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Heat pollution... as bad for observing as light pollution?


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I noticed over time that the best solar observing sessions I've had always tend to be when I am observing anywhere away from home and I've had lunar sessions away from home and noticed the views were consistently better also.

I live in a relatively new estate (maybe 20 years old or so) where the plots are quite small so the houses are quite close together, gardens are small, and everyone tarmacs as much of their drive as possible to maximise parking.

This means lots of surfaces putting out heat during the day and well into the night and this has a significant man-made impact on the seeing but heat pollution isn't something I've ever really heard talked about.

I find that looking out over a nice grassy field or forest tends to be best for avoiding ground heat, or even better observing from the side of a hill where the ground falls quickly away from you so your line of sight more quickly passes above the murk is good.

So I've been scouting good locations for solar and lunar observing away from home, looking for spots with easy parking next to southish facing fields and forests, or southish facing hill faces.

Light pollution isn't a concern and safety isn't a concern and this kind of observing  is at more civilised times of day (safety is one of the reasons I don't go to dark sites on my own).

I wondered what others think about this. Sometimes I read reports of great solar and lunar views that I rarely seem to match at home but when I go somewhere what I see is closer the the results that I read from others.

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Absolutely right. High powered planetary, lunar and solar viewing needs good seeing, and your observing location affects this a lot.

Seeing conditions can be atmospheric or local/man made. The former you can’t affect, the latter you certainly can do something about.

All the points you make are correct; concrete and tarmac are very good heat absorbers and then release this heat during the evening. Central heating flumes are terrible for seeing, and poorly insulated houses also cause convection currents above then. I used to find that planetary and lunar observing was always best when the target was between the gaps between my house and the neighbours.

Observing on grass, over open land can really help reduce this, but I also find that the early hours of the morning are often best as central heating is off and most things have cooled down so are no longer causing convection currents.

For Astro viewing the recommendation is always to observe targets at their highest. However for solar viewing it is often best to observe in the early morning or evening. This is when the atmosphere is coolest and stillest; at midday the air can be very turbulent so the views are often worse then. Even though the sun is lower at the beginning or end of the day, the views are often best.

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3 hours ago, Stu said:

Absolutely right. High powered planetary, lunar and solar viewing needs good seeing, and your observing location affects this a lot.

Seeing conditions can be atmospheric or local/man made. The former you can’t affect, the latter you certainly can do something about.

All the points you make are correct; concrete and tarmac are very good heat absorbers and then release this heat during the evening. Central heating flumes are terrible for seeing, and poorly insulated houses also cause convection currents above then. I used to find that planetary and lunar observing was always best when the target was between the gaps between my house and the neighbours.

Observing on grass, over open land can really help reduce this, but I also find that the early hours of the morning are often best as central heating is off and most things have cooled down so are no longer causing convection currents.

For Astro viewing the recommendation is always to observe targets at their highest. However for solar viewing it is often best to observe in the early morning or evening. This is when the atmosphere is coolest and stillest; at midday the air can be very turbulent so the views are often worse then. Even though the sun is lower at the beginning or end of the day, the views are often best.

Thanks, I do actually have a thin wedge looking towards about east-south-east from my garden that is trees/fields which means observing the sun in the morning and over better terrain is possible from home but only for a short time if I'm organised and time it right.

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Yep, have just this minute managed to get some time to observe WL solar. The heat output from my patio and surrounding surfaces is pretty intense and made the local viewing quite poor and turbulent. 

My experiences of best seeing is usually earlier in the morning, sometime in the evenings I still suffer with some high heat transfer. Similarly if it’s ever sunny in late autumn and winter, these can be good times to observe. 

I do make more of an effort to place my tripod on turf when I observe these days, both day and night. I struggle with the dob though as my garden isn’t very level. Pity really, as it’s the larger tubes that struggle the worst from this effect.
 

 

 

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I agree wholeheartedly, yet I often get good views from my middle of town garden as long as I set up not too close to my house. Looking over the rooftops is usually ok if sun/moon are at a high enough altitude. Otherwise, I'll try to time observing sessions to avoid looking over the rooftops.

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@Paz and others. Absolutely right. We tend to ignore daytime convection effects because they aren't readily seen or felt in day to day life.

You can still get these effects away from urban centres. During early flying training I was 'doing circuits' on a small grass strip airfield with a short runway.
On the climb out the aircraft rolled left by a good 30 degrees. I was less than 200ft above ground so a roll was a bit worrying to me.
I commented it must be a thermal effect as we were over the boundary between two fields with different crops.
I  said that I would avoid it next time around. The instructor said NO - use it.
Next time around, by flying completely over the hot field, the aircraft suddenly gained 50ft. A lot of convection current!
There are well known similar effects over quarries, railway lines and more.

Power stations are another source of convection. Coal/oil/gas burners are often 35% (or a bit more) thermally efficient.
This means almost double the power station rated output goes somewhere. Much as heat into the air.
Mostly from the flue/chimney, but cooling towers are a consideration. This is gigawatts of heat - millions of kettles.
Something to think about if you are searching out a dark site away from a town.
Though a lot of power stations seem to find it necessary to illuminate their surroundings instead of sending the energy down the wires.🥴
One way of helping us to choose dark sites elsewhere.

 
 

 

 

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On 14/05/2022 at 09:34, Stu said:

However for solar viewing it is often best to observe in the early morning or evening.

I have found this. With a single stack Lunt 50 I get much steadier viewing in the late afternoon and evening. More importantly, for me, I also get much better contrast on the Ha features.

Malcolm

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I do more imaging than visual observing, but when doing solar, I try and set up first thing in the morning, to image around mid morning. By that time, the Sun has risen moderately high in the sky, but before the real heat of the day has built up and before heat is being radiated back up to any significant amount. Mid afternoon is worst and by evening, while thermal currents may be decreasing, so is the altitude of the Sun. So mid morning is always my preference.

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