Talk:Outer space/Archive 1

Uncategorized
Shouldn't the possiblity of Creationism be included? I mean, it makes it sound like the Big Bang is 100% assured of a thing. Not that I'm religious, but I'm speaking on behalf of those who are, and to keep Wikipedia an unbiased place. Also... why is this page so short? --CrazyCasey 17:57, 5 July 2006 (UTC)

I agree with CrazyCasey- all Wikipedia articles should be unibiased, and I think removing all references to any sort of belief set would be great. --User:Chronology of Life —Preceding undated comment added 00:06, 22 February 2011 (UTC).


 * Religion doesn't belong in this article. Religious views can be applied to everything, doesn't mean we should list them in every article. It's not a matter of bias, but of Undue_weight. With the way outer space is related to physics and astronomy (specially the cosmology which we discuss), utilizing anything but a scientific tone would be giving whatever other view undue weight in the article. Star Ghost 02:01, 20 July 2006 (UTC)

Please leave my "See also" to the Karman line in: I was trying to search on the no-accent name and missed because the link was re-labeled with the accents. I will propose a rename on the page. -- Fplay 22:55, 21 December 2005 (UTC)

If I explode then will blood come from my eyes? What if the pressure was removed very slowly, from 100 kPa at a rate of say 1 kPa a minute and supposing I had breathing equipment? --Username132 00:17, 29 January 2006 (UTC)

What is the density of air in outer space?
 * 0gm-3?

There isn't air in outerspace... --CrazyCasey 17:57, 5 July 2006 (UTC)


 * Maybe he meant matter? There are a few lonely atoms wandering around. I remember seeing this kind of statistics in some physics book. Star Ghost 02:01, 20 July 2006 (UTC)

I have placed uncategorized and undated posts in this section. Please sign all comments with 4~ and place in a new subsection.statsone 06:15, 10 July 2007 (UTC)

Conflict with religion
I don't think this section is relevant, does anyone protest it's removal?

Link Removal
I have removed the links to website in anther language for 2 reasons. One is they were the same site. Second, they were in another language. More appropriate to be placed in that wiki's language site.

Also, please sign all comments with 4 ~'s statsone 15:43, 22 July 2006 (UTC)

Wikipedia already has a terrible bias towards Evolution and its many unproven theorys and dating methods. As usual this has a terrible effect on readers as more and more people begin to accept these things as fact when any knowlegable evolutionist knows they are NOT facts at all. There is plenty of science that is real fact and disproves the whole "really old earth" theory. "Zealotii 09:45, 15 October 2006 (UTC)"

In space on the Moon?
Is one in space when on the Moon? I'd say one isn't in space when on a celestial body. Although of course there are border cases, like being on a asteroid. And on Earth you enter space when the air gets too thin, but on the Moon there is no atmosphere. Or is that not the criterium? DirkvdM 07:42, 1 August 2006 (UTC)
 * The answer would depend on the audience. I, for example would think "in space" means in freefall and outside the atmosphere of any nearby planets, but I think the Man on the Bondi Tram would think that "space" is anywhere beyond Earth, or altenatively, anywhere where a space suit was needed. (days after writing I noticed I didn't sign this) --Polysylabic Pseudonym 04:58, 5 August 2006 (UTC)
 * Assuming that one is not in space when on the moon, if one was to travel up from the lunar surface, at what point would he/she be "in space"? Would it be the same point at which a person leaving the earth's atmosphere is considered to be in space? Vsst 02:53, 20 March 2007 (UTC)
 * This kind of thing isn't a question of fact, but a question of definition, and is really rather arbitrary. If you want to know whether someone is in space because you want to know whether he'll burn up or get slowed down by the atmosphere, or whether he needs a space suit, he's in space on the moon.  If you want to know whether someone's in space because you need to know whether her microgravity experiment will be successful, she's not in space on the moon.  As to where space begins, the article explains why that's a gradual thing which also depends on what you mean by "space". --Slashme (talk) 06:40, 11 June 2009 (UTC)

Vacuum
The_monkeyhate, do you have any grounds for your assertion that unprotected humans would freeze in milliseconds in space? It's flatly contradicted by the NASA doc cited. SeanWillard 23:57, 12 October 2006 (UTC)

Their orbits never "decay" because there is almost no matter there to exert frictional drag.
I would like to change "Their orbits never "decay" because there is almost no matter there to exert frictional drag." to "Their orbits never "decay" because the pull of the earth's gravity is canceled by the centrifugal force of their tangential velocity"


 * I have removed this business. Orbits do decay!.  The Hubble Space Telescope gets raised every time it is serviced to keep it in orbit, for example.  In geosynchronous orbit, there is a lot less matter than in low Earth orbit, but it still is a issue and all satellites have a rocket and spare fuel to deal with this. --EMS | Talk 17:12, 5 February 2007 (UTC)

Outer space *vs* inner space
I realise that the popular media use the term "outer space" for everything, but it is my understanding that "outer space" refers to space outside the solar system, while inner space (or plain "space") refers to space within the solar system.

--Black Walnut 12:11, 16 January 2007 (UTC)

Hehe. I came to this talk page specifically to criticize the use of the stupid "outer space" term. For such to exist, there must also be "inner space", which is a ridiculous conecpt. Also, religion shouldn't be mentioned. That's ridiculous too. --194.251.240.114 23:19, 25 January 2007 (UTC)

I just checked the internet, and the only places I found "inner space" mentioned where in the titles of science fiction books and movies and in regard to yoga type stuff. Also, according to answers.com, outer space is defined as "Any region of space beyond limits determined with reference to the boundaries of a celestial body or system, especially: 1. The region of space immediately beyond Earth's atmosphere. 2. Interplanetary or interstellar space."

Vsst 00:56, 4 May 2007 (UTC)

I'm Confused
This isn't necessarily questioning the legitimacy of the claim..but a source would be helpful. It just seems..odd, to me, that a manned balloon flight could fly above the point where turbojets no longer function.
 * 32 km (105,000 ft) - Turbojets no longer function.
 * 34.7 km (113,740 ft) - Altitude record for manned balloon flight


 * Not so strange: a turbojet can fly up to the point where it doesn't get enough oxygen in the front to burn its fuel. At that point, the atmosphere is not yet so thin that a hydrogen balloon can't get enough buoyancy to lift. --Slashme (talk) 06:45, 11 June 2009 (UTC)

Milestones to outer space
The 62,000 km figure is totally wrong. Earth has more gravity than the Moon so this point has to be most of the way away from it. 320,000 km Earth altitude is more like it (the distance from the earth to the moon minus 62,377 km). Also, this might make a reader think the moon's zone of influence is a "layer", rather than the small sphere surrounding the moon that it is. Sagittarian Milky Way 09:11, 13 March 2007 (UTC)
 * Yes, I'm pretty sure the author mis-read the Apollo 8 article about this. Wasn't it 62,000 km from the Moon? Trojan_points puts it at "61,500 km from the Moon." Sdsds 05:02, 20 March 2007 (UTC)
 * The thing is, the moon's distance itself varies by almost as much as the 62,000 km, moving the balancing point in and out. Does it even matter? (for example, many of the spacecraft orbits are given only as an approximation). Also, perigee is wrong, I'm going to change it. Sagittarian Milky Way 03:02, 23 March 2007 (UTC)
 * You're absolutely right: the distance to the L1 balancing point doesn't matter so much. What really matters for most mission planning is the delta v required to get there. If you can get there, and if you're willing to wait long enough, then a clever sequence of gravity slingshots can get you anywhere in the universe using only minimal thrust. (See Interplanetary Transport Network.) In that sense, this point does matter, because it's the nearest place "beyond" the Earth's gravitational domain. Sdsds 00:59, 24 March 2007 (UTC)
 * Right, the cool thing is that it's a bubble of extraterrestrial gravity, deep inside Earth's Hill Sphere. What I meant though is that since the milestones to space altitudes for the ISS, Mir, Skylab, etc. are approximate then the L1 distance can be too. The section looks much cleaner that way. Sagittarian Milky Way 07:12, 25 March 2007 (UTC)

Microgravity Statements
In the "Satellites" section, I'm not sure the following statement is completely correct:
 * "A common misconception is that people in orbit are outside Earth's gravity because they are obviously "floating". They are floating because they are in "free fall": the force of gravity and their linear velocity is creating an inward centripetal force which is stopping them from flying out into space. Earth's gravity reaches out far past the Van Allen belt and keeps the Moon in orbit at an average distance of 384,403 km (238,857 miles). The gravity of all celestial bodies drops off toward zero with the inverse square of the distance."

Didn't astronauts still "float" while travelling to the moon at a constant velocity without a "free fall" state?Drawingnearisgood 16:30, 4 May 2007 (UTC)


 * There are a number of ways to be in "free fall" within the gravitational zone of a planet. One is to be in a stable circular orbit around the planet. One is to be traveling on a parabolic ballistic trajectory, typically near the surface (if necessary using thrust to overcome atmospheric friction).  A special case of this is going straight up and down.  If you go straight up fast enough, you're beyond escape velocity, and you just keep going.  You're still slowing down (i.e. not "constant velocity"), just like a stone that is tossed straight up into the air, but you're not slowing down enough to keep you from completely leaving the region.  Also, just like if you get thrown into the air, you won't feel the gravity, hence "free fall".  --Slashme (talk) 07:08, 11 June 2009 (UTC)

Centripetal/Centrifugal Confusion
The article states that:
 * "A spacecraft has not entered orbit until it is traveling with a sufficiently great horizontal velocity such that the acceleration due to gravity on the spacecraft is less than or equal to the centripetal acceleration caused being its horizontal velocity (see circular motion)."

This sentence is slightly incoherent and slightly sketchy on the physics. If you choose to describe it in the Earth's "inertial" reference frame, it is in - circular -orbit when the force of gravity is of the exact magnitude to act as a centrifugal force (put in better English though). Or, in the craft's reference frame, "until the centrifugal force cancels out the gravitational force". The non-circular case is a bit more complicated and doesn't really belong here. 163.1.99.20 21:27, 11 June 2007 (UTC)


 * I agree. In fact, if the acceleration due to gravity is less than the centripetal acceleration anywhere in the orbit, then the opposite must be true at some other point in the orbit.  To quantify this:
 * Call the minimum radius Rmin (radius of the Earth + some atmosphere). A reasonable condition for calling a spaceship in orbit is that the perigee >= Rmin.   The necessary condition in terms of Vh (horizontal velocity) is then not trivial and requires a bit of understanding of central force problems.  Assuming the typical simplifications (Newtonian gravity, spherical mass, etc.) one arrives at the inequality (please check math before including in article):
 * 1/2 ((r/Rmin)^2 - 1) * Vh^2 - (G M / Rmin + 1/2 Vr^2) >= 0.
 * Solving this yields:
 * Vh >= sqrt[(2 G M/Rmin + Vr^2) / ((r/Rmin)^2 - 1)]
 * Basically, there is no simple way of stating the condition for orbit. Someone with more experience should decide how to modify the article.  Jtepper (talk) 07:47, 25 December 2009 (UTC)

Free fall
The section for Sateliites describes satellites as being in Free Fall. This seems to be wrong. They are not in free fall ( only under the influence of gravity) butin orbit. Comments?statsone 06:20, 10 July 2007 (UTC)
 * Unless you're operating a thruster to maintain it, orbit is synonymous with freefall. —Preceding unsigned comment added by Nentuaby (talk • contribs) 01:33, 16 October 2008 (UTC)
 * Absolutely. The problem is, colloquially, "free fall" might be interpreted to mean falling closer and closer to the surface of the Earth/other body.  Nonetheless, the terminology is justified because in a scientific setting, free fall is used synonymously with inertial frame.  In other words, the satellites are moving under nothing but their own inertia through the gravitational field. Jtepper (talk) 08:05, 25 December 2009 (UTC)

Capitalization
Shouldn't the words "Outer" and "Space" both be capitalized since it designates a place name? SharkD 03:52, 22 August 2007 (UTC)


 * Wikipedia's style says no.  Just what has been agreed on. --statsone 05:44, 22 August 2007 (UTC)
 * But Outer Space is a region, not a celestial body; and it is certainly well known. SharkD 06:28, 22 August 2007 (UTC)


 * This is where it does get tricky. I would take it as small case only because it is wikipedia. You may want to post a discussion on the style talk page and ask for comments--statsone 06:33, 22 August 2007 (UTC).


 * Well, if outer space were capitalized, then interplanatary space would need to be capitalized, too. I guess I'll leave it at that. The reason I ask is because I was once corrected for not capitalizing it. SharkD 06:52, 22 August 2007 (UTC)

Vacuum in Space
For the cite needed, I found 1×10-15 Torr. ( Do a search on "pressure in interstellar space" in google). Converting back to Pa, I get 1.333×10-21 Pa which is different from what is listed. Looking back at the history of the article, there have been many numbers -- Statsone  14:41, 23 September 2007 (UTC)
 * Aren't the vacuums created here on Earth much weaker than the vacuum of outer space? The whole "what would happen if exposed in outer space" bit seems to discuss the effects in vacuums created on Earth, which I suspect would not be the same in outer space. Please correct me if I am wrong. ~ UBeR (talk) 17:08, 15 February 2008 (UTC)
 * No, they are not much weaker. In fact, laboratory equipment is capable of generating much stronger vacuums than what humans are generally talking about when we mention space (the vicinity of Earth and the Moon). More practically, most vacuum chambers are relatively weaker, but for the practical purpose of describing the effect on bodies or equipment, both they and outer space may be treated as zero pressure.Nentuaby (talk) 01:39, 16 October 2008 (UTC)

Expanding the Article
A way to flesh out this article would be to add: some definition of how crafts move in space being that there are no molecules; how much gravity exerts its force to the moon and an explanation on how that force extends to "stationary" satalites; and how distance is measured in space. I am not an astrophysicist, just a curious person, so I would appreciate those additions as I do not consider any to be "undue weight". Agreed? —Preceding unsigned comment added by 67.173.2.11 (talk) 01:37, 8 November 2007 (UTC)

space vs outer space
There's a large number of wikilinks to space that ought to be linked here instead. Anyone have any idea how these can most easily be fixed? --jwandersTalk 10:44, 21 February 2008 (UTC)

Frankly, I just searched for cislunar space, something decidedly more specific from outer space, and was re-directed here. cislunar is a unique area that should have its own page or at least a mention on this page. (cislunar is the area between the earth and the moon) 128.205.11.224 (talk) 07:44, 24 April 2008 (UTC)
 * "Cislunar space" was supposed to redirect to "geospace." I've fixed the redirect. I redirected it because all the article said was that cislunar space was the space between the Earth and the Moon, which was a bit like saying that Grant is buried in Grant's tomb.  Serendi pod ous  18:58, 19 November 2008 (UTC)

Escape velocity
The article starts with a pretty odd definition: the relatively empty regions of the universe outside the escape velocities of celestial bodies. Physically, what does it mean to be outside a velocity? (I'd answer: nothing, but maybe someone can enlighten me). Isn't there a better definition? --Cyclopia (talk) 22:26, 17 October 2008 (UTC)


 * You're right (and here I am inserting the link without noticing the nonsense). I've spent a while figuring out how to fix it, almost deciding on replacing 'escape velocities' with 'gravitational influence' which I think is what the author intended. Then comparing with the article I find that this sentence contradicts the gist of the article, which emphasises being away from ""Earth"" rather than celestial bodies. That, I think, is the common usage, and whatever view you take it's a vague concept. To be honest, I'm not sure why it merits an encyclopaedia page.--Alkhowarizmi (talk) 10:18, 18 October 2008 (UTC)
 * It should be "atmospheres".  Serendi pod ous  10:50, 18 October 2008 (UTC)
 * It surely is better, but later there is a section on the geospace where it is pretty clear that there is still substantial atmosphere in what is called outer space nonetheless. I try to detail a bit the definition. --Cyclopia (talk) 11:29, 18 October 2008 (UTC)
 * Nice improvements (both)--Alkhowarizmi (talk) 14:45, 18 October 2008 (UTC)

Milestones section
I've removed the Milestones section. Much of it was unreferenced, a lot of it was probably outdated (records usually need to be updated every year, which is a tedious task) and much of it seemed pointless (why go from Lunar apogee to Martian perigee? Venus is actually closer to Earth). Much of the information in that list can be easily expressed with the image I've placed at the top of the page.  Serendi pod ous  19:10, 19 November 2008 (UTC)

How is Torr a relevant unit?
Why should Torr, an aged non-SI unit be used in the article? —Preceding unsigned comment added by Askeuhd (talk • contribs) 23:38, 21 November 2008 (UTC)
 * I have no idea what a "torr" is, but no other science-related article I've worked on has used it, so I don't think it's needed.  Serendi pod  ous  13:26, 22 November 2008 (UTC)
 * The Torr is basically a mmHg, and is often used as a customary unit in vacuum technology. I've used vacuum pumps on freeze driers that had gauges calibrated in mTorr. But yes, it shouldn't be used here IMHO.  Go SI. --Slashme (talk) 07:18, 11 June 2009 (UTC)

Karman vs. Calgary - edge of space poll
The work described in the referenced space.com article is quite interesting, and should definitely be covered somewhere in this article. However with due respect to the space.com journalist that article is not particularly scientific, and the von Karman aeronautics/astronauitcs definition is still more practically useful. Should the lead of this article return to citing von Karman's defintion?
 * Support - as proposer (sdsds - talk) 03:15, 24 April 2009 (UTC)
 * Neutral - I understand the argument, but I prefer the well-defined, measurement-based boundary to the previous, somewhat arbitrary, definitions. It makes more sense to me. But I recognize it might be unscientific, so I'm staying neutral on this. --Waldir talk 21:16, 25 April 2009 (UTC)
 * Support. Kaman's definition should be in the lead; alternate definitions may be mentioned, but that appears to be the official one.  Serendi pod ous  21:39, 25 April 2009 (UTC)
 * Use both, something like "The FAI defines the edge of space as being the Kármán line, 100 km above mean sea level, however in 2009 scientists at the University of Calgary discovered that the edge of space is actually at an altitude of 118 km." Perhaps the definitions used in the USA should also be mentioned after this sentence. -- G W … 21:54, 25 April 2009 (UTC)
 * Oppose - How is an exact measurement from a scientific device unscientific? I think the exact measurement should be in the lead, and the previously accepted definition be covered elsewhere in the article.  Dionyseus (talk) 03:53, 26 April 2009 (UTC)
 * But the exact measurement has not replaced the accepted definition. -- G W … 07:05, 26 April 2009 (UTC)
 * Not yet perhaps. Dionyseus (talk) 07:43, 26 April 2009 (UTC)

I mailed David Knudsen, one of the authors of the original research, and he had the following to say:


 * While I'm flattered to see our measurement of the "edge of space" in the article, I have to confess I don't believe the result is fundamental enough to be included as part of the top-level definition of "outer space". I feel that the reference in the top paragraph should be removed.


 * I'm pleased to see our result in the "Boundary" section and I would only suggest a few tweaks:


 * I would say that the results were *reported* in 2009, since the experiment itself took place in 2007.


 * I'd suggest "The boundary represents the midpoint of a gradual transition over tens of kilometers from the relatively gentle winds...etc


 * This was only the second time that direct measurements *of charged particle flows* have been conducted in this region...


 * Also, the best reference is:


 * Sangalli, L., D. J. Knudsen, M. F. Larsen, T. Zhan, R. F. Pfaff, and D. Rowland (2009), Rocket-based measurements of ion velocity, neutral wind, and electric field in the collisional transition region of the auroral ionosphere, J. Geophys. Res., 114, A04306, doi:10.1029/2008JA013757

--Slashme (talk) 07:22, 11 June 2009 (UTC)

He also sent me a follow-up email, with the following comment: "I might add one point about why I think the Calgary measurement is not fundamental enough to be used as a definition. The problem is that with only one pass through that region lasting only twenty or so seconds, we have very little idea of how that transition altitude might vary, either over time or with latitude." --Slashme (talk) 05:58, 17 June 2009 (UTC)

Temperature in space
There has been some action in the article on the temperature of outer space. The temperature reported is the temperature that a piece of metal near the earch would acheive. But, by this logic, space has no particular temperature: a piece of metal at a different location (farther from the sun, closer to the sun) would have a different temperature, and another object at the same location in steady state with solar radiation would have a different temperature (that's why we are going to fry the earth with global warming by altering the greenhouse effect).

The temperature of space is typically referred to the temperature of a typical point in space far from a source of radiation such as the Sun, another star, or a galaxy. This temperature is the temperature of the microwave background, ~3K. Interstellar space (within our Galaxy) has temperatures ranging from a few K in Molecular clouds to 10,000K in Emission nebulae. David s graff (talk) 22:35, 29 May 2009 (UTC)

Geospace
I think there have been edits at cross-purposes in the second paragraph of the Geospace section. I would fix it, but I'm not sure how. Here is the paragraph:


 * Although it meets the definition of outer space, the atmospheric density within the first few hundred kilometers above the Kármán line is still sufficient to produce significant drag on satellites. Most artificial satellites operate in this region called low earth orbit and must fire their engines every few days to maintain orbit. The drag here is low enough that it could theoretically be overcome by radiation pressure on solar sails, a proposed propulsion system for interplanetary travel. Planets are too massive for their trajectories to be affected by these forces, although their atmospheres are eroded by the solar winds.

The last sentence seems to be saying that other planets within Earth's geospace are not affected by... some forces that are presumably described elsewhere. Most likely this is because other planets within Earth's geospace tend to collide with Earth, kill everyone, and leave no one to edit Wikipedia. --99.33.25.89 (talk) 20:11, 22 November 2009 (UTC)

I hadn't given this article a read through in a while; hadn't realised how badly written it is. Yes, you're right; that line belongs in interplanetary space, not geospace, and the bit about the planets being too massive to have their orbits affected by the solar wind was just lunatic. I'm not particularly massive, but it would still take a hurricane to knock me over. That something weighing a few octillion tons would not be adversely affected by the pressure of a wind that is all but pure vacuum isn't something that needs mentioning, methinks.  Serendi pod ous  20:46, 22 November 2009 (UTC)

Definition
Per WP:V and MOS:BEGIN, the intro of this article should give a concise definition based on verifiability, not truth. Google searching for "define" gives a pretty unambiguous definition as "area outside the earth's atmosphere", even when you get past the mirrors. The problem of defining as above any bodies atmosphere is what about the moon and other bodies without atmospheres? I think we mean beyond anything that is a celestial body, not its atmosphere. Fountains of Bryn Mawr (talk) 19:18, 3 December 2009 (UTC)
 * So according to this definition, the surface of Venus, with its 90 atmospheres of pressure and 900 degrees Fahrenheit temperature, would be space? We have to deal with this somehow. Otherwise the definition makes no sense.  Serendi pod ous  19:27, 3 December 2009 (UTC)
 * Venus is a celestial body, so its confines (including its atmosphere) would not be outer space. So that part (which you deleted) would be part of the def. celestial body its self is key to this article's def, but that article (Astronomical object) has many problems as well (trying to clean that up led me here - funny how that happens). Fountains of Bryn Mawr (talk) 22:55, 3 December 2009 (UTC)
 * The Outer Space Treaty includes the Moon and other celestial bodies in its definition. Thus I'm not sure astronomical objects should be excluded from this article.&mdash;RJH (talk) 18:53, 25 December 2009 (UTC)

Throwing in another stab at a def. The concept of Space "the unlimited expanse in which everything is located" redirects here. "Space" is the more notable term being defined here over "outer space". In fact this whole article should probably be moved to a more inclusive title such as Space (universe), since Outer space has a more narrow def and to me is a real 1950s term, no body calls it that anymore. The rest of the article should probably be cleaned up because it tends to define the more narrow term "outer space". Fountains of Bryn Mawr (talk) 19:22, 23 January 2010 (UTC)

Inflated balloon on top of a mountain
Hi there, this might be some kind of a mental black-out on my side, but concerning the passage
 * "This decrease in pressure was further demonstrated by carrying an inflated balloon up a mountain and watching it gradually deflate, then reinflate upon descent",

why would an inflated balloon deflate when it is carried up a mountain? Because of the lower surrounding air pressure, it should actually expand even more. I don't have the cited reference at hand. 84.63.98.54 (talk) 16:51, 29 December 2009 (UTC)
 * Yeah you're right. Good catch. It should be corrected now, per the cite.&mdash;RJH (talk) 20:48, 30 December 2009 (UTC)

Intergalactic space
I am not a specialist, maybe that's the reason, but this sections seems very confusing. In the first paragraph it says that "intergalactic space is very close to a total vacuum". In the second - that it's in fact plasma and IGM which is up to 100 times denser than the universe on average. So which is it? And if IGM is so dense then where does the low average density of the universe come from?

The first paragraph is especially confusing. Consider the second and the third sentences: What is this "is probably nearly empty" in the third sentence trying to say? That voids are about as empty as intergalactic space, or emptier or denser? Then, in the next sentences all of a sudden comes the bit about the average density of the Universe. Why Universe if we are talking about intergalactic space here?

So, after reading this sections I still have all the questions:

Are "intergalactic space" and "void" one and the same thing or not?

If not, do they differ in density and what is the average density of each?

Are intergalactic space and voids the closest things to a total vacuum or are they filled with relatively dense IGM?

92.243.183.1 (talk) 12:42, 19 April 2010 (UTC)

What heats up IGM?
From the section on Intergalactic Media (IGM): "The reason the IGM is thought to be mostly ionized gas is that its temperature is thought to be quite high by terrestrial standards (though some parts of it are only "warm" by astrophysical standards)."

Why is the IGM so hot? What is its heat source way out between the galaxies, so far away from stars?
 * My understanding (from reading the attached link) is that the high temperature of the IGM is generated by shock heating from the collision of gas/plasma. There are various sources for these shocks, including infalling plasma, collisions between gaseous intergalactic structures, and supernova explosions.&mdash;RJH (talk) 16:53, 9 June 2011 (UTC)

Please add the answer (and linked source), to the article's IGM section.

Phantom in ca (talk) 02:26, 7 November 2010 (UTC) Suppose we are in space how can we decide that we are in the state of rest or motion?

Suppose we are in motion and everything surrounding us also move in the same direction with the same speed what do we say about our state? — Preceding unsigned comment added by 27.251.110.148 (talk) 15:46, 9 June 2011 (UTC)
 * Please see the Principle of relativity and Inertial frame of reference articles.&mdash;RJH (talk) 17:08, 9 June 2011 (UTC)

Origin of "outer space"
As demonstrated by: it appears that outer space was already in use as an astronomical term by 1845. This seems to be a pretty rapid adoption considering the claim that the term was first used in 1842. Regards, RJH (talk) 16:48, 21 July 2011 (UTC)
 * Upon further investigation, I believe the statement about Lady Emmeline Stuart-Wortley being the first to put the term "outer space" in print is actually incorrect. In her poem, The Maiden of Moscow, the words she uses are "outward space", as in the outward space of a citadel. See:
 * I could find no example of "outer space" anywhere in the poem. Regards, RJH (talk) 15:17, 22 July 2011 (UTC)
 * I could find no example of "outer space" anywhere in the poem. Regards, RJH (talk) 15:17, 22 July 2011 (UTC)

Cis-lunar space
First, I concur with the assessment of this article as B-class for Wikiproject Spaceflight. In reviewing the article though I noted that no particular mention is made of the region commonly called cis-lunar space even though that redirects here. (From a spaceflight perspective, cis-lunar space can be roughly defined as the region within which the gravitational influence on a spacecraft of the sun is dominated by the gravitational influences of the earth and moon, and thus the sun's influence can largely be ignored for most trajectory analysis purposes.) Another aspect of cis-lunar space: it is apparently "swept clean" of small objects by the moon's gravitation, i.e. there are not lots of little moonlets, whereas beyond cis-lunar space there do appear to be objects which closely share the earth's orbit around the sun. My impression is that these two factors make the region "special" enough to deserve mention in this article. YMMV, of course! (sdsds - talk) 04:33, 5 May 2012 (UTC)
 * Thanks Sdsds. Cis-lunar space is briefly mentioned in the Geospace section. Regards, RJH (talk) 16:19, 5 May 2012 (UTC)


 * A search for "cislunar" finds 6.1; it should find 6.1.1. And "cislunar" seems more common than "cis-lunar", so it should appear in the section at least once. 94.30.84.71 (talk) 11:13, 13 October 2012 (UTC)
 * What is it that a search finds or should find that is described by the numbers "6.1" and "6.1.1"? - Fartherred (talk) 09:45, 16 October 2012 (UTC)

Revision of images
I reverted a wholesale re-arrangement of the images in this article, but I thought I should state on this page the reasons why. Firstly, the current arrangement and selection of images was intended to complement the neighboring text and provide additional insight, per WP:PERTINENCE. The newly added pictures didn't seem to add much of anything besides some vaguely associated imagery. They also displaced the prior images from the location where they were most relevant, while creating a gallery. However, this gallery didn't add the kind of informational value that is appropriate per WP:Galleries. The value of the existing images was already present in the previous arrangement; there was a loss of association by placing them in a gallery. Finally, several of the images were given fixed dimensions, which prevents readers from selecting their preferred image size.

If the current selection and arrangement of images is deemed unacceptable, please discuss. Thank you. Regards, RJH (talk) 23:40, 12 May 2012 (UTC)
 * No need to explain yourself, I was here to update articles effected by the missing bow shock. Good luck with the review! Fotaun (talk) 19:02, 14 May 2012 (UTC)
 * Thanks. Regards, RJH (talk) 19:41, 14 May 2012 (UTC)

Religious views on Space
I can't find any Wikipedia coverage on religious views on space, nor in this article. Nevertheless, I am aware of some religions have explicit objection to man's involvement in space. Does anyone know where this might be covered in Wikipedia? If not, should we not include a brief section in this article? — Preceding unsigned comment added by 24.106.205.232 (talk) 14:46, 17 June 2012 (UTC)
 * There's Religion in space, but that article is more about religious practices during spaceflight. I'm not aware of any particular objections of the type you mention, but perhaps you can provide some WP:RELIABLE citations to back up your perspective? WP:WEIGHT would apply to this proposal. Regards, RJH (talk) 20:04, 17 June 2012 (UTC)

Edge/boundry of a galaxy?
The article discusses the boundary between the earth's atmosphere and intrastellar space, and between intrastellar space and interstellar/intragalactic space, but not between intragalactic space and intergalactic space. In other words, are there equivalents to the heliosphere (termination shock, heliosheath, and heliopause) surrounding galaxies?

Phantom in ca (talk) 08:57, 24 June 2012 (UTC)


 * Not clearly defined ones, as far as we know. —Alex (ASHill &#124; talk &#124; contribs) 09:13, 24 June 2012 (UTC)


 * Gravity defines a galaxy. In a galaxy, matter (stars, plasma, etc.) is gravitationally bound to the galaxy. In true intergalactic space, matter doesn't orbit the center of mass of any single galaxy. In this way, one can at least define the region where the galaxy "clears the neighborhood". But, galaxies have galactic halos, and large galaxies often have satellite galaxies, so a simple sphere of gravitational influence is not enough for a definition that captures the diversity of structures of galaxies. Lenticular, spiral, elliptical and dwarf galaxies have essentially different features; the area above the disk of a spiral galaxy, for example, is well within the gravitational sphere of influence, and has the same distance to the center as in a similarly-sized elliptical galaxy, but doesn't contain stars. Also, galaxies are not solid objects but may be disturbed by other galaxies, so this definition doesn't cover all cases. Perhaps a better view is to consider the fact that galaxies are essentially concentrations of dark matter, which is apparently incapable of gravitational collapse above a certain density. It would make no sense to attempt to define an "edge" for such a diffuse object. Dark matter haloes, if they exist, are much, much larger than the optically bright center of the galaxy. Practically, however, one can always set an arbitrary (but practically useful) brightness or density limit and measure the size thus defined. --vuo (talk) 10:09, 24 June 2012 (UTC)


 * There are other astronomical objects that don't have a precise boundary either. Examples include globular clusters, open clusters, and molecular clouds. In these cases other means are used to describe their size, such as the half-mass radius for a globular cluster. Regards, RJH (talk) 18:07, 24 June 2012 (UTC)


 * A closely related question. Was trying to find information on intergalactic space but was redirected here - Outer_space which seems pretty inadequate especially compared to the article on the interstellar medium - Interstellar_medium! Anyway my question was about the basic density or range of densities of intergalactic space, mainly so I can compare it to interstellar and solar system space densities. Lucien86 (talk) 04:57, 24 August 2012 (UTC)
 * Yes I agree that we could use a well-developed article on the intergalactic space. There is Warm–hot intergalactic medium, which is also pretty sparse. Regards, RJH (talk) 05:33, 24 August 2012 (UTC)

Location categories
I think we should have categories for events, objects, etc. located off planet. categories for near earth orbit, or geostationary orbit, for objects on the moon, on mars. not a lot yet, but since we can categorize earth bound events and objects by their location, why not such off planet?Mercurywoodrose (talk) 05:01, 26 November 2012 (UTC)

Callisto picture
That's a nice picture of Callisto. But what is it doing on this page? I CTRL-F'd for Callisto material in the article and found no mention of it. So why the picture? Leitmotiv (talk) 08:23, 6 January 2013 (UTC)
 * Tue. I think a picture of a space probe would be more appropriate.  Serendi pod ous  10:30, 6 January 2013 (UTC)
 * That or a satellite. Leitmotiv (talk) 00:03, 7 January 2013 (UTC)

"Achieving orbit requires a minimum velocity of 28,400 km/h (17,600 mph)"
An orbit can be arbitrarily slow if one travels arbitrarily far from Earth; and one can travel arbitrarily far from Earth by moving vertically with an arbitrary velocity.

I suspect this statement is a misunderstanding of some other statement (probably about low orbits). — Preceding unsigned comment added by 131.111.248.243 (talk) 17:41, 25 January 2013 (UTC)
 * I think you're confusing linear velocity with angular velocity. A spacecraft in a higher orbit has a lower angular velocity, but greater linear velocity; it takes longer to go around the Earth, but not because it is moving more slowly, but because it has further to travel as the circumference of its orbit is greater. -- W.  D.   Graham  21:16, 25 January 2013 (UTC)
 * You also move more slowly going higher, see Orbital speed. -- Cycl o pia talk  21:32, 25 January 2013 (UTC)
 * Yeah, I just calculated that and dropped a T, please ignore me. -- W.  D.   Graham  21:35, 25 January 2013 (UTC)


 * It is somewhat counter-intuitive that lower orbits require speeds higher than the speeds required for higher orbits. The statement in the article that started this discussion is in some sense misleading: theoretically there are trajectories that lead to high orbits along which the speed never reaches the speed required for a low orbit. But what this sentence is trying to convey is still important: in almost every practical case a spacecraft attempting to achieve orbit is headed for a low orbit first, even if it is only a temporary "parking" orbit. We should nonetheless consider alternative wording.... (sdsds - talk) 23:46, 25 January 2013 (UTC)
 * The statement is about achieving orbit. In context, it's clear that the statement refers to achieving orbit from the ground. Properly, the number in the lede is directly from the main text of the article, where it is further explained and cited. —Alex (ASHill &#124; talk &#124; contribs) 11:21, 26 January 2013 (UTC)

Achieving orbit 'from the ground' is not a condition which makes the statement true. As it currently stands, the statement completely misleading; it's just plain false, and whatever it does mean is not explained. If one wishes to orbit the Earth, it is simply not necessary to go at that large speed. You can reach an arbitrary height above Earth with an arbitrarily small speed; and orbits can have an arbitrarily slow velocity (yes, velocity - not just angular velocity) by orbiting from a further distance [v = sqrt(GM/d)]. The article does not indicate any conditions about the height of the orbit or anything else which would render it valid. I'm removing it for now; please don't replace it without adequately rewriting it. --131.111.248.243 (talk) 00:31, 29 January 2013 (UTC)
 * Please reread my comment, and read the section "Space versus orbit", from which this (appropriately, in my opinion) shorthand phrase in the lead is taken. What in the statement is inconsistent with the cited source? Again, in context, it's clear to me that the statement refers to the spacecraft that have achieved orbit, all of which are low Earth orbit. If you want to change the phrase in the lead to "low Earth orbit", OK, but I think that that is worse because it requires more explanation. —Alex (ASHill &#124; talk &#124; contribs) 02:35, 29 January 2013 (UTC)


 * I have read your comment. The reference that supports the main text number refers to "Just what does it require to get into Low Earth Orbit?" which is what the main text refers to.  The statement in the lead makes unqualified reference to achieving orbit.  This makes it false and unsupported by the cited source.  - Fartherred (talk) 03:50, 29 January 2013 (UTC)
 * The speeds referred to in the cited source are 7814 meters/sec and 8KPS. That is 28,130 kilometers/hour and 28,800 kilometers/hour.  Rounding first figure to the nearest two significant figures gives 7800 meters/sec which I put into the text.  - Fartherred (talk) 05:59, 29 January 2013 (UTC)


 * The "space versus orbit" section does not actually address the difference between space and orbit and it gives no clear explanation of how the speed of an orbit may decrease as one goes farther into space. — Preceding unsigned comment added by 131.111.248.243 (talk) 18:10, 29 January 2013 (UTC)

GA: Should we try again?
When I visited this article and saw the size, source length and how it was written I immediately believed that it was a GA or A Class. I was surprised to find that it had failed a GA. Looking over the reasons that the GA had failed nothing was actually noted as being wrong with the article. Something tells me that this article could probably be taken in for another GA and pass. Should we have another go at putting this in? MIVP (I Can Help? ◕‿◕) - (Chocolate Cakes) 08:52, 21 May 2013 (UTC)
 * A review might be useful. Is it missing anything significant? Praemonitus (talk) 21:10, 2 June 2013 (UTC)

Stating theories as fact
As the editor at 15.211.201.82 noted the phrase "Observations now prove that it also contains dark matter and dark energy" is an "Extraordinarily claim despite unsettled science". Sources say "implying" and "evidence for" and "Theorists still don't know what the correct explanation is"... so far from "proven". And even citing "overwhelming consensus of astronomers" being (some percentage) sure about the existence of something does not add up to "100% sure" or "proven" or "are the dominant components of space" per WP:SYNTH. Also the linked articles dark matter and dark energy state "hypothesized" and "hypothetical" so that would have to be resolved (i.e. take it up on those talk pages if this has been "proven"). Fountains of Bryn Mawr (talk) 19:39, 31 May 2013 (UTC)
 * The source I added says "It turns out that roughly 68% of the Universe is dark energy. Dark matter makes up about 27%." I don't think it's synthesis to turn 95% into "dominant"; that's just rewording into language appropriate for the lede of an article not directly about this topic. There's nothing equivocal about that, and there is in fact very little debate amongst astronomers and astrophysicists that dark matter and dark energy exists. Of course, we don't know what it is. However, "dark matter" and "dark energy" are just terms that parameterise our ignorance.


 * Dark matter simply means some kind of matter that interacts with other matter by gravitational forces but not electromagnetic or strong nuclear forces (weak nuclear forces are unclear, as far as I know). Galaxy rotation curves, the CMB power spectrum, gravitational lensing are some of the observations that require that something (or somethings) meeting that description exists; whatever it is, we call it dark matter. Any particular explanation of what dark matter is is indeed far from proven. Similarly, dark energy is the word we use to describe whatever it is that causes the fourth bump in the CMB power spectrum as well as the increase in Type Ia supernova redshift as a function of observed brightness.


 * Yes, there are all sorts of subtleties about what these are; these are best left for the articles on them specifically. In the lede of this article, all that merits mention is that these things or classes of things, whatever they are, exist. It is true that nothing is ever proven; however, it's unnecessarily cumbersome to equivocate on everything in the lede as the current version of the article does about dark matter and dark energy. We don't prevaricate about everything else in the lede, even though the statement that nothing is ever proven applies equally well to the statement that outer space is a hard vacuum with a little bit of hydrogen, magnetic fields, and neutrinos.


 * I've been meaning to clean up the other articles (where going into this level of detail is worthwhile); maybe this is my reminder to do so.


 * Now, the outer space article is a bit strained in how it treats what we think of as outer space. It's a vast topic, and I normally think of outer space as much closer to home than intergalactic or even intragalactic space; certainly, within the solar system, neither dark matter nor dark energy are dominant at all, and dark energy is irrelevant even within galaxy clusters. That's why I reworded the bit in the lede to say that it's on intergalactic scales that dark matter and dark energy are dominant. —Alex (ASHill &#124; talk &#124; contribs) 22:08, 31 May 2013 (UTC)


 * The wording "dark energy is the dominant component of space" leaves it unclear in what sense this is meant. If dark energy is a property of space, then can it even be considered a component? Praemonitus (talk) 21:06, 2 June 2013 (UTC)


 * True. I've clarified this in the body and lede. I've tried to be more explicit about what's widely accepted and what's very much unknown per the sources. The bit I added about dark energy to the body in particular may be incomprehensible; I'd appreciate another pair of eyes on it. —Alex (ASHill &#124; talk &#124; contribs) 05:13, 4 June 2013 (UTC)


 * I have done a slight change to the wording. Theory needs to be indicated in the lead as well as the body. Lead must conform to verifiability and other policies WP:LEADCITE. As far as "prevaricate about everything else", its a bit of an OTHER STUFF rational; i.e we may have to check that material's prose style, not dumb down the citing of theoretical work to match it. This is an encyclopedia for general audiences and the lead (and body) have to give the verifiable general "gist of things". Fountains of Bryn Mawr (talk) 14:02, 4 June 2013 (UTC)


 * Thank you for your modification. Praemonitus (talk) 01:49, 5 June 2013 (UTC)


 * Editor Ashill writes: "... the statement that nothing is ever proven applies equally well to the statement that outer space is a hard vacuum with a little bit of hydrogen, magnetic fields, and neutrinos." He is there pushing a point of view that unduly supports speculativeness. The phrase "equally well" undoes his case. Editor Fountains of Bryn Mawr is on the right track against Editor Ashill in this.Chjoaygame (talk) 23:49, 3 June 2013 (UTC)

Density of interstellar medium
On this page is reported as 10^6 particles pre m3, while on page dedicated to interstellar medium is is reported as 10^6 particles ("molecules") per cm3 - which is correct? — Preceding unsigned comment added by 212.5.214.157 (talk) 12:50, 17 September 2013 (UTC)
 * Both are correct. 10^6 particles per m^3 (1 / cm^3) is the (very approximate) average density of the ISM, while 10^6 / cm^3 is a typical density of dense molecular clouds. However, the density of the interstellar medium ranges from 10^-4 / cm^3 to 10^+10 / cm^3; there's a huge range. The table in interstellar medium gives some indication. The text of the outer space article also indicates the range. —Alex (ASHill &#124; talk &#124; contribs) 20:29, 17 September 2013 (UTC)

Cosmic rays are not part of supernova shock waves.
The article states: "The cataclysmic explosion of a supernova will generate an expanding shock wave consisting of ejected materials (as well as galactic cosmic rays)." Cosmic rays are not part of the shock wave. I happen to know that this is so, but do not take my word for that. Instead know that the false statement should be removed because it is not supported by a reference and it will not be supported by a reliable source because it is false. Cosmic rays might be generated within a supernova shock wave, but that is another matter. - Fartherred (talk) 09:14, 19 September 2013 (UTC)

Cosmic dust
If cosmic dust is to be included in the lead, then it must be covered in the article body per WP:LEAD. Perhaps the Interstellar space section would work? Praemonitus (talk) 03:08, 1 January 2014 (UTC)
 * Dust is mentioned (by name) six times in the article body, in several different contexts. —Alex (ASHill &#124; talk &#124; contribs) 04:21, 1 January 2014 (UTC)
 * My mistake, I was searching for 'cosmic dust'. Thanks. Praemonitus (talk) 04:36, 1 January 2014 (UTC)

Formation section needs to be refocussed
Right now, it's just a rehash of the Big Bang theory, which is fine, but rather than focusing on how the Universe itself formed, it should specifically focus on how space formed, i.e. why is the universe mostly vacuum, rather than, say, fluid?  Serendi pod ous  08:35, 17 April 2014 (UTC)
 * Well... I don't think we really know. We can suggest that inflation was (supposedly) a key factor regarding the current conditions, as is the energy density needed to avoid a closed Universe that re-collapses. But why did inflation occur and are there other possibilities? There is nothing to compare against, so the answer may be unknowable. Different physical constants could allow other Universes to form, perhaps even one that has fluid properties. But would it then allow life to form and observe its properties? It's purely speculative at that point, and so out of scope. Praemonitus (talk) 06:24, 20 April 2014 (UTC)

space vs outer space
The article treats "space" and "outer space" as synonymous and uses them interchangeabley, but I don't think the terms have the same connotations. I actually came to the article to find out whether low earth orbit counts as outer space, or whether it was merely "inner" space or whatever. But I didn't find out. It seems worth researching and writing about, and I may try to do that sometime, but with any luck someone else will do it first. 70.36.142.114 (talk) 07:51, 8 May 2014 (UTC)
 * Low Earth orbit is outer space/space. It is the same environment as space. "inner space" has no meaning in an astronomical context.  Serendi pod ous  09:40, 8 May 2014 (UTC)

Discovery/History section
I love that this article devotes a good amount of space at the beginning to the history of ideas about outer space. I hope more science articles on WP will follow the great example here. Kudos! -- Michael Scott Cuthbert (talk) 05:49, 13 November 2014 (UTC)