Science and Astronomy Questions

Cantra · 08 Feb 2017 17:39

Quontex,

I would if I had the password to my steam account.

Quarior · 09 Feb 2017 03:05

This is a post by Watsisname talking about breathable atmosphere and the like, Should find your answers there.

I read this but I talk for atmosphere complety different with our planet, ie very little see nothing oxygen.
And I precise without life support (oxygen) but of course, we have food, water.

09 Feb 2017 19:47

Er, if there isn't enough oxygen, no amount of adaptation will allow you to survive. Adaptation can help a little, but not a whole lot. Humans can't survive permanently above about 6000m on Earth, for instance.

I guess I'm not quite sure what you're asking.

midtskogen · 10 Feb 2017 16:35

Humans can't survive permanently above about 6000m on Earth, for instance.

Seems correct. https://www.ncbi.nlm.nih.gov/pubmed/12631426

Handbanana · 10 Feb 2017 18:24

If backwards time travel is possible, what would determine the physical location of the time machine? The Earth is orbiting the sun, the sun is orbiting the Milky Way, and the Milky Way is gravitationally bound to other galaxies. There is no universal point of reference in space. Or, would this paradox itself make time travel impossible?

10 Feb 2017 18:32

Handbanana, it wouldn't make it impossible. The way future time-traveling humans could actually travel through time is by controlling where they are in the 4th dimension (non-euclidean). It's a piece of cake. I would image it like floating in a river and trying to go against the current. You can still control where you are in the river. In the case of time travel, the controller would be a super-computer

10 Feb 2017 20:37

If backwards time travel is possible, what would determine the physical location of the time machine?

Lol, I've asked that question sometimes, too. There is no real answer of course -- time travel into the past is impossible for causality reasons -- so it's up to however the storymaker wants the time travel to work. Usually it works by ignoring this problem completely.

Cantra · 10 Feb 2017 21:41

@Watsisname,

I am thinking the Gai-Cali barycenter would probably be above the surface, would it be somewhere around 20,000 miles from Gai?

10 Feb 2017 21:54

What is the brightest nebula in terms of absolute magnitude? A quick google search gave the orion nebula, but I think that is just apparent magnitude.

11 Feb 2017 03:15

I am thinking the Gai-Cali barycenter would probably be above the surface, would it be somewhere around 20,000 miles from Gai?

The SemiMajorAxis would be about 3800 km for Gai. That would still be within Gai.

Barycenter    "Gai-Cali"
{
    ParentBody     "Vob"
    
    Orbit
    {
        RefPlane      "Equator"
        SemiMajorAxis  0.72000
        Eccentricity   0.0167086342
        Inclination    0.0
        AscendingNode  0.0
        LongOfPericen  0.0
        MeanLongitude  0.0
    }
}

Planet    "Gai"
{
    ParentBody     "Gai-Cali"
    Class          "Terra"

    Mass            1.0
    Radius          6186.06

    RotationPeriod  28  
    Obliquity       29.0

    Life
    {
        Class   "Organic"
        Type    "Multicellular"
        Biome   "Marine/Terrestrial"
    }


    Atmosphere
    {
        Height      60
        Greenhouse  33
        Pressure    1.0
        Density     1.2929
        Adiabat     0.28
        Model      "Earth"
        Bright      10.0
        Opacity     1.0
        SkyLight    3.0
        
        Composition
        {
            N2  77.7729
            O2  20.8625
            Ar  0.9303
            H2O 0.4000
            CO2 0.0398
        }
    }


    NoRings     false

    Orbit
    {
        RefPlane      "Equator"
        SemiMajorAxis  2.52204708e-5
        Eccentricity   0.0
        Inclination    0.001
        AscendingNode   0
        ArgOfPericenter 0
        MeanAnomaly     0
    }
}

Moon  "Cali"
{
    ParentBody     "Gai-Cali"
    Class          "Selena"

    Radius  2000
    Mass    0.025873
    
    Orbit
    {
        RefPlane       "Equator"
        SemiMajorAxis   0.00097478
        Eccentricity    0.0
        Inclination     0.001
        AscendingNode   0
        ArgOfPericenter 180
        MeanAnomaly     0
    }
}

11 Feb 2017 05:08

Starlight Glimmer, JackDole is correct. To calculate in general, multiply the mass of the moon by its semimajor axis, and then divide that by the total mass (planet and moon together).

Hornblower, interesting question. The Orion Nebula is pretty bright. With a visual magnitude of +4 and being about 400pc away, it's absolute magnitude is about -4. But is it intrinsically the most bright?

I did a quick analysis of all the 'nebulae' in the Messier catalog. There are 12 of them: one supernova remnant, four planetary nebulae, six emission nebulae, and one reflection nebula. Here's a plot of their apparent magnitudes versus distance. Notice some of them have big uncertainties in how far away they are. Others don't have listed uncertainties on wikipedia, so I left them as 0. The catalog number is listed next to each point.

From this we can see the Orion Nebula (Messier 42) is apparently bright, but also fairly close. Some of the more distant ones might be intrinsically brighter, like M16 and M17. Indeed, here's what happens when we convert to absolute magnitudes (uncertainty in magnitude accounts for uncertainty in distance).

So some of the other nebulae (M16, 17, 20, and 8; all emission nebulae) do appear to be intrinsically brighter than Orion, by perhaps a magnitude or two.

Cantra · 11 Feb 2017 07:21

JackDole,

Thank you.

11 Feb 2017 08:06

Watsisname, interesting. Omega nebula and Eagle nebula. And surely there are brighter one's we just haven't been able to witness yet or that are in another catalog. Thanks

11 Feb 2017 08:29

Sure thing! And certainly there may be brighter nebulae elsewhere in the galaxy, or in other galaxies. Imagine what it would be like inside a starburst galaxy like this:

https://en.wikipedia.org/wiki/Starburst_galaxy#/media/File:Antennae_galaxies_xl.jpg

11 Feb 2017 08:34

Watsisname, alright, so the reason I asked my question is in those very bright nebula, would the surrounding gasses be extremely visible? Because those bright nebulae will become huge tourist destinations in the far future (if they're still around).

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