The sunrise is one of the most beautiful parts of our day.
One of the cool things about Alpha Centauri
is you get to watch the sun rise three times a day.
So today we are back to the Outward Bound Series, to look at Colonizing Alpha Centauri.
Our interest today deals with binary stars or multiple star systems and how these will
influence our ability to colonize them.
As we will see today, Alpha Centauri has some special complications to it which might actually
make Alpha Centauri not the first one we'd want to colonize.
We'll get to those problems in a bit.
This episode is longer than usual so you might like to get yourself a drink and a snack before
we begin.
Let us make things more interesting today and as a thought experiment make it imperative
that we colonize Alpha Centauri within the near future.
Let us say that we detect a rogue stellar mass black hole about 10 times as massive
as our Sun heading towards our Solar system that will not just graze past us, which would
be bad enough, perturbing orbits, possibly ejecting planets, and ensuring constant hails
of comets and asteroids, but is going slow enough it will actually settle into a binary
orbit with our own Sun, and drag it out of this area of the galaxy in the process.
It may even start eating it.
The only silver lining is that it is going slow enough that we can contemplate an evacuation
over the next couple centuries.
Despite the problems with Alpha Centauri, we decide to colonize it.
The main reasons for this are that there is not just one but three stars in that system.
Humanity has learned the hard way not to put all of its eggs in a single basket, and in
the Alpha Centauri system we have 3 star baskets for our precious humanity.
Another reason is that the system is the closest to Earth, being an average of 4.37 light years
away.
When the date arrives to pack up all of humanity and move them in bulk, the most economical
way is going to be a combination of stellasers and the interstellar laser highway system
we've previously discussed.
Normally you'd have to build one for each system, but another advantage of going to
Alpha Centauri is you could service all three stars with just one, and shorter is better
for such a highway.
If multiple colonies are established around those stars, even the furthest ones will be
able to receive radio messages transmitted from each other within two months.
Now two months sounds like a long time, but empires did very well here on Earth with year-long
communication delays back when the only way to get around the world was by sailing ships.
We know it is doable, so we can keep the colonies relatively cohesive for at least a time.
We also know we can evacuate Earth and I recommend watching our recent episode on that.
We decide to evacuate and send out colony ships, an initial vanguard to set things up
and a vastly larger armada to follow in several waves later.
As is the case throughout the series, it's not the journey that interests us or the spaceships
that get us there.
We've looked at those before in the Spaceship Propulsion Compendium and the Interstellar
Travel Challenges episode.
We also looked at what life on an interstellar ark ship would be like in the Life in a Space
Colony series, episode 2, Life on a Colony Ship.
However, as I said earlier, our preferred mode of transport to get there is a combination
of stellasers and the interstellar laser highway.
Now Alpha Centauri is a star system, not a star.
Alpha Centauri consists of two large stars, one a bit brighter and one a bit dimmer than
our own, which orbit each other every 80 years and get as close to each other as Saturn and
the Sun do and as far apart as Pluto and the Sun.
The larger is Alpha Centauri A, the smaller, Alpha Centauri B. However there is also a
third star, Alpha Centauri C, more commonly known as Proxima Centauri, which is actually
the closest star to Earth.
Each planet orbits its closest star in that system, not all of the stars at once.
There is a debate whether Proxima Centauri is a visitor to the Alpha Centauri system
or a permanent member.
If it is a permanent member, it is right on the extreme edge of being part of the Alpha
Centauri system.
If we use the analogy of the A and B stars as being a city centre, Proxima is at the
very outer edges of the rural outer suburbs, almost completely independent from A and B
at a fifth of a light year away from them and only very weakly gravitationally bound
to the system.
At 13,000 AU distance from the other stars, Proxima orbits the A and B system only about
twice every million years.
Now, while Proxima Centauri is the closest star to us, we can't see it with the naked
eye.
Alpha Centauri A is just 10% more massive than our own Sun, but 50% brighter, and B
is 10% less massive than our Sun and half as bright, a third the brightness of its partner.
Proxima, on the other hand, is only about an eighth of the Sun's mass and 600 times
dimmer than our Sun.
After an epic 4.24 light-years journey, our colony ships arrive in the Alpha Centauri
system at its closest star, Proxima Centauri.
The star is a red dwarf.
Its habitable zone or Goldilocks zone, where water can exist in liquid form, is much closer
to the star than our Sun's.
We already knew it has a planet in its habitable zone, called Proxima b, something we confirmed
by sending probes out ahead of the colony ships.
We suspected that the planet was rocky and one would like to think that it would be likely
we could find life there or at least make that planet habitable for us.
To our relief, the probes show that the earlier remote observations from Earth were correct
and Proxima b is indeed a rocky planet with 1.3 times Earth gravity.
Also in its favor, Proxima Centauri will survive much longer than Alpha Centauri A or B or
even our Sun.
Its expected lifespan in its main sequence is four trillion years, about 300 times the
current age of the Universe.
Being so weakly gravitationally bound to A and B, it is also likely that it will leave
that system some time in the future and well before A or B go nova at the end of their
lives.
For humans at Proxima, from a system longevity standpoint, we are trading up in a big way!
So far, so good; this is a place we want to settle.
However, we have to come to terms with several big issues.
Firstly, Proxima b is only 0.05 AU (7.5 million km) from its star.
To put that in perspective, it is 8 times closer to Proxima Centauri than Mercury is
to our Sun.
While that is a perfect distance to get temperatures that allow liquid water to exist from the
much reduced light from Proxima Centauri, the problem is that Proxima Centauri is a
variable star.
That means convection in the star's body creates magnetic fields that result in random
and frequent flaring, generating not only very bright outbursts but also a total X-ray
emission similar to that produced by our Sun, even though Proxima Centauri is much smaller
and dimmer On Proxima b, this will cause massive random
increases in deadly X-ray radiation as well as UV, visible and infrared light.
To give you an idea of the scope of the problem, in August 2015 the largest recorded flares
of the star were recorded, with the star becoming 8.3 times brighter than normal.
Imagine standing outside on Earth on a warm sunny Summer's day when the Sun suddenly
gets 8 times brighter and hotter and you start to understand the problem.
That amount of radiation is more than enough to fry and sterilize a fledgling colony that
close-in to the star.
Another problem is that Proxima b was expected to be tidally locked to Proxima Centauri,
meaning the same face always points at the star.
Yeah, our probes confirm this too - there is no day, night cycle.
We have long suspected that red dwarf planets in the habitable zone will lack atmospheres.
The solar wind is expected to be more than a thousand times that of our own sun, which
should be more than enough to blast the atmosphere off any rocky planet that strays too close.
In Proxima b's case, this is made worse by the star's regular flaring too, which
causes even more solar wind in short bursts.
Our probes confirm our suspicions, Proxima b has little to no atmosphere.
The spectrum of the red dwarf also means that it puts out more infrared radiation for the
same amount of visible light as on Earth, even when it is not flaring.
This means that if we want the same amount of visible light as on Earth, we are going
to be receiving much more heat.
Alternatively, if we want the temperature to be cooler, we have to put up with less
visible light.
We have regularly taken on the persona of a character we call our traveller at various
times in our Outward Bound series.
This episode is a thought experiment and therefore, not strictly canon, but we'll re-introduce
our traveller here too to get a human perspective on all this.
This time, he is a senior engineering crew member on the colonizing ships.
We huddle around and ask how we can colonize the system without getting fried, irradiated
or living in perpetual light or darkness or even twilight?
Now we've discussed space habitats quite a lot on the channel and you will know they
are a favorite of mine for colonization because we control every aspect of the environment
and can fully customize it to our needs.
As we discussed in the Life in a Space Colony series, it's an interesting backwards aspect
of colonization that you build your basic space stations before you colonize your planets,
and of interstellar colonization that you'd also start with space habitats before colonizing
planets.
This allows us to circumvent the lighting problems of Proxima Centauri, as we can internally
generate lighting by fission, fusion, solar power, or the use of mirrors to reflect in
Proxima's starlight, but coated to reflect away harmful or unnecessary waves with the
remaining useful wavelengths entering a window in the habitat.
As well as being able to rotate off axis so we can simulate a night phase or avoid reflecting
too much light in during a flare.
Each of these designs is very different in its requirements and internal environment,
which compounds the issue of figuring out which design is optimal to build.
Tempers flare and tensions run high, so in the end, no one design wins and, instead,
a variety of designs are proposed and adopted for a swarm of habitats to be constructed
to surround the star at various distances.
That's all very well and good but we now need the materials to actually build these
habitats.
There are other small, cold planets, asteroids and comets around, but they are not as easy
to get to compared to Proxima b.
Proxima b is a great candidate for mining as it is higher than Earth gravity and could
stand to lose some mass as a result to make it more Earth-like.
The extra gravity is not particularly difficult for fit people to live with either, even with
the apparent increase in weight.
We set about creating a mining operation supported by a planet-based colony for those who prefer
living on a planet instead of living on a space station.
We initially establish a small colony and nearby mining facility facing the star with
direct overhead sunlight.
This maximizes the solar energy collected using conventional solar panels but exposes
the area to random deadly radiation flares.
As a result, the colony and mining operations are installed into lava tubes under the surface
that provide protection from the radiation and micrometeorite bombardment.
As the lava tubes are mined, the empty space created is converted into living space.
Our probes showed that Proxima b turns out to be an iron-rich planet similar to Mars
in geological makeup.
This is good for making structures, but it is lacking sufficient quantities of other
elements vital to life, so we send out small spacecraft to locate smaller icy bodies orbiting
Proxima Centauri further out that have trapped Carbon, Nitrogen and water ice.
We wrap these bodies in insulation to prevent them from boiling away as they approach the
star and sling them towards Proxima b.
When they arrive, we process them into water, atmosphere and other materials for our future
colonies.
Mined minerals are mass driven from the planet's surface into orbit.
Even with the increased gravity, the lack of an atmosphere means mass drivers are a
good way to get the mined materials off the planet, at least in the beginning.
After we have mined enough material, we use that material to build an array of space mirrors
and we build a second larger colony on the permanently dark side of Proxima b, away from
the hellish radiation bursts.
We dome this over and supply power to it using the array of orbital mirrors that reflect
the light from the star to solar panels on the ground.
We even reflect light from a special group of mirrors in the array that have the selective
frequency reflection technology we designed for the habitats directly into the domed colony.
The mirrors mean that little of the damaging radiation reaches the colony.
It also means that we establish light and dark cycles on demand so we create day and
night and can control the light levels, even during a flare, by quickly rotating the mirrors
so that less light falls on the domed colony.
Even on the dark side of Proxima b, our design ensures that the colony is not in perpetual
darkness.
Point defence systems take care of any space debris that would hit the domes.
We build orbital rings and skyhooks and this helps to get materials off the planet a lot
more easily.
We also build nuclear power plants to help supply the increasing population and energy
needs of the colonies.
Now Earth's Sun is 600 times brighter in all spectrums, but it is 200,000 times as
bright in the range we can see than the light hitting Proxima b.
This means that on the day side of Proxima, it is still not be very bright to our eyes,
though it would still be bright.
The Sun is 400,000 times brighter than a Full Moon on Earth, for instance, and certainly
doesn't seem that way as our eyes are logarithmic in their sensitivity.
As a result, since we are filtering the frequencies of light hitting our mirrors, we actually
reflect more visible light from Proxima onto our nightside colony domes on Proxima b than
normally hits the day side of the planet.
The dark side now seems brighter than the day side, at least those parts the mirrors
are lighting.
The second colony and its infrastructure allows us to really ramp up mining and we are soon
producing the smaller O'Neill space habitats.
In short order, we have enough habitats to offload our colonists into, those who came
with us and the billions soon to begin arriving from our home solar system.
It will be a constant squeeze and strain on the life support systems and food reserves
as each new arrival is almost immediately tasked to mining or habitat construction,
but as time goes on, there will be ample room for the population as more habitats are produced
and humanity spreads out into the mix of habitats around the star.
That is the cue for the colony ships to gear up for the next leg of our journey.
Proxima Centauri is only the first of the stops on our journey.
We have two more destinations ahead.
It's time to leave, but before we go, we take the opportunity to visit the colony on
the dark side of Proxima b.
The dome inside looks very much like Earth with plants, animals and arcologies living
under a domed roof that receives what appears to be perfectly reproduced sunlight supplied
by the orbital mirror array, and we are invited to step out from the dome in a spacesuit by
an astronomer friend and walk on the barren rocky surface of the dark landscape.
We gaze up and, even though we are in an alien system more than 4 light years from our home
world, we are surprised that the stars look the same as those from Earth and we see all
of the familiar constellations and stars we would see from Earth with one exception, a
bright new star near Cassiopeia, which is the Sun from our home system.
We can't see it with our eyes, but we know even as we build here, vast stellasers are
being built in orbit of the sun to push new and giant ships our way at high speeds, and
we will soon need to build our own around Proxima Centauri to slow them down.
40 trillion kilometers from us, the most massive construction project in history is working
to build a laser highway and the ships which will venture onto it.
We are told by our friend to gaze at the horizon.
As we do, we see an even brighter star begin to rise.
It is easily the brightest star in the sky and noticeably brighter than Venus was at
its brightest from Earth, which was only barely visible during the daytime.
The star we see is our next destination, the binary pair of Alpha Centauri A with a magnitude
of -6.6 and B with a magnitude of -5.3.
They are so close together at this distance that we see them as one blobby star.
Our friend says they are so bright she has seen them with the naked eye from the surface
of the day side of Proxima b.
They are brighter here than Venus is on Earth, and the days here much dimmer in the visible
range of light.
This raises an interesting point in terms of my introductory remark about getting to
see the sunrise three times a day.
Proxima b has no natural days or nights and the stars rise because of the 11 day orbit
that Proxima b has around Proxima Centauri, meaning we would see these stars rising and
setting in an 11-day cycle.
To be honest, though, this is a bright star in the night sky, not a sun, so this is not
a sunrise the way we were expecting it.
Technically, there are no sunrises here and any that exist are courtesy of our orbital
mirror array.
Our friend points out that Proxima is actually at its farthest point in its orbit from the
binary pair, A and B. Proxima will get four times closer and as it gets closer, the A
and B binary will get brighter in the sky and we will probably be able to tell them
apart too, even with the naked eye in about a quarter of a million years.
That experience spurs our interest to move onwards in our journey and we leave Proxima
excited to visit humanity's first binary pair.
The somewhat depleted colony ships head off for a 0.2 light year journey to the Alpha
Centauri A and B binary pair with the remainder of humanity's vanguard.
The 0.2 light year journey is nothing compared to the journey that the ships made to get
to Proxima Centauri and this will be a much shorter trip.
So, what awaits humanity in its first visit to a binary pair?
You've probably heard that most stars are binary or multiple star systems, but that's
actually wrong.
The bigger a star is, the more likely it is to have a companion, which makes sense when
you think about it: more mass to pull things into orbit and more mass in that area to have
formed another star.
It was a lot easier to spot bigger stars and their companions in early astronomy, so it
skewed our figures.
According to current data, about two thirds of star systems are singular red dwarf systems.
Due to their low luminosity, we couldn't detect many red dwarfs until fairly recently
and even Proxima was only discovered in 1915 in spite of being nearer to us than any other
star.
We normally classify binaries into two types, close and distant, but they can be anywhere
from barely bound together, like with Proxima, where residents wouldn't even know they
lived in a binary till they developed advanced astronomy, to so close together they were
literally touching and sharing a column of gas between them, akin to the Rocheworlds
we discussed in the Double Planets episode way back.
For our purposes today, we will define 3 kinds that are reasonably habitable.
Close, medium, and far.
For colonization, we really aren't interested in ones where two binaries that are practically
touching or one that is a short-lived supergiant.
So we will say close is where the stars are close enough together that a habitable planet
could orbit both in something vaguely approximating a normal orbit, medium is where the planet
would orbit one, but the other is so close it seriously impacts the weather and biology,
and far is where it's just a very bright star if that, no more impacting life on that
planet than Mars or Saturn impacts us.
For this last case, Proxima is an example.
Stable planetary orbits are a major issue for close binaries and still there for the
medium variety, but let's start with the first type, a planet orbiting both stars.
This is known as a circumbinary planet, and we've found a fair number of these around
stars as old as our own, so we can say they can be stable long enough for life to evolve.
Orbital stability is only guaranteed for a planet if its distance from those stars is
significantly higher than their distance from each other, which means circumbinary planets
are outside of the habitable zone for all binary systems other than close binaries.
You can't have a habitable planet that orbits two stars who don't have overlapping habitable
zones.
A planet orbiting both those stars will see the stars orbiting each other much more often
than the planet completes an orbit around both, which might make for some weird calendars
and those sun-orbits replacing your month or seasons, and indeed they will have big
tidal and climate effects.
That's not the only weird calendar issue either.
Earth technically does not orbit the Sun, but rather the common barycenter of the solar
system.
Since the Sun is 99.8% of the mass of the solar system and half the remainder is in
Jupiter that barycenter is usually between the two but much closer to the Sun, either
inside it at times, or just above the surface.
The Earth/Luna barycenter is in our planet's mantle, but regardless, the Earth spins every
24 hours and the Sun is pretty much in the same place.
In fact the Earth spins 360 degrees every 23 hours and 56 minutes, a Sidereal Day, and
we need to spin a bit more to see the Sun rise again, an extra four minutes.
Around a close binary, this is not so.
Your planet will still have a Sidereal Day of fixed length, but neither of those stars
is going to rise at the same time throughout the year or even reset once a year.
Sometimes they'll both rise at the same time, sometimes hours apart.
Meaning even if your planet wasn't tilted like Earth is, your day length is going to
vary over the course of a year and your shortest days, your winter solstice, where both suns
rise and set about the same time, will also have your brightest noon, with both directly
overhead at the same time.
And this will happen multiple times throughout the year as they orbit each other much more
quickly than the planet does, so again, a good alternative to months or classic seasons.
Of course your planet can have axial tilt too and likely will, and it can also have
a moon.
That moon will be a bit weird too.
Our Moon orbits us once a month and appears full when it is on the opposite side of Earth
as the Sun is, and a new moon occurs when it is between us and the sun, or nominally
between, when it actually intercepts the Sun-Earth orbital plane you get eclipses, every solar
eclipse is also a new moon and every lunar eclipse a full moon.
Needless to say, just like shadows cast in a room with two lights, having two suns changes
all of this.
Again though, the stars need to be closer to each other than to the planet for a circumbinary
planet, so full moons won't be a single moment of maximum illumination, with a night
or two where the moon appears basically as a circular disc, but rather will last several
nights.
Alternatively a new moon with no visible disc at all would only ever occur if those two
stars were eclipsing each other, and even when they are lined up the same east and west,
they are likely to be a bit up and down from each other, not actually eclipsing, in which
case your moon might show a decent crescent on top or bottom.
Depending on the specifics of a system such a new moon might happen fairly regularly or
so rarely it's a major historical event, and solar eclipses where both stars and moon
are all lined up ought to be super-rare or impossible.
For a circumbinary planet though, there are still decently long night times.
Just as we have places where the sun doesn't set for months at a time - up near the poles
- they would too, only lower and longer.
While those two stars will both be very bright and visible, even if one was only a red dwarf,
they still will both appear white to the eye, but there will be noticeable variation in
coloring of objects on the planet based on which suns are up, much as clothing colors
are more or less vivid in daylight, incandescent bulb, flourescent, or LED.
You might also expect some changes to plants too, as they not only have to adjust to light
changes over the day and year but intermittent changes of day length and brightness over
periods of maybe a month or two.
However, Alpha Centauri is that other type of binary system I mentioned, the medium case,
and that is very different.
Here, the stars are far enough apart no planet could orbit both and be habitable or stable,
but also far enough apart that a planet could be stable and habitable around just one.
There's a gap by the way, where a pair of stars are too far apart for a habitable circumbinary
planet but too close together for a stable orbiting planet around just one of them.
Non-circumbinary planets orbit just one of those stars, also called S-type orbits, and
they need to be at least five times closer to their primary than the other sun or be
disrupted, and that value is very dependent on the relative mass of those stars to each
other and their orbital eccentricity.
Alpha Centauri A and B are 11 AU apart at their closest, 11 times farther apart than
Earth and the Sun, and have a mean distance of double that, so habitable planets are viable
here.
A is bigger so a hypothetical planet around it would need to be a bit farther away from
its sun than Earth is, as it is half again as bright and would provide illumination comparable
to Earth's at 22% farther away, and would have an orbital period of 470 days instead
of 365 at that distance and that sun's mass.
Needless to say it could be closer or farther, or very different in mass, and we hardly have
to abandon it if it is, we already discussed colonizing places like Venus, Mars, or various
gas giant moons and we have just successfully colonized a hostile variable star's planet,
Proxima b, that makes those others look like child's play.
So, we get back to our story at this point.
We send out probes again to both stars, A and B and confirm the existence of a rocky
planet exactly where we want it in that habitable zone in orbit around A. We name it Aurora
and we find a similar planet around B that we name Boreas.
Both are around the same mass as Earth.
Needless to say we are overjoyed by this lucky coincidence.
We are not too likely to find life on any planets or moons in the Alpha Centauri system,
at least not if we don't find it in our own solar system first, which would imply
it pops up and sticks around virtually anywhere, but making life there is actually quite viable.
We confirm that there is no life on either Aurora or Boreas, but both planets have thick
atmospheres similar to primordial Earth that makes terraforming them relatively easy.
Alpha Centauri B is dimmer than A, and its closest approach to Aurora is 10 AU, about
the same distance as Earth to Saturn, while its farthest is farther than Pluto, and it
changes over an 80 year cycle, or more like 60 Auroran years.
We land on Aurora and gaze up at the night sky.
We see B at its closest is still less than a percent as bright as A, but even at its
furthest, it is far brighter than a full moon.
It will noticeably move around the sky over the years like planets do, but again its whole
progress is over 80 years not a month like our moon or a year for the sun.
From Earth, Proxima was 13,000 times farther from us than our Sun is from Earth and only
a six-hundredth as luminous, and indeed it's not even that bright to our eyes as it gives
off far more of its light proportionally in the infrared spectrum we can't see.
That 600th is its bolometric luminosity, its total brightness in all spectrums.
So 200,000 times dimmer and 13,000 times farther away means it appears to the naked eye some
30 Trillion times dimmer.
Now, we can definitely see that on a dark night, but it has an apparent magnitude of
about a 4 or 5, about as dim as we can see.
Remember, while it was the closest star to us, we can't see it with the naked eye,
and it's only 20 times closer and 400 times brighter to A and B. So we see it just as
a regular star, and it is invisible during the day time.
We were disappointed at Proxima b because we did not see a triple sunrise and we are
again disappointed - no triple sunrises here either.
On the bright side, though, there are two sunrises.
Over the year that we work on the surface, we notice B circling around the planet relative
to where A is.
When Aurora is passing approximately in between them it has a normal day and a very bright
night, when B is closest on its 80 year progression, nights are like an overcast day, while at
its furthest in 80 years' time, night will appear very overcast to twilight.
At the full opposite, when both A and B are aligned with the planet on their far side,
the day is just a little brighter than normal, barely noticeable.
However, we get a fairly rare event when we get to the nights there where the twilight
is replaced by a true night sky.
In between that we experience extended days, with B rising before or setting after for
prolonged periods of light in the twilight to overcast range, followed by a genuine but
shorter night.
As we move around the planet on our various tasks, we experience a lot of places with
periods of extended light, tall mountain peaks and the poles experience protracted periods
of having at least one sun up.
This is of more than academic interest as photosynthesis can take place, if weakly,
and we speculate that this is likely to mess around with all sorts of biological cycles,
everything from seasonal growth to the hunting methods and anatomy of eyeballs in species
as they evolve on the planet.
Life here will evolve along its own path and species that adapt to the conditions best
will thrive and survive.
Those that stick to what they did on Earth will decline in the face of those adapters
and die out.
We are called away to the other planet to be terraformed, Boreas around Alpha Centauri
B. As I said, this is hypothetical, except we
don't have to be too hypothetical when it comes to B.
We detected a planet around B in 2012 that was later shown to be an error, we did find
one around B in 2013.
Unfortunately both the ghost planet and the new one are worse than Mercury in terms of
heat, and while we have discussed colonizing hot planets before, or even stars themselves,
planets like these would likely only be colonized in the temporary sense of mining them for
raw materials to make space habitats instead.
Fortunately Boreas is an Earth clone around B for this, and has an orbital distance of
just 0.7 AU, like Venus, to be the same temperature as Earth, and orbits it every 225 days.
That 80 year binary orbital period, which appears as 60 local years on Aurora is going
to be 130 local years on Boreas.
One would hope that our progress in colonizing star systems will be onward and upward, but
history has shown that societies can lose technology and revert to pre-technology civilizations.
If that happens here, we will hopefully have terraformed the planets sufficiently for them
to exist without technological intervention.
Assuming we did regress and then start re-establishing ourselves technologically, natives to either
planet are going to have some calendar equivalent of a century that corresponds to that period.
Amusingly, its duration would be the same for both even though we'd say it was 80
years, the Aurorans would say 60, and Boreans 130.
I stress the calendar aspect as civilizations tend to ingrain astronomy and numerology into
the mythology, mathematics, and early traditions.
Not to mention we have a lot of authors here or folks who just enjoy worldbuilding so if
you're putting together some hypothetical devolved society, alien race or fantasy planet
those are points to know.
Incidentally, if you want to figure these out for yourselves on hypothetical stars,
just check that star's brightness relative to our Sun, use the bolometric value, take
the square root of that and that's how many AU away it would orbit.
Then you need to calculate its orbital period based on that, classic Kepler method but don't
forget to change the star's mass.
This is harder for a close binary case but still works fine for our medium, non-circumbinary
case where the planet only orbits one star.
Or at least, it will most of the time anyway.
Alpha Centauri A is about three times brighter than B but conditions on Boreas are fairly
similar to Aurora.
Those protracted twilights or very bright nights are about three times brighter, though
to the naked eye, will seem about the same, and any plants adapted to make use of that
light will fare much better and be more likely to thrive.
Similarly, while A won't seem nearly as bright in the sky as B when sharing it during
the day, it's a lot closer and a period where A was at noon while B was setting or
rising would have A brighter in the sky than B.
That might make for an interesting protracted dawn because A might only provide twilight
or overcast lighting but it will still be blue sky when it's directly overhead, while
you get that red outward rainbow from B, so you'd get some strange color bands across
the sky.
You'd have those on Aurora too but not as pronounced.
On the biology of the planets, tides on Earth play an important role in ecosystems.
There is some compelling evidence that life could not have evolved on Earth without them.
On Earth, we have tides thanks to the Moon, but in Alpha Centauri, to bastardize a quote
from Back to the Future: "Moons?
Where we're going, we don't need Moons!"
On an ocean-containing world around Alpha Centauri B or Alpha Centauri A, we would get
tides from the presence of the binary star tugging at the water.
The stars are much further away than our Moon is from our planet but Alpha Centauri A is
30 million times as massive as our Moon and Alpha Centauri B is 25 million times as massive.
The effect of gravity drops off with the square of distance.
At the closest, they are about 10AU away from the planet, compared with a paltry 0.00257
AU for our Moon from Earth.
This means that for an ocean world orbiting Alpha Centauri A, tides caused by Alpha Centauri
B would be 60% higher than here on Earth and for such a world orbiting around Alpha Centauri
B, tides would be double that experienced on Earth.
Usually, when we want to communicate with other worlds orbiting other stars, communication
times are upwards of years, but not in Alpha Centauri as communicating with our friends
on Aurora, they are able to receive radio messages transmitted from here on Boreas in
just over an hour, even though they are technically orbiting a different star!
We ultimately achieve the same level of colonization in the A and B systems, including the space
habitats that we perfected when colonizing Proxima.
Humanity is certainly in a different place now and has come a long way from those early
days when we were going to be snuffed out by that black hole.
We are now getting excited about using Alpha Centauri as launch point to colonize the rest
of galaxy now that we have a colony fleet and lots of experienced colonists sitting
around, but that is a different story.
If you're curious about some of those propulsion systems that might take us to the stars, try
out the Spaceship Propulsion Compendium, and if you want to look more at the journey through
space or those early colony days far from Earth, see the Life in a Space Colony Series.
However that is the end of the Outward Bound Series, at least chronologically.
We might revisit it to add some episodes looking at Mercury or Neptune or one of the bigger
asteroids but this is as far out as we're going.
We've been to the planets, many a moon, and even out to the Oort Cloud, we headed
back to colonize the Sun and then out again today to colonize other Suns, and from here
it would continue on to our other series looking at interstellar colonization and travel.
When I first started this series, I faced the dilemma, a good one to have no doubt,
of choosing between providing a brief overview of the science that is focused on relevant
portions, or diving deep into the science but covering much fewer ideas in each video.
Neither approach felt right to me, and I didn't know how best to appeal to my varied audience.
I was then contacted by Brilliant, which has courses that explore the underlying physics
and astronomy for many of the concepts we needed to properly look at here, about a sponsorship
opportunity.
This made me feel comfortable in covering just what is relevant for a solid understanding
of the video, while recommending folks that wanted to explore and master these concepts
to check out Brilliant.
The first message on Hohmann Transfer Orbits was such a perfect fit for the channel, and
many of you appreciated the deeper insight that Brilliant offered.
We can draw on their quizzes, to help us stretch our imagination and discover what else is
possible.
For instance if you want to be able to calculate out stuff like how long a planet's year
would be in the habitable zone of an alien sun, they've got a great course on Keplerian
Orbits and when you're done with it, along with what we've discussed today, you'll
be able to create any solar system you like and know all its specifics.
Isn't that amazing?
Go to Brilliant.org/IsaacArthur and sign up for free.
And also, if you're ready to expand your mental toolbox, the first 42 people will get 20%
off the annual Premium subscription.
That's the subscription I've been using to entertain myself with thought-provoking puzzles.
We might be done for now with the Outward Bound series but next week we'll return
to the Upward Bound series to continue our look at orbital development, and look at some
necessities we'll have to have in order to do that.
We will also look at Kessler Syndrome, the possibility of a runaway destruction of orbital
platforms that could leave space littered with dangerous debris, and what we could do
about it.
In the event of a war in space destroying such equipment you could close a planet off
for generations just from the wreckage.
The week after that we will jump back into interstellar space to look at Interstellar
Warfare, and find out what the #1 rule governing space warfare will be, and the week after
that we will return to the Civilizations at the End of Time series for Dying Earth, and
what civilizations will do when the planet and sun they've always depended upon begin
to perish.
For alerts when those and other episodes come out, make sure to subscribe to the channel,
and if you enjoyed this episode, hit the like button and share it with others.
Until next time, thanks for watching, and have a great week!
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