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Watsisname
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15 Aug 2019 20:11

Cantra wrote:
Source of the post If we had an Earth around a hotter sun in a habitable, say an F, A, or O star, would we get sunburn easier?

Yes, we very probably would, for just the same reasons.  The hotter the star, the larger the fraction of its light that comes through UV, so even if we kept the total amount of sunlight at Earth the same, more of it will be causing sunburn.  This could perhaps be offset by a stronger ozone layer, depending on how the planet's atmospheric chemistry works out.

Another problem with hotter stars is that even though they're more massive, they burn through their fuel much more quickly.  An A class star may stay on the main sequence for about a billion years.  O class stars -- only millions.  They don't live long enough to harbor habitable planets.  On the other end of the scale, the cooler, lower mass M and K stars stay on the main sequence for tens of billions of years.  But they may also give off flares which could be very bad for the planets in their habitable zones, being so close to them.
 
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15 Aug 2019 20:27

Watsisname wrote:
Cantra wrote:
Source of the post If we had an Earth around a hotter sun in a habitable, say an F, A, or O star, would we get sunburn easier?

Yes, we very probably would, for just the same reasons.  The hotter the star, the larger the fraction of its light that comes through UV, so even if we kept the total amount of sunlight at Earth the same, more of it will be causing sunburn.  This could perhaps be offset by a stronger ozone layer, depending on how the planet's atmospheric chemistry works out.

Another problem with hotter stars is that even though they're more massive, they burn through their fuel much more quickly.  An A class star may stay on the main sequence for about a billion years.  O class stars -- only millions.  They don't live long enough to harbor habitable planets.  On the other end of the scale, the cooler, lower mass M and K stars stay on the main sequence for tens of billions of years.  But they may also give off flares which could be very bad for the planets in their habitable zones, being so close to them.

Lets say for a moment that the people of this planet are pretty much the same as this Earth. Despite the situation being unrealistic, it's all just there and thriving for no real reason other than it simply existing. Let's say that the Earth in this situation or rather this alternate planet has a stronger Ozone layer (by measures which I can't predict). If they are around an A or O class star, how long do you think until they found out their world is not something that should exist, and within a few million years, will be completely uninhabitable to life as they know it? Would temperature changes be noticeable in their lifetime or noticeable variations in their O or A class star be noticeable? Around an A or O class star the orbital period of the planet would take less of an importance in stellar calendars, I could see those calendars taking more importance into it's moon (s) orbits. Around an O class star, a planet would likely have an orbit in hundreds of thousands of years so such values would be rather unimportant to cultures existing around them I suppose. 

They would be able to notice their sun's rotation upon developing such technology, likely finding out it has a rapid rotation rate to be under a day or less as these stars would have less time to have their rotations slow down. Other planets would appear not as bright in the sky, likely that of distant stars as they would likely be spaced out over larger distances. These planets would likely be quite volatile surfaces, hostile planets due to the amount of heat they emit from recently forming. We would likely see different orbital patterns of moons due to these planets being relatively young, accompanied by their unrealistic neighbor of our hypothetical Earth. This Earth would likely support more than one moon due to a larger roche radius. You could likely go as far until the planet appears as a mere speck and still be in it's gravitational influence because it's so far away from it's O or A companion. 

Could also have asteroid belts and other things, impressive things, all orbiting around a small Earth like world. Due to distances involved, planetary colonization would be extremely difficult, though when it happens expect it to be quite advanced and able to support people on dozens of years or longer as it would take to go between planets. You'd have more massive gas giant planets, planets that would swallow up even our Jupiter or brown dwarfs orbiting this O class star with little affect to our Earth due to the massive blue sun holding them in place, not allowing barycenter like systems. A small earth next door to giants that would put our jupiter to shame.

Could be possible this planet has a property that render's it's plant life to resemble ours for some reason. By which property, I wouldn't know. Rather it could be a certain chemical existing in the atmosphere or something to do with the atmosphere / plant color. On lower class stars, such as K and M stars, we would see the star basically be massive in the sky, I don't think that would be a very pleasant thing to see. Kinda scary I guess, we would be tidal locked unless we are in a resonance which would result in massive Earthquakes due to the proximity to the star and we'd be unable to hold onto any natural moons due to the close proximity. Lower class star worlds don't really appeal all that much to me. Orbital periods would likely be in dozens or less, being rather unimportant due to how fast their orbits are.

 We wouldn't be celebrating christmas every dozen days or so, likely the actual calender would depend on an outer planet. A planet that has a longer orbit that would be the year to the cultures on the planet. A very interesting world, no moons. Possibly other planets could be close in, rather other cycles depending on those planets orbital periods. With apparent brightnesses quickly fading out as they go further than the sun. You could have large fuzzy disks of planets in the sky, that are quite large but dim. Or you could have planets on the interior of the habitable world's orbit, appearing quite bright, always accompanying it's apparent massive companion of the 'sun' in the sky. It would be extremely easy to visit other planets, making colonization quick and easier.

You wouldn't have massive jupiter planets around these stars unless they are further out as they would offset the balance of the inner solar systems because they would create a binary with the smaller, cooler star. Even our Jupiter would probably do that, expect smaller worlds. Larger worlds further out would not be seen until telescopes are invented, leading these people to realize their system is far larger than they imagined. Cooler stars could have planets close in that would be easily seen, then planets further out at massive distances. Would allow for many many planets to exist, and not even be detected until they have technology like ours. Imagine knowing there are like 5 large planets out there, yet you don't know what they look like.

The question is, which of these situations would you prefer to live in? Blue or red. Blue or red pill, if you will.
Last edited by Cantra on 15 Aug 2019 20:52, edited 7 times in total.
 
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slimy
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15 Aug 2019 20:34

Thank you for giving a detailed answer!

FastFourierTransform:

Image

When I compare this map to Space Engine, the Pleiades nebula is located on the very edge of the Pleiades bubble, instead of near the center. Is that it's actual location?


FastFourierTransform:

The Local Bubble at another scale is also not alone. Connected to it by interstellar tunnels in the gas there is the Loop I bubble and other structures of hundreths of parsec in size.

Image

They are not filamentary like the much smaller interstellar clouds inside the bubbles, they are shaped like spherical and cilindrical cavities (results of supernova shells overlapping toghether). It is indeed like cheese in the sense that there are lots of tunnels connecting these "voids" traversing the more dense walls of the galactic interstellar medium.

Are the loops just sparser shells located within the local chimmney? Are they distinct structures? Or am I misunderstanding and the bubbles/loops and chimneys are the same thing?

Are these maps accurate? (I can't find a source, but it seems to get thrown around the internet often. I assume they are older maps.)
http://www.stdimension.org/Cartography/ ... real25.jpg
http://www.stdimension.org/Cartography/ ... real50.jpg
http://www.stdimension.org/Cartography/ ... eal250.jpg


FastFourierTransform:

For the 100 pc to 600 pc surroundings of the Solar System:
Image

I've never seen this particular map before. That is helpful.

FastFourierTransform:

For the 600 pc to the 4000 pc we have this http://gruze.org/galaxymap/poster4/

I notice that the 600 pc to 4000 pc map does not show bubbles at all, only star density and dust. Is 600 pc as far as we can detect it? Can we only guess at what other chimney structures in the galaxy might look like, or how they might all connect together?
 
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16 Aug 2019 21:36

I would be curious if Space Engine could simulate magnification processes from gravity lensing as well as atmospheric lensing.  I know we can zoom in on anything and visit anything, but I think it would be kind of a cool effect.  I'm assuming it's possible based on the distortion filters that already exist for black holes and warping ships.

Please check out this video to see what I'm referring to:
https://www.youtube.com/watch?v=jgOTZe07eHA

Also, is there a way to view Space Engine in other wavelengths of light that are simulated in the visible range?  If not, are there plans to do that?
 
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16 Aug 2019 23:35

Watsisname
Fascinating! Thinking more into this, it could also be considered a conservation of momentum problem. So all the energies of the system aren't lost, just exchanged, and the lack of an orbit can be considered a "ground state", where an object orbiting another is an "excited state", where it still has potential energy to be exchanged. The closest I can come to imagining a situation where the "ground state" is an orbit would be some kind of ergosphere type scenario. Where you have a rotating spacetime, there should still be energy loss in this system though. So ya, this is a super computer's job xD
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19 Aug 2019 00:59

Cantra wrote:
The question is, which of these situations would you prefer to live in? Blue or red. Blue or red pill, if you will.

I think the best stellar classes for habitable planets are G and K.
I can't tell which one of those is the best. The Sun releases a fairly high amount of UV radiation and, if wasn't for ozone layer, life would be very different if there was complex life at all. With that sad probably first K stars/late G stars are the best because the conditions in which life develops appears more frequently. Also if there is any life out there (but I think there is) is surely more common on K stars since their number is higher than G stars, problems like flares and tidal forces are negligible.
Returning back to the original question: I would prefer... the red pill!
Having the sun very big in the sky would be amazing! It would indeed be scary for us but for eventual life living there wouldn't be at all since it's normal! The blue pill wouldn't be bad since plant-like life forms would be blue and the sighting would amazing and be very bright, but I'm afraid life wouldn't be as diffused as it is on earth and years would take forever. An hard choice though  :)
The universe is not required to be in perfect harmony with human ambition.

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19 Aug 2019 12:21

Salvo wrote:
Cantra wrote:
The question is, which of these situations would you prefer to live in? Blue or red. Blue or red pill, if you will.

I think the best stellar classes for habitable planets are G and K.
I can't tell which one of those is the best. The Sun releases a fairly high amount of UV radiation and, if wasn't for ozone layer, life would be very different if there was complex life at all. With that sad probably first K stars/late G stars are the best because the conditions in which life develops appears more frequently. Also if there is any life out there (but I think there is) is surely more common on K stars since their number is higher than G stars, problems like flares and tidal forces are negligible.
Returning back to the original question: I would prefer... the red pill!
Having the sun very big in the sky would be amazing! It would indeed be scary for us but for eventual life living there wouldn't be at all since it's normal! The blue pill wouldn't be bad since plant-like life forms would be blue and the sighting would amazing and be very bright, but I'm afraid life wouldn't be as diffused as it is on earth and years would take forever. An hard choice though  :)

Hard for me to choose. A K class star would be interesting, though I wouldn't want plants to be black though. Hmm, maybe a K class star a bit cooler than the sun, cool enough for an Earth like world to exist in a resonance with it's star, having extremely long days and nights but otherwise habitable.
 
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21 Aug 2019 05:28

Watsisname wrote:
Terran wrote:
Source of the post Is there such thing as a stable orbit, or do the laws of physics forbid this? As in, any two body system should lose energy to gravitational radiation right?

Yep, you're completely right.  All orbital motion generates gravitational waves, which while for most situations is a really, really small effect, would nevertheless cause all objects to spiral together given enough time... assuming proton decay, cosmic expansion, or a Big Rip doesn't get in the way first.

You raise a fascinating question though with introducing a curvature to the space.  If the universe is positively curved then the gravitational waves could eventually come back together at the "opposite side" or antipode of the universe, just like how all lines of longitude radiating out from the North pole eventually converge at the South pole on the Earth.  And then they'll converge once again back where they started, at the system that was radiating them.

Could those waves somehow actually pump orbital energy back into that system, cancelling out their decay?  Well, we'd need to calculate the propagation of those gravitational waves through the positively curved 3D space, while that space is presumably expanding or contracting (unless we perfectly balance it with dark energy?), and then how the re-converging waves then affect those two orbiting bodies much later.  

As I contemplate the notion of doing such a calculation to see if it could work that way, the following meme comes to mind,

► Show Spoiler


and I conclude the answer is "it probably doesn't work that way".  :P

(Actually I am quite sure it could not work that way, because as time goes on the rate of energy radiated by the decaying orbits will increase, and so even if the system could perfectly re-absorb that energy (totally dubious) after it has traveled across the whole universe, by the time those waves come back they won't offset the current decay rate.)

I find it highly interesting that Bode's Law might also apply to exoplanetary systems (it seems to be holding true in most cases), is this because it mimics aspects of the law of gravity (inverse square rule)?
 
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07 Sep 2019 18:52

What if the other side of the moon faced the Earth rather than the one with he Lunar seas?
 
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08 Sep 2019 00:26

If liquid N2 is totally colorless as it says everywhere, then how would a planet covered on deep oceans of pure liquid nitrogen look like?
Blue? Black?
I have the same question about liquid CO2
 
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09 Sep 2019 02:09

DeMooniC wrote:
Source of the post If liquid N2 is totally colorless as it says everywhere, then how would a planet covered on deep oceans of pure liquid nitrogen look like?

This is an interesting question.  I have looked around, but cannot seem to find literature on the absorption spectrum of liquid nitrogen over visible wavelengths.  (There is however abundant study of its absorption and scattering properties at longer wavelengths).  

While it is certainly very clear/colorless, I would be surprised if it is perfectly non-absorbing and non-scattering of visible light.  So I would predict that a deep ocean of it would have some color (ignoring contribution from the atmosphere, which for a nitrogen atmosphere would be blue), but I couldn't say what it would be.  You would also probably be able to see to much greater depths in a liquid N2 ocean than in the oceans on Earth.  I'd expect the same for liquid CO2 oceans.

I like to also point out that even pure water is not colorless, but is actually intrinsically blue, because it is more strongly absorbing at redder wavelengths.  That combined with the scattering of light makes a deep column of pure water appear blue (though again with oceans this is augmented by the color of the sky and scattering by additional particles in the water.)


Cantra wrote:
Source of the post What if the other side of the moon faced the Earth rather than the one with he Lunar seas?

I think this would raise the question of "how did it form/evolve that way?"  

A popular idea is that the far side of the Moon is much more cratered than the near side because the Earth shields it from impacts.  But if we crunch the numbers we find the shielding ability of the Earth on the Moon (or vice versa) is very small and unimportant, even when they were much closer together billions of years ago.  Both sides of the Moon have experienced basically the same cratering rates over time, and on the near side many have simply been covered by the seas of lava.  

But why so many big seas on the near side?  One of the more recent and compelling ideas is that when the Moon had just formed after the "Giant Impact", its proximity to Earth plus the intense heat given off by the remelted Earth, combined with tidal locking, kept the near side of the Moon hotter than the farside.  This slowed the solidification of crust on the Moon's nearside, which meant impacts on the near side had an easier time punching through to the molten mantle beneath and flooding the surroundings.

So if the Moon faced us the other way, we'd need to come up with some other way to explain why it turned out that way.  Example: could it have formed the way just described, but then another impact rotated it until it became tidally locked the other way?  I doubt it, since an impact big enough to do that would probably leave behind obvious evidence or even resurface most of the Moon.

Otherwise, what differences would it make to us?  Probably not much.  I guess there wouldn't be that lore of the man/face in the Moon at least.  Although I prefer the Rabbit in the Moon. :P

Image
 
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09 Sep 2019 03:29

Watsisname wrote:
Cantra wrote:
Source of the post What if the other side of the moon faced the Earth rather than the one with he Lunar seas?

I think this would raise the question of "how did it form/evolve that way?"  

A popular idea is that the far side of the Moon is much more cratered than the near side because the Earth shields it from impacts.  But if we crunch the numbers we find the shielding ability of the Earth on the Moon (or vice versa) is very small and unimportant, even when they were much closer together billions of years ago.  Both sides of the Moon have experienced basically the same cratering rates over time, and on the near side many have simply been covered by the seas of lava.  

But why so many big seas on the near side?  One of the more recent and compelling ideas is that when the Moon had just formed after the "Giant Impact", its proximity to Earth plus the intense heat given off by the remelted Earth, combined with tidal locking, kept the near side of the Moon hotter than the farside.  This slowed the solidification of crust on the Moon's nearside, which meant impacts on the near side had an easier time punching through to the molten mantle beneath and flooding the surroundings.

So if the Moon faced us the other way, we'd need to come up with some other way to explain why it turned out that way.  Example: could it have formed the way just described, but then another impact rotated it until it became tidally locked the other way?  I doubt it, since an impact big enough to do that would probably leave behind obvious evidence or even resurface most of the Moon.

Otherwise, what differences would it make to us?  Probably not much.  I guess there wouldn't be that lore of the man/face in the Moon at least.  Although I prefer the Rabbit in the Moon. :P

Image

I would imagine that without the seas that the moon would be slightly brighter in the sky. We would lack the knowledge of craters on the moon due to its brightness except that one small Lunar sea and maybe that other small one. I don't know what legends we would come up with about the moon, however when we see the other side of the moon we'd see the Lunar seas and probably be very surprised.
Image
 
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09 Sep 2019 09:42

DeMooniC wrote:
If liquid N2 is totally colorless as it says everywhere, then how would a planet covered on deep oceans of pure liquid nitrogen look like?
Blue? Black?
I have the same question about liquid CO2

pure water is generally colourless too... i guess it'd depend on what wavelengths liquid N2 or CO2 or anything else absorbed preferentially?
 
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09 Sep 2019 10:09

evildrganymede wrote:
Source of the post pure water is generally colourless too...

Pure water is not colorless.  :)  It is intrinsically slightly blue, which becomes apparent when viewing through a long (few meters) column of it.
 
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19 Sep 2019 03:39

What if the moon revolved around Earth in the opposite direction? Getting closer each year rather than farther?

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