Noctilucent Cloud from London this morning July 19

[nytecam]

Better luck this morning with NLC very low on NNE horizon over London recorded from bedroom window ;-) 

How do you estimate the NLC range from its altitude above the horizon knowing the angular width of the photo?  

Nytecam

 

[Tiki]

There are a few ways to estimate the cloud-range.

 

eg.   angular distance per pixel= angular distance across photo / no. of pixels across photo

angular height of NLC = (height of NLC above horizon in pixels) x (angular distance per pixel)

From trigonometry, tangent( angular height of NLC)= height of NLC / distance to a point directly below the NLC

If we suppose that the earth is flat and NLC's reside at 50 miles altitude, then

distance to a point directly below the NLC in miles = 50 x  tangent( angular height of NLC).

You can calculate the range( hypotenuse) using Pythagoras.

All approximate but good enough for a rough idea.

 

So approximately how far away are the clouds?