Well of Souls Forums

Absalom wrote:

AndrejaKo wrote:Just a dumb question: Why would 1 kg of helium and 1 kg of lead have different weights, with same gravity? In both cases, it should be around 9.81 N, give or take for the local gravity constant.

Density. For any normal conditions, the density of lead is going to be reasonably stable. Helium is a gas under "room conditions", so it'll have variable density, but the density will be much lower than lead regardless: about 1/100th at it's boiling point, while at 1 atmosphere. You can get the same weight in a vacuum, but space suits are rarely used on the surface of the Earth, so...

That's if you include buoyancy force as part of the weight. To complicate things further, the buoyancy effects are far more significant in the water which covers most of the planet, and vary depending on temperature and salinity. And then there's the centrifugal pseudo-force from Earth's rotation, depending on latitude. Most weight measuring devices will include all of these, but weight is defined as just m*g...practically speaking, if you want the true weight, you'd have to measure the mass and calculate it, and you might as well just use mass at that point.

Oh, that's interesting way of looking at things. In my culture, we strictly define weight as mass times gravity acceleration and do not include buoyancy into it. Instead, we consider it a separate force. That's probably the reason we use mass for everything.

re: the exoplanet debate, the loroi are probably poring over every star looking for something with an appropriate mass in the liquid water zone with an oxygen atmosphere. there aren't going to be many candidates around the wastes for such a star/planet.

Nathan_ wrote:re: the exoplanet debate, the loroi are probably poring over every star looking for something with an appropriate mass in the liquid water zone with an oxygen atmosphere. there aren't going to be many candidates around the wastes for such a star/planet.

There seem to be plenty of planets with a similar mass within the Union and Hierarchy alone. And the Wastes are several times larger in volume. So I doubt it would be so easy. Interstellar space is huge.

GeoModder wrote:

Nathan_ wrote:re: the exoplanet debate, the loroi are probably poring over every star looking for something with an appropriate mass in the liquid water zone with an oxygen atmosphere. there aren't going to be many candidates around the wastes for such a star/planet.

There seem to be plenty of planets with a similar mass within the Union and Hierarchy alone. And the Wastes are several times larger in volume. So I doubt it would be so easy. Interstellar space is huge.

stars in the wastes are fairly well spread out, and the immediate volume of stars where Earth could be is constrained by: 1)distance the Jardin could have traveled 2)the Union taking up space 3) the hierarchy taking up space. the time value for planet earth's location is probably a few months at most.

For all the Loroi know, the Bellarmine and other ships of the expedition could have come from the other side of the Coal Sack. The only hard fact at this moment in the comic is that the relay ship is '10 jumps away' from Naam. Vector/direction of location undetermined.

Further more, you seem to assume the Loroi (and/or their allies) continue to make the effort for passive astronomic data gathering (telescopes and such) during the last centuries while having the capacity to jump around at will within the Local Bubble. It takes with our current passive methods years to determine that yes, yonder G-type star is very likely to have a Deinar-sized/mass planet in the habitable zone. That is to say, the Loroi have to make the assumption Earth is orbiting a G-type star at this point.

Do you realize how many stars there are on a 'short' interstellar leg like 250 lightyears? I just checked on Celestia, and within a radius of barely 45 lightyears from Earth there are already 500 known stars. The number must run in the tens of thousands. Even G-type stars alone likely exceed a thousand over that distance.

Also, our best planet detection method (transit photometry) only works for the tiny fraction of planetary systems that are edge-on to us, and so transit the face of the star. The odds that a particular system that you're looking for happens to be discoverable using this method are very remote.

At this tech level looking for a system means sending out a scout ship, not busting out a telescope.

Arioch wrote:Also, our best planet detection method (transit photometry) only works for the tiny fraction of planetary systems that are edge-on to us, and so transit the face of the star. The odds that a particular system that you're looking for happens to be discoverable using this method are very remote.

Would the Terrestrial Planet Finder have worked on other angles? It would have only needed the light from a planet to see it, after all.

The light from a planet is so utterly drowned out by its parent star as to be completely unworkable. It's like trying to spot someone with a switched on flashlight while staring at the sun.

As for angles, you'd more or less need to travel several dozen light years to even begin to appreciably change your angle relative to what you're observing, and even then it might not be the correct or even desirable angle, since you've got nothing on where or how a planet is orbiting.

Even supposing that the TPF would have worked out as planned, the more distant the object you're trying to sniff out the more time you'd need to determine if anything is there at all.

Talking about passive planet-finding techniques. I wonder if the gravitational lensing effect of one of those old Soia tonsillat would be detectable.
Imagine one or the other moon-sized derelict orbiting its sun face-on respective to Earth, and being detected.

RedDwarfIV wrote:Would the Terrestrial Planet Finder have worked on other angles? It would have only needed the light from a planet to see it, after all.

As I understand it, both of the direct-observation methods planned for the TPF (interferometry and coronography) involved large or composite optical telescopes with the ability to blot out the light of the central star, either through special optics or destructive interference. I think that in order for either of these methods to work, the target system would have to be relatively close. The target systems planned for TPF all appear to have been closer than 30 LY.

The radial velocity method works at greater distances and at any angle, but works best when the target planet has a high mass and a short orbital period. Complex systems like Sol that have outer planets with orbital periods in the ~200 year range would take a very long time of watching to be able to figure out.

GeoModder wrote:Talking about passive planet-finding techniques. I wonder if the gravitational lensing effect of one of those old Soia tonsillat would be detectable.
Imagine one or the other moon-sized derelict orbiting its sun face-on respective to Earth, and being detected.

I believe that there are some Kepler candidates in which they think they're seeing moons, so moon-sized objects could be detectable with the transit method. However, gravitational lensing implies very high density, and so I think we wouldn't expect to see lensing unless we assume that the tonsillat was composed of superdense material.

Arioch wrote:

RedDwarfIV wrote:Would the Terrestrial Planet Finder have worked on other angles? It would have only needed the light from a planet to see it, after all.

As I understand it, both of the direct-observation methods planned for the TPF (interferometry and coronography) involved large or composite optical telescopes with the ability to blot out the light of the central star, either through special optics or destructive interference. I think that in order for either of these methods to work, the target system would have to be relatively close. The target systems planned for TPF all appear to have been closer than 30 LY.

The basic approaches should scale up fine, you just need big instruments. The Loroi shouldn't have any trouble building something 10 or 20 times the size of something we would consider building today.

It might take months or years of observations to pick out the different planets and work out their orbits, though...and a telescope doing this kind of work can really only look at one thing at a time. If they have a general direction to work with and don't have to go through Umiak territory, it could easily be faster to just send some ships out to take closer range observations (and in the meantime, that planet finder can be doing a survey of Umiak territory where Loroi ships can't go).

What's a tonsillat?

Carl Miller wrote:What's a tonsillat?

He's referring to the mythical moon-sized spacecraft that the Soia supposedly tooled around in.

I just checked on Celestia, and within a radius of barely 45 lightyears from Earth there are already 500 known stars.

Counting binary and trinary star-systems? I was under the(probably false) idea that the 400ish closest star systems to us were within a 150 LY radius.

As for angles, you'd more or less need to travel several dozen light years to even begin to appreciably change your angle relative to what you're observing

How tall is union space, and how many discrete points therein would they have?

Nathan_ wrote:Counting binary and trinary star-systems? I was under the(probably false) idea that the 400ish closest star systems to us were within a 150 LY radius.

The RECONS 25 database of known stars within 25 parsecs (81.5 light years) lists 3,069 objects in 2,167 systems. The actual number is probably much larger, as the majority of stars are dim red and brown dwarfs that are difficult to detect at greater distances. The estimated density of stars within 5 parsecs is about 0.14 stars per cubic parsec, so the expected number of stars within 25 parsecs is about 9,100.

For a sphere with 150 light year radius, using this density we would expect about 57,000 stars. For a box 250 light years on a side, we would expect about 63,000 stars.

Here's a nice visualization of the RECONS 25 database:



Note how the stars become less red as distance increases, because they're missing from the database.

I suppose that settles it.

Arioch I have been examining programs like Space Engine and Universe Sandbox, were there any space programs you enjoy or think highly of?

hi hi

I had high hopes for Universe Sandbox, since it claimed it could keep track of the velocities of star systems, but it turned out that it was impossible to easily compare them with each other. My search continues for a star map that handles the relative velocities between stars easily. ((In the setting I use for scifi tabletop RPGs, FTL travel doesn't change the traveler's velocity, so knowing the difference between star systems becomes very important.))

Other than that, Universe Sandbox is kind of neat. It's more of a curiosity than a mapping system.