Ever went somewhere like a quite dark street with only few working street lamps? Notice how the illuminated part of the ground radially decrease intensity? Or noticed that a campfire is less 'hot' when you are far from it? Ever wondered why?
Some might instantaneously shout "CUZ' AM FAR AWAY, DUH", which is not actually wrong, but, there is way more than that.
The same way you can't see/feel the waves generated by a pebble thrown 10 miles away from you in a calm sea, you can't hear someone more than 300m away or be illuminated by a street lamp from 20km...
The kinetic force of the pebble in the water creates waves that radially expand outwards through the medium (water surface), all waves behave the same way, as a consequence of our tridimensional space, these radii in a 3D medium like Space gradually expand outwards, BUT as far the number of particles (in the case of light, photons) still the same, these particles are spread out in larger and larger areas as distance increases.
Now you know that when you're away from the campfire, you're receiving less infrared light than being closer to it.
The amount of anything that spread in space is inversely propotional to the square of the distance you're measuring from the source.
Mathematically, using light as example:
LR = (LS / D²)
Where:
LR = Light Received
LS = Light from Source
D = Distance
Of course, result value is proportional to you unit of distance (m/mi/Km/AU) and your unit of measuring the 'thing', which is light or intensity of a force, it could be Joules, or Watts or a standard luminous parameter.
Let's calculate how much light reaches Venus.
Taking the Sun intensity as 1.
Taking the Light that reaches Earth from 1 AU is 1.
Venus orbits the Sun at ~0,73 AU.
Then we have:
LR = 1 / 0,73²
LR= 1 / 0,5329
LR= 1,876524676299493
Venus receives ~1,87x as much light as Earth.
Proportionally, if you move closer to the source by ~25% (almost like Venus), expect the intensity to rise up by ~75%, if you 50% the original distance away, then the final intensity is 400% the original.
If you double the distance, light will be 4x weaker, if you triple it, light is 9x weaker and so on.
What if we create our Tatooine? (cliché citation ugh). A Type-P(arental?) system, is a system with two close stars orbiting each other while the planets orbit the dancing pair of suns.
My lazy attempt of reproducing Tatooine's landscape without being sued by Disney...
Before going into physics and orbital parameters, let's look what exactly is a P system...
The proper naming for a double-star system is Binary System. For this case, where the two stars are so close that planets orbit around both is a Close Binary System.
And believe it or not, it happens that planets around close binary stars are not so odd in the universe, since nearly 1/3 of stars in the Milky Way have 1 or more partners.
According to Wikipedia, the likelihood of stars having 1 or more partners increases along the components mass, for example, if you randomly pick 1000 Red Dwarfs and another 1000 F stars, is more likely that you find around 500 stars in the F group that are members of multi-star systems in comparison to the less than 200 stars in the M group that are members of multi-star systems.
Here is what a Close Binary system map look like:
Is rather common that close binary have similar properties to each other (mass, composition, luminosity etc), because most of then are born from the same molecular cloud.
Imagine a different reality where the Sun didn't become the Sun, but instead started to spin so fast that its central blob divided into two smaller proto-stars orbiting very close, the sum of both Suns would be very close to 1 Solar mass (or they would sum to 2 solar masses, e .e as there would be two Suns).
Maybe it doesn't sound pretty much of a thing for you, but we know the Sun had a decisive value in evolution of life on Earth, maybe the two stars could have created a reality where primitive sharks colonized the land during the Devonian rather than vertebrate fish, or it wouldn't have changed much until the rise of mankind, imagine every culture having two Sun Gods, maybe such a world would have been easier to unify for one aspect as such the effects of one god over another would have been very noticeable, and there comes the first physics topic...
BINARIES COOK BETTER PLANETS
LIKE, LITERALLY THEY COOK BETTER PLANETS...
Ever heard of a Planetary Mixer? Those stirring machines used in bakery and cement production.
Astrophysicists believe that the gravity resonance of multiple stars in a system can better mix the molecular cloud in the planetary disk, lets say, more stars easily stir the proto-planets better than only one, maybe even creating more planets, and more planets inside their habitable zones.
Have some examples and what I want you to visualize...
01. 5-star 'Planetary' Mixer...
02. 6-star 'Planetary' Mixer...
03. 3-star 'Planetary' Mixer...
Those configurations of binary and tertiary systems are far simple, take the Castor System for a view of how crazy this can get in nature...
More about advanced planetary mixers in future posts.
Eclipsing Binaries
As the planets orbit the pair, and the stars orbit each other, from somewhere in the system is possible the see the stars eclipsing each other, like when the Moon lines the Sun, as stars are not transparent, their partner's light can be obscured when they pass behind. If your stars have different colors and brightness, this can create colder days or weeks with different sky colors when one star eclipses the other.
Ex; A purple sky when the red dwarf eclipses the orange one, and a grey-navy sky when the orange eclipses the red dwarf. And while both are shown, the skies are tinted in a dull blueish-grey light.
This kind of event can create some very beautiful scenes and even become part of the locals culture and way of counting time.
The sky, is something worth observing...
The same way the planets orbit the Sun, stars that orbit each other can be observed over time, eventually, as some people notice the movement follows a specific pattern, and every time this pattern repeats something in the world happens, let's say, when the red sun sets first winter is about to come...
Notice that the orbits of Mercury and Venus are inclined in the GIF above, this not only happens because the planet's orbits are inclined relative to Earth, but also because of the viewer's position on the globe.
If we consider the North pole as being upwards (which usually happens), the planets orbits, which are along the ecliptic plan appear horizontally. Then, someone standing on the equator of the planet sees everything sideways in the sky (like the in gif above).
This is valid for everything from moons, to planets, and to the parent stars.
Keep this plan in mind.
And now lets assume we have two viewers, one on the North, and another near the equator.
Both watching the sun-rise of the double stars through the year.
Green lines represents their horizons, notice how they are inclined relative to each other and to the planet's latitude.
View of A:
View of B:
Notices also how in the GIFs, the planet lighting changes color slightly according to which star is on top.
Here is another view of what happens:
This blog's name used to be Heavens of No Earth
Is pretty evident that moving lights (stars) will create a wobble in lighting on nearby planets, the greater the angular separation between them (how far apart they appear to be), the more evident is the light wobble, as one star sets before the other, temperatures suddenly drop, sky color changes and etc, is a neat niche for amazing views in those worlds.
THE SYSTEM BARYCENTER
Noticed double stars mostly don't orbit each other like planets and moons do, instead they orbit a common point in space, it is called Barycenter, or Center of Mass.
In planets and moons, the system's center of mass is usually inside the planet (larger body) all times and is usually very small. The Earth wobbles as the Moon moves around, but the barycenter still inside Earth.
But for large bodies like stars and entire solar systems, the thing is way different.
Here is a map of motion of our Solar System barycenter:
All this wobble is caused by the motion of ~0,1% of the Sun mass (about everything around the SUN).
What about the mass of another star???With newtonian physics we can define what is the center of mass of two bodies, or two stars in the case.
By a rough definition, close binary stars are separated between 0,15 AU and 6 AU.
Now, masses still range from the Habitable Star Basket, but kinda obligatory only for the primary.
Choose your Primary's mass between 0,6 and 1,4 solar masses. We will call it Star A.
For your Secondary's mass, wander between being EQUAL or smaller than your Primary, like a sun-like star orbited by a red dwarf, it can be as small as 0,08 solar masses, but not smaller than that, or it's partner will be called a planet or brown dwarf.
Now, the distance from your Primary star from the Barycenter is given in AU by:
If my stars are respectively 0,75 and 0,3 solar masses, separated by ~0,33 AU (50 million km).
Then my barycenter is 0,094 AU from the primary, ie, both orbit a common point in space that is 4,7 million km from the primary star.
From this we can automatically take the secondary as being 45,3 million km from the barycenter.
Wanna improve this? State orbital eccentricity, just remember Kepler's Laws, every planet orbit its not an absolute circle but rather an ellipse, with one focci being on the star and other in space, well this also apply to stars (duh < .< ). 0 value is a absolute circle, and 1 is something like an hyperbola.
The closest to 1 your orbiting bodies will behave like comets, and the closest to 0 will orbit more circle like.
I would advice to choose values between 0 and 0,6 for anything you might do around eccentricity topics, okayz?
Pick your eccentricity value and add/subtract the corresponding portion from orbit distance.
Now, taking from our previous example. I choose 0,15 as eccentricity value.
Primary
Avg. dist.: 4,7 million km
Min. dist.: 4,7 - (4,7*0,15) = 3,995 million km
Max. dist.: 4,7 + (4,7*0,15) = 5,405 million km
Secondary
Avg. dist.: 45,3 million km
Min. dist.: 45,3 - (45,3*0,15) = 38,505 million km
Max. dist.: 45,3 + (45,3*0,15) = 52,095 million km
Binary bodies are on opposite sides of the barycenter, if your primary is on the minimal distance, then your secondary is on the maximum distance, and vice versa.
