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I'm confused, I know, I'm always confused

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Re: I'm confused, I know, I'm always confused
Post by ThinksMarkedly   » Thu Aug 04, 2022 3:10 pm

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Louis R wrote:You have 2 additional issues to deal with:

Signal velocity is degenerate with range - to calculate the former you have to obtain the latter independently.


Good point. You can't calculate both speed and distance using a single time measurement. If we could still observe the probes in telescopes, we could calculate the distance using parallax, but they're too far for that.
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Re: I'm confused, I know, I'm always confused
Post by Joat42   » Thu Aug 04, 2022 3:44 pm

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ThinksMarkedly wrote:If we could still observe the probes in telescopes, we could calculate the distance using parallax, but they're too far for that.

It's literally how they do it today with radio-telescopes. They have a pretty good idea where Voyager is, they point the radio-telescope where they calculated it should be, hunt around until they find the signal, lock on to the signal and track it - that gives the distance and the speed which are derived from the the tracking motion.

---
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Anyone who have simple solutions for complex problems is a fool.
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Re: I'm confused, I know, I'm always confused
Post by isaac_newton   » Fri Aug 05, 2022 11:20 am

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Theemile wrote:SNIP

Technically, you are correct for "Sub-c", but I've never heard the phrase. The speed of light in Copper can drop to as low as 72% but coax can be as high as 83% - Earth's atmosphere at sea level drops the speed of light by a factor of 1.0003, So anything interstelllar matter can do is almost insignificant - but from a physics point of view, it is sub-c. And at the distances we're discussing, timing signals will be distorted.


I was waiting for an appt yesterday, and on the wall opposite was that famous Hubble photo of the 'Pillars of Creation'. I was sort of wondering how big they were [about 5 light years it turns out] and then how dense.

After a bit of seaching I found:
- 'standard' space is about 1 atom of hydrogen/cc [dropping down to maybe 0.1 atoms/cc in certain region
- in the Pillars - about 4,000 atoms/cc
- our atmosphere - about 2.5x10^25 molecules/cc
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Re: I'm confused, I know, I'm always confused
Post by ThinksMarkedly   » Fri Aug 05, 2022 12:28 pm

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isaac_newton wrote:I was waiting for an appt yesterday, and on the wall opposite was that famous Hubble photo of the 'Pillars of Creation'. I was sort of wondering how big they were [about 5 light years it turns out] and then how dense.


I trust you've seen the new one from the JWST?
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Re: I'm confused, I know, I'm always confused
Post by ThinksMarkedly   » Fri Aug 05, 2022 12:37 pm

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isaac_newton wrote:- our atmosphere - about 2.5x10^25 molecules/cc


Uh.. this seems high. That's about 40 mol/cm³. The atmosphere is 78% N₂ and 21% O₂, so it should have an average mass of roughly 0.78 * 28 + 0.22 * 32 = 28.88 g/mol. Multiplying by that average molecular density would give us 1155 g/cm³, which is 1155x denser than water.

One of us is off by a few orders of magnitude.
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Re: I'm confused, I know, I'm always confused
Post by Gun Boat Diplomacy   » Sun Aug 14, 2022 3:05 pm

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ThinksMarkedly wrote:
Gun Boat Diplomacy wrote:Thank you for your replies. I got to wondering if maybe I missed some sort of Manticoran electronics magic/vodoo that slowed down signals ;)


Why would they want to do that?


It was meant as a joke
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Re: I'm confused, I know, I'm always confused
Post by Fox2!   » Sun Aug 14, 2022 9:17 pm

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ThinksMarkedly wrote:
isaac_newton wrote:- our atmosphere - about 2.5x10^25 molecules/cc


Uh.. this seems high. That's about 40 mol/cm³. The atmosphere is 78% N₂ and 21% O₂, so it should have an average mass of roughly 0.78 * 28 + 0.22 * 32 = 28.88 g/mol. Multiplying by that average molecular density would give us 1155 g/cm³, which is 1155x denser than water.

One of us is off by a few orders of magnitude.


From Byjus.com (https://byjus.com/physics/density-of-air/), the density of air at 273.15 deg K and 760 torr pressure is 1.29 grams per litre or 0.07967 pounds per cubic foot.

/Pedant
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Re: I'm confused, I know, I'm always confused
Post by ThinksMarkedly   » Mon Aug 15, 2022 6:54 pm

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Fox2! wrote:From Byjus.com (https://byjus.com/physics/density-of-air/), the density of air at 273.15 deg K and 760 torr pressure is 1.29 grams per litre or 0.07967 pounds per cubic foot.

/Pedant


That's much less than 1 mol/dm³, which means it's less than 0.001 mol/cm³.
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Re: I'm confused, I know, I'm always confused
Post by cthia   » Tue Aug 16, 2022 9:16 pm

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ThinksMarkedly wrote:
isaac_newton wrote:- our atmosphere - about 2.5x10^25 molecules/cc


Uh.. this seems high. That's about 40 mol/cm³. The atmosphere is 78% N₂ and 21% O₂, so it should have an average mass of roughly 0.78 * 28 + 0.22 * 32 = 28.88 g/mol. Multiplying by that average molecular density would give us 1155 g/cm³, which is 1155x denser than water.

One of us is off by a few orders of magnitude.

Particulates should make up the difference. Matter in particulate form, like diesel exhaust. Soot. Dust. Etc.

Son, your mother says I have to hang you. Personally I don't think this is a capital offense. But if I don't hang you, she's gonna hang me and frankly, I'm not the one in trouble. —cthia's father. Incident in ? Axiom of Common Sense
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Re: I'm confused, I know, I'm always confused
Post by ThinksMarkedly   » Wed Aug 17, 2022 5:53 pm

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cthia wrote:Particulates should make up the difference. Matter in particulate form, like diesel exhaust. Soot. Dust. Etc.


That can't make up for the difference. We're talking about a 1000:1 more other things than O₂ and N₂. Even if the dust were pure C-12 atoms, at a 1000:1 ratio it would outmass the atmosphere by roughly 400:1.
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