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does elevation make that much difference


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In this part of Scotland we are well supplied with mountains but having tried observing at sea level and about 1200 feet I have to admit that not much if any difference have I noticed. All serious observatories seem to be up mountains and I find myself wondering how high you have to be to improve visibility?

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The lower you are the more atmosphere there is between your scope and space. The atmosphere is turbulent and causes a shimmering effect on observed objects. The higher up your scope is, then obviously the less atmosphere there is refracting light from stars. You can prove this at any elevation buy looking at stars on the horizon and stars at the zenith. You're always looking through more atmosphere when viewing close to the horizon.

Professional obsys tend to be not only high up but also in areas where they are least affected by weather. But to all intents and purposes, for the amateur observer, the elevation of the object is probably more important - everything looks better the higher it is in the sky. Hth :)

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I'm at 1300ft - the only difference it makes is that often we are above the fog blanket and that helps. Other times we are just inside the clouds! To make a real difference you need to be say 6000ft plus. When I travel by plane I often wonder what it would be like to observe at say 30,000 feet where the blue daylight sky looks almost black?

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I'm at 1300ft - the only difference it makes is that often we are above the fog blanket and that helps. Other times we are just inside the clouds! To make a real difference you need to be say 6000ft plus. When I travel by plane I often wonder what it would be like to observe at say 30,000 feet where the blue daylight sky looks almost black?

I was listening to an interview with an astronaut who had been round the dark side of the moon and he said that in space and with no sun glare there were so many stars the sky appeared grey rather than black. Want to go there with a scope.

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The only problem with observing at a much higher elevation is that eventually the atmosphere gets so thin that you need a constant supply of oxygen as you can't get enough from the air around you. It certainly helps to be above a cloud layer or two though ;).

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I was listening to an interview with an astronaut who had been round the dark side of the moon and he said that in space and with no sun glare there were so many stars the sky appeared grey rather than black. Want to go there with a scope.

I bet it was cold though?

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The main reason why modern observatories are built at such high altitudes, is due to clearer air, less atmospheric disturbance etc.

But I live on a mountain in Wales, about 1000 feet ASL, and I find it does make a difference. Objects that are often described as "low altitude" I find to be much higher above the horizon than at sea-level. It means Sagittarius is much easier to spot (apart from the neighbor's beech tree).

The best thing is to get out onto the summit of a large hill or mountain, where you get that "endless sky" effect...

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Unfortunately I don't think a few hundred feet, more or less, is going to make much difference? Having a dark site with clean air will. Your location in Dunoon is a good spot when the clouds clear :rolleyes: I was lucky enough to stay just out of Dunoon a few years back and took my 12" lx200. Managed to see a few galaxys not seen before or since from the Midlands :huh::smiley:

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I think it makes a big difference indeed, especially in hilly areas where temperature inversion, and trapped air can ruin everything down below. It's almost exponential too, so the first few 1000' you can go up make the biggest difference.

Flying everyday - in my job - I marvel at the night sky when I'm on the night shift, and feel very optimistic for some observing or photographing that night, descending down to land those last 1000' or so where all the junk in the air lingers and on the ground, that great black sky is gone!

/Jesper

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If you ever get to go high up in the Andes... 3000+ metres, the thing that strikes you (apart from the lack of oxygen!) is the clarity of the air.

Mountains on the horizon appear razor sharp as the air really is thinner and there is also very little water vapour in the air.

Perfect viewing, but make sure you don't have heavy gear to carry around!

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Air density also decreases with height also as well as the atmosphere getting thinner from top to bottom, both of these factors should help, not that I ever tested it. The difference is appreciable, to put a measure on it, your cuppa will boil at around 70 degrees Celsius if you did all your observation on top of Everest, no way to keep warm, so I'll stay down low :D

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I suspect that on a given night, being on top of a hill could make a significant difference. This is due to the immediate environment not being close to the ground. The free wind is much steadier and the air more stable.

In my light aircraft flying days, there was sometimes a huge difference in the stability of the air near the ground, and at altitude.

On some days it would be really bumpy after take off. Gradually improving until you got to around 2000ft above ground when it became smooth.

This effect is a combination of turbulence from the lie of the land and man made structures, as well as thermals.

Once quite early in training I had a really good example of the effect of thermals. On a climb out at around 200/300ft, the plane suddenly rolled 30deg to the right. The instructor told me it was the difference in heat rising from two farm fields, left and right. We were over their border. Next time around I deviated to the left to go over the 'hot' field and the plane lifted (level this time) about 100ft in a couple of seconds.

OK this was a summers day. But at night as the land cools, this effect has to there again.

Over to the experts.....

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I used to find that heading into the Blackdowns south of Taunton made quite a difference, even though the elevation change was only something like 700ft. You often get above the fog and whenever the wind was from the east or south east the valley Taunton is in fills up with murky air. Going up just a short distance made quite a difference. The flip side though was in autumn the hills would often have the fog and the valley wouldn't...

James

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Objects that are often described as "low altitude" I find to be much higher above the horizon than at sea-level.

Hmm - the Earth is a very big ball and mountains are not very tall relative to it. I think being on top of 1000m mountain only alters your apparent horizon by about 1 deg.

NigelM

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Hmm - the Earth is a very big ball and mountains are not very tall relative to it. I think being on top of 1000m mountain only alters your apparent horizon by about 1 deg.

NigelM

I think what the OP is seeing is that the horizons are lower, so objects appear less obstructed.

Being on top of a mountain means there's less air between you and your target. At 2000m ASL, the barametric pressure is about 780, c.f. 1000-ish at sea level. That means that 20% of the atmosphere is out of the way. However being on top of the right mountain means you have chosen a site with laminar air flow, so you could well get seeing of 1 arc-sec or thereabouts.

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