temperature

[brrttpaul]

I have managed to get hold of some insulated cladding about 3" thick so i can make an obsy, the one side is black the other is white, I know white reflects heat and black absorbs it but would it make much of a difference in the UK, the black (charcoal grey) looks the better colour to have outside but if it compromises the telescope I will have the white outside, would it matter much here?

[Charic]

If both sides are not reflective, ie matt, I would line the obsy with black facing you, to have a darker interior.
If this  cladding is the  complete wall structure, ie. not just an internal feature, then white outermost.

[MARS1960]

Is the cladding for the inside or the outside?

Remember the basic physics lesson that black clothes keep you cooler in the sun than white clothes, you dont want the inside of your obsy getting hot.

[brrttpaul]

both, its white sheet steel then 3 inch thick insulation then black sheet steel, I got the corner fittings and its cut so all i got to do is drill it together, its quite high spec  (fire retardant etc)

 Um isnt that white clothes keep you cooler in the sun lol

[Charic]

Black keeps you cooler, and a hot shower helps cool sunburn! yet  so many folk  still take a cold shower?

 

[brrttpaul]

You sure? pretty sure cricketers wear white because its cooler, white reflects the heat black absorbs it, I think you wrong on that TBH.  thats what I was always taught anyway

[Charic]

7 minutes ago, brrttpaul said:

 white reflects the heat black absorbs it,

Which is why black is cooler, it does not radiate your body heat back to your skin!
There are many articles on the subject, just search the web.

Hard to accept when all along we thought that only white will do?
And back inside the Obsy!, their supposed to be dark in there, are they not? so why not alternate the panels if your undecided!.........nah, folk will question that one?
I still say black inside.

[brrttpaul]

I agree black inside without doubt and white outside, think we had our wires crossed end of

[Charic]

Not necessarily wires  crossed ? If you have black outside, it will tone down the Obsy, making it  less conspicuous, and to be honest if your construction is light-tight, then it makes no difference what colour it is inside until you add any light source, be that red or white, or whatever!
Metal cladding, like those in some metal clad sheds can rust, so treat any scratches or cuts, seal the joints, and install a filtered (lady stockings?) light tight air vent, to keep the bugs out, and the Obsy cool.

[RuralBill]

56 minutes ago, Charic said:

Black keeps you cooler, and a hot shower helps cool sunburn! yet  so many folk  still take a cold shower?

 

You got that wrong I am afraid, black keeps you warmer, everybody knows that.......

always wear lighter colours in the sun....

That is why cricketers wear white.....

 

[Charic]

Clothing, especially black, absorbs sunlight, and if thick enough,  loosely-fitted with some wind blowing past you, the  absorbed heat will be convected away faster than it is absorbed!
Your right, white clothing does indeed reflect sunlight, its true, we all know this, but most folk forget or don't understand the basic physics, that white clothing  also reflects your body heat, sending it back towards your body, so the net effect under identical conditions will be less cooling than if you were to wear black.
Many desert-dwelling folk wear loose-fitting dark clothing, and have been doing so for ages, for this very reason, surely from their own experience, they can't all be wrong?

Cricketers  wear white as was  the assumption back in the 18th century that  its the best colour to reflect heat on a hot summers day, but as cricket was also known as the 'Gentlemans' game, they had to be  smart and tidy,  so what better, but awkward colour to choose , for rolling around on the grass ? But I  think its the norm now,  to play  in  your  white flannels, during test cricket, and a  more colorful club attire for 1 Day Internationals and the like.

Like I said earlier, there is much more theory and information on the internet.

[RuralBill]

Black clothes absorb heat, yes, and then as it is next to your skin it keeps you very warm, as it is extra heat over and above your own generated body heat, (excess heat getting in) so you get too hot, as the material acts as a heater, if you wear white clothes, the heat from outside stays outside, as it is reflected, and the heat from inside ( your body heat) stays stays inside, so you stay at your normal body heat temp, and there is no excess heat getting in.... So you stay at normal temp, which is a lot less than wearing black, so white clothes don't cool you down, you stay the same, but black clothes certainly make you hotter....Simples...

Bill

[brrttpaul]

I honestly cant believe this has come back to haunt me, when I was in school (40yrs ago)  when my science teacher said the best colour for radiators was black as the heat from inside would be released far better, I think we also had  a box which was different colours from white to black and the temperature was higher on the dark side. Trying to convimce my parents to paint my bedroom rad black didnt go down to well with them lol. .  Im doing it white outside and black inside thats it, only reason i asked was the wife would prefer the black outside as it wouldnt stand out so much lol

[Charic]

1 hour ago, brrttpaul said:

black outside as it wouldnt stand out so much lol

.......I  sometimes believe our partners think  that ANYTHING new in the garden "shouldn't be there,  its an eye-sore, and stands out like a sore thumb!"  Until they get used to it 

[MARS1960]

1 hour ago, brrttpaul said:

I honestly cant believe this has come back to haunt me, when I was in school (40yrs ago)  when my science teacher said the best colour for radiators was black as the heat from inside would be released far better, I think we also had  a box which was different colours from white to black and the temperature was higher on the dark side. Trying to convimce my parents to paint my bedroom rad black didnt go down to well with them lol. .  Im doing it white outside and black inside thats it, only reason i asked was the wife would prefer the black outside as it wouldnt stand out so much lol

I honestly wish i had never posted .

[Charic]

...........all part of the fun and being a member of a forum.

[Davey-T]

I remember that experiment from school but can't remember the conclusion, black bodies radiate more heat but don't know if they reflect more heat, if it's heat we're talking about not light.

Dave

[laudropb]

I think that talking about the colour of clothing just confuses the issue. Go to hot countries in the Med. what colour are the buildings ? Have you ever seen a black dome on a professional Obsy ? I rest my case.

[Charic]

Royal Observatory London was Black domed  back in 2010, but the OP has  already decided on the fate of their Observatory now,  so any further debate of  'Black over White'  should really continue in a new thread, if there's still  the  need?

Knowledge is available on the internet, its how its interpreted, but it looks like we will have to agree to disagree for now!
 

[SilverAstro]

4 minutes ago, Charic said:

Royal Observatory London was Black domed  back in 2010, 

if there's still  the  need?

Or desire !

Was any astronomy done from there in 2010 ?

The Tuareg in the sahara seem to wear both white and black turbans, so if they cant decide I'm sure we cant trust the average English batsman to be the arbiter of best togs

The Tuareg women seem to be mostly in black, so perhaps they are the wise ones, what was the question Is it cloudy again ?

 

 

[freewheeler]

Don't forget that this business of white reflecting and black absorbing (true statement) applies only to radiated heat (not conducted or convected) i.e. sunlight if you're outdoors. If you're building in a shaded area it's no big deal which way round you have it as far as temperature is concerned.

p.s. A bit of a silly statement as ideally you would normally build an observatory clear of all  obstructions that are likely to give shade.

[MARS1960]

5 minutes ago, freewheeler said:

Don't forget that this business of white reflecting and black absorbing (true statement) applies to radiated heat i.e. sunlight if you're outdoors. If you're building in a shaded area it's no big deal which way round you have it as far as temperature is concerned.

I concur, but if it's only a partly shaded (AM) area, would the internal space be hotter at sunset if the cladding was applied with black side outside or inside? .

[Louis D]

So, we need clothing that is white on the outside and black on the inside to get optimal summer cooling?  I know that many places cover their black tar building roofs with lighter materials to help reject solar heat gain.  They even put reflective radiant barriers under the roofing material to aid in this.  Sounds like a niche clothing opportunity for someone to exploit. 

[freewheeler]

8 hours ago, MARS1960 said:

I concur, but if it's only a partly shaded (AM) area, would the internal space be hotter at sunset if the cladding was applied with black side outside or inside? .

In theory, with black on the outside, it should be warmer on the inside after a day in the sun. In practice it probably doesn't matter. The proposed building is unlike glass, as in a greenhouse or conservatory where the sun's radiation passes through immediately, is trapped inside and builds up alarmingly. In the proposed building only the outer sheet of steel gets hot, hotter if it's black and less hot if it's white. However that is as far as the radiation gets. from then on it's conduction, slowed down enormously by the choice of insulating material and the fact that conduction is slowed down noticeably when being transferred from one surface to another, both leaving and entering. so as well as the insulation you have "leaving, entering, leaving, entering, leaving" factors slowing down the rate of heat transfer through the building's walls. Meanwhile on the outside breezes are probably removing heat and virtually negating any real difference between black and white. So, just in the case of a building of your construction, I don't think you would notice any difference whichever way round you had the walls.

[Peter Drew]

Try it and see, you can always reverse paint the colours (SWMBO permitting!)