A close to Earth Nebula.

Magnetic · Post by **Magnetic** » 2006-09-05 03:13pm

Hopefully, this question isn't as dumb as the last one.

I've seen many photos of stellar photography, and especially admire those true color photos of the Orion Nebula. I would love to look into the night sky and visibly see a fairly good sized nebula. The question is, would a nebula that could be easily seen from earth cause any problems?

Ace Pace · Post by **Ace Pace** » 2006-09-05 03:15pm

No, why should it?

A nebula is basicly a cloud of dust, the worst it would do is block out some stars.

Magnetic · Post by **Magnetic** » 2006-09-05 03:43pm

Are some nebula the result of an exploaded star?

Wyrm · Post by **Wyrm** » 2006-09-05 05:08pm

"Easily seen from Earth" does not imply that it is close. Nebulae are really big things, on the order of a few cubic light years and up. The angular size of the Orion Nebula (M42), for instance, is a whopping 65 arcminutes -- that's about 6 degrees of arc -- in angular size, but it's a nebula ~1,600 ly away.

Second, even the dense dark nebulae, which have a molar density of 200-300 molecules per cubic centimeter, attain their opacity thorugh, again, distances on the order of light years. Not much extinction of light will occur over distances of a couple of AU, even if the sun did not sweep out its immediate neighborhood free of dust while it was forming.

Stark · Post by **Stark** » 2006-09-05 05:59pm

I'm hardly an expert, but if a star exploded to form a nebula, far far beyond the limits of the dust cloud I'd assume the inverse square law keeps us safe.

Doesn't the system deflect stuff really far out, where the Voyagers are? Is that like Earths' magnetic field protecting us from solar wind etc?

Wyrm · Post by **Wyrm** » 2006-09-05 06:39pm

Yes, the extreme outer edge of the solar system does indeed deflect stuff, for a similar cause and reason. But a supernova really close would still fuck us up. Quite frankly, the nebulous remnant left behind would be the least of our problems.

Stark · Post by **Stark** » 2006-09-05 06:42pm

'Stuff' is my technical term for 'that dangerous stuff in space'.

How close would a supernova have to be? All of the large nebulas I read about as a child were pretty damn far away - the intensity of radiation at that distance would be pretty small.

RedImperator · Post by **RedImperator** » 2006-09-05 07:38pm

There's more than one type of nebula. The largest kind are giant clouds of gas and dust in space, like the Orion Nebula, which collapse and form stars once they're disturbed, possibly by nearby supernovas. Those are, so far as I know, perfectly safe, though if one was nearby it would be a pain in the ass for astronomers. Dying sun-like stars generate planetary nebulas when they reach the end of the red giant phase and shed their outer layers. This isn't a very energetic event and would be totally harmless even Alpha Centauri did it. Supernovas create nebulas similar to planetary nebulas (the Crab Nebula is one of these) called, surprisingly enough, supernova remnants, when they blast off their outer layers. Those nebulas are also harmless, but the events which create them are not. The most violent type of supernova (type Ia) could damage Earth's biosphere from 1000 parsecs away, and since they are caused by white dwarfs and not very large stars, we might not realize one is coming until the sky lights up.

Magnetic · Post by **Magnetic** » 2006-09-06 09:20am

RedImperator sir, first I would like to say that you posted some very interesting information there. I appreciate it.

How may light years is 1000 parsecs...hold on one second. Decided to do an internet search. 3.26 light years. What is the closest star to earth?

darthkommandant · Post by **darthkommandant** » 2006-09-06 11:14am

Proxima centauri is the closest with alpha centauri which is a binary system a close secons at about 4.5 light years. Proxima and Alpha are part of the same star system.

Hawkwings · Post by **Hawkwings** » 2006-09-06 11:44am

um... 1 parsec is about 3.2 light-years...

1000 parsecs... that's a whole lot of stars.

drachefly · Post by **drachefly** » 2006-09-06 12:46pm

He did say the most violent type.

Junghalli · Post by **Junghalli** » 2006-09-07 05:27pm

RedImperator wrote:Those are, so far as I know, perfectly safe, though if one was nearby it would be a pain in the ass for astronomers.

On the other hand, think of the views you'd get at night on such a planet.

Dying sun-like stars generate planetary nebulas when they reach the end of the red giant phase and shed their outer layers. This isn't a very energetic event and would be totally harmless even Alpha Centauri did it.

Hmm. How large are planetary nebulae? IIRC they're about solar-system sized, so if you had one as a prominent body in the night sky wouldn't that mean you'd probably have to be part of a multiple star system of which the nebula's central star is one of its components?
I tend to think if so having a companion star go through a red giant phase might not be very healthy for a planet's biosphere... although in this scenario it'd be a very widely seperated binary system (otherwise the planet would be actually inside the nebula) so I guess it might not matter.

Ariphaos · Post by **Ariphaos** » 2006-09-08 02:56am

Magnetic wrote:Are some nebula the result of an exploaded star?

Planetary nebula are the results of novas occuring at the end of a star's life, though not termed a supernova (still, IIRC the energy emitted is still immense). This could occur fairly nearby without causing much more than a rather spectacular light show. They get quite large (larger than our solar system) but not quite as fast or as brilliantly as the more violent types.

Supernova remnants remain after a supernova. The actual effect of these is somewhat debated. A type Ia supernova can cause more intense gamma ray bursts than Earth has ever felt at a range of 3,000 light-years. Type II only do this out to 10. It's suspected that hypernova, where the core collapses straight into a black hole, may be significantly more intense, and there may be polar jets pushing out intense radiation, causing the gamma ray bursts that alarm us today.

Honestly, though, we look at RS Ophiuchi (maybe 2k light-years away), and the thought of it actually significantly impacting Earth when it goes up seems laughable. It should be pretty clear that Earth's ozone layer has a buffer zone regarding how much energy it can take, and simply doubling the amount of radiation that hits it probably isn't enough.

Red supergiants and red hypergiants are believed to become blue by violently throwing off their outer layers. This also results in a nebula, like Eta Carinae. Massive as it is, that hypergiant - and the nebula it just made - are both a part of the far larger Carinae Nebulae, one of the largest in the Milky Way. It's about 2 degrees square as seen from Earth (120x120 arcmin), or nearly 100 parsecs across (give or a few dozen depending on its actual distance).

Anyway, as long as whatever creates the nebula is more than a few parsecs away (further depending on it being more powerful), you can have the rather abrupt creation of a new nebulae form close enough to be visible with the naked eye and not be terribly implausible (beyond the fact that no candidate object is close to Sol at this point). You probably don't want to use a hypernova, but something like the nova that made the Homunculus nebula around Eta Carinae (stretching what, two light-years across now after only a few centuries) could be a bit more chilling.

SirNitram · Post by **SirNitram** » 2006-09-08 03:14am

Magnetic wrote:RedImperator sir, first I would like to say that you posted some very interesting information there. I appreciate it.

How may light years is 1000 parsecs...hold on one second. Decided to do an internet search. 3.26 light years. What is the closest star to earth?

Keep in mind Type Ia supernovae are caused by a specific kind of star. Of course, the problem remains that the type making them are a pain in the ass to find, so we might not know.

The universe is a hostile place. Best reason there is to get spread out.

Magnetic · Post by **Magnetic** » 2006-09-08 10:01am

Junghalli wrote:
RedImperator wrote:Those are, so far as I know, perfectly safe, though if one was nearby it would be a pain in the ass for astronomers.
On the other hand, think of the views you'd get at night on such a planet.

Yes, I agree. On a clear night, away from the city, the stars themselves are quite awe inspiring. To have a visible nebula, perhaps 3-4 times the size of the moon, would be even MORE inspiring.

Seeing the whispy arm of the Milkyway is pretty good, but you have to be in a REALLY dark place to enjoy it fully. It's just a shame we can't see MORE of it.

Actually, isn't there a "dark nebula" (I have no idea of this is right or not) that blocks us from seeing the center of our galaxy? I've always thought it was odd that such a bright reagion of the galaxy is obscured enough to not be seen. When I look at a photograph of another galaxy, the center is immensly bright, so I would think that it would easily be seen from the arms.

Ariphaos · Post by **Ariphaos** » 2006-09-08 04:00pm

Magnetic wrote:Actually, isn't there a "dark nebula" (I have no idea of this is right or not) that blocks us from seeing the center of our galaxy? I've always thought it was odd that such a bright reagion of the galaxy is obscured enough to not be seen. When I look at a photograph of another galaxy, the center is immensly bright, so I would think that it would easily be seen from the arms.

There's a dark nebula obscuring a notable region of the sky in the southern hemisphere, and the LMC is quite visible too, apparently.

The Saggitarius region has a lot of clouds, yes, but it's also because our galaxy, for its size and age, is also quite dim. Most galaxies around our mass (like Andromeda) have gone through more violent collisions. This leaves our galaxy a rather dark, dusty place. In fact, from Andromeda, it wouldn't even be visible to the naked eye, even though Andromeda is visible (barely) to the naked eye on Earth, despite Andromeda having 2/3rds of the Milky Way's mass.

Magnetic · Post by **Magnetic** » 2006-09-08 04:11pm

I did not know that fact.

So, if someone in another galaxy was looking at the Milkyway galaxy, it wouldn't be nearly as bright as other?

Ariphaos · Post by **Ariphaos** » 2006-09-08 10:49pm

Magnetic wrote:I did not know that fact. :!: So, if someone in another galaxy was looking at the Milkyway galaxy, it wouldn't be nearly as bright as other?

Nearly is a bit of an extreme term - the Milky Way has an absolute magnitude of -20.5, which is certainly brighter than most galaxies, but it's a bit dim in comparison to other giants like Andromeda or the three that dominate the Virgo cluster. Even then, I think their absolute magnitudes top out at -22 or so - rarely even ten times as bright. The brightest quasar - basically the brightest object in the Universe, is believed to be -26.7. About two hundred and fifty times as bright as our Milky Way.

It also depends on which galaxy. From Andromeda or Triangulum, to our eyes, the Milky Way would be invisible.

From the Large Magellenic Cloud, the Milky Way would be a grand sight crossing about a fifth of the sky with a total apparent magnitude of about -2.0, and not terribly irregular supernovas which will outshine the whole thing.