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29 votes
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Starting a fire in a cold planet that was full of flammable gas

The outer parts of Neptune are mostly hydrogen and helium. There are small amounts of other gases such as methane, ammonia and water vapour. However, there is no oxygen at all. If you took some of ...
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20 votes
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What is the difference between gas and dust in astronomy?

Yes, metals and other elements and molecules can exist in gaseous form under the right conditions of temperature and pressure. A "gas" is simply one of the fundamental states of matter, as in solid, ...
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17 votes
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What will happen when landing on Jupiter?

Jupiter does not have a "surface" and nor is there anything but an arbitrary division between interplanetary space and where its atmosphere begins. The crushing pressure is its atmospheric pressure. ...
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13 votes
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Why argon instead of another noble gas?

Doing a bit of reading up on this, I might have an answer, though credit where credit is due, the answer isn't really mine: https://www.reddit.com/r/askscience/comments/3wsy99/...
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9 votes
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Gas halo of our Milky Way Galaxy

The scale height of gas in a disk (if it were in equilibrium) is roughly $kT/mg$, where $T$ is the temperature, $g$ is the gravitational field, $m$ the mean mass of agas particle, and $k$ the ...
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9 votes

Why argon instead of another noble gas?

why Argon specifically? Both helium and neon are pretty lightweight, tend to vaporize easily even at low temperatures, and are chemically inert. For all these reasons combined, they tend to not get ...
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7 votes

What is the difference between gas and dust in astronomy?

In astronomy, there is no formal definition of the threshold between gas and dust. Gas can be monoatomic, diatomic, or molecular (or made of photons, in principle). Molecules can be very large, and in ...
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6 votes
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What would the pressure and temperature of gas be, right above Jupiter's gas/liquid boundary?

Technically there isn't really a gas-liquid boundary because temperatures are well above the critical point of hydrogen (33K and about 18bar). It's a supercritical fluid. There are important changes ...
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6 votes
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How do astronomers detect gases that are in the atmosphere of exoplanets?

It is only possible to detect gases in transiting Exoplanets. The spectrum of the star is taken when the Exoplanet is not in transit and again when in transit. The differences between the spectrums is ...
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6 votes
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Are gas giants supported by thermal pressure?

I am not sure what you mean by "thermal" pressure. Jupiter is supported by pressure, just like all objects that are in (approximate) hydrostatic equilibrium. That pressure is provided by your ...
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5 votes
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Why is the "green" comet C/2014 Q2 (Lovejoy) red in this picture?

Mainzer et al. 2014 characterize the performance of the reactivated NEOWISE. Having run out of cryogenic coolant for the original WISE's 12 and 22 μm bands, it only detects in the 3.4 and 4.6 μm ...
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5 votes
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What is the diffuse ionized gas?

The "diffuse ionized gas" (DIG) is another term for the phase of the interstellar medium (ISM) usually called the warm ionized medium (WIM). With a temperature of the order $10^4\,\mathrm{K}$, but ...
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5 votes
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Why is it safe to assume that K = 3/2kT in a self-gravitating gas

I will use some concepts form statistical mechanics, I hope you are familiar with some of the concepts. Consider a gas of $N$ particles of mass $m$ with Hamiltonian function $$H(\bar{q}, \bar{p}) = \...
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4 votes

How does gas in accretion disks of supermassive black holes create orbital torques on smaller black holes within the disks causing them to migrate?

Not really my area, but this question is probably related to the planetary migration in circumstellar disks. In this case, the migration is caused by gravitational interactions between the planet and ...
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4 votes
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What are the so called clouds of dust and gas made of?

The clouds of gas and dust that form stars are usually what are called Molecular Clouds and Giant Molecular Clouds (GMCs). The "Molecular" means that most of the atoms are combined into molecules ...
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4 votes

Would a spacecraft just go "through" a gas giant?

In short, No. Side detail: Uranus and Neptune consist likely of 20% gas and 80% rock, coming from simple density considerations. They have large inner cores with masses around $\rm 12-14 \; m_{earth} ...
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4 votes

What is the difference between gas and dust in astronomy?

I may just add to the excellent answer by Robert that interstellar dust particles, very much like cigarette smoke in air, hangs in the interstellar gas and interacts with it both kinematically (is ...
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4 votes

Why is molecular hydrogen (H2) so difficult for astronomers to detect?

There are a few reasons molecular hydrogen (H2) is hard to detect depending on what band you are looking. In the UV, it can be detected in absorption of the electronically excited Lyman–Werner bands, ...
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3 votes
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Beta profile fit of Virgo cluster gas?

Schindler et al. 1999: Morphology of the Virgo Cluster: Gas versus Galaxies has details for $\beta$ model fits for Virgo and its subclusters.
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3 votes
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How is interstellar gas density mapped from GAIA data?

Two techniques immediately spring to mind. For the stars you detect, you can compare their colours and luminosities (Gaia provides photometric colours and distances) with what you expect for a star ...
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3 votes
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Why are Bok globules so cold?

Most of my information is sourced from here: https://apod.nasa.gov/apod/ap990511.html To summarize the source, Bok globules are extremely cold because of their composition -- they're generally just ...
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3 votes
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Galactic winds/outflows: why and how are they detected via blueshifted absorption lines in spectra?

Yes, a blueshift here would mean relative to the systemic velocity of the galaxy - which means that, relative to the galaxy, the material is moving at least partly in the direction of Earth. In many ...
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3 votes
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How do they know the newly-spotted gas near the center of our galaxy is molecular without knowing what gas it is?

They know there's molecular gas because they observed emission from the CO molecule in two of the previously identified (atomic-hydrogen-emitting) gas clouds. From the paper: ... we targeted two ...
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3 votes

Why is molecular hydrogen (H2) so difficult for astronomers to detect?

The light that we receive from space contains a lot of information. Specifically, because of quantum nature of molecules and atoms, theses small species absorb light at very specific wavelengths.Each ...
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2 votes
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How does gas in accretion disks of supermassive black holes create orbital torques on smaller black holes within the disks causing them to migrate?

A gravitating object in a disk creates a wake on the inner edge of its orbit as well on the outer edge of its orbit. The inner wake is the leading wake, while the outer wake is trailing. The torques ...
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2 votes
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Can we get the gas compositions from a gas planets?

Yes. It's certainly feasible to obtain a sample from Jupiter or Saturn, effectively getting gas from the planet, but it's not easy. Massive planets, as a byproduct of their high mass, create large ...
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2 votes

When is it a good aproximation to consider a star to be an ideal gas?

There is no hard and fast answer. To be treated as an idea gas (your title question), the particles in your gas should be point-like and they should be non-interacting if you are to use the ideal gas ...
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2 votes
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What is the equation of state for a relativistic fluid/gas?

Your equations seem correct. Note, you can also get $v$ without having to differentiate, from $E=\gamma mc^2$ and $p=\gamma mv$. Here are some notes on relativistic fluids as related to stellar ...
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2 votes
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Weight of a gas measured in Space and other planets of Solar System

Weight is a property of mass which you can experience only when on the solid surface of a gravitating body - but not when you are in free fall. Yet even in free fall you retain your mass. Weight is ...
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2 votes

Using Saha's equation knowing the overall pressure

The pressure of a gas depends on the number density of particles and the temperature. There is therefore no unique relationship between $P_g$ and $N_{I+1}/N_I$.
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