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A-L-E-X
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25 May 2017 11:22

haha thanks, I was looking around for some menu option to do that :P  Does that setting get saved or does it always default back to 45 degrees after restart?

One other thing with respect to navigation.  If I'm on a planet and want to scan around the horizon is there a way to keep the horizon straight?  Using the mouse and panning around I find that my horizon gets slanted :(  Is there any way to lock panning so you can only move left and right and up and down?  Or maybe I should use the arrow keys instead of the mouse?  And is there any way to mark compass points on the horizon so I can mark my bearings?

By the way with respect to planets there is one particularly noteworthy image where you can actually see five planets orbiting around a star viewed from above the plane of that solar system.
 
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Watsisname
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25 May 2017 15:30

It resets to the default.  You can change the default value in main-user.cfg, under Controls Settings.  There is also a "quick zoom" (Home or middle mouse button) that you can customize as well. :)
A-L-E-X wrote:
Source of the post If I'm on a planet and want to scan around the horizon is there a way to keep the horizon straight?

Not automatically. To compensate you must bank (roll) as or after you rotate.  Maybe someday the camera system will have an option for rotating with respect to the axes defined by the surface of a selected body.
A-L-E-X wrote:
Source of the post And is there any way to mark compass points on the horizon so I can mark my bearings?

Not that I'm aware of.
 
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JackDole
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25 May 2017 23:40

A-L-E-X wrote:
Source of the post Or in general, how do I change the angle of view?  The default is 45 degrees I believe.

You can also use the console. (Open it with the tilde '~')
For example, type 'fov 30'
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PlutonianEmpire
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26 May 2017 14:58

Watsisname wrote:
Even if observing angle wasn't a problem, detecting this on an exoplanet would be pretty impractical.  In visible light, the planet provides less than a billionth of the light that the star does, and then the glint of sunlight off of ice crystals is an even smaller fraction of that.  It would be totally lost in the noise of the star.

This is why it's so difficult to obtain direct images of exoplanets.  It's much easier to see them by the amount of starlight they block if they transit, or by the Doppler shift of the starlight as they tug on it.

What about spectral analysis? Might it be detectable in some way in a spectrum? Thats kinda what I had in mind when I initally asked, since I kinda figured visual detection would be impossible
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Watsisname
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26 May 2017 20:00

The challenges would actually work out to be about the same in that case.   The idea is that you're trying to tease a particular spectrum (in this case a reflection spectrum of the planet) out of a signal that is almost completely due to something you're not interested in (the star).  So you have to remove the star somehow.

This is doable, and the main technique is to block out the star with an occulting disk.  But it works best if the planet is large and far from the star (same idea as for direct imaging).  When this does work it is a very powerful tool that can reveal a lot about the composition of the atmosphere and of clouds and haze layers.  The glints themselves would be a very small change in this spectrum though, and most likely still lost in the noise.

Another spectroscopic technique is to take the absorption spectrum.  In that case you're looking at the light which was passed through the atmosphere of the planet en route to Earth, rather than being reflected off of it (no glints in this case).  It's like seeing the light of all the sunsets and sunrises on the planet simultaneously.  Then the idea is to take the spectrum when the planet is transiting in front of its star, and then substract the spectrum immediately before or after the transit.  You'll be left with just the absorption spectrum of the planet's atmosphere, which again reveals a lot of information.  The benefit of this technique is that it is more applicable to planets that are very close to their stars, since they are more likely to be transiting and transit more often.
 
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Banana
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30 May 2017 14:41

How fast could a black hole feasibly travel, and how would high speeds affect its properties?
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midtskogen
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31 May 2017 02:22

Relativity applies, so the relative speed between you and the black hole can be up to light speed regardless of who you think is travelling.  There's nothing special about a black hole in this respect.
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31 May 2017 05:10

A-L-E-X wrote:
One other thing with respect to navigation.  If I'm on a planet and want to scan around the horizon is there a way to keep the horizon straight?

You can level off the horizon with the End button or use Numpad 4 and 6 to rotate the camera.
 
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Watsisname
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01 Jun 2017 02:44

Banana wrote:
Source of the post how would high speeds affect its properties?

Doesn't affect them at all.  The black hole would still appear spherical, the same size and mass, and all the rest.   

Incidentally, black holes do achieve very fast speeds in nature.  Right before a pair of them merge together, their relative speeds can exceed half the speed of light!
 
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midtskogen
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01 Jun 2017 03:12

Watsisname wrote:
Source of the post The black hole would still appear spherical, the same size and mass, and all the rest.

Which begs the question: What about special relativity, m = E/c², where increased kinetic energy means that the mass increases?
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Watsisname
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01 Jun 2017 09:42

Great question and this is a famous confusion in special relativity.  In our frame of reference, it becomes more and more difficult to accelerate a particle, and infinitely so as it approaches the speed of light.  It seems as if the particle is gaining inertia -- its mass trending to infinity.  But it isn't.  This is simply a property of the Lorentz transformation between the two frames of reference.  It is the same particle, with the same mass, and according to its clock and meterstick it is accelerating just fine and not growing infinitely overweight thankyouverymuch.

The confusion arises because [math] is the internal energy, where [math] is the rest mass -- a property of the object itself and independent of its speed.  You can increase the internal energy of something by, say, heating it up (raising the thermal energy), which will increase its rest mass.  In other words your mass measures your internal energy!  But the internal energy does not change when you speed it up.  A simple reason is that motion is relative.  There is no local experiment that you can do that will tell you how fast you are moving -- your motion only makes sense with respect to something else.  Therefore your speed is not an internal property, and your kinetic energy cannot affect your rest mass.

The total energy (internal plus kinetic) in relativity is [math], where γ is the relativistic factor that approaches infinity as the speed approaches the speed of light.  (It's 1/sqrt[1-v^2/c^2]).  But m is still constant!

It may be tempting to define a "relativistic mass", as [math], to capture this idea that the particle appears to gain inertial mass as its speed increases. But it is a poor choice, and Einstein himself advised against it.  There is no need to consider any mass besides the rest mass.  All of the properties of the object at varying speed follow directly from there.  Then the familiar formulas for energy and momentum become [math], and [math].

So, a black hole moving at near the speed of light still has the same mass and gravitating effect as if it was at rest.  If this was not true, then the principle of relativity (that motion is relative and cannot be measured with respect to absolute space) would be violated!
 
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Gnargenox
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01 Jun 2017 10:20

If an objects mass in relation to itself does not increase as it accelerates, why does it take infinite energy to travel at the speed of light?
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Watsisname
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01 Jun 2017 10:31

In this case I'm not sure of a satisfying explanation for why, other than this is the way the universe works.  Or we can say that if this wasn't the way it worked, then it would violate deep principles of physics and lead to problems.  Like, the location of a black hole's event horizon depending on how fast you're moving, which in turn would make it such that a particle does or does not get swallowed by a black hole depending on your frame of reference, which is equivalent to saying an event both does and does not occur, and that's bad and leads to paradoxes.

Probably the best answer I can give is that it is because of the relationship between space and time -- the Lorentz transformation.  From there you can show that the speed of light can only be approached asymptotically with relativistic velocity addition formulas, without requiring any reference to mass or energy whatsoever!  It is simply a property of the geometry of space-time.

In particular, if you consider an object moving away from you (let's say in the +X direction) at half the speed of light, and a second object moving at half the speed of light relative to the first, also in the +X direction, then the second object is not moving at the speed of light relative to you.

Maybe I'll derive the velocity addition formula later. :)
 
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midtskogen
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01 Jun 2017 14:07

Good question by Gnargenox. E=mc² is simple yet confusing.
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Gnargenox
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01 Jun 2017 14:36

Slightly understandable then. My brain can only think of these things in non-mathematical ways, and I instinctively turn to the concept that everything is the universe is connected in some way. While things relative to me and some other object can seem to bend and twist and warp compared to one another, it is the connection to the rest of the universe that requires this greater energy to change its relationship with the rest of everything. Trying to think in math terms, I suppose objects can have multiple values for its mass, all depending on what other part of the universe is moving in relation to it AND everything else. So, if I apply a force to something, I would be increasing it's kinetic energy compared to everything else, I think, which objects don't "like". This is half of its mass times its velocity... times its velocity (or v squared). If I limit its velocity for some reason and increase the force applied, then I would be increasing its mass also. It is this balance or "Stikyness" of things not wanting to move around in the universe other than towards other things, also with mass.... that makes me think matter would prefer to be in a state of energy, so we end up with gravity and special relativity. I think I'm going to need a beer or two before reading this pdf: Energy and Mass in Relativity Theory
Ooo kay.. 3 pages into that and I realize I need to read this first: The cause of Gravity (& other Strong Force mumbo jumbo)
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