What is a good sky?

[Juan Carlos]

Hello:

What is a good sky for observing. Is there a minimal requeriment or standard?

Kind regards

JC

[hobsey]

I don't think there really is a minimum, a good sky is one with no clouds in it.

[Pete Presland]

yep one without clouds would do at the moment, i supose the bortle scale is as good a measurement as any http://en.wikipedia.org/wiki/Bortle_Dark-Sky_Scale

[Qualia]

Hello:

What is a good sky for observing. Is there a minimal requeriment or standard?

Kind regards

JC

For stargazing it has to be a relatively clear, dark sky. My own subjective preference considers an average 3 out of 5 night sky is one where I can clearly see the Milky Way above my head but without any significant detail to it, the principal stars of Ursa Minor are clearly visible naked eye, as is something like M 31, there's less than a total of an estimated 20% cloud and the stars are not twinkling 10º to 15º above the horizon.

Hope that helps

[ghostdance]

From here, little to no orange would be nice (thank you Stratford & Olympic Park). No twinkles = little higher air turbulence = good. No clahds, especially those pesky high net-curtain ones, and for me being able to make out (just) the principal stars in Lyra & not just Vega (which is more usual). Then a good night is had by all! Haven't a mole's-eye chance of seeing a naked Milky Way as such from 'ere....but then my eyes are rather old & like my wits, dim...

Should have got into this when I was young, but then I was happy in the haze of a drunken hour or binoculars so never thought of a scope 

[jetstream]

Hello:

What is a good sky for observing. Is there a minimal requeriment or standard?

Kind regards

JC

It sort of depends on what you want to view, good "seeing" and clear, sharp skies don't always coincide. Good seeing provides great planetary/lunar views and has light cloud or haze up there at times. For DSO dark, clear and transparent skies are most important IMHO.

[acey]

For deep sky observing, a good sky is one in which you can clearly see the Milky Way, and stars don't look hazy. Cloud is fine as long as its moving and there's a likelihood of long clear spells.

For planetary observing the answer has already been given: steady air, i.e. good "seeing". For DSOs you want good "transparency", i.e. the faintest possible limiting magnitude.

"Sky quality" is often measured by zenith limiting magnitude, or else using a Sky Quality Meter, which measures luminance, and is aimed at the zenith. But the overall quality of the sky at a dark site is affected by light domes on the horizon from distant towns.

At urban/suburban locations you can have a good sky for lunar/planetary viewing, but never for DSO. There are only varying degrees of bad - though it can still be possible to see some of the brightest targets.

[Juan Carlos]

Thank you for your replies!

I live in a place far away 25 km from the nearest town, in the mountains, where I can see the Milk Way, and a lot of minor stars are visible. Unfortunately, there are clouds frecuently on Autum, last year 40 consecutive days cloudy. I hope in Winter the sky will be clear for observing deep space.

[Gazabone]

Interesting opinions here, helped me too, thanks Pete for starting the thread.

[glowingturnip]

Thank you for your replies!

I live in a place far away 25 km from the nearest town, in the mountains, where I can see the Milk Way, and a lot of minor stars are visible. Unfortunately, there are clouds frecuently on Autum, last year 40 consecutive days cloudy. I hope in Winter the sky will be clear for observing deep space.

whereabouts are you, Juan Carlos ?  I do my imaging and observing at our place in Montes de Malaga, not far from Casabermeja.  Cracking skies I'd say, much better than here in London !  I think some of the local astronomers go up the Torcal on a clear night.

Bortle scale I'd say 3.5, maybe 3.  

[stevetynant]

Thank you for your replies!

I live in a place far away 25 km from the nearest town, in the mountains, where I can see the Milk Way, and a lot of minor stars are visible. Unfortunately, there are clouds frecuently on Autum, last year 40 consecutive days cloudy. I hope in Winter the sky will be clear for observing deep space.

That's interesting Juan Carlos .in the last two years there has not been a period in excess of 9 nights where you could not have enjoyed an observing session in s Wales and this must be one of the wettest places in Europe lol

[Juan Carlos]

whereabouts are you, Juan Carlos ? I do my imaging and observing at our place in Montes de Malaga, not far from Casabermeja. Cracking skies I'd say, much better than here in London ! I think some of the local astronomers go up the Torcal on a clear night.

Bortle scale I'd say 3.5, maybe 3.

Yes, I'm near Casabermeja and at 15 km from El Torcal (this last is a good place for observing)

[Juan Carlos]

That's interesting Juan Carlos .in the last two years there has not been a period in excess of 9 nights where you could not have enjoyed an observing session in s Wales and this must be one of the wettest places in Europe lol

Yes, this mountains in Malaga are very cloudy in autum, without serious rain but the fog is present every day while in Málaga is sunny!

[Qualia]

I'm finding the same here, Juan. On a good night the skies are okay - I'm about twenty minutes outside Xàtiva in Valencia region - and I'd estimate a Bortle scale of about 4. However, over the summer I noticed that although the skies were clear and sun shining blue, by evening they were completely clouded over. It's also quite a hilly area and I've kept a record since July (since moving here) and I've had about 14 clear evenings in the last 50 or so Back up north in Aragón the situation was the opposite. Although where I used to live had worse light pollution, I'd count about 12 cloudy nights in 50 clear ones.

From this experience and also traveling around Spain quite a bit, I guess to find optimum skies here would be to move slightly away from the coast, more inland. I'm thinking that the arid lands around Teruel or Los Monegros would be perfect. Bortle scale 1 and beyond  

[Juan Carlos]

I'm finding the same here, Juan. On a good night the skies are okay - I'm about twenty minutes outside Xàtiva in Valencia region - and I'd estimate a Bortle scale of about 4. However, over the summer I noticed that although the skies were clear and sun shining blue, by evening they were completely clouded over. It's also quite a hilly area and I've kept a record since July (since moving here) and I've had about 14 clear evenings in the last 50 or so Back up north in Aragón the situation was the opposite. Although where I used to live had worse light pollution, I'd count about 12 cloudy nights in 50 clear ones.

From this experience and also traveling around Spain quite a bit, I guess to find optimum skies here would be to move slightly away from the coast, more inland. I'm thinking that the arid lands around Teruel or Los Monegros would be perfect. Bortle scale 1 and beyond

Very insteresting info, Qualia.

Your reference is the Bortle scale, I don't know this scale, and I will look how it works.

Thank you!

[Qualia]

Take it with a pinch of salt, Juan It's pretty vague for my liking and doesn't take into account all the nightly nuances I still prefer going by my description above

[Special K]

Hi Juan Carlos, the quick answer would be:  a good sky is one that you enjoy and come in from your session feeling like you've achieved something! 

But a longer answer based on my limited experience (and a goodly amount of reading about seeing and transparency), is a good sky is subject to a great many factors of everyday life on Earth, which combined, determines if the conditions are good or not.  One thing that struck me getting deeper into Astro is how we are cast into the role of Meteorologist, Optician, and all sorts in order to understand our hobby that bit better and improve the experience!

Seeing will be subject to the turbulence of the air between us and the target and may limit the magnification we can apply, thus typical targets which can take a hearty amount of mag like planets and double stars need a good steady atmosphere.  The Antoniadi Scale or similar is used by many to describe the conditions on the night and there are some great images on the net if you look this up to show the appearance of the airy disk and diffraction rings against the five scales. 

I had read (and believed) that transparency was just the amount of water vapor in the air, but this isn't totally correct.  A degradation of transparency could be any matter getting between us and the target including pollution, smog and smoke, etc.  What seems typical is that Seeing and Transparency often work in different circles and it can be rare to get both overnight, which is a shame.  But good transparency is the time to pursue low power views and DSO's for sure.  Sadly, transparency is a delicate thing and often disrupted by light pollution and humidity, and seems the hardest to come by.  

Regarding the minimum requirements you asked, I think it would have to be answered for each type of thing you wanted to view, but here's hoping you get the good skies to view them! 

[ollypenrice]

You are not far from some of the best skies in mainland Europe, though, Juan Carlos. Calar Alto takes some beating! 

When you go into the Alpujarras it is incredible how the weather changes (as shown by the vegetation) as you move north east. In a few kilometres it changes from green to semi-desert. Inland from Almeria is excellent. Perfect for weekends away. 

My good sky shortlist says,

No cloud

Dry atmosphere

Low turbulence

No wind

No light pollution

High altitude.

Finding that lot all at once doesn't happen every day!

Olly

[Knight of Clear Skies]

With a long enough ladder to stand on every locale has a good sky. Unfortunately this is about as helpful as Archimedes famous quote.

A good sky for me up here in Hertfordshire is just being able to make out the Milky Way, Andromeda and 7 stars in Ursa Minor.

[Juan Carlos]

You are not far from some of the best skies in mainland Europe, though, Juan Carlos. Calar Alto takes some beating!

When you go into the Alpujarras it is incredible how the weather changes (as shown by the vegetation) as you move north east. In a few kilometres it changes from green to semi-desert. Inland from Almeria is excellent. Perfect for weekends away.

My good sky shortlist says,

No cloud

Dry atmosphere

Low turbulence

No wind

No light pollution

High altitude.

Finding that lot all at once doesn't happen every day!

Olly

Thank you. I did't knew about Calar! Alpujarras us a commun weekend place for people around. This sound fantastic.

Your list is very interesrimg too!

Greetings

[Juan Carlos]

With a long enough ladder to stand on every locale has a good sky. Unfortunately this is about as helpful as Archimedes famous quote.

A good sky for me up here in Hertfordshire is just being able to make out the Milky Way, Andromeda and 7 stars in Ursa Minor.

a very clear concept of a good sky indeed!

[dick_dangerous]

Here in London, a good sky is one where the Light Pollution isn't reflecting too badly off the air pollution. It's quite rare to get that golden combo though.

Speaking of Spain, the skies in Asturias are pretty spectacular. I'd have loved to have driven up to Covadonga lakes with my scope but frankly the road from our holiday cottage scared the bejeebers out of me even in daylight, let alone the thought of driving up that mountain road in pitch darkness... There are similar fog-bound problems there too. But then Bushy Park is a fog trap too, so you can't win. I do remember staying near Gaucín and the stars being spectacular in late August - Scorpio rises to shine as it should, one of the most spectacular constellations in the sky!

I am envious...

DD

[Algieba]

Great list!

You are not far from some of the best skies in mainland Europe, though, Juan Carlos. Calar Alto takes some beating! 

When you go into the Alpujarras it is incredible how the weather changes (as shown by the vegetation) as you move north east. In a few kilometres it changes from green to semi-desert. Inland from Almeria is excellent. Perfect for weekends away. 

My good sky shortlist says,

No cloud

Dry atmosphere

Low turbulence

No wind

No light pollution

High altitude.

Finding that lot all at once doesn't happen every day!

Olly

Also a good time to observe is when the moon not when the moon is full as it makes it too bright to see dimmer stars, the closer the phase is to new, the better.

[kirkster501]

Very rare we get dark and transparent skies in the UK.  A handful per year if that.  Indeed, in recent winters being able to see the stars at all has been an achievement.