Green Baron

Agreed :-) (Edit: though i would take the hillsphere as the main criteria. Nuances ....) ... just tried to argue against the idea the moon is in orbit of the sun. That'll be, for my understanding, too broadly a use of "orbit". We might end up with moon orbiting the Great Attractor ... :-)

I only saw the gravitational force for the sun and the earth on the moon, not the orbital elements. Maybe google failed me, i have to reconfigure my network access to reach google. Anyway, the moon performs a different motion around the sun as the earth, so the elements cannot be "exactly the same". "Nearly as perfect as earths ellipse" is too sloppy for my understanding and only valid if you see earth and moon "almost" as a single mass or from very far away. Which is ok, but not sufficient e.g. for orbit calculations inside the earth/moon system. Maybe i misunderstand your point of view, sorry if i do ...

Or else the poor guys will be in a very bad shape after a few months ...

Ah, oh, yeah. You are right, i argued with the wrong person. Should read more thoroughly. Sorry, i apologize for my eagerness :-) And basically i agree with you concerning orbits and moons, i think. Yet we are missing a hard definition of "orbit" and "moon" but i think that when saying "a moon orbits a planet" most people think something similar to what you wrote. The Sun will, as far as i know, not pull strong enough to tear the moon out. The moon's orbit rises because of impulse preservation due to the breaking effect of tidal forces, they exert mechanical friction, break the earths rotation and in response the moon gets away. But it will most probably not leave earth's orbit in the lifetime of the solar system.

My point is, the conclusion "the moon orbits around the sun and not earth" is based on too little data. It only takes into account the force the sun exerts on the moon, not the fact that the same force is exerted on the earth as well. Better, on the barycenter of the system earth/moon. The moon goes it goes "up and down" around the earth on it's path around the sun. And that is because it is in earth's orbit. Earth and moon and some other stuff together are in sun's orbit. Would you, for example, accept that a tidal wave is in orbit around the body that causes it ? I define "orbit" of a A around B as: A's path is at all time inside the hill sphere of B. That does not exclude that other external or internal bodies can have an influence (aka perturbations), but this influence does not put A inside another body's hill sphere. The orbit of A around B can approximately be described by Kepler's laws of motion. You definition looks like: A is in orbit around B if B exerts the greatest gravitational force on it. Whether B exerts that same force on another body that co-orbits with B is ignored. Kepler's laws are not applicable. The path of the moon around the sun can only very coarsely be described by them. A moon of Jupiter for example does weird things. In my defintion the moon is in orbit around earth. The sun acts as a perturber. The tidal forces between moon and earth are dominated by those two, though the Sun and Jupiter must be taken into account for naval and navigational considerations (tidal heights and streams). Are we together ? :-)

The conclusion comes because you only look at the force the sun has on the moon. The same a similar force is exerted on the earth, so you can ignore it for the moons orbital considerations and replace it with the difference of the force on the earth and the moon. We go into tidal forces then, an then the suns influence is much less (not neglectable). This is clearly reflected in reality because the moon is in a bound rotation around earth, not sun. No, they wobble around the sun, no "round" there :-) But "round" in respect to the planet, not to the sun.

Morning *yawn*. Lol, funny how one can get excited about definitions. If you define an orbit by the force that's being exerted the moon is in orbit around the sun. If you define it by Kepler's laws then it is in orbit around the earth. It is just a point of view. I do not accept the first idea because it leads to a wavy orbit and ignores the presence of hill spheres and barycenter, which are actually quite nice because with their help we can put satellites in places. Which actually works. Trojans stay where they are (or are attracted). Push them towards the planet and they enter an orbit around the planet, push them in the other direction and they fly around the sun. This is for ease of talk, just to know that if someone talks of an orbit in respect to a body he means that body. Again: even in astronaut around the moon would in a "sun orbit" according to that definition. @K^2, your definition leads to misunderstanding and unclear use of the word orbit. I doubt it will make into every day use. I am still waiting for the moons orbital parameters in a sun orbit. Peace, love & understanding :-)

Uneven mass distribution ... wouldn't that be forced into a bound rotation soon ? And wouldn't the momentum change then cause that thing to rotate around the longitudinal axis ? Not sure, a question .... If so, don't look out of the window :-)

Is that real or hypothetical ? If real, source pls. Because afaik only a few asteroids / kbos go withershins. May be caught from outside or exchanged with neighbours (hypothetical) or forced by encounters with inner planets. These objects don't need much to change their path. Edit.: oh, the picture does not show the solar system, just Jupiter and its kin. So, option 3, forced by big daddy :-)

I don't think that categorization should not depend on orbital parameters. The orbital state of any body is not "hammered in stone", after and before all these systems are dynamic. So a moon can become a (dwarf-)planet (ours could if it had enough time), a dwarf planet can be captured and thus become a moon. Even a planet can loose its state due to dynamics. Any categorization is just a helper, so that the other one knows what i mean when i say "planet" or "dwarf planet". These two now have a definition, we can accept it for convenience or not. Good thing, everyone now knows what an astronomer means if he says "dwarf planet" (until re-definition). With moons this is less clear as "moon" isn't defined that hard (obviously they were clever enough to avoid the discussion :-)), same goes with orbit or pseudo orbit. We can accept the hill sphere and a barycenter as the elements or the projected orbital path, the exerted force, whatever. It's only a convention, and after all anything describes a current state in a dynamic system. I think that one day soon someone will come up with a definition of moon or natural satellite, as we describe more and more of these systems. Not to degrade or promote anything, just for the convenience of being able ffor a description with as little misunderstandings as possible.

True, that was a false assumption from my side. That's a geometrical thing resulting from the orbital speeds of the bodies projected on a two-dimensional plane. Nevertheless, the moon is completely within the earths hill sphere, no way it leaves in foreseeable time and orbits the sun independently. The sun could pull it out if the system earth moon fell below the roche limit, as far as one can speak of such a thing for a two body system whose common center revolves around a central body (sun in this case). Sure, both earth and moon orbit the sun, but while doing so the moon is bound to earths gravity. It will never not so soon cross L1, like an astronaut in orbit around the moon will not fall towards earth even if earths pull is stronger than the moon's (didn't do the math). Not ready to accept the moon as an (independent) satellite of the sun :-)

*scratchbaldhead* rejected :-) The moons orbit around the sun is a spiral movement around the common centre with the earth. Like the Ptolemaian outer planets, but several times a (edit: earth)year. I need something better ... Edit: Heathen ! You want to put the Sun in the centre ? (of the 3-body-system earth-sun-moon) :-))) Edit: scrub it, you are right, the moons orbit around the sun is totally convex ! Nevertheless the earth is the dominating body ;-)

Thanks, @K^2. But this is the first time i read that the suns pulls more at the moon than earth does. All my information until now was that the moon revolves completely inside earth's hill sphere where the earth is the dominating force, not the sun. So, i have my problems accepting the moon as a satellite of the sun. The moon follows Kepler's laws (afaik) in respect to its (imo) earth bound orbit, it's orbital plane around the earth is slightly tilted in respect to the earth's ecliptical plane and the tilt is stable (afaik). Were it in an orbit around sun but co-orbiting earth, it would perform a cycle once a year, not an odd number one. The moon stabilizes earths axis and it is forced in a bound rotation in respect to earth, not to the sun. I would be more willing to accept the idea if you could provide me with let's say the moons orbital parameters in respect to a sun orbit ... Edit: of course the moon is influenced by the sun as well, but afaik not as the dominating force.

Hey, don't cite me after i liked your post ;-) (i know, the forum software merged this without being asked) Yeah, we are looking for a definition of "moon" and "orbit". Still even Jupiter and a dust particle have a common barycenter if they orbit each other. Size doesn't matter. Or does it ? How much less mass than the bigger one must the smaller one of the bodies have in order to be called a moon of the bigger one ? Furthermore, what defines an orbit ? It was posted above that common barycenter is no criteria. But is that so ? If the moon and earth would co-orbit the sun as independent bodies (without catching each other) other then they must be in 1:1 resonance (like 2016 HO3). But we know the moon orbits earth several times a year. Though it gets higher and higher due to impulse preservation the moon will not leave the earth's orbit during the solar system's life time. If it had more time .... Edit: to further complicate things i leave this link here: https://en.wikipedia.org/wiki/(469219)_2016_HO3 and kindly bid mercy for linking to wikipedia.

Pls. elaborate a bit on that. Why isn't the moon (Luna/Mond ...) a satellite of earth (Terra/Erde ...) ? I have absolutely no problem with that, i'd just be happy if i get a defintion of moon or satellite. Common barycentre apparently is no criteria fo you if i follow your thoughts. The iau doesn't have a definiton of "moon" because it makes no sense. In principle you can go down from planet, moon, natural satellite of moon, satellite of satellite and so on. If a body orbits another they have a common barycentre. A body can co-orbit with another body around the same central body, you can name it a quasi-satellite if you like, but they have no common barycentre then, instead they have to be in resonance in order for that constellation to happen. Earth/Moon have a common barycentre and orbit each other. Together they orbit the sun. Edit: partly ninja'd by @Streetwind

In principle and following theory: no. With a dslr you should take darks for every series of light frames so they where made at the same temperature as the corresponding lights. You shouldn't use darks taken at 10°C to raise the snr of light frames taken at 15°C. Otoh, photography in general can be a very personal hobby. If you are content with the outcome of mixing "warm lights" and "cold darks" (or vice versa) then why not ... just try it. Even with ccd that can be set to a temperature i would take a new set of darks every few months. A chip changes over time, it doesn't get better, because entropy and so on ... :-)

Have been playing a bit with Pioneer. The game is already a few years old but still developed. It's completely open source and for that actually quite nice. Gets a little repetitive after some time but still much better than Freelancer for example. Although, because of the ridiculous dV and acceleration the ships have, the feeling is more 2 dimensional than in ksp/orbiter.

Some people actually do pay money to have a ride on fast rotating devices at fun fairs. But this probably a European phenomenon. Might be connected to the age old habit of self castigation or something :-))

Blowing in the same horn. I'd be happy if we could at least pretend to keep a science background. Or rename the forum :-) There isn't even a first generation emdrive and there is no reliable proof that the thing works. Nobody can explain what was measured, if something was measured at all. The saucer shape is from fun pictures of the second third of the last century (maybe older) :-) A fusion reactor is far from a working example. All the coils and magnets to contain a plasma of a few grams are heavy. I mean, that all is fun as an add-on for computer game, but that is all imo.

Condolences. "My" cat (an adopted stray cat as well) was coiled up on the keyboard this morning, purring slightly distorted. But that only lasts minutes, she is a killer. I have to clean half chewed up lizard zombies (the other half lives for quite a while) or catch mice from between the furniture. Sometimes she vomits on the carpet and once a year or so we have to go to the veterinary to cure her from parasites ...

I am confident that Traptolemaios finds away to construct his own planet in the centre and the others spiralling about. What must not be, cannot be :-) A little OT but interesting: Here is about a planet very close to an A/B star. The planet has a dayside temperature of >4000K. Will completely dissolve loose significant amount of mass over time in the hard radiation. How do these things form in the first place ? We are just at the beginning of understanding solar systems ...

I am fascinated by procedurally generated worlds too. Simulations with a geoscience background are actually quite far generating e. g. erosional structures and drainage systems from centimeter to mountain range and subcontinental size. Advances in climate research are a driving force because it touches all fields of geoscience and much of handling the huge amount of information. Some of it has been packed into algorithms and visualization. But that costs, not so much computing power (the parallel power e.g. in modern graphics cards is barely used, and all the layers between the machine and the user eat up most of a pc's power for just pushing around data) but rather storage space. If someone wanted to do something like this in connection with a computer game that'll be much work on the generator side because it needs more than just game physics (i mean force calculation, -integration, movement and dynamics, collisions, physics based shading). So one would need a solid framework written in code that can be executed fast and without intermediate layers like ready made game engines. That is why i would say KSP in its actual form isn't exactly suitable for that. Maybe a 2.0 or so. But until then maybe others have taken over. Of course, i may be wrong ...

I could just barely hold me back, it looks so ... sweet :-)

I am not sure if i understand what your question is. I have difficulties comparing the pictures because they show different clipping. What comes to my mind is that you haven't found the focus yet and suffer from severe coma, as one would expect with a newton f/4 and an aps-c size chip. Both problems can be overcome. Combining steps makes it much more difficult to find difficulties and sort out problems, address one problem after the other. With a series of exposures do the stacking as described in all the tutorials and save the stacked image. When stacking you can play with the stacking parameters but nothing more. DSS shows a stretched image after the process, you can save it as a suggestion by DSS, but always keep the unprocessed stacked fits or tiff image. That image, though it looks less impressive than the suggestion, includes many magnitudes more of information and is the working base for you post processing in another program(s). To sum up: find the right focus on a star in the center of the image, if that is solved then try the stacking. Afterwards address the coma problem (because that is going to cost a little something), then you can do successful post processing.

Have a look at this project: http://proland.inrialpes.fr/ The source code is online on github. That would be a nice idea, but I assume that this cannot be realized with a game engine because of lack of performance and storage issues. A planet like earth needs 20GB (compressed) just for the surface data. A solar system would bust a pc's capabilities. Naive thoughts on this: since proland and ork are based on opengl which apparently is not developed farther any more, let's start with a render framework based on newer technology (vulkan). Then terrain generation and storage, generation of surface elements, level of detail control, physics based shading (probably the most tedious part), etc. After that a physics framework (peanuts these days :-)) and a nice gui for player interactions. But i am not a programmer :-)