-Velocity-

But anyway, if we CAN find some way to mass produce sail material in space, and IF we could find some way to actuate it and make it maintain precise shapes (within an accuracy of like, 80 nm), then you have incredibly good telescopes and mirrors- no need for interferometers. One way to possibly do this is to correct for aberrations in the large focusing mirror in a much smaller, adaptive mirror, similar to how adaptive optics works today. Anyway, you could potentially form some very, very low divergence, Gaussian laser beams for your laser-pushed light sail. You could focus almost all of your laser energy on your light sail, even out to hundreds of AU. It's fun to dream about.

No, not necessarily. If you make it very thin, you can get high speeds out of it, because the force applied by the sunlight does not change as you make the sail material thinner and thinner. You just reduce mass, which, of course, increases acceleration. But, while it's fairly easy to make small samples of a thin sail material that would be suitable for an interstellar (~0.01c+) laser-pushed light sail or even possibly an interstellar SOLAR sail, it's a WHOLE OTHER MATTER to try to make a lightweight rigging system, and to produce the hundreds or thousands of square kilometers of material that is necessary to carry a useful payload.

An object inside the Sun's corona will not heat up to 1 million degrees. Probably, some kind of process with magnetic fields there is causing the ionized gases to heat up, and despite the fact that I don't know what it is (and I don't think astronomers really know either) one thing is for certain - it's not going to affect a blackbody. You have to have an electric charge (and be moving, but everything is moving to some degree), a magnetic susceptibility, or a flow of charge (all three of these are really just different ways in which you can have a difference between the movement of positive and negative charges) for a magnetic field to affect you. In the case of the corona, it's the electric charges of the ionized gases that allows them to be affected by the Sun's magnetic fields. A solar sail isn't going to have an electric charge! So your solar sail isn't going to be subject whatever processes are heating up the gases in the Sun's corona. It's not a problem of temperature- anything that absorbed a bit of heat from the superheated gases of the corona would quickly re-emit it into space as EM radiation (mostly as IR, but some visible will be mixed in too if it's hot enough to start glowing). However, you're talking about a ridiculously thin membrane of carbon, that would be bombarded by very high speed (as atoms heated to millions of degrees are moving really fast!), ionized atoms. Luckily, they would be very light atoms. Even so, that could very well damage your graphene, but I don't know enough about chemistry to say. All I know is you're going to have A LOT of electron-hungry atoms hitting your carbon at very high speed...

I've never heard of anyone spotting M32 or M110 naked eye, I am 99.99% certain that they are much too faint to be seen. Someone with ridiculously good vision MIGHT claim a successful sighting of M32 (they would have to have almost unbelievably good vision), but M110, in particular, is low surface brightness too- and 9th magnitude IIRC. No one will see that. As far as adverted or direct vision, you'd probably need direct or semi-direct. The problem with adverted vision is that it has very low spatial resolution. VERY low spatial resolution. So your adverted vision wouldn't be able to separate Callisto from Jupiter's glare. You could probably use semi-adverted vision though. Maybe some of these observing techniques though are particular to my own visual system, my adverted vision sweet spots are located very far from the center of my visual field, and in very low spatial resolution areas of my visual field. When observing DSOs, I frequently have to use semi-adverted vision to increase my spatial resolution at the cost of a little sensitivity. Anyway, I doubt my vision is low enough scatter to spot any of Jupiter's moons naked eye anyway. At the darkest skies in North America, I can barely get below magnitude 6.5. My daytime vision is good, so the central 3 or 4 mm of my eye's lens is good, but the outer areas of my eye's lens might be a little astigmatic, as I definitely notice a little astigmatism when looking at stars and rotating my head- the astigmatism rotates with my head movement.

"You must spread around some reputation before you can give it to K^2 again." Thanks for the info! I didn't know about this technical challenge. Do you have some good technical references on it? I could look up some IEEE papers, but technical papers are not a good place to start on something that you don't know much about, unless you can find one of those rare "An overview of -" papers. I did take a class on lasers, but we didn't mention this topic at all, not that I remember. If I remember, maybe I can dig out the textbook we used tonight to see if it there's mention of coherence length.

Well, I highly doubt that Mars ever had a biosphere thick enough to produce oil. Earth didn't either, not for the first 4 billion years of its existence.

Anyway, I was curious if gravity waves actually make a noise floor that makes optical interferometers larger than a certain size impossible, or could that be compensated too... Still, if it does make a noise floor, it would probably not kick in till what... optical interferometers like the size of the solar system?

K^2, I fail to see how your pessimism is justified. First of all, the 20 km diameter was clearly stated as simply being able to resolve an Earth-sized planet as a "disk" from 50 light-years. "Resolving as a disk" is the common term used when we talk about what resolution is required before a point source first begins to resolve. It is obvious I was talking about simply a fuzzy picture of something just barely larger than a point source. Clearly, if you want a true terrestrial planet imager, you'll need something like on the order of at least 100 km across, and then, you'd only be able to get halfway decent images of the very closest planets. I had almost added that if we could make an interferometer some day with a diameter of 1000 km, we could put the equivalent of 50 pixels across an Earth-like planet 50 light years away, but I cut that part out; I thought it was too much detail and too distant of a proposition. Perhaps I should have left it in to make my meaning more clear? Perhaps I misspoke when I said we can do it with today's technology, but we should be able to do it soon, especially if more funding and study was put into it. I don't see where there are any major show-stopper issues. Perhaps I misspoke because what I really mean, when I think of "today's technology", is that it is something that we either already have, or could immediately begin research and development on, and have ready in a reasonable time span like 10 or 20 years. Clearly, if we directed NASA to build a space interferometer composed of a separately-flying, telescope constellation, we wouldn't be getting in for at least 10 years, probably more like 20- just look how long it took for just the "simple" JWST. But at least, we'd be working on it, and it would be coming. I would assuming that station keeping would be accomplished with something like small electric ion thrusters. You can probably have some small adjustable optical elements to make up for really small, fast perturbations. You can determine the precise distance between the spacecraft with laser interferometry, and it is accurate to the required precision for optical interferometry. How can this not be extended to kilometer+ distances? I would think that the lack of atmosphere, ground vibrations, the ability to smoothly change the distances between the telescopes means space is a far better environment to build an optical interferometer than the ground. I don't see what you find so worrisome about drift. In space, perterbation forces are extremely weak, as opposed to on Earth, where we have wind, Earth quakes, even the minor seismic distrubances caused by people walking around or cars passing by; temperature swings, etc. Space is empty and constant. We have the thruster and MEMS technology to precisely position the telescopes, or there is no reason to think we couldn't develop it. We have laser interferometers capable of measuring extremely precise distances, precise enough for the task. And if by some chance a visible light laser interferometer isn't good enough, why not just use a UV laser interferometer? Where do I go wrong here?

Oh by my calculations, you'd "only" need an interferometer baseline of around 22 km to resolve the disk of Earth at the distance of 50 light-years in visible light- Diameter of the Earth ~13e7 meters 50 light years = 4.75e17 meters Angular size of Earth's disk at 50 light-years: 13e7/4.65e17 = 2.74e-11 radians Visible light wavelength: ~500e-9 meters Require telescope diameter to resolve 2.74e-11 radians: D = 1.22*500e-9/2.74e-11 = 2.24e4 meters = ~22 km. An interferometer gets around having to actually have an impractically large telescope by combining the light gathered by two much smaller telescopes, precisely positioned a known and large distance apart from each other. With some clever signal processing and utilizing some of light's wave effects, you get the same maximum resolution as a telescope the diameter of the distance between the two smaller telescopes. And you can do with with alot more than two telescopes at a time. There are some drawbacks, you collect less information on lower spatial frequencies (you can "fill in" the gaps by using multiple, and shorter baselines). You also want a 2D, not one dimensional array, otherwise your interferometer only has high resolution in one dimension. Radio astronomy, which has been using interferometers for decades, has techniques to counter some remaining drawbacks as well (it is vastly easier to build radio interferometers than it is to build optical interferometers). So you "just" need a fleet of space telescopes flying in formation across a few dozen kilometers of space, station-keeping with respect to each other with nanometer precision. Sounds tough, but this is achievable with today's technology, believe it or not. Just expensive. BUT A HELL OF A LOT LESS EXPENSIVE THAN AN INTERSTELLAR PROBE!!!! The cost of each space telescope would also be significantly lowered because you'd be effectively mass-producing them.

Yup, biomarker molecules can be detected in the atmosphere. Earth light has O2, O3, water vapor, and methane absorption lines that would be detectable for dozens of light-years by aliens utilizing the just the kind of technology we have today. These molecules, together, scream life- there is no known way for these molecules to coexist in large quantities outside of biological processes The JWST could possibly find an Earth-like planet with life, especially if they get that star shade made for it. It seems likely within 100 years we will have telescopes capable of detecting life on Earth-like planets out to 1000 light-years or more. It gets better too- for example, it seems the spectral signature of chlorophyll is detectable in Earth light too- astronomers analyzed Earth shine on the Moon and found what appeared to be a weak signal from chlorophyll. Also, aliens looking at Earth would easily be able to tell our planet rotated in ~24 hours, by changes in the color and albedo, and graphing these. They could tell how much cloud cover Earth has, what percentage was land and what percentage was water. They could tell that some areas of land were brownish/orangish, while some were very green. With a really big telescope, of the kind we'll have in a few decades, they would be able to see the light pollution from our cities- for example, there is no reason a planet like Earth should have mercury emission lines, other than artificial lighting. All this kind of information can be determined just by analyzing the light of a distant, point-source Earth. No need to resolve the disk.

I've got a 25" dob, but between moving and just plain terrible weather and luck, I haven't gotten to use it, other than for public outreach, for over a year now A couple weeks ago, the day after Thanksgiving, I finally had clear skies coincide with time off and a new Moon. Guess what? For the first time in over a year, I was sick. F*** my luck.

I would think that the main issue with spotting the Moons of Jupiter naked eye would be glare and scattered light. Both in the atmosphere and on your retina. Jupiter is so bright that it has a little aura of scattered light around it in the sky... and of course, the lens in your eye and your cornea scatters even more. I did some observing from West Texas a couple years ago when Jupiter crossed the summer Milky Way (was that 2010 or 2011? I forgot) and Jupiter was annoyingly bright, nearly bright enough to cast noticeable shadows like I'd seen before with Venus. P.S.- the idea that from very dark sky sites the Milky Way is bright enough to cast shadows is mostly a myth. The sky is always capable of casting shadows, whether the brightest portions of the Milky Way are above the horizon or not. You're a more sensitive than I am if you can notice a very slightly darker shadow when the Milky Way is up as opposed to hours before or later when it is not. Sorry, but I digress...

ihtoit, The Pleiades are M45. I always wondered why M45 was included in the Messier catalog (M44 is another one that is impossible to confuse with a comet, at least with any kind of telescope...). I think that Charles Messier, while maybe his original intention was a catalog of objects that might be mistaken for comets, must have branched out a bit and just decided to include a few undeniably stellar objects. It makes you wonder why he didn't include the Double Cluster though.

Vetrox, You're thinking of M42, not M21. Which is confusing, because you mention M42 in your post. M21 is not in the winter sky, and, being an open cluster, it's a boring object. Open clusters suck. Ok, some are kinda pretty, but nebulae and galaxies are just so much more interesting

Yup, same. We need to explore Mars, Europa, Enceladus, Titan, and the whole host of solar system bodies in much more detail before we spend a lot of money on interstellar probes. If it becomes possible to create an interstellar probe for "only" like today's equivalent of like $100B, and we find a VERY exciting target to explore (like a nearby habitable world with signs of life) then we should launch the mission. Otherwise, our money is better spent on solar system exploration until we either run out of exploration objectives in the solar system and/or the cost of interstellar missions comes down enough to allow us to mix them economically into our exploration program. But... in answer to the poster's original question- yes, again, we could probably build an interstellar probe, not with today's technology but with near-future technology developed after a couple decades of a focused tech surge on things like fusion-pulse propulsion. But we probably won't for quite some time, because it just wouldn't be a wise investment. Exploration wise, it would be "putting the cart before the horse".

We could probably build an interstellar probe if we focused on fusion propulsion or building laser/maser-pushed light sails, but our money right now is better spent exploring our own solar system, and building bigger and better space telescopes. Doing this, we will naturally develop the technology to go to the stars (there are folks investigating fusion pulse propulsion for Mars missions, for example). Additionally, the space telescopes will answer the kinds of questions we need to ask right now, such as- How common are Earth-like habitable worlds in the galaxy? Where are some nearby ones? Do they harbor an Earth-like biosphere? Are they inhabited? Space telescopes will answer these questions, and for a FRACTION of the price of an interstellar probe. Eventually though, if we continue to develop space technology, then the costs of interstellar probes may drop enough that they will begin to compete with space telescopes. Eventually, you get to a point with space telescopes that it becomes impossible to build them much larger, and to get better information, you have to send an actual probe to your exploration target. But that won't come for a long time, if ever.

That's simply not possible. The universe can only be fully simulated on a computer at least as complex as the universe itself. We can't even get close to that level of complexity, and we never could- the speed of light limit, for example, would make really large computers run extremely slowly, and we simply can't utilize enough particles to make a computer that complex (we would basically have to utilize the entire universe). So, at best, we can make a computer maybe something like 1/10^15 as complex as the universe itself, MAYBE after a billion years of advancement. That does not mean that we are not capable of creating a computer simulation that could include intelligent beings, but their universe will be, by necessity, much more simple than ours. As you go down the chain, eventually you get a universe that is too simple for intelligences smart enough create computers to exist. Clearly, reality cannot be an infinite series of nested computer simulations, unless we are VERY near the bottom, and it is "simulations all the way up"- which is impossible. There must be a "real" universe "up there" somewhere to get the ball rolling. And even if you somehow discount this, and claim that it can be "simulations all the way up" we find ourselves very near the "bottom", which is just about infinitely unlikely. And you claim that the simulations just run more slowly in each nested universe. Again, impossible. Regardless of the simulation speed, you still need memory to store all the particle positions, velocities, states, etc. Your computer is still at least as complex as the universe it is simulating (in reality, your computer must of course be at least many times more complex). For example, consider that if you install a video game on a dual core, 2 GHz computer, it is the same installed size as on a eight core, 4 GHz beast. Another reason it is impossible, besides the fact that running the simulation more slowly doesn't really save you in computer complexity, is that as you go up the chain, the simulations must run for a longer and longer and longer and longer time period. At some point, you get to the point where you have to run the computer for longer than the age of the simulated universe, just so your lowest universe can live long enough to evolve to the point where they can create a simulated universe. But the simulated the universe they create cannot even live long enough to create a simulated universe of its own, so the chain has to end. So in the end, the idea that reality is some kind of huge or infinite chain of simulated universes just does not stand to reason. At best, there could be a couple nested simulated universes. The most simple explanation is that we are not a simulation and the universe is, in fact, "real"- that there is no "higher" law of physics.

Well, yes, but mostly no. You are missing an important distinction. The reason the apple is falling we know for a 99.99999999999999999999999999% surety is because of gravity. This is because it is an environment and physics we are very familiar with. We can safely eliminate invisible pink unicorns as the reason for the apple falling. However, if we spot something on Mars that looks like slopes darkened by water, we cannot say with a 99.99999999% certainty that it is water. Not even CLOSE. Why? Because we do not know enough about Mars yet. We know for a fact that Mars has geological processes we know nothing about, and we have not been monitoring Mars long enough, or collected enough data, to safely eliminate the possibility that this is just something that looks like water. So, you CANNOT say that water is the only reasonable explanation, because it is reasonable, given the limited nature of the observations so far, to suppose that there is a strong possibility of non-hydrological processes going on that merely mimic the look of water. However, you can safely state that water is our best explanation so far.

If the universe naturally emerged, and there is no God, then the answer to "Why does the universe exist?" must eventually come down to a "just because" statement. If God created the universe, then the first answer to the question of "Why?" is "because God wanted it". Of course, in this case, the next logical question to ask is "Why does God exist?". A religious person has to say at this point, "just because", or at best, can delay the "just because" by only one more answer. Eventually, the religious person has to say it. So the ultimate "why?" even in a theistic universe, is still "just because". So ultimately, neither a theistic or atheistic origin of the universe gives an "satisfactory" answer to the ultimate origin of reality, unless you are willing to accept "just because". So, in answer to "Ultimately, why does the universe exist?", regardless of the existence or nonexistence of God, I feel I am fairly certain to be correct by simply saying, "just because". But why shouldn't "just because" be a satisfactory answer? I think we find "just because" unsatisfactory because we want there to be a reason or purpose behind everything. But the fact of the matter is, there doesn't have to be a reason or purpose behind something. 1 + 1 = 2 just because it does. In fact, the very meaning of "purpose" only makes sense in context to the actions of an intelligent being.

An interesting take. How do you manage the government employees and make them reasonably efficient though? Inefficient private corporations go bankrupt or are out-competed if they are not successful. The government doesn't have to worry about that.

I donno. The simple fact of the matter is space exploration has taught us to expect the unexpected. There are geological processes that are occurring on the other worlds in the solar system that we simply haven't thought of yet or encountered, because they don't occur on Earth, and our imaginations are limited and colored by our experiences on Earth. We also don't have huge labs to simulate what the surfaces or subsurfaces of the other planets are truly like, and we couldn't even construct such labs because we don't actually know the conditions on the other planets in enough detail. So, while I believe that water is likely to be the correct explanation, I'd still amend your statement to- "If temperature rules out dry ice, then it's either water or some process we haven't yet encountered or imagined yet."

Yup, it sure does. My post mainly refers to flying over land that has vegetation on it. As you say, ice-covered regions are tough to judge. I'm betting that over certain, very dry, desert regions, it might also be very tough to judge your altitude. At least you have haze/dust over deserts though.

I would say that Earth could offer its biology and history for export. Other civilizations will have scientists too, and they would appreciate information we could give them on the geological and biological history of Earth. Their biologists would be interested in Earth species, and we could offer the information we have collected on them. They might also want samples, though a full description of an organism's genome and the ways in which DNA information is catalyzed into proteins might be enough for an alien civilization to recreate that organism from scratch. Maybe we'd have to provide information on cellular structure and mitochondrial DNA too, I donno I'm not a biologist. But theoretically, we could transmit all the information they needed to recreate an Earth organism, if they had a method for assembling the requisite proteins from scratch. And of course, we could offer human history and maybe the human arts, if the aliens appreciate the arts. So yea, other than perhaps biological samples, I can't imagine we'd have any physical goods to offer for export. And besides, interstellar trade of physical goods is likely too expensive and difficult to really be feasible. We don't have resources that can't be accessed more easily by asteroid mining, and like they always say, knowledge is power. We'd offer information for export. And a bunch of politicians and celebrities. We'd find out if there was some prison planet we could export them to.

Yea, it's not NASA that needs to wake up, it's the American taxpayers and our congressional representatives. IMO, NASA should be funded at at least $30B a year, and we need to try cutting down on the bureaucracy. Easier said than done though... entrenched bureaucracies are some of the hardest infestations to eradicate. They only get bigger and more incompetent. Remember when the government used to develop hardware ITSELF? NASA designed the Saturn V; the US Army, the USAF, the Navy used to develop some of their weapon systems themselves, even systems complex as guided missiles, in-house. This rarely happens today. It's all done by outside contractors, while the government beaurocracy just gets bigger, hungrier, and ever more wasteful. We could do so much more in space if NASA were just managed better. But it's nearly impossible to force the government to become more efficient, so realistically, the only thing we can do to get more out of NASA is to give them more money.

Maybe terraforming Mars to offload population growth makes sense, but in order to make it feasible, we'll need multiple space elevators to lift all those people from Earth into space and a swarm of ultra-cheap spacecraft to ferry them to Mars. That might be a tougher challenge than actually terraforming Mars, but it MIGHT be realizable with space-based manufacturing (especially if a lot of AI and robotics and asteroid mining are involved). I'm betting that either it never becomes economically feasible, or overpopultion forces us to address the real problem (that we're breeding out of control) before spaceflight advances and terraforming open up very cheap Earth-Mars travel and habitation.