Does the sky look black?

[domstar]

I've been observing at a new darkish site ( sqm 21.26 Bortle 4) . The milky way is clear and the Double Cluster is evident. It's away from lights although I do see the village below and the glare from a town 9km away. However, the sky is greyish. When I drive back to base 500m away and park, there is an awful LED streetlight. With my back to the streetlight the sky is inky black and perhaps there are more visible stars. The view is obstructed by houses and trees.

My question is- is this normal or should I look for blacker skies? Does the light horizon turn the sky grey? Does my dark adaptation turn the sky grey? What is going on?

[Rob Sellent]

I'm honestly not sure but it sounds about right. My skies are probably around Bortle 4 and when my eyes are dark adapted, I too see a possible deep blue-grey charcoal appearance to the skies. Unless I'm blinded momentarily by white light, or watch the sky in the vicinity of a street lamp, the sky is never pitch-black. 

If I'm evaluating the conditions of the sky in terms of transparency, I prefer using Ursa Minor or the stars I see within Pegasus' box rather than relying on Bortle

Sounds to me your skies are just fine 🙂

Edited September 5, 2019 by Rob Sellent
typo

[Star101]

When I view...Not often these days, but still, it has been known. I see a murky brown background to a blue/red/orange and white starry sky. I think I confuse the green with blues sometimes

Personally, I do get a little niggled when I see images with black backgrounds. Lets just say I have to think "Art" and not "Science" when that happens   But it's all personal choice!

I think we all see the sky differently depending on our eyes, our perception and the location( Bortle # ) itself.

 

[scarp15]

Transparency will be a key factor concerning appreciating a good quality dark sky, particularly when planning to observe lower elevation objects. Distant light domes become expansively reflected by thin cloud and moisture. Assessing a dark sky presently, could be determined if you can see M31 directly. Taking sky brightness readings, can greatly assist and inform concerning observable targets on a given night at a given location within a particular time frame. At the weekend, I was averaging SQM-L readings at 21.2 mag, not my darkest location option (based on a place practical for a same night return trip home) although the windy conditions made it the most desirable. Looking S/W, W, and N were not hindered by any trace of light dome. High up into Cygnus and the milky way was particularly distinct. Andromeda, straight forward naked eye. Certain low lying targets in Sagittarius (based on my 55 degree Latitude location), were a rare and very impressive treat. The wind probably an advantage to the good transparency. One considered clear night to another at the same location, often may yield a different sky quality. Dark adaption may play a role, yet as always the sky above approaching Zenith is where it ought be visually darkest.      

[jetstream]

3 hours ago, domstar said:

However, the sky is greyish

This is a good sign!

This means you were well dark adapted. Under 21.8 mag, transparent skies I see the sky as grey and can see well in the open. If I turn a light on to read something for instance and then turn it off the same sky is now jet black.

As Vogel says:

"All cats are gray in the dark"

http://www.reinervogel.net/index_e.html?/Hickson/hickson_e.html

 

[Paz]

1 hour ago, jetstream said:

This is a good sign!

This means you were well dark adapted. Under 21.8 mag, transparent skies I see the sky as grey and can see well in the open. If I turn a light on to read something for instance and then turn it off the same sky is now jet black

I notice this when I come home from observing somewhere dark. I'll get out of the car and look up and the sky looks jet black, at first sight better than where I came back from, but then you realise you can see a lot less stars and it's just that I've lost my dark adaptation.

[domstar]

Thanks guys. It was confusing me. Every time I get back I look up and think 'Why did I pack up?'  I think when I get out of the car I have to look up high because of all the houses and trees, which makes the difference seem even worse. It's good to know it's normal.

[Rob Sellent]

@domstarI am no expert on sky darkness, so I guess I'm just pointing out the obvious, but our expectations can sometimes exceed reality. I live in Spain and the skies in the Pyrenees or a little down south in desert parts of Almeria are dark. But on most nights I've visited, you can walk around without a red light, see your scope and tent outlines etc. I guess it's just the way the eye is built. I can't speak for darker sites than mountains and deserts in Spain, but when we read of reports we might think, 'aye, the grass seems greener over yonder' but this is not necessarily the case. 

It's difficult with words because I really don't want this to sound like a sermon. I think the best we've got is to embrace our skies no matter how light polluted they appear and try to work our way around them. I know you're doing this, but I just wanted to say, everything you've experienced is completely normal and perhaps any doubts really boil down to reading other folks' own natural enthuiasm when reporting about 'amazing', 'unbelievable', 'extraordinary' dark skies and the such.

Hope that makes sense 🙂

[Ben the Ignorant]

On ‎05‎/‎09‎/‎2019 at 19:01, domstar said:

I've been observing at a new darkish site ( sqm 21.26 Bortle 4) . The milky way is clear and the Double Cluster is evident. It's away from lights although I do see the village below and the glare from a town 9km away. However, the sky is greyish.

The sky should be grey. The collective glow of stars (and to a lesser extent, nebulas and galaxies) that are too faint to be seen individually turns the black of space into a dark grey. It's like seeing an open cluster to the naked eye as a greyish smudge that is resolved into stars by an instrument. You could say the whole sky is a star cluster so the whole sky is also a grey smudge. To have a truly black sky would mean it has nothing beyond the stars you see with the naked eye, so nothing more to see with telescopes.

Edited September 7, 2019 by Ben the Ignorant

[Captain Scarlet]

My understanding of a sky at, say, 21.3, means that the patch of sky being measured has the same average brightness as if each square arcsecond contained one star of mag 21.3.

With only your rods working at that level of brightness, that’s a shade of grey.

M

[Sagitta]

I've recently moved from a Bortle 3-4 at the coastline to a Bortle 2-3 at about 500 meters above sealevel. I still have light pollution from a coastal village due south (grrrr) but from about 35° towards zenith, the sky is awesome. I have no sqm meter (yet) but I figure it'd be about 21.8. Now here the sky does indeed looks brighter, especially with the summer Milky Way overhead. It rather looks dark bluish gray.

Edited September 12, 2019 by Sagitta