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!
If terrestrial planet, close to its star like hypothetical Proxima 2, was tidally locked wouldn't it's night side be covered with ice? Depending on how long it had been tidally locked that is - it would have to be hundreds of millions of years at least I suppose for ice to accrete from comets. This would make such a planet easier to colonize. If Mercury had been tidally locked it would be more hospitable than it is.