How much of a difference does a dark sky make

[Kronos831]

Hey guys. For. A while now, i have been wondering, just how much difference does a dark sky make. I live in moderate light pollution, as i live in the city.The orion nebula is just a little fainter than most stars when viewed with the naked eye.

The limiting magnitude for my 8" dob so far(that i have tried) is 8.4. i could just make out the crab nebula at 37.5x . extremely faint and just visible with adverted vision.I can also see the blackeyed galaxy quite clearly.

I will be going on holiday in the summertime.I ll be visiting a place with clear dark skies.I will bring my 5" Skywatcher heritage with me. How many inches of aperature will the dark skies"add" to my scope compared to its original aperature at a light polluted location.Will it be able to rival my 8" dob?

Just wondering

Clear skies

Kronos

Edited April 20, 2019 by Kronos831
Typo

[mark81]

It's an interesting subject Kronos.  I am very lucky to have Bottle 3/4 skies so many of the large DSOs like the Beehive, Andromeda etc are clearly naked eye visible.  My 10x50 binoculars here for example, can resolve mag 8 stars on a good night and mag 9 as very small grey pixels, but in outer London visiting family where the bottle is 8 I really struggle with everything through the bins so more aperture is essential.  Also reading other members observing reports from light polluted areas I have sometimes been surprised how little can be seen, so I would imagine an 8inch newt under bottle 3/4 to be amazing.  I think the 130 heritage will be very pleasing under dark skies - so many people sing it's praises and I wouldn't be surprised if it would rival your dob.

Mark

[John]

When I've observed from a dark sky site I've found quite a lot of difference in the views of deep sky objects from those that I get from my back yard (which are not too bad but I live on the edge of a large town so there is some light pollution.

A few years ago I took a 6 inch scope to the SGL star party and under dark skies there it was showing me the sorts of views of galaxies and nebulae that I needed a 10 or 12 inch scope to see from home.

Remember that you will be able to see a fainter point source or condensed light target than you can a dispersed target such as the Crab Nebula. If the Crab Nebula is close to your limit for a dispersed (spread out) target then you may well be able to see point sources quite a lot fainter.

From my back yard I can get down to about magnitude 13 - 13.5 galaxies on a good night. The faintest point source that I've seen so far is around magnitude 14.7.

Under a dark sky you don't just see fainter objects though, you see more structure, more extension and more features in the brighter ones !

 

[Kronos831]

Thanks guys.Cant wait to get to these dark skies! I ve been sick for the past 2 weeks and i miss my scope so much :/. This sickness just wont go away.

clear skies

thanks

kronos

[Stu]

Have a play around on this calculator Kronos. It lets you gain an understanding of the impact of different sky brightness on both stellar visibility and non point sources such as nebulae.

http://www.bbastrodesigns.com/VisualDetectionCalculator.htm

Note that the aperture has to be in inches, it doesn't seem to work in mm

I did these two comparisons on the Crab Nebula to start you off. The first one is your dob under mag 18.5 skies, roughly NELM of 4.5 I think. The second is the 5" under a mag 21 sky which is reasonably dark, though not the darkest by any means.

This shows that your 5" will outperform the 8" under a dark enough sky

[Kronos831]

Um 

XD i don't under half the stuff here.

What are the inches in the visual chart, (most likely comparison in between different size telescope)and how do i determine the object dimensions

Thanks btw

Kronos

[Stu]

23 minutes ago, Kronos831 said:

Um 

XD i don't under half the stuff here.

What are the inches in the visual chart, (most likely comparison in between different size telescope)and how do i determine the object dimensions

Thanks btw

Kronos

Hi Kronos, sorry if that was confusing.

The first chart is for an 8" scope under skies which the faintest stars you can see with the naked eye (NELM) are magnitude 4.5. Under these conditions the faintest star you can see through the scope is between 11.3 and 12.3 magnitude.

The next chart is for a 5" scope under skies which the faintest stars you can see are around magnitude 6. In this case the dimmest star seen in the scope would be between magnitude 12.8 and 13.8, showing that the smaller scope will go deep under a darker sky than the larger one.

If you also look at the chart, it shows that the Crab Nebula would be much easier to see in the smaller scope under darker skies than the larger one. If you go to the link provided it explains the scale of visibility used.

Hope that helps a little.

[Kronos831]

Yea i got that i just dont know how to find the objective diameter and the limiting mag

Thanks

Kronos

[Stu]

16 minutes ago, Kronos831 said:

Yea i got that i just dont know how to find the objective diameter and the limiting mag

Thanks

Kronos

Well the objective diameter is just the aperture of your scope, and the limiting magnitude will be the faintest star you can see on a clear night. If you look at Ursa Minor, the faintest star is just under mag 5 so if you can see all seven then you NELM is about 5.

[Kronos831]

On 21/04/2019 at 14:31, Stu said:

Well the objective diameter is just the aperture of your scope, and the limiting magnitude will be the faintest star you can see on a clear night. If you look at Ursa Minor, the faintest star is just under mag 5 so if you can see all seven then you NELM is about 5.

Thanks stu! Also, sorry, ny objective diameter i meant the objective size of the object.

[Stu]

5 minutes ago, Kronos831 said:

Thanks stu! Also, sorry, ny objective diameter i meant the objective size of the object.

Doh! Sorry about that! ??

I checked on Skysafari info for the object but if you Google Messier object apparent size then you will find info out there such as this site:

http://astropixels.com/messier/messiercat.html

[Kronos831]

Thanks stu!The typo was my bad, taking the scope out tommorow!

Hope i can get some good views. Am trying my first globular m53 in Coma berenices.

Best wishes and clear skies,

kronos.

Edited April 22, 2019 by Kronos831
T

[wookie1965]

You cannot beat a dark sky, I have light pollution I was lucky enough go to Galloway last winter,  Friday night was no good but Saturday was a dream the stuff you can see by eye is amazing and deep sky stuff even with my 5" Refractor was superb.

[Stu]

3 hours ago, Kronos831 said:

Thanks stu!The typo was my bad, taking the scope out tommorow!

Hope i can get some good views. Am trying my first globular m53 in Coma berenices.

Best wishes and clear skies,

kronos.

Good luck! Let us know how you get on. You could also try M3 which is nearby and a little brighter.

[kirkster501]

From Bortle 1 skies the North American nebula is easy to see and I have done so numerous times.  I have seen M81 with the naked eye as well under such skies in Northern Russia.  Alas, never seen this from UK.  Not sure there is anywhere in the UK that would get a Bortle 1?

Indeed, from Bortle 1 the sky is almost scary, almost like you could fall into it.

[JSeaman]

Just head north, according to this there are plenty of Bortle 1 up towards Mull etc

https://www.lightpollutionmap.info/#zoom=7&lat=7688165&lon=-467085&layers=B0FFFFFTFFFF

 

[kirkster501]

Yes on the very outskirts of the Hebrides there is a bit of Class 1.  Even Galloway is only 2.

[Gfamily]

Though at this time of year you won't get a decent dark sky so far north. 

But a dark sky makes a huge difference. At the recent Astrocamp, M13 was fantastic against the dark sky, whereas it was very indistinct when viewed at home last weekend. 

I was forced to look at double stars, it was so bad!

[Fraunhoffer]

From my very limited experience of 2 visits to a darker place it made an incredible difference.
E.g with binoculars, at home I have to carefully work out how to hop from place to place to see star clusters and look carefully. 
The 2 visits I have made - no problem - straight there, obvious where they were and they stood out clearly. At the second one, the milky was very clear - something I ve not seen for many years, so many stars, it was actually a bit confusing to pick out some of the constellations.