Scale and horizon

[mrcharly-YHT]

I want to work out the apparent height and size of wind turbines out to sea (from the point of view of someone on the shore). I know the height from the water (260m, the diameter (220m) and the distance out to sea (5km).

Anyone have guidance on how to do this?

[L CC]

https://youtu.be/MMiKyfd6hA0

[D.A.L.E.]

About 10723.354031 arcseconds I think

https://sizecalc.com/#distance=5kilometers&physical-size=260meters&perceived-size-units=dmm

[james]

At this size and distance, it's pretty much just a case that if it's twice the distance, it will look twice as small. So by my rough calculations, if you are looking at the height of the tower (260m), it's equivalent to a 9m telegraph pole 173m away, or if you are looking at the maximum tip height (220+260)m, it's like a 9m pole 94m away.

(Edited to add, this is assuming the blade length is 220m. If it's 110m, then to the blade tip it would be like a 9m pole 122m away!)

[aidan.f]

When I was a sailor before Prat Nav horizon dipping of known height features was a thing for (very approximate) distance. At 5km none of the wind turbine will be obscured
http://www.ringbell.co.uk/info/hdist.htm

LCC, (Lindsay's) reply is the best by far tho' - I wondered why a video link? then yes, watched it 

[jiberjaber]

I want to work out the apparent height and size of wind turbines out to sea (from the point of view of someone on the shore). I know the height from the water (260m, the diameter (220m) and the distance out to sea (5km).

Anyone have guidance on how to do this?

You can use your hand as a rough guide to degrees above the 'orizon and then use trig to calculate?

eg: https://earthsky.org/astronomy-essentials/sky-measurements-degrees-arc-minutes-arc-seconds/#:~:text=The%20general%20rule%20amateur%20astronomers,the%20length%20of%20their%20arms.

[mrcharly-YHT]

About 10723.354031 arcseconds I think

Using inverse tangent, I get 3 degrees. That's 3x3600 arc seconds, or 3x60 arc minutes.

So the 260m wind turbines would be about equivalent to 1.5 finger widths at arms length.

[Socks]

Or you could use Father Ted's method:  These are small (small plastic cows on the table) they are far away (cows in the field)

[mrcharly-YHT]

Sadly, I need reproducible calculations and facts.

There is a windfarm to be built at sea off Lewis. A local very vocal group spout a load of nonsense, but it draws people in. Need to be able to counter it with hard facts that people can verify for themselves.

I'm not at this stage particularly in favour of the windfarm, just don't like nonsense being spoken.

Please check my maths:
Height of turbine = 260
Distance from shore = 5000

Angle = arctan(260/5000) = 3

[D.A.L.E.]

Sadly, I need reproducible calculations and facts.

There is a windfarm to be built at sea off Lewis. A local very vocal group spout a load of nonsense, but it draws people in. Need to be able to counter it with hard facts that people can verify for themselves.

I'm not at this stage particularly in favour of the windfarm, just don't like nonsense being spoken.

Please check my maths:
Height of turbine = 260
Distance from shore = 5000

Angle = arctan(260/5000) = 3

Checks out for me. I linked to my working in an edit above. It handily gives dmm/1mm@1m measurements too.

Mind, this is not taking into account blades, but the blades will be effectively invisible at that distance I reckon.

[Tim Hall]

Sadly, I need reproducible calculations and facts.

There is a windfarm to be built at sea off Lewis. A local very vocal group spout a load of nonsense, but it draws people in. Need to be able to counter it with hard facts that people can verify for themselves.

I'm not at this stage particularly in favour of the windfarm, just don't like nonsense being spoken.

Please check my maths:
Height of turbine = 260
Distance from shore = 5000

Angle = arctan(260/5000) = 3

That looks right. It only goes to the top of the tower, not the tower plus blade, but it's a fair assumption to say the blade will be effectively invisible at that distance.

Don't forget that assumes the observer is standing on the beach. Things will be different if they're on a cliff top, although whether that difference is significant I know not.

[Mr Larrington]

Coat please...

[mrcharly-YHT]

Sadly, I need reproducible calculations and facts.

There is a windfarm to be built at sea off Lewis. A local very vocal group spout a load of nonsense, but it draws people in. Need to be able to counter it with hard facts that people can verify for themselves.

I'm not at this stage particularly in favour of the windfarm, just don't like nonsense being spoken.

Please check my maths:
Height of turbine = 260
Distance from shore = 5000

Angle = arctan(260/5000) = 3

That looks right. It only goes to the top of the tower, not the tower plus blade, but it's a fair assumption to say the blade will be effectively invisible at that distance.

Don't forget that assumes the observer is standing on the beach. Things will be different if they're on a cliff top, although whether that difference is significant I know not.

Yes, if they are up a hilltop the horizon changes quickly, so it isn't quite right.

Still gives a decent idea of the scale.

Sadly, the night-time lights will be quite obtrusive.

[TheLurker]

Sadly, the night-time lights will be quite obtrusive.

Granted this is a matter of taste and personal preference, but, having seen the wind-farms off the North Kent coast (Whitstable - Herne Bay) at night, I find the nav/warning lights quite a pretty sight. 

[Tim Hall]

Coat please...

Third reference so far in this thread...DKUATB.

(My Young Lady bought me a plastic cow. It has starred in a photo with Real Cows a suitable distance away in the background)

[Asterix, the former Gaul.]

When sailing my boat in a dead flat calm I suddenly discovered that when I stood up a navigation buoy could be seen on the horizon. As soon as I sat down it disappeared. I tried it several times. Next thing I saw was the head of a grey seal watching me from the water as if wondering what was going on.

I have sailed through wind farms. It’s very easy to find yourself being swept towards the turbine pillars, if you don’t pay enough attention to the tidal flow.  The look pretty huge close up.

[Asterix, the former Gaul.]

Sadly, the night-time lights will be quite obtrusive.

Granted this is a matter of taste and personal preference, but, having seen the wind-farms off the North Kent coast (Whitstable - Herne Bay) at night, I find the nav/warning lights quite a pretty sight.

In France the land-based turbines used to flash independently. It was weirdly disorientating. Now they have got them synchronised which is rather boring.

[Jaded]

When sailing my boat in a dead flat calm I suddenly discovered that when I stood up a navigation buoy could be seen on the horizon. As soon as I sat down it disappeared. I tried it several times. Next thing I saw was the head of a grey seal watching me from the water as if wondering what was going on.

I have sailed through wind farms. It’s very easy to find yourself being swept towards the turbine pillars, if you don’t pay enough attention to the tidal flow.  The look pretty huge close up.

That is because they are not far away.

[mrcharly-YHT]

When sailing my boat in a dead flat calm I suddenly discovered that when I stood up a navigation buoy could be seen on the horizon. As soon as I sat down it disappeared. I tried it several times. Next thing I saw was the head of a grey seal watching me from the water as if wondering what was going on.

I have sailed through wind farms. It’s very easy to find yourself being swept towards the turbine pillars, if you don’t pay enough attention to the tidal flow.  The look pretty huge close up.

Careful, according to Flerfers, you are a delusional shill for globe earth.