Most science studies are intended to discover new knowledge. In astronomy, the goal is often to find different types of objects in space, or learn how astronomical objects are formed and behave. But often from studying things that exist, we also learn about limits of the kinds of things that can exist; when this happens, we say that we've "ruled out" the excluded phenomena.
The joke is that you don't actually have to study anything to come to these almost patently obvious conclusions. The counter-proposals would need far more effort to even justify them as valid theories, by common understanding, and greater still to try to observe any supporting proof.
Some studies are also done to confirm the results of previous studies, to ensure that the conclusions were not mistaken or a fluke. The title text describes a study that was done to confirm the existence of a moon orbiting Earth, even though any sighted person can walk outside and see the Moon, the existence of the Moon has been known for at least as long as humanity has existed, and the fact that it orbits the Earth has been assumed or known for upwards of 3,000 years. The ancient Greeks and Babylonians, for example, thought that the Moon orbited the Earth, though they lacked a detailed physical understanding of the system (they also believed, erroneously, that everything else in the universe orbited the Earth too). Anaxagoras (c. 500–428 BC) is credited with the correct explanation of lunar eclipses, and reportedly was the first to explain that the Moon shines due to reflected light from the Sun. However, it was not until the work of Nicolaus Copernicus in the 16th century that a detailed and accurate model of the Moon's orbit around the Earth was developed. Regardless, at this stage, a study to confirm the validity of Copernican orbits would contribute nothing to the scientific process, much less a study confirming the mere existence of the Moon.
Wow. the amount of citation needed tags is excessive. Here's a fun idea, do like that SMBC comic and actually find and give citations. 188.8.131.52 19:41, 31 May 2023 (UTC)Bumpf
- Definitely. I fixed one (it should have been after the comma), during some other edits, but was sorely tempted to remove maybe two of them to just keep the funniest one(s). Whichever that(/they) might be. I expect they'll almost all evaporate in a future edit, though, as there's plenty of editting bound to be done. 184.108.40.206 19:47, 31 May 2023 (UTC)
- Nice work to whomever on that! Xkcd never fails to make me smile if not LOL, and Explainxkcd never fails to teach cool facts. o7 220.127.116.11 21:28, 31 May 2023 (UTC)
I'm pretty sure there has been serious scholarship about the habitable zone of some quasars. Let's see.... Here: https://iopscience.iop.org/article/10.1088/1742-6596/2364/1/012057/pdf Not absolutely certain, but absolutely not ruled out. 18.104.22.168 20:02, 31 May 2023 (UTC)
- I think that Cueball's scientific team did a study to discount the possibilities of quasars in the habitable zone of a star, not of a habitable zone around a quasar.22.214.171.124 20:52, 31 May 2023 (UTC)
- A quasar could exist in the habitable zone of a star, and if it was particularly dim, it wouldn't make the zone inhabitable. There's no minimum brightness for quasars, is there? For example,  defines quasars in terms of relative magnitude, so I don't see why a tiny black hole with a small but sufficient accretion disk in translunar orbit couldn't qualify. 126.96.36.199 20:54, 31 May 2023 (UTC)
- Relative to their entire galaxy! Fixed explanation. 188.8.131.52 09:02, 1 June 2023 (UTC)
I don't know how to properly describe the length of time the Moon's orbit of the Earth has been known. If you think that the moon orbits the earth, but you also think the sun, stars, and planets orbit the earth, do you actually have any way to justifiably say that you know that the Moon orbits the Earth? Also, is it worth pointing out the reasons that the moon is such an obvious thing to know about (i.e. its visibility and prominence to the naked eye, its cultural significance,...)?184.108.40.206 20:59, 31 May 2023 (UTC)
- Interesting xkcd (sort-of) reference here. Back when What-If questions started being solicited, I sent in something (roughly) like "When trying to justify the original geocentric theory of the solar system, it is said that it had always 'looked like everything went round the Earth'... What would it have looked like if it had always looked like everything, including the Earth, went round the Sun?" ...which I'm pretty sure never got answered. Probably didn't spark enough possible scope for that good old xkcd magic. But I saw plenty of other good stuff, so no regrets on my part. 220.127.116.11 23:14, 31 May 2023 (UTC)
- I think your question was particularly difficult to answer in any way other than "Everything does go around the sun. To see what that looks like, look up." I suppose your question (if I'm understanding what you may be looking for) may be stated otherwise as "How different would the movement of our Solar System need to be in order to make it obvious that everything revolves around the sun (to a layperson observer on Earth)"? 18.104.22.168 14:50, 1 June 2023 (UTC)
- I don't see much difference between the two ways of putting it (unless you think your one means seeing the 'orbital rails' upon which everything encircles things, or something).
- Maybe, though, a fairly visible (lunar-sized) satellite of Mars/Venus might be on the edge of discernability (not needing Galileo's assisted view of the Saturnian system, just the kind of patience that raw-eyeballing astronomers used with discerning 'close' stars from each other) thus demonstrating non-geocentrism much earlier and easier and somewhat more undeniable. 22.214.171.124 17:29, 1 June 2023 (UTC)
- Terry Pratchett's Strata has exactly this - Venus has a naked-eye visible moon, so people on Earth figured out early on that "everything orbits something else" 126.96.36.199 08:53, 6 June 2023 (UTC)
- My proposed question was meant to clarify, so it shouldn't be much different :-) I don't know what the answer would be, but my hope was to clear up that the question wasn't simply "What would it look like if the Earth revolved around the sun?" which is what I had originally interpreted the question as before I decided that it probably wasn't the question that was meant to be asked 188.8.131.52 17:40, 1 June 2023 (UTC)
- Maybe clunkily given here (really we need to see the original Q, not the half-recalled paraphrasing so many years after) but "in order to make it obvious that everything revolves around the [S]un" doesn't look like what you say you first read it as. So to bad writing (capital 'S'!) perhaps add bad reading, I suspect. But we're all fallible. 184.108.40.206 17:57, 1 June 2023 (UTC)
Y'know, I'm not entirely convinced that "tectonically active black holes" is something that we're actually capable of ruling out 220.127.116.11 22:33, 31 May 2023 (UTC)
- Even if the black hole is tectonically active, its activity is in one direction only: forward, where you can never catch up to it. The damage is extreme, but it's held safely in the boundary of the singularity. 18.104.22.168 01:10, 1 June 2023 (UTC)
- I agree; black holes occupy a non-zero volume. Since the space below the event horizon has depth, I don't see any reason why the arrangement of mass inside could not shift. Indeed, the evidence of gravitational irregularities affecting their accretion discs, seems like evidence of nonhomogeneity within that volume. I think black holes probably do have "tectonic" activity!
- ProphetZarquon (talk) 16:27, 2 June 2023 (UTC)
- Counting all the volume within the event horizon (infinite, due to the infinite curvature), the density wouldn't support tectonics. The acretion disc is affected by what is on the verge of falling in (minus what has actually fallen in which just acts as a hairless 'lump'). Not sure you can call what happens in the disc as 'tectonics'... No pressures from below (the opposite) it's just interactions of decaying orbits. 22.214.171.124 18:43, 2 June 2023 (UTC)
Did anyone else see the connection between this comic and the NASA briefing yesterday on UAPs (Unidentified Aerial Phenomena, their term for UFOs)? In the briefing they discussed that the approach they'd need to take is one of ruling out everything else instead of saying for certain that "this is a UAP". I think that's the entire intent of this joke - to comment on the NASA briefing. 126.96.36.199 11:50, 1 June 2023 (UTC)
Strictly speaking, the first two classes of object listed couldn't be 'ruled out' by a study, since they're non-existent by definition, and therefore can't be subject to any meaningful proof or disproof.188.8.131.52 15:58, 1 June 2023 (UTC)
- While exoplanets in our solar system are non-existent by definition, ruling out earth-like stars does need some study to prove that earth is neither star nor sufficiently star-like. Note that you CAN find Jupiter-like stars. -- Hkmaly (talk) 20:55, 1 June 2023 (UTC)
- I think part of the joke is that the "study" is just a scientist saying "Yup, that can't exist." Barmar (talk) 01:19, 2 June 2023 (UTC)
I think the entire point of including “habitable-zone quasars” was completely missed so far. It’s not that a quasar can’t have a habitable zone near it, even if that’s unlikely, nor is it that a quasar couldn’t be in a star’s habitable zone. It’s that SO WHAT IF IT IS? You couldn’t inhabit a quasar regardless what ‘zone’ it was in. If you were looking for a new home, you’d look at homes within a price range you could afford (not too expensive, but not TOO cheap). Looking for a quasar in the habitable zone of a star would be like asking a realtor to show you an active volcano within your price range. 184.108.40.206 20:13, 1 June 2023 (UTC)
- Well ... "active volcano within my price range" is exactly what traditional Evil Overlord asks for. The smarter ones ask for volcanos which are non-active but can be made looking active. -- Hkmaly (talk) 20:55, 1 June 2023 (UTC)
- Volcano?!? Most of us can't even afford a sinkhole. ProphetZarquon (talk) 16:31, 2 June 2023 (UTC)
- You need to up your evil overlord game, Zarquon. 220.127.116.11 20:44, 2 June 2023 (UTC)
- Afford? In Florida, many people get one for free. SDSpivey (talk) 18:43, 4 June 2023 (UTC)
Given the text at the bottom of the drawing, this also sounds like a reference to Hempel's paradox (aka raven paradox) https://en.m.wikipedia.org/wiki/Raven_paradox
Gisbert (talk) 21:01, 1 June 2023 (UTC)
"has to be brighter than our Sun because it's part of the containing galaxy" (edit comment) - I interpret the spec differently. This makes a quasar far more unbalancingly relative, whereby perfectly valid quasars in the next galaxy over, or further, are considered nothing of the sort for (some/most/nearly all/..?) any residents of the quasar's own galaxy who just 'happen' to be (their equivalent of) 1AU from even a very non-descript star of their own that yet easily outshines their non-quasar galactic centre (at the equivalent time, even direction, of observation). And how does that juustify multi-quasar galaxies, where the output of one may (or may not, it could result in mutual exclusion) outshine the total power of the rest of the galaxy including the other potential one(s). Yet true examples exist, that are not just false bedfellows through near-occluding asterisms. 18.104.22.168 10:42, 4 June 2023 (UTC)
Just wondering. What would a rogue planet (clearly an exoplanet) that travels through our solar system be called? MDwayne (talk) 12:47, 4 June 2023 (UTC)
- Its page on Wikipedia is Rogue planet, as you named it, though I would gravitate (NPI!) towards the term Nomad. And noting that the category "Exoplanets" tends to exclude planetary-mass bodies unbound to extrasolar stars, so already really something else. (If we get better at studying them, perhaps ejected ones, i.e. "ex-exoplanets", might be brought into the fold, but any actual "failed sub-brown-dwarf" bodies were never planets to start with.)
- Such an itinerant visitor (unless it is lucky and somehow snags a gravitational reverse-slingshot to try at least a few orbits to try to become a new Solar planet; or we're unlucky enough that it collides with/deflects one or other of the current contingent and causes ourselves problems of some degree or other) would probably zoom through our system and out pretty quickly (in observational terms), and if it was happening frequentlt then the purturbations would probably be identified as aperiodic/randomly-orientated influences, so we're probably not likely to get one to even try to falsify that particular statement. Never say never but, even if you want to argue terminology, you might have to wait a while before seeing a non-solar planet do a "Bronson Beta/Zyra" (When Worlds Collide) and pass through, with or without the damage of the Bronson Alpha/Bellus partner. 22.214.171.124 16:58, 4 June 2023 (UTC)
- Interesting response to my mildly sarcastic jab at part of the comic's content. I'm not sure, however, if your thesis statement about the definition of an exoplanet is set. Contradicting the claim that Wikipedia suggests a rogue planet cannot be an exoplanet, NASA suggests it is:NASA Exoplanet - in terms of this type of stuff, I give NASA an edge as a reference.
- With regards to any event that could happen, even if it is rare, still has a non-zero probability of happening. Who conceived we would witness Oumuamua? How much bigger would it have to be to be a planet? So, in the spirit of the topic, maybe it COULD be a legitimate area of study.MDwayne.ca (talk) 18:52, 4 June 2023 (UTC)
- NASA is all well and good, when it comes to physical rocketry or the associated human-sphere of space, but I'd probably defer to the IAU definition as the (best current, terran) authority on the greater expanses of the universe. (It's hinted at, early on, but section 2.6 deals explicitly with this, then Section 3 Item 3 says it plainly, with possible modifications (that only reinforces this) in Section 4.)
- That also helps with "how much bigger", re: Oumuamua, I suspect. 126.96.36.199 19:22, 4 June 2023 (UTC)
- The same as it would be called when it wasn't passing through our solar system. It wouldn't be in our system, even if it happened to be spatially coexistent, because the system is orbitally rather than spatially defined.188.8.131.52 13:24, 7 June 2023 (UTC)
(New comment) I added a cite for Earth not a star 184.108.40.206 (talk) 14:59, 5 June 2023 (please sign your comments with ~~~~)
- In light of that, I removed the Citation Needed connected to that 'citation'. But I also made the link not include the highlight text bit (you've gone to the top link on a Google search, I imagine?) and also turned it into a much more aesthetic straight text link rather than a [number] thing that did it no favours. 220.127.116.11 16:46, 5 June 2023 (UTC)