on his salsa steps, or in bed.