There is a reason why even the most ancient humans were amateur astronomers, mapping the orbit of the moon and the movements of the stars. There’s a reason too that kids are as fascinated by space as they are by dinosaurs, thinking about the Big Bang, distant galaxies, and stars and planets.

There’s a reason too why many religions from history have often identified the ‘celestial sphere’ with the gods, the heavens, and the angels.

Maybe there are two reasons.

Firstly, space – that area above and all around us that astronomers, astrophysicists, and cosmologists are so interested in – is a place so alien (excuse the pun), so completely different and unknown, that it is a source of fascination. We don’t really know what’s there – and the accretion of our knowledge has been very slow.

And secondly, it is a place of total wonder. Every night of our lives we are surrounded by the sight of this place, a place so incredibly beautiful and so completely massive that it is no surprise that it was associated with the gods. Looking up at the sky – and thinking of our place in the galaxy – is a humbling experience.

Here, we are going to dive into space and uncover the answers to some of the most common questions about the world outside our world, the place outside our Earth’s atmosphere.

Starting from a technical question – what is the difference between the astronomical, the astrophysical, and the cosmological? – we’ll end with perhaps the biggest question of all: is there life outside of our world?

Let’s get cracking.

a distant galaxy
Some images of space are just jaw-dropping.

Astronomy, Astrophysics, and Cosmology: What’s are these Different Disciplines?

Yes, we know. It’s not, on the surface, the most interesting question about space. However, it draws out some important – and actually quite fascinating – problems that space scientists have to deal with.

Because not everyone who studies space does the same thing – and nor do they ask the same questions. Just as a scientist who studies life might ask different questions – how many species of plant are there? how do cells work? what is the meaning of life? – these same differences between questions occur in questions of space too.

So, you tell us which sort of space scientist you would like to be: an astronomer, an astrophysicist, or a cosmologist?

You can find out more on this subject, by the way, in our article on the differences between astronomy, astrophysics, and cosmology!


Astronomy, broadly speaking, is the study of the things in the universe – celestial bodies, asteroids and comets, constellations, and the stuff between them – and their positions and their movements.

Astronomers use fairly traditional observational techniques – including highly sophisticated telescopes - to describe what they see and to calculate the interactions between orbits and objects.

We have been practising astronomy for millennia – in all different civilisations and parts of the world – and the recent history of the discipline has been concerned with discovering new objects, galaxies, and background radiation.


If astronomy is the larger, umbrella term, astrophysics makes up part of this discipline. Where we might say that astronomy is mainly descriptive, astrophysics seeks to explain the processes and mechanics of the universe.

This means applying our knowledge of physics to the phenomena in space – using theories of thermodynamics, nuclear fusion, quantum mechanics, and particle physics.

Some say that all astronomy these days – given its complexity – is essentially astrophysics, as attention has turned from describing the universe to explaining it.

Dark matter, dark energy, and black hole theory are all problematics with which astrophysicists work.


Finally, cosmology asks the big questions. This discipline grew out of the ancient practice of explaining the origin, development, and structure of the universe as a whole.

Is the universe expanding and why? Did the Big Bang start the universe, and if so, why did it happen?

Cosmology deals with the big theoretical questions that the others sort of leave aside. However, cosmologists rely on the data drawn from the other subjects.

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planetary nebula - astronomy
Nebulae are some of the most beautiful things in the universe.

Major Milestones in Astronomy and Astrophysics.

As we know, the progress of astronomy and astrophysics has been slow. However, in recent centuries, it has sped up dramatically.

Here we’re going to look at the biggest discoveries in astronomy – from the present up until now. However, we’re talking the very biggest right now, for reasons of space. If you want to read more about this, check out our article on the developments of astronomy.

Galileo Proves Heliocentrism – 1610.

Up until the sixteenth century, people were really quite convinced that the Sun and the rest of the universe were orbiting the Earth.

And whilst Copernicus theorised that the Earth in fact orbits the sun in the 1540s, Galileo proved it at the beginning of the seventeenth century. This literally changed science forever.

Isaac Newton Cracks Gravity – 1687.

Without Newton, we’d understand nothing. Because, the cute little story about the apple landing on his head besides, his understanding of gravity made everything else possible.

Joseph van Fraunhofer – 1814.

A little-known bloke outside of science, Joseph van Fraunhofer made astrophysics a discipline that matters – with his invention of spectroscopy.

Einstein Changes the World with his Theory of General Relativity – 1905.

We all know now that e equals mc². Yet, we didn’t before Einstein. All that stuff with atomic theory we do these days? That’s Einstein.

The First Person on the Moon – 1969.

Not really a development in the science, but, you know, a huge leap for mankind and all that. Neil Armstrong and NASA made everyone interested in space.

What’s in the Solar System?

The Solar System is everything that orbits the Sun – everything that is in that star’s gravitational field. Of course, our solar system is one of billions in the Milky Way galaxy. And, considering that there are potentially billions of galaxies, the number of solar systems in the universe is eye-watering.

Here’s what is in our solar system – and you can find more in our article on The Solar System.

The Sun.

At the centre of it all sits the Sun. Say what you like – it blazes, boils, or burns – but really it does none of these things. It turns hydrogen into helium and converts mass to energy – but, sure, it is as hot as hell.

The Planets.

You know these: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. We don’t talk about Pluto anymore.

Planets need to clear their neighbourhood – meaning they have to be big enough to have destroyed all in their orbit.

Other Celestial Objects.

Dwarf planets (that’s where Pluto comes in), asteroids, comets, and all sorts of other bits and bobs. They are all held together by the Sun’s gravity.

And Beyond our Solar System?

After Neptune and the Kuiper Belt, you have the interstellar medium – the space between stars. What happens there? We’re not quite sure just yet.

The Life Cycle of a Star.

Stars form, release huge amounts of energy for billions of years and then, when their hydrogen has burned up, they and disappear – or else, explode into supernovae or become black holes.

In short, that’s that, but let’s have a look at the main stages in greater detail. If you want more detail, check out our article on the lifecycle of stars.

Nebulae and Protostars.

Star formation begins from the debris of previous stars – the gas and dust left over from past astrophysical phenomena.

These clouds we call nebulae. A nebula will float around in space, under conditions of great cold. As they become colder, their gases become denser, and their gravitational strength grows.

Slowly, they pull in all this dust into the nebula core, which slowly becomes warmer with the pressure. As they grow, they become protostars.

the sun
The sun is the centre of our solar system

Main Sequence Stars.

Stars remain protostars when they are still growing and become main sequence stars when they reach stability.

Stars will remain main sequence stars for ninety percent of their life.

Dwarfs and Supernovae.

Toward the end of their life, stars run out of fuel. Without this energy, they cannot sustain their shape.

The smaller stars become white dwarfs – dense stars that cool down from the outside. They tend to fade away.

The bigger ones, as the result of various chemical reactions, collapse in seconds – causing a supernova that is brighter than a galaxy.

Black Holes.

The very biggest stars become black holes as the result of collapsing in one themselves. Hugely dense, their gravity is massive – meaning they pull everything in that is around them.

Is there Alien Life in the Universe?

With all this action, there’s quite an interesting question. Surely, we can’t be the only consciousnesses in the universe to have the honour of appreciating all this drama?

Maybe we are, maybe we’re not. But it would be very unlikely if, in the universe’s infiniteness, there were only us that could be called ‘life’.

Find out more about this in our article on alien life.


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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.