What % of the sky can i see?
Discussion
MartG said:
As height tends to infinity, visible sky tends to 100%
On the surface, the horizon is at 0 degrees elevation all around you - you can see all parts of the sky with a +ve elevation for your location, but can't see any of the sky with a -ve elevation - so you can see 50% of the sky
This.On the surface, the horizon is at 0 degrees elevation all around you - you can see all parts of the sky with a +ve elevation for your location, but can't see any of the sky with a -ve elevation - so you can see 50% of the sky
MartG said:
As height tends to infinity, visible sky tends to 100%
On the surface, the horizon is at 0 degrees elevation all around you - you can see all parts of the sky with a +ve elevation for your location, but can't see any of the sky with a -ve elevation - so you can see 50% of the sky
At 0 elevation, sightlines from both poles would indeed be straight and make 180 degrees.On the surface, the horizon is at 0 degrees elevation all around you - you can see all parts of the sky with a +ve elevation for your location, but can't see any of the sky with a -ve elevation - so you can see 50% of the sky
But there is a bit missing between them that represents the diameter of the earth. So whilst a view from each pole will see 180 degrees, there is a thin slice missing... to see ALL the sky you need to get higher so the angle becomes more than 180 degrees.
This is doing my head in...I mean, if we can see 50% of the sky, then by the time a plane is over the horizon, perhaps in 5 mins, it would be seen over the horizon by someone standing on the other side of the Earth...so that does not make sense to me.
Maybe if I elaborated a bit...imagine the Earth was at the centre of the Sun..so we would see an area of x sq Km on the 'surface' of the Sun....so this would be y% of the total area of the Sun...now, from what I know of maths (CSE grade D and A level grade E!!), is that if there was a bigger sphere put there instead of the Sun, then the ratio would not change i.e. we would still see the same % of the area of the sphere...
Dunno if the question makes sense....head hurts just thinking about it
Maybe if I elaborated a bit...imagine the Earth was at the centre of the Sun..so we would see an area of x sq Km on the 'surface' of the Sun....so this would be y% of the total area of the Sun...now, from what I know of maths (CSE grade D and A level grade E!!), is that if there was a bigger sphere put there instead of the Sun, then the ratio would not change i.e. we would still see the same % of the area of the sphere...
Dunno if the question makes sense....head hurts just thinking about it
dkatwa said:
This is doing my head in...I mean, if we can see 50% of the sky, then by the time a plane is over the horizon, perhaps in 5 mins, it would be seen over the horizon by someone standing on the other side of the Earth...so that does not make sense to me.
But if you are standing at the North pole and some penguin shagging planespotter is at the South pole, then once the aircraft gets over your horizon it is below you, but still below the penguin shagger. Therefore not part of either sky.To put it another way, if the earth was transparent and you both looked down, you would both see exactly the same angle as if you looked up, but you would both see the aircraft at the same time.
0000 said:
MartG said:
As height tends to infinity, visible sky tends to 100%
On the surface, the horizon is at 0 degrees elevation all around you - you can see all parts of the sky with a +ve elevation for your location, but can't see any of the sky with a -ve elevation - so you can see 50% of the sky
This.On the surface, the horizon is at 0 degrees elevation all around you - you can see all parts of the sky with a +ve elevation for your location, but can't see any of the sky with a -ve elevation - so you can see 50% of the sky
Kawasicki said:
0000 said:
MartG said:
As height tends to infinity, visible sky tends to 100%
On the surface, the horizon is at 0 degrees elevation all around you - you can see all parts of the sky with a +ve elevation for your location, but can't see any of the sky with a -ve elevation - so you can see 50% of the sky
This.On the surface, the horizon is at 0 degrees elevation all around you - you can see all parts of the sky with a +ve elevation for your location, but can't see any of the sky with a -ve elevation - so you can see 50% of the sky
Assuming your eyes are a small but non-zero height above the ground, you can see a tiny smidge more than 50% of the sky.
The Earth is preventing you from seeing a tiny smidge less than 50%.
Dr Jekyll said:
SpeckledJim said:
The horizon is actually slightly below your eyes, at the same elevation as your feet.
Slightly lower than your feet, don't know how to calculate how much lower though.Good pedanting.
SpeckledJim said:
OK, lower than the centre of gravity of your feet. Basically level with the soles of your feet, or shoes.
Good pedanting.
No, lower than that. How low depending on your eye level. If you could see half way round the world the horizon would be nearly 4000 miles lower. Good pedanting.
dkatwa said:
This is doing my head in...I mean, if we can see 50% of the sky, then by the time a plane is over the horizon, perhaps in 5 mins, it would be seen over the horizon by someone standing on the other side of the Earth...so that does not make sense to me.
Maybe if I elaborated a bit...imagine the Earth was at the centre of the Sun..so we would see an area of x sq Km on the 'surface' of the Sun....so this would be y% of the total area of the Sun...now, from what I know of maths (CSE grade D and A level grade E!!), is that if there was a bigger sphere put there instead of the Sun, then the ratio would not change i.e. we would still see the same % of the area of the sphere...
Dunno if the question makes sense....head hurts just thinking about it
The sky is infinite - so as a percentage of the available sky the diameter of any object is equivalent to 0%. Maybe if I elaborated a bit...imagine the Earth was at the centre of the Sun..so we would see an area of x sq Km on the 'surface' of the Sun....so this would be y% of the total area of the Sun...now, from what I know of maths (CSE grade D and A level grade E!!), is that if there was a bigger sphere put there instead of the Sun, then the ratio would not change i.e. we would still see the same % of the area of the sphere...
Dunno if the question makes sense....head hurts just thinking about it
Dr Jekyll said:
SpeckledJim said:
OK, lower than the centre of gravity of your feet. Basically level with the soles of your feet, or shoes.
Good pedanting.
No, lower than that. How low depending on your eye level. If you could see half way round the world the horizon would be nearly 4000 miles lower. Good pedanting.
I still say it depends what you mean by "the sky".
If you mean the blue sunlight that reaches your eye by Rayleigh scattering in the daytime then (assuming the earth is a sphere and your eye is at ground level) you see a perfect hemisphere centred on you. I'd argue that is 100% of the sky by that definition. That sky isn't a "thing" you can measure fractions of.
If you think of the sky as a physical sphere then you have a radius and can calculate the area of the spherical cap you can actually see allowing for the earth being in the way, and compare with the area of the whole sphere you could see if the earth disappeared (4 pi r squared).
I haven't plugged in numbers but it might be interesting to compare:
a) a sphere that's uniform cloud cover one mile up.
b) a sphere that's the night sky; say just our galaxy (a few hundred thousand light years)
My guess is that for (a) you'd see considerably less than 50% of the cloudbase but for (b) you couldn't possibly calculate the difference from 50%.
If you mean the blue sunlight that reaches your eye by Rayleigh scattering in the daytime then (assuming the earth is a sphere and your eye is at ground level) you see a perfect hemisphere centred on you. I'd argue that is 100% of the sky by that definition. That sky isn't a "thing" you can measure fractions of.
If you think of the sky as a physical sphere then you have a radius and can calculate the area of the spherical cap you can actually see allowing for the earth being in the way, and compare with the area of the whole sphere you could see if the earth disappeared (4 pi r squared).
I haven't plugged in numbers but it might be interesting to compare:
a) a sphere that's uniform cloud cover one mile up.
b) a sphere that's the night sky; say just our galaxy (a few hundred thousand light years)
My guess is that for (a) you'd see considerably less than 50% of the cloudbase but for (b) you couldn't possibly calculate the difference from 50%.
The OP's original question might have better been phrased referencing 'atmosphere' rather than 'sky'. That's how I read it until all the pedants got involved to confuse things with arguing over the definition of 'sky'! 
Of course the answer depends on how thick you decide the atmospheric ring around the earth is, and I can't be bothered to take this any further.
Of course the answer depends on how thick you decide the atmospheric ring around the earth is, and I can't be bothered to take this any further.
Gassing Station | Science! | Top of Page | What's New | My Stuff