* Posts by mr.K

377 posts • joined 14 Nov 2007

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There's a new comet in town and you don't need a fancy multi-million-dollar telescope to see it. Just regular eyeballs

mr.K

Re: I'd like to see it

Wouldn't that be because Mars' orbit is closer to ours so that distance vary much more? At it's closest it is less that 0.4 AU and furthest over 2.5 AU, six times more. Yes, the eccentric orbit factors in there a little bit, but with a circular orbit it would be around 0.5 AU and 2.5AU. While Jupiter is around 4AU at its closest and 6 AU furthest away, only 50% more.

Okay, you might not see it clearly when it is furthest away due to some other bright object out there, but I think my point still stand...I think.

Royal Navy nuclear submarine captain rapped for letting crew throw shoreside BBQ party

mr.K

Re: Same property?

Well, I live alone now...

Boffins examine interstellar comet Borisov to find out what its home was like. Pretty unpleasant, it seems

mr.K

Re: Why a red dwarf?

“We think it’s more likely to be the latter case – it comes from a cold red dwarf because there are far more red dwarfs in our Milky Way galaxy than other hotter stars. However, we are still far from saying exactly what’s going on around its host star when planets formed there."

mr.K

I can't say that they are more frequent than we realised or not, but they are more frequent than we have been able to detect. Think about it, it has taken us a great while to detect most objects in our solar system. They are here for a long time while these just pass through, quite quickly. To be able to detect them we need several things to happen. They need to come close enough, be big enough and bright enough, and we need to look in their direction over a period of time. If we are really lucky they get so close that they start to send out gas and dust making them much more easy to spot. Also, and here I am guessing it will help if they come in close to the plane of our solar system, since we have more cameras looking for things in that plane. (not sure if plane is the right word here, plane of orbits..dunno)

Kepler telescope is dead but the data lives on: Earth-sized habitable zone planet found after boffins check for errors

mr.K

Re: Age?

Did I hear somebody mention toast? How about a muffin?

mr.K

What is this "simply by getting there"? What do you know? I want answers.

COVID-19 is pretty nasty but maybe this is taking social distancing too far? Universe may not be expanding equally in all directions

mr.K

Re: Dark energy

Nah, you should try to change the point of reference.

"Yes, I was driving 85 mph in reference to this state, but I believe this is an interstate highway and thus I should use Washington DC as a reference frame. So according to this bit of trigonometry and factoring in that DC also is further north thus moving slower and I was moving against the rotation of the earth, I would like to point out that..."

mr.K

flat = infinite ?

Okay, this interests me. I have never understood why a flat universe equals an infinite one, or believed to equal at least. I do not see the link. I would really welcome a feedback on this and feel free to correct my assumptions below.

As I understand it, if it is flat the parts that we currently can see can't be all of it, because that would mean that we are in the centre given that we see an equal distance in every direction. Also we do know that it is expanding and stuff should keep falling outside the "visibility edge" (in lack a of a better term), so if it is what we currently see then we have reached a point in time where we see exactly to the edge. Both of which is possible, but so unlikely that it can be disregarded.

However, why can't there be a number between one and infinity? Why can't the universe be one point eleven trillion times bigger than what we can see?

Second question: The surface of a balloon mental picture, isn't that reserved for a curved universe?

Academic showdown as boffins biff-baff over when Version 1.0 of Earth's magnetic core was released

mr.K

No opinion

I have no opinion on this.

Good luck pitching a tent on exoplanet WASP-76b, the bloody raindrops here are made out of molten iron

mr.K

Re: Puzzled!

That it is a gas giant.

Astroboffin Kurtz ends 40-year quest to find a predicted one-sided vibrating star that was never seen – until now

mr.K
Boffin

Re: Why doesn't the red dwarf bulge too?

If I understand this correctly the gravity on the surface of red dwarfs is actually higher than on bigger stars. The simple explanation for this is that they are less hot so more dense. It might help the understanding to think of red giants which the sun will become where the mass remains the same but the radius expands out to Earth.

The little more complex explanation you get from doing the calculation with:

g = Gm/r^2

Punch in the numbers from the table at:

https://en.wikipedia.org/wiki/Red_dwarf#Description_and_characteristics

Where you see that the radius and mass is nearly linked and results in the gravity on the surface of the red dwarf is way higher.

There are some caveats though. Since it is relative to the actual radius to the objects it will decrease much more rapidly when you go out of the gravity well of the smaller star than the bigger one. I.e. you are already so far out from the centre of gravity on the bigger one that any additional distance will have less impact. But I do think this will not counter the overall effect enough so that the gravitational effect from each will be bigger on the larger star than the smaller.

Alternate explanation: The artist got it wrong and mainly wanted to illustrate the bulge in the bigger one.

Ever dream of being an astronaut? Now’s your chance. NASA wants new people for the Moon and Mars

mr.K

Kinda, less than 100km doesn't qualify

In case you wanna launch your boss into the Sun, good news: Earth's largest solar telescope just checked and, yeah, it's still pretty fiery

mr.K

Re: Reg units

I like it when it is possible with an exact conversion between my units of measurements so Wales being so close to 3%, can we just define it to be exactly that? We just need to add 135 km2 to Wales or remove 4495 km2 from Texas. I am sure people will understand the reasoning and thus not create any tension.

Star wreck: There's a 1 in 20 chance a NASA telescope and US military satellite will smash into each other today

mr.K

Re: Recycling

Sigh... you are mixing up two different TV-shows, Star Galactica and Trek Wars 5.

World-record-breaking boffins reveal the fastest spinning thing on Earth – and it's not George Orwell in his grave

mr.K

Re: A tiny amount of drag

I always thought drag quarks to be a little strange...

Google ex-employees demand retribution for Thanksgiving massacre

mr.K

Formal?

What does that even mean, "Formally adopted as the company's motto."?

Do they have to go to town hall or a nearby church, or is enough to publicly announce it?

"We here at Google, in front of God, countrymen and these witnesses, which to make it clear...."

Isn't the whole concept of a motto informal to it's core?

Space-wrecks: Elon's prototype Moon ferry Starship blows its top during fuel tank test

mr.K
Mushroom

Re: "anomaly"

Maybe he did, but he also keeps referring to "hard starts" etc.

Reaction Engines' precooler tech demo chills 1,000°C air in less than 1/20th of a second

mr.K

Re: This is truely impressive

Does it? After reading up, I don't see any mention on splitting air into nitrogen and oxygen. I don't see how -150C should help with that anyway. At least as far as the Wikipedia article suggests the precooler is there to prevent the engine from melting or blowing up due to the high pressure without the need for very heavy parts. It seems that during air-breathing mode air is used directly in the combustion. Feel free to correct me if I am mistaken.

When one of NASA's sun-studying satellites went down, AI was there to fill in the gaps

mr.K

Re: Models, fits, and wild guesses

It is faking data if they claim they are actual measurements, they are not. Interpolating or predicting data based on known data is in the core in more or less everything we do, from radio communication, wether forcast and election, even down to how our own brain function. It is perfectly fine to infer anything regardless if we can mesure it or not. Your job is to make good judgements on how reliable the data are, which you have to do anyway since no measurements are accurate anyway, prone to failure and most instruments you use doesn't actually measure the actual phenonoma, but usually something else before infering what you are after.

Experts: No need to worry about Europe's navigation sats going dark for days. Also: What the hell is going on with those satellites?!

mr.K
Holmes

As I understand it

An operator error would be somebody pressed the wrong key or miscalculated the delta-v or punched in the wrong burn time on the engine.

A fundamental design problem is a problem that simply cannot be fixed. Somewhere along the line that your fuel of choice produce a chamber temperature which is borderline of what you can handle and sometimes it doesn't work. Meaning you have to either add active cooling and thus adding too much weight or change fuel, but that would mean loosing specific impulse so thus reducing the weight limit. Which means you have to basically start over.

They are not claiming this is an act of god, it is a design problem, but can probably be solved with a pound's worth of insulation.

OK, Google, please do a half-hearted U-turn: Stay of execution for smart home APIs after Big G goes cuckoo in the Nest

mr.K

Re: I'll never buy anything that relies on "the cloud"

"Many salespeople lie, often by wilful ignorance."

But not everybody, not the bad ones.

Either Facebook is building yet another massive bit barn in Iowa, and doesn't want you to know about it....

mr.K

Free market?

Can somebody in USA start to advocate for a free market again?

Two Soyuz launches, Starhopper hops, sats play chicken with Indian weapons test fallout

mr.K
Mushroom

Re: 5 million pounds of thrust

You can add 50% on that number.

Boffins baffled by planet nugget whizzing round white dwarf that should have killed it

mr.K

Yes, a lot smaller

Their physical size is comparable to that of earth, so yes, they are small. According to the kepler's third law calculator I just used the orbit is around 500 000 km which is a little less than the radius of our own sun. The orbital velocity would be around 400 km/s.

The fact that they collapse to such a small volume allows you to fall pretty deep into the gravity well.

Boffins discover new dust clouds in the Solar System, Mercury has a surprisingly filthy ring

mr.K

Re: Make Pluto great again

Like it or not, but this is not what the definition entails. "Clearing the neighbourhood" was never intended to mean and does not mean that the neighbourhood should be completely empty. That will be an impossible standard for a number of reasons, the obvious one are the moons. A little harder to grasp is all the minor objects that will end up in the stable Lagrange points L4 and L5 or orbit both in a horseshoe orbit. And I suspect most of this dust have in fact a horseshoe orbit. Read more about it:

https://en.wikipedia.org/wiki/Horseshoe_orbit

Third we have the orbital resonances of some bodies. Pluto is in such a resonance with Neptune, but so is Orcus which have the exact same orbit as Pluto.

And this is exactly the point of all these examples. Remove Neptune and Pluto will eventually pull Orcus in and they will merge. As of now their orbit is not their neighbourhood, it is Neptune's. The Trojans are not merging because of Jupiter. The same with the asteroid belt etc. They obviously was aware of this, and no they have not made a definition that excludes Jupiter and Neptune by mistake.

Personally I think we should remove the criteria and have a larger number of planets and instead call the eight major planets or something. I really fail to see why it was an argument that they had to because if Pluto should be a planet then a lot of other bodies would be planets to. So what? Regardless the definition they have now stands perfectly well. But I bet it will exclude exoplanets at some point that we would really think of as planets.

Real life sci-fi: Massive exoplanet booted out of home by binary parents – then slipped back inside by passing friendly stars

mr.K

Re: Probability

Not knowing for sure, I imagine at least that for a planet to be captured by another system is unlikely. The reason for this is that any object falling from the outside into the gravity well of a body will fall out again unless it somehow looses some of it's energy. The same way any object originating inside a gravity well will remain there.

Now you can easily construct a scenario where the object part of some of it's velocity to another object already there. All encounters in space can be regarded as elastic collisions (part of actually collisions of course) meaning that both momentum and kinetic energy will be conserved. But can part with enough energy to another object, either ejecting that one or at least give it a greater orbit. But this one is a massive object and if it originating from the other system it would have high relative velocity. The chance is slim that it managed to encounter some planet there, matching it's orbit to such a fine detail that it lost just enough velocity to remain there.

So, yeah, possible, still at least not just as likely.

Dawn of the dead: NASA space probe runs out of gas in asteroid belt after 6.4 billion-mile trip

mr.K

Re: Then what??

Orbits are impossible to calculate precisely, except if there are only two bodies in the entire universe. For shorter periods you can simply calculations so that you only consider the object you are orbiting. However, for longer timespans you need to factor in everything else in the solar system. And you cannot describe it as a pure solvable mathematical system. You have solve it numerically where you enter all the coordinates for all objects or at least the major ones and their velocity vectors, step ahead a small amount of time, recalculate velocity and coordinates and repeat. The smaller the steps the more accurate you get. Mistakes accumulate though and in time you can get discrepancies.

For Dawn the orbit is so low that they risk a collision if it gets tugged into a lower orbit but for instance Jupiter. They have a very low chance within the next twenty years, and with fifty it is less than a percentage.

SpaceX touches down in California as Voyager 2 spies interstellar space

mr.K

Re: 17.7 billion kilometres from Earth

There are no clear definition on what the boundaries of the solar system are. The one they use here is where the galactic wind overcomes the solar wind. Another would be the farthest out planet. A more common one would be where the gravitational pull of the sun is no longer dominant. This will be much much farther out.

In a galaxy, as we are, it would be usefully to think that the boundary is the border to next solar system and thus you would use gravitational border. But if you have some rouge object skipping through the galaxy it will never be outside of a solar system, but can you say that this object really have visited us if it pass us a light years distance? Also, will an intergalactic system (if there is such a thing) then have no boundary?

But if you use the "solar wind" boundary does that mean that comets and such regularly leave the solar system before returning?

It is simple, use the one that gives the best headlines.

FCC boss slams new Californian net neutrality law, brands it illegal

mr.K

Free market = regulations

For any market to function all participants has to make informed choices, otherwise competition simply will not work. This is why a functioning free market needs to be well regulated. The downside of regulation is that in impedes on freedom of choice. Thus the more professional a participant can be said to be, the less protection the regulation has to offer. Consumers are not however, and needs simple well established regulations that lets them make informed choices.

The simple market is that an ISP provide access at a certain speed, and possibly a certain amount, at a certain cost. In this type of market, Netflix does not use up any of the bandwith, the consumer does. No matter how you put it, it is the consumers that end up paying anyway. If they pay Netflix more since they have to pay the ISP or they simply pay the ISP directly does not matter. It will simply muddy the water, prevent informed choice and thus preventing the free market.

NASA's Kepler probe rouses from its slumber, up and running again

mr.K

Re: 12 kg fuel

Isn't the fuel usually hydrazine? Okay, it's density is 1.02 kg/L which is above 1 kg/L, but volume and kg seems interchangeable enough for that particular fuel. As for gallons, American spacecraft means American gallons. (btw, the numbers are pulled directly from NASA’s Kepler Spacecraft Fuel Status Frequently Asked Questions)

NASA spots asteroid on crash course with Earth – with just hours to go

mr.K

Re: velocity of a sheep in a vacuum in El Reg units

To simply the calculations we set the wool drag to one. We also assume the sheep to be spherical.

'Autopilot' Tesla crashed into our parked patrol car, say SoCal cops

mr.K
Holmes

Wise choice

"...walk away from the crash uninjured and refused an offer of medical treatment."

Pro life tip, always refuse medical treatment when uninjured and healthy.

Buggy software could lock a Jeep's cruise control

mr.K

Re: Oh Lord

The issue here is that with computers it was fun careless days before we connected them together. In the early days computers were mostly islands and security was really not an issue. Programs were written to work and testing was testing with normal usage and not to check for buffer overflows to break the program. In other words, it was a simpler world. A world that car manufacturers still live in. I do not know if it is a good idea to let these people network a lot of two ton computers with wheels and hurl them down the highway.

Where one human driver can only manage to do so much damage. What happens when the entire line of some self driving cars on feb 12, 13.15 triggers a bug that slams on the breaks on all of them, or more likely they get hacked by some terrorist. We have to assume at least that foreign nations and probably our own will exploit this as a weapon of war.

Through many dangers, toils and snares.... SpaceX to send amazing GRACE to spaaaaace

mr.K

Re: Spaaaaace trash

It is just that the world is a little more complicated than that. "..make these things always recoverable" isn't all that hard, it is just that it requires more fuel and less cargo sent to space. Trying to protect the environment is a good thing indeed, but there has to be a cost-benefit analysis even there. You do not drive a lorry to the other side of the country to pick up piece of plastic bag and then drive back.

Slap some sort tax on them which should be used to collect tenfold the amount of garbage out of the sea from the shore line.

SpaceX Bangabandhu-1 launch held up while Dragon splashes down on time

mr.K

The good ol' days

No, good old fashioned racism would be the justification they used for slavery, colonization, ethnic cleansing, apartheid and segregation.

Calling everything that can be regarded as intolerant, any hint of lack of cultural understanding, unthoughtful jokes, and using common neutral words of yesterday that has changed meaning today, for racism is a newfangled idea. And quite frankly it is crude.

That doesn't mean we can't discuss what is okay to say, and what is not. Feel free to think joking with names is lame, but would you stand on the barricade if it was a German name? Did you go to arms when John Oliver did a lengthy segment on the presidents last name?

Ariane 5 primed for second launch of year after trajectory cockup

mr.K

Re: Reusable?

As far as I know, as of yet, they only land the first stage and that is never left in orbit anyway. Less junk in the ocean though. And I think second stages are often turned around and gets a retro burn to deorbit and those burn up at reentry.

And we do not know how much money they spend getting a Falcon 9 ready for another flight. Personally I believe they have cracked it and will bring costs down. We'll see.

Let's go to Mars, dude: Euro space parachute passes maiden test

mr.K

Re: If I could..

I tried to do the math on how much uranium we would need to heat up the core to get it going again. We are talking back of the envelope calculations here, but around 300 billion tons of uranium 235. If we go for an matter-antimatter reaction we could get away with 5 million tons.

Pitch it to Elon and I bet he'll say that it can be done by 2023 or something.

mr.K

Re: not a fluid dynamics expert but...

I am neither a fluid dynamics expert, and I wonder does gravity matter that much? The point of this thing is to slow it down at entry*, right? And it feels like there is basically three things that should affect how a parachute performs, velocity, air density and the force the payload drags it along with. Shouldn't the momentum of the thing at deployment be the main contributor of said force, and not gravity that maintains it when it has slowed down to terminal velocity?

*sounds wrong, but it can't be reentry.

Microsoft's Windows 7 Meltdown fixes from January, February made PCs MORE INSECURE

mr.K

Re: Should I be worried...

Their updates could break windows machines that ran certain kind of anti virus programs. So they made a key in the registry that had to be set before windows update would allow those updates to be applied. If the anti virus vendor had cleared their own software they should send out an update that should set that key. Of course if you do not run any AV you are screwed.

https://www.theregister.co.uk/2018/01/09/meltdown_patch_anti_malware_conflict/

I don't know if your problem is that, but should be able to check if the key is set manually.

You always wanted to be an astronaut, right? Careful: Space is getting more and more deadly

mr.K

I am not sure I see the reasoning here. Without a limiting time frame I don't see why we shouldn't solve most of the problems:

-radiation. Solvable by bring enough materials with you which currently is limited by launch cost and launch cost only. The energy requirement for getting stuff into orbit isn't really all that much so the problem is purely technological and not a problem of physics. With half a century of space travel so far there has to be limits there still possible to push.

-lack of gravity. Large enough acceleration and it is solved, but there we might bump into what's physical possible to achieve. But, tether two crafts together and send them into a spin and you are set. Just a matter of big enough spacecraft, see above. I suspect a 10 km rope would do wonders.

-supplies. As of now, humans still need an ecosystem to function. We are less and less dependent, but we are not there yet. However, there is no reason we can not achieve an artificial ecosystem where food is either grown on the waste or synthesised directly. Carbon dioxide capture and oxygen production will regardless be a side effect.

-energy. Some sort of nuclear reactor (be it fission or fusion) has to be brought along and fuel to feed it. But we should be able to do that today, if we really wanted to, so no problem there either.

The problems that might be unsolvable is time or speed. Even at light speed, you are correct, we will not reach very far in a life time, just a second, some guy is calling about relativity. Where was I. Yes, if we achieve on the outside, half the speed of light, we will not get very far in a life time. So either we have to extend the life time or we have to send our children even further and so on.

Becoming intergalactic might also be out of limits. The distances can become so large that without physics yet to be known can come to our aid, we can for all practical solutions be stuck in the Milky Way.

mr.K

Re: Climate Change

The increase is in harmful radiation and not radiated power. Also a good part of it comes from space due to the sun not shielding us due to lower output.

So the radiation bit here does not directly affect the power budget of Earth. However there is a theory that cosmic rays that reach as far in as Earth and hits the atmosphere can on impact start a cascade of reactions ending up with nuclei for water vapour to turn into clouds. This will in turn isolate the Earth during the night and trap heat. This is of course disputed as all that relates to climate is. And since there are two debates over climates, one scientific and one political, I really can't be bothered to figure out which is which. (I just read a debunking of the theory, but it was a straw man where they refuted the claim that cosmic rays are the cause of climate change where the claim is that it can affect it.)

Poop to save planet as boffins devise bullsh*t way of extracting gas

mr.K

Re: Ok, but...

You still get all the fertilizer here. During the digestive process the body breaks up the food and extracts nutrients. A lot of energy rich molecules can't be broken down in the digestive process and is sent down to the large intestines. There bacteria that are able to break down and feed of the left overs thrive. In return they break out vitamins etc that is extracted by the body. Crucial when it leaves the cow, in this instance, there is still a lot of fibres left that are continued to be broken down in a process that produces a mixture of carbon dioxide and methane. If you collect the manure in tanks, collect the gas produced and then use it as fertilizer makes no difference than if use it as fertilizer straight away and gas will be released straight into the air instead.

I don't know if I quite see the big breakthrough here though. Basically what they are doing is collecting the carbon dioxide in the biogas, enriching it with hydrogen and producing methane. A well known process I would think. And it requires an energy input so where is the benefit?

Paul Allen's six-engined monster plane prepares for space deliveries

mr.K

Re: Balloons/airships ?

Low earth orbit is not a particular height, but a height and speed. The height is not really where all the energy go, most go into obtaining the speed.

A conveyor belt can't be built up to LEO without anything supporting it, so basically you have to build a couple of hundred kilometres tall structure. Our current record is about one. Then there is the space elevator which is a theoretical possible idea. The basic principle is that if you go further out the orbital velocity decreases and the length of the orbit increases. Both of these contribute to the length of the orbital period increases also. At some point it goes up to 24 hours instead of one and a half which is about what it is in LEO. At equator the ground also "orbits" the centre of earth in 24 hours. Thus an object that far out over the equator will seem to stay put or as we say synchronous. Call it geosynchronous if you will. Since you then have an object seemingly floating out there you could tie a rope to it and lower it down to the ground. This will of course shift the centre of mass of the object downwards which you compensate by having a more massive object and also place it a little outside GEO so that the rope and the object combine has a centre of mass in GEO. Pull yourself up along that rope and you have an space elevator.

First problem, it doesn't go to LEO, but GEO. You could get something to height of LEO using it, but you still need the velocity afterwards.

Second building it. At the moment we are not sure if there even exists a material strong enough to hold it's own weight while stretched out so far. The distance to GEO is about 36 thousand kilometres.

Who wanted a future in which AI can copy your voice and say things you never uttered? Who?!

mr.K

Not a single lawful one?!

"Cant think of any lawful ones though yet."

Imagine a world where every text ever written can be read aloud by Morgan Freeman.

Bright idea: Make H when the Sun shines, and H when it doesn't

mr.K

Re: carbon monoxide as byproduct???

First of all, I would argue that carbon monoxide isn't a highly toxic gas, but the Wikipedia does indeed say that. I guess it comes down to what qualifies as "highly".

Second, carbon monoxide isn't the byproduct, but the product and it is used as an example. In their report it says that the use are for endothermic gas reactions that requires heat and a catalyst. As an example where you want to produce carbon monoxide and hydrogen gas from water and methane. That require heat and you end up burning some of the methane to keep the process going. However, if you use the sun as the heat source you can save some of the methane. In addition due to it being an endothermic reaction there is more energy in the end product than the gas you feed into it.

What you most certainly will not do is to dump it into the atmosphere. You have after all gone through great lengths to produce it. You either use it as a energy carrier i.e. fuel, or as a component in further chemical reactions.

In addition I see some commentards claiming the use it as heat during the night, but no. Their proposal is to use air as a thermal storage to tap into at night.

Oi! Verizon leaked my fiancée's nude pix to her ex-coworker, says bloke

mr.K

Re: Four million dollars?

Thanks for informing me of punitive damages. A term I have heard lots of times, but never have really taken the time to read up on. Now I have, and looking back on my original statement I have to say I have to let it stay. Maybe refine it a little and just say that punitive damages is mindblowingly ridiculous.

Civil lawsuits should be that somebody asks the state to settle a dispute and possibly decide a compensation for a loss due to said dispute. If it follows that crime might have been committed then the state should bring up criminal charges in addition. Financial gain (as in gain and not compensation) for any party should never be the outcome.

mr.K

Re: Four million dollars?

"..could have been.." Can you sue for things that could have happened in USA?

mr.K

Four million dollars?

It is hard to assess the value of quite a lot of things and thus also hard how to compensate the loss of such thing. But these lawsuits you have over there are just ridiculous. It is not even she that sues. How on earth does the damage caused by ONE other person seen your girlfriends vagina amount to four million dollars?

Astro-boffinry world rocked to its very core: Shock as Andromeda found to be not much bigger than Milky Way

mr.K

Re: "By measuring the escape velocity, scientists have recalculated the galaxy’s mass and size."

I have no idea on what they actually did, but if you can determine the orbital speed you can also determine the escape velocity. This is since both only rely on the mass of what you orbit and the distance to the centre of it. You have to assume the orbit to be circular, or establish the entire orbit and with galactic years tending to be long years I don't think they have waited for that.

You also have the assumption that you orbit something where the mass is in the centre. Witch is of course not true for galaxies. The neat thing about calculating gravitational pull from within an object is that you can disregard all the mass situated further out from the centre than yourself, assuming the mass is symmetrically placed i.e. in rings or shells around the centre.* Thus when you start to escape you start to pass more and more of the mass further out to you that adds to the gravitational pull.

But I assume that if you manage to map the average orbital velocity on objects far enough out then you should be able to determine the entire mass. And if you map for enough orbits then you should be able to map the mass profile distribution. So easily I thought that I wonder why they either have gotten it wrong with that method or why they havn't done it before.

*Among other things enabling the fun fact that inside a hollow planet if it is a sphere you are weightless, regardless of where you are in it.

mr.K

Re: dodgy maths?

https://en.wikipedia.org/wiki/Long_and_short_scales#Long_scale_users

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