One thing worth noting is our popular notion of what a star seems to be is quite different from what astronomers have.
One example, Canis Majoris has a radius of about 1420 solar radii. But its mass is roughly
17±8 times the mass of the Sun and therefore an average density of 5.33 to 8.38 mg/m3. “It is over 100.000 times less dense than Earth’s atmosphere at sea level.”
The surface radius of a star is defined based on optical thickness. If you were there, the star would in fact look like a fairly well-defined opaque spheroid with the reported radius. The density of the photosphere plasma is near zero, but there’s a lot of it.
What’s particularly interesting to me is that for stars the size of our sun, regular old gas pressure dominates. The sun’s atmosphere is held up essentially just from the temperature (and therefore high kinetic energy) of the plasma.
Only once you get to 10+ solar masses does radiation (light) pressure begin to become significant, and at 50+ solar masses is when it dominates and the atmosphere is held up by the momentum of light.
To add on to the other response, think of it like the star “leaking” into space. It’ll be defined as a pretty radically different size at some point in the future, even as it’s still undergoing fusion.
I always wonder when do they stop considering the outer layers part of the star and not relatively dense solar wind soup. Nobody says Earth has 7000km radius, even tho there's traces of exosphere past 500km.
Depending what kind of reading material you're looking for (e.g. high level details or mathematically/jargon dense papers) look for things discussing "Rosseland optical depth" and "grey atmosphere approximation".
At a high level, the common convention is to define the radius by finding where the optical depth is 2/3 when using Rosselands clever way of calculating a weighted mean of the opacity from that layer in the star to space across different wavelengths of light. 2/3 being a clever derivation from Eddington where, in an idealized model of a star, that's when the actual temperature of the star should equal its blackbody equivalent temperature.
Pedantically, this distance to the point of equality is an ever so slightly different value than the "distance from the center where there is a 50% chance a photon traveling directly outward will escape the star without another interaction" rule of thumb (in the same idealized grey model). Practically, that the difference is so small is why it's a fantastic rule of thumb explanation.
The radius is based on visual observation. We have good theories and models about what's happening inside the star. We are quite sure that it's mostly empty space inside the radius. But that's not a good enough reason to say that the star's radius is anything other than what we see through our telescope.
Importantly, this works for stars relatively close to us (the farthest I can find is 16,000 light years for one hyper giant) but the majority of the stars catalogued in even our own galaxy have only been assigned a radius via taking the temperature (via color) and luminosity.
> therefore an average density of 5.33 to 8.38 mg/m3
That's nuts. How on earth does fusion happen at that density? Is there a denser core that actually fuses, and the outer fluffy bits just glow from the inner heat?
Averages are quite misleading. The core is obviously a lot denser. Our sun has an average energy output per cubic meter that is comparable to a compost heap.
Sure, but now I'm left wondering what the size of the body doing fusion is. If most of the star is glorified glowing atmosphere, I want to know the mass and radius of the fusing bits.
Depends on the class of the star. Our sun? About 1/4 radius and in is fusion reaction. But it gets weird in other stars. In red giants the fusion zone is a very small shell around a dead core. Maybe something like earths orbit in radius, but very very thin.
Astra says this claim is misleading. Sun's average energy output per cubic meter is three orders of magnitude smaller than that of a compost heap. The fusion core is comparable though.
The energy density of specific compost heaps varies by several orders of magnitude it’s not a single number. Volume, moisture content, internal temperature, external temperature, materials being composted, etc all play a significant role.
Average density for non-uniform objects is pretty useless, since the cubic volume scaling makes a mess of things.
As an example, I pulled the stats for an electric locomotive. 19x3x4.4 meters, mass 90 metric tonnes. That's an average density of about 1/3rd of water.
Locomotive itself? Probably not. If you turned its abstract bounding box into real box - thin, negligible mass, enough strength not to break up - and evacuated the air inside, then yes, the box with locomotive in it should float.
I worked for a financial org with over a trillion in assets, and they had a 100% acceptable variance on project length predictions. Made for a laid-back atmosphere at work but boy. How they ever swung that is beyond me.
“We predict a year, so it’ll take anywhere between 8 seconds and 24 months!” AND IT WORKED???
I've bought 14kwh of anker solix max ac for €3900, and added 2 zendure 800 plus's for €320 each (1.9kwh + 2 solar mppt ports each).
It's all connected and managed through homeassistant.
People have had the capability to spread already existing biological weapons for decades. Sometimes they even do (anthrax in the post). What’s changed?
I suspect awards are one of the more profitable niches of the wider events industry.
They're cheaper to produce than a full-scale conference (needing just a 1 day hire of a hotel ballroom or similar) and are easy to sell - every business or team nominated for an award will pay for a table, as will various suppliers and vendors who see it as a great marketing opportunity.
I was at one committee meeting when the annual award ceremony came up. One person was considered for an award because she had a big family with many cousins and nieces. All the better to sell tables.
you know an award is actually legit when someone from a trade body contacts you the week before sounding slightly put out that nobody from your member company is flying to Europe to attend their event even though you did fill out an application form, you assume their event must be a bit short of attendees but reluctantly dip into the small startup budget for a single person to fly out there because "something something networking", and then your colleague gets surprised by actually winning it whilst surrounded by the teams everyone else sent.
on the other hand, I found it hilarious one of my father's old companies publicly sponsored a special new category of award at a legit-seeming construction event. You'll never guess who won...
It looks more like awards for events, e.g. "Most Creative and Engaging Event" and "Best Event Series (over 1800 attendees)," none of which seem to have anything to do with the quality of any awards given at those events. What am I missing here?
That’s part of his standard bag of tricks. Say loads of ridiculous offensive threatening stuff. See what sticks with his base. Let the sycophants around him laugh nervously but not explicitly say he’s joking unless he does first. He’s only joking when it suits and not joking when it also suits.
Henry Hill: You're a pistol, you're really funny. You're really funny.
Tommy DeVito: What do you mean I'm funny?
Henry Hill: It's funny, you know. It's a good story, it's funny, you're a funny guy.
[laughs]
Tommy DeVito: What do you mean, you mean the way I talk? What?
Henry Hill: It's just, you know. You're just funny, it's... funny, you know the way you tell the story and everything.
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