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

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.

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.

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

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?

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.

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

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

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.

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.

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.