Could you ever see a nebula with your own eyes?

[m74z00219]

Hi all.

Is it possible to see a reflection or emission nebula? Can you get close enough to a nebula so that is wasn't too dim to see and still be far enough away that its high diffusivity prevents you from seeing it (like if you were in it)?

[ngc3314]

Hi all.

Is it possible to see a reflection or emission nebula? Can you get close enough to a nebula so that is wasn't too dim to see and still be far enough away that its high diffusivity prevents you from seeing it (like if you were in it)?

Sure. Surface brightness is distance-independent (except on scales were the expansion of the Universe factors in...), and a telescope cannot increase visual surface brightness, so if you could see one close up, a nebula would look at least as bright as you can see in any telescope. Refection nebulae don't seem to come as bright as emission nebulae, but there are some examples like M78 which are plain enough telescopically. The difference between naked-eye and telescopic views from our vantage point is that most nebulae are so small in angular extent that the eye sees them as points, so we undersample their surface brightness.

[grant hutchison]

But they would look completely different from those brightly coloured photographs which are generated by long exposures.
The Orion Nebula is easily visible to the naked eye as a small dim patch of colourless light. Get closer, and it will look like a large dim patch of colourless light, although I've no doubt we'd be able to discern interesting detail.

Grant Hutchison

[aurora]

You can probably see the Orion Nebula on a dark night. If you look closely, you may be able to detect that it is not a point of light (like a star).

[Starfury]

But go out to the country. It's really not visible from the middle of the metropolitan area where I live.

[George]

There are some nebulae that have just enough surface brightness so that you will see some of the colors that are portrayed in the beautiful color images -- the colors are more often than not false color presentations for various reasons.

I recall seeing a bluish-white ring in the Eskimo nebula when we (us tourists) observed it through the McDonald Observatory 87 inch telescope. My son saw this ring with even more blue than I did. Other nebula also exhibit observable color, but never like the color images because of a camera's advantage of taking long exposures.

If you could travel toward a nebula, it will appear somewhat brighter due to the fact you receive greater total flux. However, the brightness per unit area will not change since both brightness and apparent size vary as the square (inversely) of the distance, so their effect per unit area cancels each other (as others have stated above).

[Moonhead]

But they would look completely different from those brightly coloured photographs which are generated by long exposures.
The Orion Nebula is easily visible to the naked eye as a small dim patch of colourless light. Get closer, and it will look like a large dim patch of colourless light, although I've no doubt we'd be able to discern interesting detail.

Grant Hutchison

In a well-know photo editing programme, there is a set of filters/functions called auto-levels, auto-brightness and auto-color; if applied, these stretch out the minimum and maximum (for saturation, brightness, color) levels found in a given picture, so that they correspond to the 'absolute' (within the program) levels for these attributes. Have those nebula pics gone through a similar proces?

[Celestial Mechanic]

I can see the Orion nebula without optical aid even here in Milwaukee. I live about a mile and a half from downtown, and Interstate 43/94 is one block from my house, a veritable hell for optical astronomy.

I was fortunate once to glimpse the open cluster M35 in Gemini without optical aid in the country once. I've never had the chance to try for M31, though.

[astromark]

So. From a dark site you can see The Orion Nebular. Its not so spectacular because our eyesight is not so flash... Binoculars or a telescope fix that. From a clear dark site we in the deep south can see a few fuzzy blobs... So, yes. I would go look at 'Sky maps' they have this covered.

[Argos]

In a well-know photo editing programme, there is a set of filters/functions called auto-levels, auto-brightness and auto-color; if applied, these stretch out the minimum and maximum (for saturation, brightness, color) levels found in a given picture, so that they correspond to the 'absolute' (within the program) levels for these attributes. Have those nebula pics gone through a similar proces?

Surely the images undergo those corrections, but the important thing is that the images are acquired via different filters. That´s the process that makes them so rich.

[Tog]

In a well-know photo editing programme, there is a set of filters/functions called auto-levels, auto-brightness and auto-color; if applied, these stretch out the minimum and maximum (for saturation, brightness, color) levels found in a given picture, so that they correspond to the 'absolute' (within the program) levels for these attributes. Have those nebula pics gone through a similar proces?

As Argos said, there is more to it than taking a picture and tweaking the levels. In most deep sky stuff, pictures re taken through different filters. What that means is an image opf maybe an hour or so is taken that shows only the Blue parts of the spectrum. Then another is taken for 40 minutes in the green band, then 25 minutes in the red. It's possible that even more frames are taken through Infra-red, X-ray, Hydrogen, or Oxygen3 filters to highlight different parts. Each section is processed as an individual image, then stacked into one, and tweaked a bit more.

Also, the red band tends to be far more prominent in photos (film) than in reality. That's why the red filters are usually shorter exposures.

The reason for this that I've always seen is that film is more sensitive to red light than blue in order to make more realistic skin tones. I'd wait for confirmation on others before accepting that though. I'm not sure why that would be the case for a digital imager.

[astromark]

The OP clearly asked " Could you ever see a nebula with your own eyes? "

Yes.

All those fabulous images we have all seen are long exposures of larger magnitude, aperture than the human eye. We do not see outside of natural light. Unaided we can see these things. They just do not look the same.

[parejkoj]

CCDs are generally more sensitive to red than they are to blue, which is why people often expose less in the red band. This is due to how CCDs are constructed, not whether they make realistic skin tones (which is something that digital cameras adjust on the fly anyway).

As for nebulae, M42 is definitely naked-eye visible at a dark site, as is M8 (from a *very* dark site), which is noticeably extended. M42 shows some color (purplish to my eye) when viewed through a decent telescope. They aren't reflection nebula, though.

[George]

CCDs are generally more sensitive to red than they are to blue, which is why people often expose less in the red band. This is due to how CCDs are constructed, not whether they make realistic skin tones (which is something that digital cameras adjust on the fly anyway).

Yes. Some, if not most, cameras have a filter to counteract this red imbalance. The Canon 20Da was available for astrophotography with the "a" in the model designation representing this feature; namely the filter removal allowing for improved red nebulae imaging.

[m74z00219]

The OP clearly asked " Could you ever see a nebula with your own eyes? "

Yes.

All those fabulous images we have all seen are long exposures of larger magnitude, aperture than the human eye. We do not see outside of natural light. Unaided we can see these things. They just do not look the same.

thanks astromark, so if we could travel to say 10 cy from the horsehead nebula, we would see similar structure (as we do in the perdy pictures) and some of the red coloring, but less bright?

[blueshift]

thanks astromark, so if we could travel to say 10 cy from the horsehead nebula, we would see similar structure (as we do in the perdy pictures) and some of the red coloring, but less bright?

Sure, with hydrogen beta eyes. As for naked eye observing, I can't even make out the words on this page with the naked eye. I wear glasses. Stars? What stars? In a dark sky site I once hit the panic button looking for my glasses in the night for 2 hours. Turned out they were right on my forehead, right where I tilted them upright, still notched behind each ear.

[Hornblower]

thanks astromark, so if we could travel to say 10 cy from the horsehead nebula, we would see similar structure (as we do in the perdy pictures) and some of the red coloring, but less bright?

I have seen it in a 17.5" reflector at 80x, which is a good match for the naked eye at 1/80 the distance, about 20 light years. No color, just shades of gray. The light is simply too faint for our color vision.

[Tim Thompson]

I can see the Orion nebula without optical aid even here in Milwaukee.

NGC 604 in M33 is the largest HII region in the local group. About 1200 light years across, its diameter is the same as the distance from here to M42. Put NGC 604 in place of M42 in our sky, at the same distance, and it would be not only clearly visible, but about 50 degrees across as well!

[Sam5]

Hi all.

Is it possible to see a reflection or emission nebula? Can you get close enough to a nebula so that is wasn't too dim to see and still be far enough away that its high diffusivity prevents you from seeing it (like if you were in it)?

M31 is generally visible with just eyes, but of course it is very small and somewhat dim. While viewing in a dark place, you should be able to see a small fuzzy patch of light.

http://en.wikipedia.org/wiki/Andromeda_Galaxy

[m74z00219]

Thanks all.

[chornedsnorkack]

Is the Carina Nebula visible to naked eye? And is it more or less spectacular than the Orion Nebula?

Also, if the nebulae are not a sphere in whose centre the observer is, shouldn´t their uneven light distribution be visible, even from inside them? Like the Milky Way is a rather prominent object?