will I see these nebula?

[Stu]

14 minutes ago, DavidJM said:

Might be a daft question but what is a SQM21+ location?

Not daft at all! It is a measure of the brightness of the sky background.

Think of it a bit like water levels and tides. Stars are like islands, they stand up clearly above the water level so are visible even when the tide is in (e.g. bright sky background caused by light pollution or the moon).

Nebulae and galaxies are like mud flats only exposed at low tide, you only see them at their best when the light pollution is low and the sky background is dark. When the water level (sky brightness) rises  they are quickly covered and become invisible.

Hope my crazy analogy works for you  

[DavidJM]

15 minutes ago, Marci said:

A location which scores higher than 21 on a Sky Quality Meter: https://www.globeatnight.org/sqm.php#Observations

The value represents magnitude per square arc-second... aka a squim... and 21 pretty much translates to the dark blue / grey on the scale yonder: http://darksitefinder.com/maps/world.html

Wow thanks, using the darksitefinder I'm between dark green and yellow so for the UK not too bad

[DavidJM]

5 minutes ago, Stu said:

Not daft at all! It is a measure of the brightness of the sky background.

Think of it a bit like water levels and tides. Stars are like islands, they stand up clearly above the water level so are visible even when the tide is in (e.g. bright sky background caused by light pollution or the moon).

Nebulae and galaxies are like mud flats only exposed at low tide, you only see them at their best when the light pollution is low and the sky background is dark. When the water level (sky brightness) rises  they are quickly covered and become invisible.

Hope my crazy analogy works for you  

Actually that's a really cool analogy and makes sense, street lights are my pain but I'm lucky enough to be 20 mins from the moors

[Stu]

15 hours ago, DavidJM said:

Actually that's a really cool analogy and makes sense, street lights are my pain but I'm lucky enough to be 20 mins from the moors

Great  

Actually local streetlights are a pain in that they can stop you getting properly dark adapted, but if the sky background is dark and you can shield yourself from them you can still see faint targets.

When the sky background is bright and washed out by city lights for instance, or the moon then you just won't be able to see the faint objects.

20 mins from the moors sounds fab!

[Stu]

Thanks to @Allinthehead for permission to post these versions of his lovely Veil image.

Just trying to illustrate the impact of raised sky background on what you can see on these delicate objects.

First is the original image, 2nd is say under a dark sky with a 4" widefield scope and an OIII filter, last is perhaps a filtered view under a light polluted sky. An inexact science but hopefully illustrates the point.

[DavidJM]

4 hours ago, Stu said:

Thanks to @Allinthehead for permission to post these versions of his lovely Veil image.

Just trying to illustrate the impact of raised sky background on what you can see on these delicate objects.

First is the original image, 2nd is say under a dark sky with a 4" widefield scope and an OIII filter, last is perhaps a filtered view under a light polluted sky. An inexact science but hopefully illustrates the point.

I clearly need a filter to consider nebulae, great pics