Science questions not worth a thread I: I'm a moron!

[hobbsyoyo]

Does a geosynchronous orbit have to be an equatorial orbit or close to it? How far off the equator can they get?

I really hope this question means you have picked up Kerbal Space Program.

 

[Eran of Arcadia]

What is the name of the clade that includes humans and all species more closely related to humans than chimps, but not chimps or their relatives? Wikipedia says in one place that it's "hominina", and in another that hominina includes chimps.

 

[Arakhor]

I believe that "hominids" is used to describe all humans and human ancestors since homo erectus at the least.

 

[Eran of Arcadia]

I think "hominid" refers not only to humans but to at least chimps, maybe gorillas, and all the descendants of our last common ancestor. What I am looking for would be defined as "human>chimp", I think.

 

[Arakhor]

Well, hominidae is the family of great apes, from which the sub-family homininae descends and from that our own genus homo. However:

The term "hominid" is also used in the more restricted sense as hominins or "humans and relatives of humans closer than chimpanzees".

 

[PlutonianEmpire]

I dunno how well this question will work out, but...

What is the most detailed, "step-by-step"* timeline that we know of about star formation, from the nebula to the main sequence, for sunlike and near-sunlike stars?

* I'm well aware the universe is analog, as star formation, IIRC, is always in transition from one phase to another, I just need something to work with for an addon I'm making for Celestia, since the latest version let's me go 2 Gy into the past and future and I'm taking advantage of that.

 

[hobbsyoyo]

I also suspect it might be able to happen incredibly fast, geologically speaking. Say, and less than 1000 years.

However, I don't think it could happen anywhere close to that fast today owing to the pattern of ocean distribution. The Pacific, Indian, and Atlantic are well shaped to transfer equatorial heat to the poles. Plus, there's a ton of land within 30 degrees of the equator. If that land were more towards the poles, and situated along latitudes blocking heat transfer, we'd have a potential for much faster snowball.

According to a BBC documentary called The Planets, a snowball Earth can take millions of years to form. However, that particular episode was riddled with factual errors and the whole series is out of date (c. 1999) so take from that what you will.

 

[Arakhor]

I remember watching that at the time!

 

[Bluemofia]

I dunno how well this question will work out, but...

What is the most detailed, "step-by-step"* timeline that we know of about star formation, from the nebula to the main sequence, for sunlike and near-sunlike stars?

* I'm well aware the universe is analog, as star formation, IIRC, is always in transition from one phase to another, I just need something to work with for an addon I'm making for Celestia, since the latest version let's me go 2 Gy into the past and future and I'm taking advantage of that.

Note to self: answer this question eventually.

Just letting you know I'm typing up a response on this intermittently. I'm assuming sunlike and near-sunlike means metal rich stars of similar mass to the sun, yes?

 

[hobbsyoyo]

I remember watching that at the time!

All in all it's pretty good. I don't fault the show for being out of date given it's age and how much (and how quickly) we are learning all sorts of new stuff about the Cosmos. And only that one episode contained stuff of questionable factuality (even for 1999), but they were clear that some of the things they were presenting were theoretical.

I watch space shows like this and The Universe to help me fall asleep at night. Plus, I actually learn stuff, so it's win-win.

Unfortunately, Netflix lost The Universe and a few other good Sciencey/Space-themed documentary series and I just finished The Planets series.

 

[PlutonianEmpire]

Note to self: answer this question eventually.

Just letting you know I'm typing up a response on this intermittently. I'm assuming sunlike and near-sunlike means metal rich stars of similar mass to the sun, yes?

Actually, the addon is the formation of a close-orbiting binary, where today, they are in the main sequence as a G0V and K3V (1.09 and 0.75 Msun respectively) at the age of 1.9 Gy.

Spoiler :

This doen't shake things up too much, does it?

 

[stfoskey12]

Unrelated Questions:
If Earth was at Pluto's distance from the Sun and the atmosphere stayed gaseous, could you see stars other than the Sun during the day and if so how many?

How far away did people go deaf from the Krakatoa eruption?

Why aren't all the one letter element symbols used that could be (titanium is Ti, not T)?

 

[madviking]

Boiling point of nitrogen: 77 K

Surface temperature of Pluto: 35 to 45 K

Yea, just saying.

 

[Arakhor]

Why aren't all the one letter element symbols used that could be (titanium is Ti, not T)?

Not all scientists speak English as their first language and IUPAC is an international organisation. Read up on tungsten/wolfram if you want to know why it has the symbol W.

 

[strijder20]

Why does light move slower than the speed of light ( in a vacuum, of course) in liquids/solids than in gases, and why does it move even slower in extremely cold substances?

 

[dutchfire]

One way to look at this is that light is absorbed by atoms in a solid, temporarily exiting the atom to a higher energy level. The atom will then fall back to the original level, emitting the light again. At any point "between interactions", it is moving at the speed of light, however, since it spends some time standing still, the average speed is lower.

I don't know if this simple explanation survives in a field theory picture.

 

[uppi]

One way to look at this is that light is absorbed by atoms in a solid, temporarily exiting the atom to a higher energy level. The atom will then fall back to the original level, emitting the light again. At any point "between interactions", it is moving at the speed of light, however, since it spends some time standing still, the average speed is lower.

I don't know if this simple explanation survives in a field theory picture.

Sort of. Light traveling in a medium is not a pure electromagnetic wave, but a compound wave. One part is the electromagnetic wave and the other one is the polarization of the medium, which also travels through the medium as a wave. (Solid state physicists refer to this compound as "polariton"). This compound wave is no "light" in the strictest sense anymore and thus moves slower.

It is particular instructive to look at the extreme case: Slow light as seen in EIT experiments. There you can tune the refractive index of the medium to such extremes that a light pulse can travel at the speed of a cyclist. In that case the electromagnetic component of the wave gets very small and it is mostly an atomic excitation wave ("spin wave") that is traveling through the medium. But you can go even further and reduce the speed of light to zero: Then there is no traveling electromagnetic field anymore, all that remains is the spin wave that is stationary (as long as the atoms don't move). When you increase the speed of light again, the pulse comes out, so this can be used to store light in the medium.

 

[dutchfire]

That explanation works best in condensed/strongly interacting matter, I suppose. I doesn't really explain much about why light is slower in air, there are few polaritons there!

 

[uppi]

That explanation works best in condensed/strongly interacting matter, I suppose. I doesn't really explain much about why light is slower in air, there are few polaritons there!

The air is still polarized, if only slightly. Obviously the effect is much weaker than in condensed matter, but I see no fundamental difference. A photon in air could be called a polariton, even if its properties are very close to that of a photon in vacuum.

 

[hobbsyoyo]

Boiling point of nitrogen: 77 K

Surface temperature of Pluto: 35 to 45 K

Yea, just saying.

Pluto actually does have a thin nitogren atmosphere at times.

Unrelated Questions:
If Earth was at Pluto's distance from the Sun and the atmosphere stayed gaseous, could you see stars other than the Sun during the day and if so how many?

Yes, you could see all the stars because the sun is so small and dim at that distance. It'd be just like nighttime here, mostly. You could also probably see almost all of them except those close to the sun in the sky.