Whether the weather...

[Skywatcher130]

Hi all,  

Is there much difference in the sky quality across the seasons?  It's obviously darker in the winter months therefore there's more observing time,  but is a cold,  crisp November night any different to a clear evening in May? Does the quality of the sky change with temperature or is it just a random combination of events that lead to the ideal seeing conditions? Do you observe over the summer months or just pack away your kit until the Autumn? 

Since owning my scope I have found that I really don't mind being outside in the cold as long as it's not too windy,  and I'm not adverse to getting up really early, but likewise, what if anything can I expect if I were to take my kit on a camping trip in June (assuming clear skies of course ?)

Lastly,  with all this weird weather we've been having lately (storms/floods/heatwaves!)  are things really changing say as opposed to 10/20 years ago, have you noticed a difference?  

Thanks, 

Deb 

[laudropb]

Hi Deb. The problem in summer is that the Sun never goes far enough below the horizon to give astronomical darkness. There is always a sky glow this far North. In summer my observing is mainly restricted to Solar sessions during the day. Of course this requires investing in specialist equipment to ensure safe practices. I do do a little night work, but this is mainly on the Moon.  As for climate change, over the past few years I have seen a drop in the number of sessions I get compared to the past. Is this a permanent situation? I do not think anyone really knows.

[vlaiv]

I think there is difference, as there are couple of factors that depend on temperature.

Firstly, water vapor content depends on temperature, when it's cold it is more likely to have very transparent skies. 70% relative humidity in 20C and 0C differs much in absolute terms (hence we use measure relative humidity). This is the reason for "pitch black" skies in the winter as light pollution scatters of the water vapor as well. Less water vapor - less LP scatter / glow.

Second one is related to general energy content in atmosphere. In winter time there is less energy in atmosphere on our hemisphere (switch for southern hemisphere), and less energy in the system means less motion / turbulence and extremes. Things that we are witnessing recently in terms of increased frequency and intensity of extreme weather is due to this same effect - on global scale. Global warming is causing change in weather patterns all over the place because there is more energy in the system.

One also has to take into account local geography and weather patterns when comparing summer/winter conditions. Here where I live, it's often misty in the winter because we are in the lowlands. There are also seasonal winds of a certain type that have impact on seeing - either improving it or with detrimental effect. Wind blowing steadily over large area flat terrain can actually improve seeing - air motion turns into laminar and there is no much turbulence.

[SteveNickolls]

Hi, thanks for posting. 

I've recently purchased a Unihedron SQM-L meter and one of the things I want to do is record how the light levels change here over the months so hopefully I will be able to produce some figures in the future. Light levels are just one factor in 'sky quality'.

I run my season for astronomy from June to the following May and here's a record of my observing and imaging work since 2012, you can see there's big fluctuations by month and between seasons with 2012-13 and 2016-17 being particularly poor seasons. Don't have data going back any further though for you.

Total number of observing and Imaging sessions-

And imaging opportunities since I began imaging-

I'm old enough not to believe in global warming but accept climate has always been variable in the past. I'd like more clear, dark nights in which to image and observe but have to put up with whatever nature provides. ?

Enjoy your hobby.

Best Regards,
Steve

 

P.S.

Whether the weather be fine,
Or whether the weather be not,
Whether the weather be cold,
Or whether the weather be hot,
We'll weather the weather
Whatever the weather,
Whether we like it or not!

[bingevader]

1 hour ago, SteveNickolls said:

I'm old enough not to believe in global warming but accept climate has always been variable in the past.

Oh dear!

But I guess, you don't have to be a scientist to have an interest in astronomy!

Slightly invalidates your data though....

[vlaiv]

11 minutes ago, bingevader said:

Oh dear!

But I guess, you don't have to be a scientist to have an interest in astronomy!

Slightly invalidates your data though....

Not really, it depends what disbelief is aimed at. Not believing that average temperature is climbing and that there is global warming / average temperature increases is not rational thing - data clearly shows it is so.

Not believing that it is anthropogenic in nature is not irrational thing. Some people may need further confirmation to be fully convinced. Although I personally have no doubt it is anthropogenic in nature as we have no other plausible explanation for it and that this one fits the data and is in my view very rational explanation, others might be more reserved or have alternative explanation that makes more sense to them.

It's not like we can run multiple experiments or have a control sample to raise certainty of it to higher level.

[domstar]

I've noticed that the best conditions are usually at the height of winter. A freezing January sky beats a slightly milder February sky. I usually find autumn is moist and dew is a problem. Summer nights when it's still warm at night have given me spectacular skies too. I look at aeroplane trails. If they hang around a long time, that means the transparency isn't going to be up to much when it gets dark. If I can see tight detail in the fresh trails, I get excited about the night. 

[Astro Imp]

@SteveNickolls your records make interesting reading as they appear to show the current year is the best for which you have records. This is surprising as there have been numerous posts over the last few months claiming this is one of the worst periods for observing in recent memory.
It's always nice to have empirical data rather than just a feeling for the situation.
Thanks for posting.

[Unklewhale]

Heat haze and shimmering of the image will be more significant in Summer months, both from air and ground heat effects.

[bingevader]

2 hours ago, vlaiv said:

Not really, it depends what disbelief is aimed at. Not believing that average temperature is climbing and that there is global warming / average temperature increases is not rational thing - data clearly shows it is so.

Not believing that it is anthropogenic in nature is not irrational thing. Some people may need further confirmation to be fully convinced. Although I personally have no doubt it is anthropogenic in nature as we have no other plausible explanation for it and that this one fits the data and is in my view very rational explanation, others might be more reserved or have alternative explanation that makes more sense to them.

It's not like we can run multiple experiments or have a control sample to raise certainty of it to higher level.

But it was the, "not to believe in global warming...", that prompted the, "Oh, dear!". That at least is irrefutable fact, even Trump agrees it's happening. However, there are still those who would argue the toss over the anthropogenic element!