10 ms·
How far could the sun possibly be?
- cwillu 3y agoSeries starts at https://profmattstrassler.com/2024/01/16/the-value-of-check-it-yourself-science/ https://profmattstrassler.com/2024/01/16/the-value-of-check-...
- ltbarcly3 3y agoThis is a great introduction into how real astrophysics is done. We don't know how far away things are until we measure, but our measurements are never precise, and we don't have very many 'calibrated' distances to compare to. Little by little it's possible to exclude possibilities and narrow down on the likely true value.
- ForOldHack 3y agoI almost got my degree on astrophysics. Yes, I read a lot of bad and good textbooks. This one is rather brilliant, lucid, and well done. But I have to follow up with: "Well, but... how do we really know?" A: We have followed up well worn paths of scientific inquiry, and looked at our assumptions, in designing an experiment that, we assume to fail. When it does not follow our assumption, then we can only rule out failure, and call it a success. This follows centuries of this type of exacting and painstaking scientific work. Although I would normally have 10 ~ 12 citations of very diverse work, that exercise is left to the reader.
- eichin 3y agoIndeed, this might be good methodology background for the current "crisis in cosmology" where new JWST observations "close the gap" so that it no longer includes some previous upper/lower bounds at all ( https://www.youtube.com/watch?v=-kTe0xRAU1w https://www.youtube.com/watch?v=-kTe0xRAU1w for a scicomm explainer with more detail )
- ltbarcly3 3y agoWell, and the crisis! The allowed regions from different methodologies don't overlap, pointing to one of the pillars of cosmology potentially being wrong.
- empath-nirvana 3y agoOne thing he sort of implies but doesn't directly state -- which I think a lot of people don't know -- is that it's impossible to measure the "one way" speed of light. We can only measure the speed it takes for light to go "there and back". It's possible (but not likely), that light goes faster in one direction than in another direction, and AFAIK, there's no possible way to measure it. You'd think you could do it based on clock synchronization, but clock synchronization itself depends on the assumption that the speed of light is equal both directions. https://en.wikipedia.org/wiki/One-way_speed_of_light https://en.wikipedia.org/wiki/One-way_speed_of_light
- readams 3y agoAlso a Veritasium video on the subject: https://www.youtube.com/watch?v=pTn6Ewhb27k https://www.youtube.com/watch?v=pTn6Ewhb27k
- andersa 3y agoWhy doesn't it work to have the emitter and sensor together at the same location, synchronize them at that moment, and then move them apart a distance so large the initial delay no longer matters, before running the test? Do we not have accurate enough clock sources to keep the synchronization?
- Tagbert 3y agoMoving the emitters affects the pace of time for them.
- AnimalMuppet 3y agoRight, so move them at identical speeds, with identical acceleration profiles.
- rjp0008 3y agoIf you do this, the clocks will be in the same place, it would have to be opposite acceleration profiles to get them moving away from each other.
- Civitello 3y agoSo, without reading, here are my uninformed thoughts on how I would do it: You could probably figure out the distance by using a technique we use to figure out the distance to nearby stars, measuring the change in position in the sky relative to very far away stars. I think you'd only need to observe two stars to figure out the distance. Could also use pulsar timing like gps signals to track the location of the Earth throughout its orbit. Could also take measurements after launching a pair of space probes away from the earth.
- mannykannot 3y agoUnfortunately, the parallax method depends on knowing the diameter of Earth's orbit, which is (except for a factor of two) the value we are seeking. There's also the issue that the change the Sun's position with respect to the stars over six months is about 180 degrees (with some fluctuation, perhaps, depending on where the earth is in relation to its orbit's major axis when the measurement begins), and will be regardless of the Sun's distance. The distance of Venus was measured by the parallax method during a transit, with a baseline on the Earth's surface. This then yields all the other planets' distances from their orbital periods. This has me wondering why this had not been done for the Sun's distance, and perhaps the first reason to be considered is the difficulty of observing the Sun eclipsing distant stars. Update: According to Wikipedia [1], Jeremiah Horrocks came up with reasonable figures for both the size of Venus and the distance of the Earth from the Sun from a single observation of a transit, but the article says he made use of a false premise, so does that just mean he was lucky? [1] https://en.wikipedia.org/wiki/Transit_of_Venus#1639_%E2%80%93_first_scientific_observation https://en.wikipedia.org/wiki/Transit_of_Venus#1639_%E2%80%9...
- ginko 3y agoThere was a pretty good CCC talk on this a couple years ago: https://www.youtube.com/watch?v=HFWV6XAXyx0 https://www.youtube.com/watch?v=HFWV6XAXyx0
- temptemptemp111 3y ago[dead]
- g4zj 3y agoThis is way outside my area of expertise (if I have one at all), but assuming we know the diameters of the sun, Earth, and our moon, as well as the distance between Earth and our moon, could we not determine the distance between Earth and the sun based on the scale of the shadow Earth projects onto the moon during a partial lunar eclipse?
- gpm 3y agoIf you know the diameter of the sun you should be able to measure the distance by just measuring the size of the sun in the sky and using some simple geometry. I.e. if the sun takes up x degrees of space in the sky then tan(x) = (radius of sun / distance to sun). But... how do you measure the diameter of the sun?
- andrewclunn 3y agoIf you sent out probes to calculate the travel time of beams of light between two points, but at Lagrange points from one another, and then had them simultaneously slow their orbits to fall into the sun, and considered the "edge" of the sun the point at which it destroyed the probes...
- lifeisstillgood 3y agoHow do you measure the diameter of the sun when your most advanced technology does not include a telescope. And even when it does, but just a telescope about 8x power (approx Gallileo’s first one) That Copernicus got there at all is incredible
- zamadatix 3y agoI feel like shadows are the "simple tech" path. It was known since ancient times you can get the circumference of the Earth (remarkably accurately) by doing some calculations based on the angles of shadows from the mid-day sun at two points sufficiently north/south from each other (a fantastic application of trig). Knowing the circumference of the Earth and these angles lets you know the diameter/radius as well which lets you create a "straight line" distance (i.e. not the over the surface distance) between those two points. Using those two points and known angles to construct a triangle with the Sun should let you see it is at least extraordinarily far away, even if your measurements are relatively innacurate.
- titzer 3y agoThe story of how they actually first measured the distance to the Sun is quite fascinating. They timed the transit Venus and used Kepler's laws to figure out the rest. https://phys.org/news/2015-01-distance-sun.html https://phys.org/news/2015-01-distance-sun.html
- notso411 3y ago[dead]
- lttlrck 3y agoAnd they got within 3% of the true value. Incredible!
- angiosperm 3y agoAnd measured light speed by watching Jupiter's moons coming around late.
- optimalsolver 3y agoDo you think you could have deduced that stars are distant suns if you'd lived in the ancient world? Apparently the only pre-modern people (i.e. pre-Giordano Bruno) recorded as making the claim were Anaxagoras and Aristarchus of Samos, but their ideas were completely rejected by contemporaries: https://solar-center.stanford.edu/FAQ/Qsunasstar.html https://solar-center.stanford.edu/FAQ/Qsunasstar.html In retrospect, it just seems so blindingly obvious that I'm tempted to believe that I too would have seen through the Aristotelean BS. But surely there must be aspects of reality that will seem similarly obvious to future generations, and yet I don't feel any insights coming on. I should say, Aristarchus is the ideal of maximizing information from minimal data: "Aristarchus of Samos (Samos is a Greek island in the Aegean Sea) lived from about 310 to 230 BC, about 2250 years ago. He measured the size and distance of the Sun and, though his observations were inaccurate, found that the Sun is much larger than the Earth. Aristarchus then suggested that the small Earth orbits around the big Sun rather than the other way around, and he also suspected that stars were nothing but distant suns, but his ideas were rejected and later forgotten, and he, too, was threatened for suggesting such things."
- jbaber 3y agoWith the naked eye what similarities are there between the sun and distant stars?
- alan-crowe 3y agoOne sees signal beacons (a bonfire on a hill, used to send a simple warning message) both up close, and from a distance of many miles. Thus one sees with the naked eye that a great fire looks like a mere candle from far enough away. Then one boldly extrapolates: perhaps it is the same with the sun and the stars.
- gpm 3y agoI definitely wouldn't have reached that conclusion. Evidence in favour: The sun is a light source, they are much dimmer light sources with much smaller radii, consistent with the hypothesis. Evidence against: There are none at intermediate distance, they're either the sun or so far away to practically be a point light [1]. The sun is yellow, they are not [2]. The sun has a partner in size (measured in portion of the sky it takes up) with the moon, which I presumably know is relatively close by, suggesting some form of relation between them [3]. Ultimately I know that there are lots of ways to give off light. Fire, fireflys, lightning, the sun (if it isn't fire), hot metal, sparks from static electricity, ... There just isn't enough evidence to believe that it's more likely that the stars are the same source as the sun than yet another source. [1] As it turns out "so far away to be a point light" is the intermediate distance, but that result requires an amount of empty space that I would find unlikely. I haven't checked this but I suspect a statistical analysis would also find it unlikely. Assuming all stars are the same size as our sun, and that they're distributed uniformly in space. Given that I count the stars and come up with a reasonable minimum and maximum distance bound from their brightness, I suspect it is extremely unlikely that there are as many as there are but none close enough to be noticeably brighter. This result (assuming it is true) is of course the result of the fact that many stars are far larger/brighter than the sun, so we're actually sampling from a much larger volume than my naive estimate suggests. [2] I'm not sure I fully understand this one... the sun appears yellow because of some quirk to do with the light the atmosphere lets in, but why doesn't that make the other stars yellow too? [3] Pure coincidence
- angiosperm 3y agoBy watching solar mass ejections you can see how fast they leave those in transverse directions, and assuming those directed at us (whose speed we can't track by watching) go the same speed, we can measure how long they take to generate an aurora.
- caf 3y agoYou can only measure the speed of those transverse ones in angular units though, so I don't think it helps.
- Aeolun 3y ago[flagged]
- jurgenaut23 3y agoI believe this is an attempt at vulgarization, as the exact opposite effect happens for anglo-saxon non-scientist readers when they come across metric units...
- BasilInc 3y agoI'm unfamiliar with Anglo-Saxon used like this. Do you mean people from the US?
- esrauch 3y agoThe British still use imperial for "informal" usages as well, which I think is what the other commentator had in mind.
- eigenket 3y agoNah, we don't do anything like as consistent and understandable as that. We use a random mixture of imperial and metric measurements where the "right" one to use in each context is determined by cultural norms. E.g. we measure petrol in litres, beer in pints, wine in litres (but actually centilitres), long distances in miles, short distances in metres, weights of people in stones, weights of everything else in kilograms (except home cooking which is split between imperial and metric) and fuel efficiency in miles per gallon. The fuel efficiency one is really dumb given that we buy fuel in litres.
- jurgenaut23 3y agoI meant US/british ;-)
- mikhailfranco 3y agoCheckout Terry Tao's 'Distance Ladder' slides and video: https://terrytao.files.wordpress.com/2017/11/cosmic-distance-ladder2.pdf https://terrytao.files.wordpress.com/2017/11/cosmic-distance... https://www.youtube.com/playlist?list=PLldN_DpkXL3ZQWmwmwIzeITvK3a8Yd1Sz https://www.youtube.com/playlist?list=PLldN_DpkXL3ZQWmwmwIze...