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Sunday 17 December 2017

Two new acheivements in private spaceflight...

The view over the engine bell of a SpaceX rocket, leaving Earth behind for the  GEO satellite belt.

Over the last fifteen years a lot of words associated with the fledgling private space flight industry have gone from being said almost in mockery to being said in earnest - even admiration. This week has seen two events that highlight why....

SpaceX has flown a flight proven booster, with a flight proven space capsule, to the International Space Station:

When Elon Musk's ground breaking 'SpaceX' (Space eXploration technologies) company announced they were planning to start re-using the first stage boosters from their rockets they were referred to as 'flight proven' - a euphemism for  'risky and unproven technology'.

Today that phrase 'flight-proven' is being used in earnest. And, to prove it, last week they flew not just a flight proven booster - but a flight proven booster carrying a flight-proven capsule, on a supply run to the international space station:


That's a milestone, because it makes SpaceX's vehicles mostly re-usable and therefore well positioned to bring the costs of spaceflight down. And, coming in the same week that Trump signed his (fairly vague) instructions for NASA to make a manned return to the Moon, it makes the upcoming decade look rather interesting for fans of manned space exploration....

Blue Origin flies 'Mannequin skywalker' to the edge of space:

Jeff Bezo's secretive company 'Blue Origin' has made impressive  progress in getting their 'New Shepherd' space vehicle ready to start ferrying passengers and missions to the edge of space. But a hydraulic malfunction on their first full tale test flight last year put a crimp in their plans. Now they've resumed  by flying a test dummy to the edge of space... a test dummy named Mannequin Skywalker.

No say anything about wanting to send Hayden Christensen into space.

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Thursday 7 December 2017

'Liquid' - in deep frozen interstellar ice.

The rings of Saturn, made of trillions of ciy particles loaded with organic matter - how far can chemical evolution get in such places? 

Life arose here on Earth... but how far did purely chemical evolution get towards life, on the planetoids and protoplanets of the early solar system? New research from Hokkaido University implies it might have been further than we thought. 

Meteorites dating from long before Earth have been found to contain the chemical components of proteins, cell walls, and even building blocks of DNA. Exactly how that happens is badly understood. We know these meteorites are fragments of ancient proto-worlds - worlds which were surprisingly planet like, with liquid water percolating through their rocks, planet like cores and volcanism, out gassing driving short lived atmospheres, and magnetic fields. They could have provided the right environments to process the more primitive chemistry in the Sun's protoplanetary disk.

But some meteorites contain relatively advanced pre-biotic chemistry despite showing no sign of ever having gotten above freezing. So where did it come from?

Now a surprising explanation has been discovered: Researchers from Hokkaido University in Japan have discovered that simple organic compounds, frozen in interstellar ice, start reacting with each other as if they are in a liquid, when exposed to ultraviolet light. The interstellar ice itself, despite being far below freezing, seems to behave like a super cold fluid - somehow. 

Above: Deep frozen, artificial, 'interstellar ice' bubbling like boiling water under UV light.

That's plenty of a mystery itself, but discovering that this kind of chemistry can take place in the ice grains floating in space (instead of a planetary environment) literally opens up a sky full of new possibilities: Across large parts of the universe worlds could be forming with half the chemical steps towards starting life already done.

Our skies might just have become a lot more crowded. For the original paper click here.

Thursday 23 November 2017

Did Earth just get buzzed by an alien starship?

If it was one of these then we're all in trouble.

To answer the question in the title....No. 

Well. Almost certainly no.

But hang on, I should fill in the back-story here.... the object causing all this fuss is pretty odd. Called 'Oumuamua' it's (we think) an asteroid... although it's probably the weirdest, most scientifically compelling, asteroid we've ever found. 

Oumuamua was spotted in mid October of 2017. At first it was a fairly unremarkable spot of light: Probably some small, dim comet that no-one had ever picked up on before, was what most astronomers thought. 

Then they plotted its course backwards, to see where it had originated from: Oumuamua came from outside our solar system - from interstellar space. And, if it came from outside our solar system then it was, originally, a piece of another star system. No-one has ever seen such an object before - a natural interstellar traveller. Computer simulations have tentatively suggested that about one such object should pass through our solar system every year, but to actually spot one was like actually filming a Sasquatch - a mythic beast, captured on film.  

Above: The course Oumuamua took through our solar system, passing right by Earth.

The weirdness then got weirder, turning from " minor but historic discovery" to "whoa.. what?". Firstly this asteroid had, as you can see in the video above, swung relatively close by Earth. That's interesting, but maybe not very surprising - if it hadn't been in our neighbourhood we might well have never spotted it. 
But its shape is what has got everyone's heads a-scratching: Asteroids and comets range from potato to ball shaped. But Oumuamua is a stick shape: Ten times as long (about 800 meters long) as it is wide. 

Sasquatch has sprouted a third leg, and wings.*  

Above: The odd shape of Oumuamua. 

The colour of the asteroid (which can be broken down to reveal clues to it's surface composition) is reddish. that implies the surface is covered in the same kind of organic molecules - the same kind implicated in the origin of early life on Earth - that we see on the surface of comets. But, unlike a comet, this object has no trace of vapour coming from it, or of any ice. That suggests it's a rocky or metallic object beneath the organics... but how that squares with its strange shape, extreme origin point, is anyone's guess. 

So we get to the crux of the question: This looks like no natural object we've ever seen. So could it be an artificial one? it's extremely unlikely. At present there is no news of any heat signature, radio or microwave emissions, or other behaviour suggesting technology. Its speed, whilst very high (26 km/ sec) is still very slow for an interstellar probe - although that is assuming any probe building aliens would have similar life spans to ours (and there's no reason to assume that really, they could live much longer and be much more patient). 

But none of that is confirmation of a natural origin either - and while that's the most likely scenario by a long way, it must still be a spectacularly unusual natural origin to have produced such a strange object. That means it could a be a window into some truly alien geological processes, happening far, far across the universe from us.... Not aliens, but very, very alien natural processes. For that reason the astronomical community is gathering all the information it can on this object, before it disappears beyond the range of our telescopes. And, just in case, Centauri dreams website reports that SETI (Search for Extra Terrestrial Intelligence) and Breakthrough Listen organisations are/have been keeping Oumuamua under observation. 

As they say, watch this space.... 

UPDATE: To make things even more interesting a mission to hunt down and examine Oumuamua (or any other interstellar asteroids) is being proposed - some details here.

Sunday 12 November 2017

The Universe in 101 words: Will we return to Saturn's moon Enceladus?

Above: Enceladus, an ocean world covered in ice.

Our solar system is awash* with ocean worlds. And thanks to the Cassini missionary we've gotten to know one, Enceladus a 500km wide moon of Saturn, really well.

So what's it ocean like?

Dark - the ocean's covered in 20km of ice - but maybe not totally black: There's volcanic activity on the ocean floor, possibly like the white smoker vents of Earth, so there'd be the dim carmine glow of volcanism. More importantly the salty, alkaline, water contains organic chemicals and hydrogen - food for possible micro-life.

Cassini's mission is over - but its now hard to imagine us not returning to Enceladus....


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Above: The geysers of Enceladus, backlit: The ocean is literally leaking into space!

Sunday 22 October 2017

Answers for students: What is a light year?

Above: A nebula. The smallest part of this picture you can see in this picture is thousands of times bigger than our whole world - so normal measurements of distance just don't work. Unless you're a linguistic masochist who likes having to saying "billion trillion trillion trillion quadrillion" after everything.

This one comes up a lot - It comes up in exam questions, and everyone seems to stumble over it: What are these 'light years' that keep being mentioned by astronomers and sci-fi shows? Do you have to eat less calories, or keep at least one house light on nonstop for 365 days to make them?

And the answer is: No. I eat however many calories I like (to be fair I'm starting to get a bit fat and have to go for runs) and I leave all the lights on in my house all the time anyway.

I'm not scared of the dark. I never admitted to that. Ahem


A light year is NOT a measure of time. Yes, I know it has the word 'year' in it's name. Yes, that's a pretty dumb and confusing thing to name a measure of distance. No, I can't do anything about it.

The important bit is that we understand the dumbness: It's called a 'light-year' because it is how far a beam of light will travel in one year (if it doesn't hit anything). So, to the astronomers that first came up with it, 'light-year' seemed to fit.

So, how far is it? Well we can convert light years to meters like this: 

A beam of light travels at 300,000,000 meters per second. To work out how many meters are in a light year, we just need to work out how many seconds are in a year and multiply that number by 300,000,000 meters.

Seconds in a minute = 60
Minutes in an hour = 60
Hours in a day = 24
Days in a year = 365.25*

So the number of seconds in a year is 60 x 60 x 24 x 365.25 = 31557600. 
And, for our grand finale, the number of meters in a light year is 31557600 x 300,000,000 = 9,467,280,000,000,000 meters.

Or, in other words, a very, very long way. It's the absurdly big size of the distances out in space that makes astronomers use light years as their units of distance.

Above: This is the Pleides star cluster, which is 43 light years across. Work that out in meters, using the method above - how many millions of millions of millions is it? And how much longer does it take you to say "Captain the engines cannae take it for another (insert millions of meters)" than "Captain the engines cannae take it for another 43 light years"?

Where things get  kind of crazy is when you think about what those huge distances mean for how we see the Universe: We see stars with light, which is the fastest thing we've ever discovered. The nearest star to Earth (after the Sun) is four light years away. That means it takes light from it four years to reach us - when you see it in the sky you are seeing it as it was four years back. Most stars are much further away, hundreds or thousands of light-years. Which means that, if you look up at the night sky, you are not seeing those stars as they are today but as they were hundreds or thousands of years ago. 

When you look at a star you are, very literally, looking hundreds or thousands of years into the past.

So... yes Doctor: Time travel is possible - in this limited way at least.

A really good example of this is the star Betelgeuse, in the constellation of Orion. Betelgeuse is unstable, and in danger of going supernova. But, because it is 650 light years away, it might already have exploded in a supernova. Right now it could well be a huge cloud of debris. If that had happened anytime over the last 650 years we wouldn't know about it yet, because the light that makes up the image of  the explosion wont have reached us yet. 

When you see Betelgeuse in the sky, you might actually be looking at its ghost.

So cut astronomers a bit of slack. Yes they're a bit odd and out of this world. But if your job started at that level of weird (and it gets a lot worse from there, with hairy black holes, lenses made of empty space, and invisible matter that passes through us all the time like ghosts) you'd be a bit odd to by the time you hit retirement.

* The 0.25 is because each orbit of Earth around the Sun doesn't quite match a whole number of days, leaving us with a quarter of a day over. For this reason every four years we have a leap year, with an extra day, to compensate and keep the calenders in line with what Earth is actually doing.

Saturday 14 October 2017

Sound In Space: The Song of Jupiter

Above: The chaotic, Shoggoth inspired, swirl of massive storm systems at Jupiter's pole. Courtesy of NASA/JPL
The JUNO space probe has been wowing the Earth as it returns astounding images of the beautiful and titanic weather systems that shroud Jupiter - but there's another side to the exploration of the King of the Giant Planets: Jupiter's song. 

While space probes cannot pick up the actual sounds in Jupiter's clouds, (due to there being the vacuum of space between them and the planet), their radio antenna can pick up the natural radio transmissions from the giant world's immense magnetic field. 
So, for the full 'Jupiter experiance' try playing the two videos below - one a high def flyby of Jupier's cloud tops and one a recording of its eerie radio song - at the same time....

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Sunday 1 October 2017

Five of the strangest asteroids and dwarf planets...

Above: Pluto, a world half the size of the US but stranger than anything dreamed up by sci-fi writers.

Most people thinking of space exploration think of the planets - Mars, Venus, even Jupiter and its Moons. But that's missing something - hundreds of somethings in fact: The large asteroids and dwarf planets make up a collection of worlds as varied and compelling as the terrestrial planets. So here are a few of the oddest...

The king of the asteroid belt, Ceres is a dwarf planet nearly a thousand kilometres across. It's also one of the relatively few asteroids to have been visited by a human space craft - in fact the Dawn space probe is still in orbit, surveying this small world. Despite its small size Dawn has shown that there's still recent signs of geologic activity on that 4 billion year old surface, and perhaps even hints of subsurface water.

Above: A simulated flight over Ceres, assembled from data supplied by the Dawn probe.

The first small world visited by the Dawn probe, Vesta proved to be a world with a history of cataclysmic violence. Already suspected to have been a hot, churning, volcanic world in its youth, Dawn found that the tiny world’s entire South Pole had been obliterated, not once but twice, by gigantic asteroid impacts. The largest of these was so huge it left the 'ripples' caused by the shockwave permanently imprinted in the Vestan rock.

Above: Dawn's greatest finds at Vesta

Although we've only ever seen this world at a distance, through telescopes, it is due to be visited by a unique space probe (also called 'Psyche') in 2026. Why? Because it's a solid chunk of metal the size of the state of Massachusetts. The only sensible explanation anyone has come up with (so far) is that Psyche was once the core of a planet - a planet that suffered some terrible fate which stripped down to its metal core...

 Above: The bizarre metal asteroid Psyche, and the mission to explore it.

It's unlikely that Sedna, a world 8 billion kilometres from Earth with a year over 11,000 Earth years long, will get a visit from any spacecraft soon. Even so, it's playing a pivotal role in our exploration of the dim outer reaches of our solar system. The dwarf planet's odd shaped orbit could be the result of the gravity of a ninth major planet, far out in space. Or, perhaps even more intriguingly, it could be a sign that Sedna is not really a member of our solar system at all: It could have been a loosely bound dwarf planet of another star, kidnapped by our sun during a rare stellar flyby.

Above: Think you know how far a long way is? Well take a look at the orbit of Sedna...

I take it you've heard of this one? Although the debate still rages in parts as to whether its demotion from planet to dwarf planet was a fair one, I really don't think this immense and incredibly complex ice world cares. From it's weird hundred meter blades of ice, to its nitrogen ice glacier ocean on which mountains float like ice bergs, to the hints that rivers of liquid nitrogen once flowed on its surface and might well still run beneath its subsurface, Pluto has every reason not to give a damn what we teeny humans classify it as. But, thanks to the New Horizons space probe, this beautifully weird world has, been opened up to human eyes...

Above: A virtual fly over of Pluto, assembled using data from the New Horizons mission.

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Wednesday 12 July 2017

Sound in Space: The drumbeats of pulsars

The Allen Antenna array.

The stars are beautiful, or at least very sparkly. But most people will tell you they're not much to listen to - after all, in space no-one can here you scream, so how would you hear the stars? But there are signals out there - radio wavelength signals - that we can listen to with the right equipment.

So, if you wore radio dishes on your ears, what would you hear?*

Not a peaceful sky, or even a snatch of Beethoven. No, you'd hear a Milky Way echoing to the buzzing, humming, and drumming sounds of pulsars. These are incredibly dense objects, forged from the collapsing cores of supernova - and spun up to incredible speeds by them. Never more than twenty kilometres across, a new born pulsar can spin hundreds times a second. They give out intense beams of radiation, including radio waves, so as they spin radio antenna on Earth hear the click of the beam briefly sweeping over us.

There are old, slow ones that drum like a runners footsteps...

... and there are fast young ones that swarm in star clusters like 47 Tucanae, filling the sky with a whine like the universe's most terrifying cloud of mosquitoes...

But a universe full of strange knocking and humming sounds isn't the odd bit. The odd bit is that you can buy an album of music made using them.

*Given my knowledge of fashion this could actually be a thing for all I know

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Friday 7 July 2017

The Universe in 101 words: Why should we return to Enceladus?

Above: The dwarf planet Ceres, which is suspected of having once held an underground ocean. Um. It doesn't really turn back and forth in that way
Our solar system is, well, awash with ocean worlds. And, thanks to the Cassini mission, we've gotten to know one really well: Enceladus, 500km wide moon of Saturn.

So what's it like?

Dark - the ocean's covered in 20Km of ice - but maybe not totally black: There's volcanic activity on the ocean floor, like the white smoker vents of earth, so there'd be the dim  glow of volcanism. More importantly the salty, alkaline, water contains organic chemicals and hydrogen - food for possible micro-life.

Cassini's mission is nearly over - but it's now hard to imagine us not returning to Enceladus....

Tuesday 4 July 2017

Sound in Space: The noise of interstellar space

It may be true that in space no-one can hear you scream, but you can hear some far stranger things out there.

The recording above was taken by the Voyager 1space probe, as it left our solar system - it's of waves with the same frequency as sound, but it's not sound as we know it. Where regular sound is a vibration in a gas, solid or liquid, these sounds are vibrations in the ultra thin soup of ions, called plasma, that fills space. Far too faint for any human sense to detect, Voyager had been listening to vibrations like these for decades. But this set was different - their pitch was suddenly a lot higher. That meant the density of the plasma they travelled through had changed dramatically in a short space of time - one of the markers for the boundary with interstellar space.

So the weird little vibrations are literally the sound of Voyager going where no-one had been before...

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Friday 30 June 2017

The Universe on 101 words: What's the fastest star?

Above: A hypervelocity star creates a huge bow wave of dust and gas as it ploughs through the Orion nebula.
What phrase describes the night sky? Not 'full of speed demons', unless you've ingested something hallucinogenic. But stars only appear unmoving because they're incredibly distant - most are actually travelling at hundreds of kilometres a second. And some,  called hypervelocity stars, are travelling at thousands.

The record holder for straight line speed? The star US 708, at 1200 kilometres per second.

What could throw a whole star so hard? 

Some were blasted up to speed by supernova. Others got accelerated by the gigantic black hole in centre of our galaxy

And some we can't explain - even after years studying them...

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Above: The Milky Way. Full of the stellar equivalent of angry teenage boy racers. Comforting thought,hey?

Friday 23 June 2017

The best images of planets beyond our solar system

The last ten years have been an amazing time: Growing up the idea of finding planets around other stars was mentioned to me in textbooks... at the very end, usually in the same very short chapter that mentioned ideas like space hotels, finding intelligent aliens, or building colonies on Mars.

Above: A private SpaceX space capsule on Mars. Good luck borrowing sugar from the neighbours guys...
  And, now, we have found thousands of planets around other stars. Many of them are far stranger than my textbooks expected, which assumed we'd find that solar systems similar to our own. The reality has been that solar systems come in all kinds of exotic configurations. Those books thought we'd be finding these worlds with direct imaging, using massive telescopes - by and large we haven't: Almost all of them were found by indirect means, like watching for stars wobbling, planets occulting the stars they orbit, or gravitational lensing of the light from background stars*.

But not quite all: Although it's still very hard to do, some exo planets have been photographed directly by very, very large telescopes just like my textbooks expected. Below are some of the best. Think of them as a teaser for the future: These fuzzy points of light are what the next generation of telescopes will be improving on - and they're also actually images of something I thought I might never get to see. 

Which is pretty damn cool...

1: Formalhuat b

NASA Hubble Space Telescope has revealed this: A gigantic disk of debris surrounding the nearby star Fomalhaut. Circling it is a planet on an unusual elliptical orbit that carries it on a path straight through the debris - probably not great news for the planet itself. The planet, called Fomalhaut b, swings as close to its star as 4.6 billion miles, and the outermost point of its orbit is 27 billion miles away. 
"We are shocked. This is not what we expected," said Paul Kalas of the University of California and the SETI Institute. They suspect that this is evidence of another planet gravitationally 'interacting' with Fomalhaut b. That's scientist code for 'having a huge fight which Formalhaut b lost', hence why this planet is on an orbit that exiles it to the far end of its solar system. .  

2: Beta Pictoris B

This image was taken by the Gemini Planet Imager (GPI) , and it shows a planet, beta Pictoris b, orbiting the star Beta Pictoris. Beta Pictoris b is a new born giant planet -- several times larger than Jupiter and just ten million years old. Its so young it's still glowing in infrared light from the heat released in its formation. The bright star Beta Pictoris is hidden behind a mask in the center of the image - the large blank circle.

3: ROXs428b

This possibly-planet has an estimated mass between 6 and 15 Jupiter masses. Exactly how much it weighs is important, because things lighter than 13 Jupiter masses can't generate enough pressure in their cores for nuclear fusion, and are definitely planets. Objects heavier than that can generate enough pressure in their cores for a brief burst of deuterium fusion (the weediest kind - true stars use hydrogen fusion) in their youth, which makes them 'brown dwarf' sub stars. Whichever side of that division it's on it's a bigger object than Jupiter, and like Beta Pictoris b it's young enough to still glow with heat from its birth.

4: HR8799

An image of an exoplanet is rare, but videos of them are like diamond dust. The star HR 8799 is even rarer: It has not one but four planets big enough to be imaged from earth, andhere they are gently orbiting their primary. This time lapse video took seven years to make, with each frame being shot using at the W.M. Keck observatory in Hawaii. The black circle in the middle blocks the blinding light of the star, and thus make the planets visible.

5: GJ504 b


Several times the mass of Jupiter and similar in size, this new world, dubbed GJ 504b (what's with all the dull-ass names I wonder), is the lowest-mass planet ever detected around a star like the sun using direct imaging techniques. "If we could travel to this giant planet, we would see a world still glowing from the heat of its formation with a colour reminiscent of a dark cherry blossom, a dull magenta," said Michael McElwain, a member of the discovery team at NASA's Goddard Space Flight Center in Greenbelt, Md. "Our near-infrared camera reveals that its colour is much more blue than other imaged planets, which may indicate that its atmosphere has fewer clouds."

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Saturday 17 June 2017

Answers for Authors: Where should I site a Galactic Empire? (re-published)

It's good to be Emperor...

You need an evil galactic empire, or a benevolent  planetary federation, to set your scorching page turner of space opera in. The problem is that, to help your readers suspend their disbelief, you now have to figure out a believable interstellar civilisation. And write it a plausible sounding history. With a way of being founded and of expanding that makes sense. And you can't look that stuff up with Google...

....weeeeell.... actually... 

I've spent far too much time reading papers and sitting courses on the search for extraterrestrial intelligences, so I know a surprising fact: Some very very clever brains (they include Stephen Hawking and Carl Sagan) have devoted serious man hours to what a huge galactic civilisation could be like. Not for fiction, but because they think we should be checking the sky in case there really is one somewhere.

That means there's a lot of stuff been written that can help you. Much more than a blog posts worth (I'll have to write a book... hmmm) so here I'll just try and sum up their thoughts on most important aspect, re-mixed for SciFi instead of SETI. And that big important aspect is, of course: Location, location, location.

It’s very much like looking for a house – you need to think about location, access to amenities, commuting, and what won’t break your budget. Admittedly the the plumbing is rather more complicated on an interstellar empire. And the call-out fees are a nightmare if it breaks...

"Suitable for a buyer who really likes space... ahahaha..." Never trust an estate agent nicknamed 'Slick' guys.
In much the same way that it’s only a truly exceptional house that doesn’t need the ground*, unless your empire builders can wave away fundamental laws of physics** you’ll at least need your location to fill some really basic needs:
  • It will need an energy source. This probably means stars, but other energy sources – like the matter falling into a super massive black hole or the radiation beams of a pulsar, do exist. There is even a scale - the Kardashev scale - for rating any alien empires by how much power they use.
  • It will need planets, or at the very least the kind of heavy elements planets are made out of  as building materials for artificial living structures like ringworlds.
  • It doesn’t have to be friendly to life – your empire builders could have migrated there from a more hospitable part of the universe when they had the technology to handle the difficult conditions – but it needs to be close enough to at least one friendly environment for someone to have made the trip.
Then there are other things that it’s very useful to have, but a lack (or overabundance) of which could be overcome to a greater or lesser extent using technology or good planning:
  • Commuting: You’ll probably want your empire to be small enough to get messages across in a reasonable time. Many authors do this by introducing a Faster Than Lightspeed (FTL) drive - although other methods, such as much longer than human-normal lifespans (via gene engineering or suspended animation), are also thrown about by both authors and scientists. But another way, if you’re not committed to an Earth centred civilisation, is to just set your empire in a part of the universe where the distances between stars are smaller than the five light years that the stars near Earth average (see below). If George Lucas can have a galaxy far, far away then why not you...?
  • Stable environment: In the same way at you wouldn’t buy a house in the part of town where gangs occasionally leave heads in dustbins (although I once rented such a place), you wouldn’t set up a civilisation in a part of the galaxy where there are good odds that radiation from a supernova, neutron star collision, or belch from a supermassive black hole might fry it to a crisp. True, you could overcome this with technology, but let me assure you: No house alarm is truly unbeatable, and I expect that so no technological solution to stellar dangers will be either.
  • Minimum age requirement: This goes hand in hand with the need for a quiet neighbourhood – young areas of the galaxy, like young clusters and star forming nebula, tend to be crowded with troublemakers like unstable blue giant stars, dense molecular clouds, and wandering black holes. Older locales tend to be much quieter, since the dangerous stars tend to have blown up or burnt out eons back. Older locales also have had more time to spawn native life forms who can rebel against (or ally with) your empire.
  • Conditions suitable for life (of some kind) to arise: Not an absolute need - a sterile locale could be colonised from outside. Still, it’s simpler in terms of backstory for a thriving civilisation to grow up near to the planets that spawned them, and that means they need a few things: A stable environment, a ready supply of chemical energy, some form of chemistry complex enough to support things like DNA, and some way of mixing everything together – usually a good solvent like water – are generally regarded as the minimum. You can waive at least some of them, however, if you make your life form exotic : A.I, sentient gas clouds, energy based, or whatever your imagination can conjure.
  • Life forms suitable to reach technological era: NASA and ESA are spending a lot of money looking for evidence of bacterial life on Mars, but it’s unlikely bacteria are going to build stargates or leave their home planet by anything other than accident^* . Hence you need creatures that could invent and use technology. 
Above: The stunning colours (which a human eye would never actually see) of a star forming nebula. A beautiful sight, but a very dangerous place to live.

Just based on those we can rule out some locations already: The great voids between galaxies would be impossible to build in without importing massive amounts of both matter and energy across billions of light years. Some galaxies have stars that are much further apart than normal, so trips would take longer and they would be scarce of energy and building material too. The same applies to the galactic halo, and intergalactic space. Active galaxies, where massive black holes are sucking down matter and belching back out radiation, are hard places for life to ever arise in or anywhere near. 

Above: The Andromeda galaxy - nice a roomy, lots of close packed stars, and private parking.
If you’re not employing FTL engines, or if they’re limited to some practical upper limit, you probably want some improvement on the travel times to the nearest stars to Earth -  so the Milky Way's galactic core is attractive with its close packed solar systems, but the risk of supernova, neutron star collisions, and mega flares from giant black holes make it much less attractive long-term. Something similar applies to young clusters of new formed stars, or active star forming nebula.

But there are good locations to be found - here are a few suggestions: 
  • A multiple star system. The Universe abounds with stars and solar systems that are bound in small clusters by gravity, orbiting about each other. The individual stars are usually much less than a light year apart, often only light months or weeks, but there’s usually enough room between them for each star to have a habitable zone and fully developed system of planets. You could invent your own such star system - which is what the writers of the Battlestar Galactica remake did - for example: Four red dwarf stars with seven planets orbiting each star, might plausibly give you twelve habitable worlds (three in the habitable zone of each star) all packed into a light month of space^.  There would also be another sixteen uninhabitable but potentially mineable worlds. True, this is the entry level galactic empire - but it’s limited extent is compensated for with other advantages. In particular, if you want a real locale that is also close to Earth, then the nearest star system to Earth (the three star cluster of Proxima, Alpha, and Beta Centauri) actually fits the bill^^: Small by galactic standards, but still an empire greater than every civilisation of Earth combined.
  • Globular clusters:  These collections of hundreds of thousands of stars have a lot to recommend them – they’re old, so there are few or no dangerous, radiation spitting, potentially explode-ey young stars around. Instead most of the stellar population are red dwarfs, with their tight wound systems of planets, or red giants destined to die relatively quiet deaths. Average distance between stars is down to less than three light months – so even a sub-light speed starship could cross between several star systems over the course of a year. On the downside: Planets orbiting any Sun-like stars would be pulled out of orbit by neighbouring stars, and Globular clusters are generally quite poor in heavy, planet building elements, so only fairly small planets (like Earth) would form around their stars. But these aren't showstoppers: Planets orbiting red dwarf stars would be much more likely to stay with their suns, as these hug their planets much closer, and some of these clusters do have enough planet forming elements. On top of that the age of these stars - 5 billion years at least -  makes it more likely for a technological civilisation to have had time to arise^°. Globular clusters are not without hazards to navigation However: The long dead blue super stars, the absence of which makes the cluster fairly quite, will have left behind things like black holes and pulsars, which will be concentrated in the core. 
  • Open clusters: Open clusters, on the whole, are not great spots for civilisation building - most open clusters are both too young for any worlds to have given rise to complex life, and are filled with big, radiation spitting, supernova prone, blue stars. Older ones, where things have settled down, are rare – the members of open clusters are usually born with enough speed to escape the cluster, so they drift apart in a few tens of millions of years. But some of the biggest have got enough gravity to have stayed together for hundreds of millions, or even billions, of years. Examples are places like the Beehive cluster, which is coming up on 3/4 of a billion years old, and is composed mainly of red dwarfs and sunlike stars. Near the clusters core these are packed within maybe as little as 1/2 a light ear of each other, and while these clusters may not be old enough time for technological life to arise (that took over 4 billion years on Earth), they have had time for a stable ecosystem to form that would support colonists. 
  • Ultra compact dwarf galaxies. These are quite a new discovery, and something of a mystery – tiny galaxies less than 200 light years across, that are as jam packed as the cores of globular clusters. Like globular clusters they’re mainly made of older, redder, stars and many of the same things apply to them, but they have higher levels of planet building heavy elements. 
  • Giant elliptical galaxies: For the big dawgs only – old and stable but up to 6,000,000 light years across, one of these could be home to a titanic empire of trillions of star systems – and is more likely to be so than the Milky Way ever will: The majority of stars in these galaxies are old, stable, and long lived - and there are trillions, so they have a good chance of having spawned a civilisation. But these are vast, vast places that could swallow our galaxy without noticing, so your empire builders better have mastered a powerful means of FTL travel, immortality, or both. 

These are just suggestions, but there are locations out there to fit most plot needs. The question is, simply, what kind of empire does your Imperial Majesty want? 

Above: The Voyager 2 probe encounters the planets of a red dwarf star.

*  Space stations, maybe, would count.

** You could write an empire like that: A civilisation so advanced it can more or less conjure matter and energy out of nothing, lurking in the utter darkness between the galaxies. Sounds like it might have some potential in a very Lovecraftian way, no? But a civilisation that advanced would be capable of almost anything, and so would suffer from the superman effect – it’s almost impossible to write a story for them because it’s impossible to think up a problem or obstacle they couldn’t solve almost instantly. If you don’t believe me I cite every superman film since superman 2 as evidence. 

^* There really are plausible ways bacteria might naturally leave their home planet and colonise another by accident, such as riding the debris from a giant asteroid strike, but you’d need to be writing a very esoteric story for that to count as an empire. Some kind of communal bacterial intelligence might work, but you’d have to have your heroes charge into battle against the evil empire by scrubbing every kitchen work surface on the planet with Dettol. 

^For hard SF writers: That means the furthest worlds could be travelled between in five months with a starship that could hit 20% of lightspeed – a speed many researchers believe we could reach with engine designs we could build in the next century. A radio message could make the same journey in one month, giving a slightly better messaging time than existed between the furthest corners of the Roman empire.

^^Two sun like stars (alpha and beta centauri)about the same distance apart as the Sun and Saturn, with a red dwarf star (proxima centauri) orbiting the larger two at a distance of ¼ of a light year. There’s a confirmed planet in the habitable zone of the red dwarf, and a possible detection of one in a very tight orbit around one fo the Sun like stars. Small, undetected planets in the habitable zones of the sun like stars are possible. It’s very plausible to put a human colony around each of the stars, with the occupants able to visit each star system in less than a year with sub light speed engines. A small empire of three solar systems - but still bigger than every empire on Earth combined.

°^A civilisation taking in a whole such cluster would control hundreds of thousands of systems, but its inhabitents would need to be longer lived than modern humans, or have FTL – these clusters are often over a hundred light years in dimeter despite being so close packed.