You find yourself floating in space near (ish) to the main Messier objects..what do you see?

[MKHACHFE]

Hi all, I have a hypothetical question.

Having dabbled in astronomy with an XT8 for a couple of years before moving onto astrophotography, I understand the difference between a long exposure image and direct eyesight viewing.

So, I'm wondering, just HOW faint are galaxies and nebulae?

Let's imagine we are floating in space and M31 is directly in front of us and filling our field of view..what does it look like? (Assuming perfect vision and eyes).

I assume it would still look nothing like an AP image. Am I right? Do galaxies still look like mostly faint fuzzy objects even from closer up?

Would one see individual stars in the Andromeda galaxy for example?

What about floating near M57, say? Are we seeing the ring clearly? 

Just an interesting thought experiment to understand just how faint these things are..

Thanks for reading.

[Stu]

I did wonder the same thing a while back, not sure I got to a definitive answer; mine was thinking about M42, would you know you were ‘in it’ as it were.

I suspect the answer will vary depending on the type of object, whether it is ultimately stellar like a galaxy or nebulous like a... well a nebula 😉.

My basic understanding is that the surface brightness of extended objects does not increase as you get nearer to them, because the light gets more spread out as it gets closer. Overall it will appear brighter because it is bigger of course, much like using a large dob to   Increase the size of faint objects whilst maintaining their surface brightness.

I would expect that something like M57 would retain its ring shape until it got so big that you couldn’t tell where the edges were, again similar to looking ‘through’ a large object such as the Rosette nebula where it is hard to detect if it is filling the field of view and you can’t see the edges.

Stars in Andromeda can actually be resolved with Hubble, so I should think as you approach them the stars will get brighter and brighter as they behave as point sources (say like close stars such Sirius being much brighter than distance stars of similar absolute magnitude) and then it would be like approaching a huge star cluster. Unless you got very close to an individual star though, they  would stay as point sources and once in it, I guess it would be no different to being where we are now in the galaxy, as the distances between stars are so vast even in a galaxy.

https://skyandtelescope.org/astronomy-blogs/explore-night-bob-king/see-stars-andromeda-galaxy/

[Knight of Clear Skies]

Stu is right that surface brightness doesn't change with distance. However, some reflection and emission nebulae might appear brighter from the right vantage point, with less obscuring dust in the way.

Probably the most impressive Messier object to see up close with the naked eye would be a dense globular cluster. (Or, if this qualifies, the accretion disc and jet of M87.)

Edited May 5, 2021 by Knight of Clear Skies

[Gfamily]

Given that we live inside a galaxy very similar to M31, I think we can expect that the view from 'close up' would be similar to our view of the Milky Way, i.e. visible but not overwhelmingly bright. 

[Andy ES]

I’ve often seen those sweeping videos around galaxies on programmes about cosmology and wondered how many times greater than the speed of light would the camera have to be moving to really make the film!

[Stu]

54 minutes ago, Knight of Clear Skies said:

Probably the most impressive Messier object to see up close with the naked eye would be a dense globular cluster.

Yep! Star densities seem pretty crazy in those!

https://astronomy.com/magazine/ask-astro/2006/01/how-close-can-stars-get-to-each-other-in-galaxy-cores
 

I wonder how close a star has to be to begin to resolve into a disk? Depends on it’s size obviously as they vary massively.

[Stu]

8 minutes ago, Gfamily said:

Given that we live inside a galaxy very similar to M31, I think we can expect that the view from 'close up' would be similar to our view of the Milky Way, i.e. visible but not overwhelmingly bright. 

Yes, that sounds right. Basically it will maintain brightness as it approaches, the more distant stars will remain as a ‘Milky Way’ type effect and the nearer ones will appear just like our visible stars do.

[Zermelo]

5 minutes ago, Stu said:

I wonder how close a star has to be to begin to resolve into a disk?

https://en.wikipedia.org/wiki/List_of_stars_with_resolved_images

[MKHACHFE]

20 hours ago, Knight of Clear Skies said:

Stu is right that surface brightness doesn't change with distance. However, some reflection and emission nebulae might appear brighter from the right vantage point, with less obscuring dust in the way.

Probably the most impressive Messier object to see up close with the naked eye would be a dense globular cluster. (Or, if this qualifies, the accretion disc and jet of M87.)

Yes, I had thought the same thing. That GCs must look fantastic up close. 

Thanks for reply

[MKHACHFE]

21 hours ago, Stu said:

I did wonder the same thing a while back, not sure I got to a definitive answer; mine was thinking about M42, would you know you were ‘in it’ as it were.

I suspect the answer will vary depending on the type of object, whether it is ultimately stellar like a galaxy or nebulous like a... well a nebula 😉.

My basic understanding is that the surface brightness of extended objects does not increase as you get nearer to them, because the light gets more spread out as it gets closer. Overall it will appear brighter because it is bigger of course, much like using a large dob to   Increase the size of faint objects whilst maintaining their surface brightness.

I would expect that something like M57 would retain its ring shape until it got so big that you couldn’t tell where the edges were, again similar to looking ‘through’ a large object such as the Rosette nebula where it is hard to detect if it is filling the field of view and you can’t see the edges.

Stars in Andromeda can actually be resolved with Hubble, so I should think as you approach them the stars will get brighter and brighter as they behave as point sources (say like close stars such Sirius being much brighter than distance stars of similar absolute magnitude) and then it would be like approaching a huge star cluster. Unless you got very close to an individual star though, they  would stay as point sources and once in it, I guess it would be no different to being where we are now in the galaxy, as the distances between stars are so vast even in a galaxy.

https://skyandtelescope.org/astronomy-blogs/explore-night-bob-king/see-stars-andromeda-galaxy/

Stu, thank you for the long reply. I didn't know about the surface brightness thing. Very interesting and goes a long way to answering my question.

I know Hubble can resolve individual stars in M31, but don't forget, my hypothetical scenario involves just eyesight. 

Cheers

[MKHACHFE]

20 hours ago, Gfamily said:

Given that we live inside a galaxy very similar to M31, I think we can expect that the view from 'close up' would be similar to our view of the Milky Way, i.e. visible but not overwhelmingly bright. 

That is an excellent point. Didn't think of that.

 

Cheers

[MKHACHFE]

20 hours ago, Stu said:

Yep! Star densities seem pretty crazy in those!

https://astronomy.com/magazine/ask-astro/2006/01/how-close-can-stars-get-to-each-other-in-galaxy-cores
 

I wonder how close a star has to be to begin to resolve into a disk? Depends on it’s size obviously as they vary massively.

Amazing. Can you imagine the night sky if we lived near the galactic core? I've read various articles and posts suggesting it would be possible to read a book by the starlight alone. 

Either way, I can't imagine life could ever develop there, it's far too dangerous a place.

Cheers

[MKHACHFE]

19 hours ago, Zermelo said:

https://en.wikipedia.org/wiki/List_of_stars_with_resolved_images

Wow. I had no idea any star had been resolved like that.. thanks for the link.

[Stu]

2 hours ago, MKHACHFE said:

Wow. I had no idea any star had been resolved like that.. thanks for the link.

Betelgeuse is one of the best I think, bulging like crazy like a ball of jelly!

https://www.google.co.uk/amp/s/www.inverse.com/article/33408-supergiant-star-betelgeuse-is-bulging/amp

[reezeh]

Just going back a minute  to how diffuse nebulae would look if you were within: I have been led to believe that our solar system actually is in a hole in a nebula complex that surrounds us at only a few light years away.

So, you might have quite a job seeing it. 

[Alien 13]

9 hours ago, Stu said:

Betelgeuse is one of the best I think, bulging like crazy like a ball of jelly!

https://www.google.co.uk/amp/s/www.inverse.com/article/33408-supergiant-star-betelgeuse-is-bulging/amp

Makes you wonder when it goes Supernova if the energy released will be directional or offset.

Alan

[Stu]

4 minutes ago, Alien 13 said:

Makes you wonder when it goes Supernova if the energy released will be directional or offset.

Alan

I guess it will definitely give some shape or structure to the resulting planetary nebula, much like many of them that we can observe.

[MKHACHFE]

21 hours ago, Stu said:

Betelgeuse is one of the best I think, bulging like crazy like a ball of jelly!

https://www.google.co.uk/amp/s/www.inverse.com/article/33408-supergiant-star-betelgeuse-is-bulging/amp

That picture is absolutely astounding.

How have I never seen it before??

Amazing