6 ms·

To add to that, the sun's average power density barely rivals a compost heap.

techdragon 7y ago
That’s awfully simplistic. Having spent most of today day wrestling with permutations of the various radiometric flux and power formulas. It’s pretty clear that depending on what you count as the “edge” you can get some very disingenuous results when it comes to anything related to the sun’s density. What’s the math behind the compost heap estimate there? (Genuinely curious since I’ve spent the day doing math adjacent to this one)
- erik_landerholm 7y ago
  Physics exchange has a calculation. Bunch of articles about it accessible from google.
- analog31 7y ago
  That was my reaction too. Indeed, among the many possible ways to think about it, the sun can warm the compost heap, but not vice versa. On the other hand, the sun is a cosmic compost heap. ;-)
  - maxander 7y ago
    Remember the square-cube law; for two things of different sizes, the difference in surface area is proportional to the square and the difference in volume is proportional to the cube of the difference in sizes. So, compared to any Earth-bound compost heap, each bit of the sun's surface (wherever you draw the boundary) has more heat-generating interior backing it up.
- jws 7y ago
  According to the inarguable science of taking the first google result for my questions… The sun releases 3.846×10²⁶ watts. The sun has a volume of 1.4×10²⁷ cubic meters. Therefore the sun releases less than one watt per cubic meter. Scanning a 2010 article: Energy from Waste: Reuse of Compost Heat as a Source of Renewable Energy it looks like composting facilities make about 1 to 10 megajoules/kilogram over a fortnight. At 10⁶ seconds per fortnight gets us 1 to 10 watts per kilogram of compost. At a minimum of 100kg/heap (anything less is a pile, a mess, or a spill) it is a trivial exercise to show that compost is orders of magnitude more energetic than the sun. Now if Hacker News would just allow stick figure cartoons maybe we could lure Randall Munroe into answering these questions for us.
JudgeWapner 7y ago
Using average power is kind of misleading: The core inside 0.20 of the solar radius contains 34% of the Sun's mass, but only 3.4% of the Sun's volume. Inside the 0.24 solar radius is the core which generates 99% of the fusion power of the Sun. https://en.wikipedia.org/wiki/Solar_core https://en.wikipedia.org/wiki/Solar_core

That’s awfully simplistic. Having spent most of today day wrestling with permutations of the various radiometric flux and power formulas. It’s pretty clear that depending on what you count as the “edge” you can get some very disingenuous results when it comes to anything related to the sun’s density. What’s the math behind the compost heap estimate there? (Genuinely curious since I’ve spent the day doing math adjacent to this one)

erik_landerholm 7y ago
Physics exchange has a calculation. Bunch of articles about it accessible from google.
analog31 7y ago
That was my reaction too. Indeed, among the many possible ways to think about it, the sun can warm the compost heap, but not vice versa. On the other hand, the sun is a cosmic compost heap. ;-)
- maxander 7y ago
  Remember the square-cube law; for two things of different sizes, the difference in surface area is proportional to the square and the difference in volume is proportional to the cube of the difference in sizes. So, compared to any Earth-bound compost heap, each bit of the sun's surface (wherever you draw the boundary) has more heat-generating interior backing it up.
jws 7y ago
According to the inarguable science of taking the first google result for my questions… The sun releases 3.846×10²⁶ watts. The sun has a volume of 1.4×10²⁷ cubic meters. Therefore the sun releases less than one watt per cubic meter. Scanning a 2010 article: Energy from Waste: Reuse of Compost Heat as a Source of Renewable Energy it looks like composting facilities make about 1 to 10 megajoules/kilogram over a fortnight. At 10⁶ seconds per fortnight gets us 1 to 10 watts per kilogram of compost. At a minimum of 100kg/heap (anything less is a pile, a mess, or a spill) it is a trivial exercise to show that compost is orders of magnitude more energetic than the sun. Now if Hacker News would just allow stick figure cartoons maybe we could lure Randall Munroe into answering these questions for us.

JudgeWapner 7y ago

Using average power is kind of misleading: The core inside 0.20 of the solar radius contains 34% of the Sun's mass, but only 3.4% of the Sun's volume. Inside the 0.24 solar radius is the core which generates 99% of the fusion power of the Sun. https://en.wikipedia.org/wiki/Solar_core https://en.wikipedia.org/wiki/Solar_core