Star Wars, the very name brings up images of childhoods spent in front of a TV or cinema screen, absorbing up stories of a galaxy far, far away. For many, it was the thing to ignite their passion for storytelling, and for others it was the thing that ignited their love of space and science.

We at the Armagh Observatory and Planetarium do not like spoilers, and so we will not be talking about Star Wars Episode VIII: The Last Jedi, to respect the people who have not yet been able to see the film. Instead we will be looking at the previous films, and certain scientific Sci-Fi things that intrigued us.


On a personal level, I started watching Star Wars when I was a mere girl of 10. Naturally it was Christmas time and the films were being shown on terrestrial TV.  My father urged me to sit down and watch them. Initially I was wary, at this point I liked the topic of space, but I had never really watched a sci-fi film. I grabbed a snack, settled in and was immediately hooked. The spaceships, the heroes, the Jedi, the Sith, the different planets, the Death Star, the music, all of it was just what I needed to kick off my now 17 year love affair with the franchise. It was only when I started working at AOP that I started to think more about the science behind the story. How could these things be possible? Yes I know it is all science fiction, a fantasy dreamt up by George Lucas, but still I started to analyse (much to the despair of my equally as fanatical, and partial to the dark side, husband).

Regarding the franchise, PhD Student Lauren Doyle said:

Star wars has played a massive role in my interests in Astronomy. I first saw A New Hope when I was around five years old and let’s just say that VHS tape was very well used! I am definitely more Jedi than Sith but my favourite characters are Han Solo and Chewbacca. I love the strong female heroines who are in the new movies, however, the original trilogy will always be my favourite!

Resident Astronomer at the Armagh Observatory and Planetarium, Tolis Christou said:

I consider myself fortunate to have been a teenager when the first trilogy came out. Enough said! [Did or has Star Wars inspired your interest in space?] It certainly didn’t harm it. It taught me that all spacecraft are white and baddies wear black. [Are you more Sith or Jedi?] Have been tempted by the dark side, but never veered too far from the light.

Resident Astronomer Simon Jeffery (no not the Simon Jeffery that was president of LucasArts):

I saw the first Star Wars movie when it came out in 1977 at the Dominion Theatre on Tottenham Court Road in London. I went with a group of friends from Imperial College.  The sound effects were brilliant —surround sound for the first time ever in a cinema. This was awesome when you had star fighters coming from behind and past you, and the giant subwoofers made the whole cinema shake. You instinctively had to duck. I still haven’t seen all of the subsequent films … and only one other in a cinema. You need the big screen and surround sound (loud) for them to work properly. Obi-Wan Kenobi was epic, but I liked the Wookie best. By 1977 I’d watched too much Star Trek to think that Star Wars had anything to do with space!  The Apollo programme was my childhood.  I’ve always been amused that a “Simon Jeffery” was the president of LucasArts who steered the spinoff Star Wars games to market.

Education Support Officer Nick Parke, stated:

[Why do you love Star Wars?] The hum of lightsabres (I recall a particularly ‘believable’ sound to Obi-Wan’s sabre when battling Jango Fett on a rain-drenched lander platform on Kamino… in the cinema – it gave a little shiver down the spine!) oh and if I’m allowed a 2nd: ‘seismic charges’!? [Did or has Star Wars inspired your interest in space?] Not that much to be honest – that said however, after first seeing a star cruiser move at ‘light speed’ – the image evermore pops into my head whenever referring to the speed of light and light years etc! (Also I think it should be mandatory for anyone learning about an asteroid belt to watch the chase through the asteroid belt in episode II between Jango Fett and Obi-Wan-Kenobi – very cool…) [Are you more Sith or Jedi?] Ummm well while I once battled a Sith Lord briefly during an Emerald Garrison event at the planetarium some years ago. My favourite colour was always red.. and I’ve always kind of fancied a bit of Sith Force lightning?… so I’ve a feeling I’m slipping towards the darkside…

So let’s look at a fraction of the science behind Star Wars. Many books have been written on this topic such as “The Physics of Star Wars,” by Patrick Johnson, “The Science of Star Wars,” by Mark Brake and Jon Chase, and “The Science of Star Wars,” by Jeanne Cavelos, a former NASA astrophysicist! As we come up to Christmas these would make great gifts for those fans who want to know even more about the science behind it all. You can even read a previous article from our archives called “The Star Wars Galaxy!”

I’m going to start with the Death Star. When you think of Star Wars, one of the many images that springs to mind is that of the HUGE space station. Upon seeing it for the first time, Luke Skywalker, Han Solo and Chewbacca mistake it for a moon, but Obi-Wan Kenobi is able to see it for what it really is. So how big is it? Sources state that the Death Star is around 140 to 160 kilometres across. It is larger than the International Space Station, which is about the length of a football field, but not as large as our own Moon, which is 3,500 kilometres across.

“That’s no Moon, it’s a space station” – Obi Wan Kenobi. Image of Saturn’s moon Mimas, which does look an awful lot like the Death Star (Credit: NASA)


Saturn has a moon called Mimas, and if you look at a picture of it, it looks suspiciously like the Death Star, however it is 396 kilometres across and so bigger than the original. Death Star II however is said to be around 900 kilometres across and so is more than twice as large as Mimas.

The smallest moon in our Solar System is a moon of Mars, Deimos. It is only 12 kilometres across and so much smaller than the Death Star. In fact you could fit Deimos 13 times, side-by-side, inside the Death Star and still have room to spare!

If you were to size up the Death Star to any moon in our solar system the closest to it in size is the moon of Uranus known as Puck. At 162 kilometres across, Puck is just slightly larger than the Death Star.

Are we really sure that’s not the Death Star? (Credit: NASA)


The Death Star is famed for having a huge laser that can destroy entire planets. In fact that is one of the first things it actually does in the first film Star Wars Episode IV: A New Hope. The planet Alderaan comes under fire and is completely destroyed by the laser. Alderaan is roughly 12,500 kilometres across and is said to have an orbital period of 364 days around its star. It is an inhabited planet with roughly 2 billion human-like lifeforms. In comparison the Earth is 12,742 kilometres across and has an orbital period of 365 days with around 7 billion humans in its population.

With such similarities being drawn up between Alderaan and Earth, how much power then would the Death Star need to destroy the planet. Brilliantly, three men from the Department of Physics and Astronomy, University of Leicester compiled a short paper on this very topic. Their full treatise can be read online and is hilariously called “That’s No Moon”. They state:

“This planet is going to be modelled after Earth with the exception that it is a solid planet. It is then possible to use the gravitational binding energy of the target planet to estimate the amount of energy required to be supplied to the Death Star’s laser beam in order to destroy it. For a spherical mass with uniform energy density, the gravitational binding energy U is given by: ? = 3???2/ 5?? where Mp is the mass of the planet (Earth equals to 6 x 1024 kilograms) and Rp is the radius of the planet (Earth’s radius is equal to 6 x 106 metres).  The energy required to destroy the planet in question is then 2.25 ⨉ 1032J. However, the destruction of large planets such as Jupiter require even more prodigious energy demands. We can estimate the energy to be 2 ⨉ 1036J to destroy Jupiter.”

We can now work out how many bombs are required to blow up an entire planet (and I’m not saying we should try this!). Simon Jeffery, the astronomer, was able to help out with the mathematics here. The energy delivered (E) = the total energy per bomb (b) times the number of bombs (n), i.e.

E = n x b

To get the number of bombs you need to divide the total energy by the of energy per bomb:

n = E / b

A Trident II warhead can deliver 2×1015J each, and the atomic bomb detonated over Hiroshima in World War II was 6.3×1013J. Substituting into the equation yields:

n=2.25 x 1032 / 2 x 1015 = 1017 Trident II warheads and

n=2.25 x 1032 / 6.3 x 1013 = 4 x 1018  Hiroshima bombs.


100 million billion Trident II warheads and 4 billion billion Hiroshima atomic bombs!  Slightly unbelievable, isn’t it!!


(Credit: WPromote: The Challenger Agency)


Coming to the newer films, but still staying in the same vein as the Death Star, in Episode VII: The Force Awakes, we are introduced to the First Order, and they have the immense Starkiller Base. Starkiller Base is basically an Ice Planet, transformed into a larger version of the Death Star. It is able to absorb the energy of a Sun to produce an explosive beam that is capable of destroying an entire planetary system.

Amazing as this is, one thing that always struck me is how can an ice planet absorb the entire power of a star? Looking at the star that is absorbed into the planet, it appeared very similar to our own Sun, which is a G type main sequence star. Starkiller Base has a diameter of 660 kilometres, so is bigger than the Death Star, but if it is absorbing the energy of a star like our own Sun, then it is absorbing 4 x 1026  Joules of energy every single second! How could a planet, a small ice planet none the less, hold that much energy? The answer that is given comes from the Thermal Oscillator that is installed in the planet to help. Thanks to the amazing site Wookiepedia it is stated that:

Using a star as a power source, an array of collectors on one side of the planet would gather dark energy in stages, redirecting it to the planetary core, where it was held in place by the natural magnetic field of the planet, as well as an artificial containment field maintained by the machinery the First Order had installed within the crust. As the planetary magnetic field would not be strong enough to contain the amount of energy that the weapon required, a thermal oscillator was built into the planet. It generated an oscillating containment field which allowed the installation to expend considerably less energy at containing the dark energy than would be required using a steady containment field. A colossal hollow cylinder, large enough to dominate the view of the planet from orbit, penetrated the containment field to a predetermined distance, in order to direct the blast towards its target, and also to absorb its energy, which would otherwise cause catastrophic groundquakes. This design made the weapon vulnerable when it was fully charged, as the destruction of the containment field oscillator the moment before the weapon fired would release the accumulated energy not through the firing cylinder, but throughout the planetary core where it was being held, leading to the gradual collapse of the surface into the core.

This explanation is provided in the novelisation of The Force Awakens. Of course you do need to retain a healthy degree of scepticism reading statements like this, but this is science fiction not science fact! I still need to ask the question though, would this work if the type of star was different? Could the same method be used if they were trying to completely absorb an O class star or M class star? Would they need to build more oscillators in order to contain the larger amounts of energy, perhaps a thousand times greater for an O star?!  Though it could be a thousand times less for the faint M star.  Might this be possible for some futuristic technology?  Also, if Starkiller Base needs to completely absorb a star in order to fire its weapon, how can people survive on the planet when the star is absorbed, and how do they get to another star? Surely a planet couldn’t travel that fast even if it has incredibly powerful engines within its core?? Rogue One was able to show us that the Death Star could travel at light speed, but it was smaller.  Nevertheless, accelerating any physical object to light speed requires an infinite amount of energy according to Einstein’s special theory of relativity!  Nothing can do that.

a classical nova binary system just before an explosion on the surface of the white dwarf. Classical novas occur in a system where a white dwarf closely orbits a normal, companion star. In this illustration, gas is flowing from the large red,companion star into a disk and then onto the white dwarf that is hidden inside the white area. As the gas flows ever closer to the white dwarf, it gets increasingly hotter, as indicated by the change in colours from yellow to white. When the explosion occurs, it engulfs the disk of gas and the red companion star.


When Starkiller Base is absorbing the star, it looks like a white dwarf star stripping matter from a much larger companion star.  But surely at a certain point this would become unstable and explode as a nova, thus destroying the planet?!

Okay multiple question ranting time over! I understand this is all science fiction, but still, when you work in an Observatory and Planetarium, you think about these kind of things.  Enjoy Star Wars this festive season but don’t try and take the science too seriously (a bit like I have just tried to do!) – it’s just science fiction, and pretty darn epic science fiction at that!


Article by Heather Alexander, Education Support Officer

Heather Alexander, Education Support Officer


Scott Manley · December 15, 2017 at 15:05

Former Armagh observatory student myself, I made this video on the subject a couple of years ago:

    admin · December 15, 2017 at 15:34

    Hi Scott,

    Great to hear from you dude! Watched your video there, really brilliant, thanks for linking that in 😀

    Hope you’re well!

Star Wars: A look at the Science – MeasurementDataBases for Industry & Science · December 15, 2017 at 07:59

[…] Astronotes Astronotes: Star Wars, the very name brings up images of childhoods spent in front of a TV or […]

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