What's the best way to find an angle subtended in a video?

[Null]

I figured you guys would be the best to ask. If I have a video of a skyline and an object in the sky (say an al jazeera video of a rocket that may have fallen and hit a hospital parking lot), what's the best way to find the angle that object is making with the horizon at the point of the camera? i know trigonometry and i know id use a sextant if i were actually standing at the position of the camera. but doing it from a video seems tricky. any advice?

 

[Mick West]

Can you post a frame or so of the video or a diagram and indicate better what angle you are looking for?

 

[Null]

Of course, sorry. Here's a screen grab. You can see the video in the first few seconds here https://www.channel4.com/news/who-was-behind-the-gaza-hospital-blast-visual-investigation. Of course I'd be most interested in the angle when the rocket explodes (or is intercepted) in the air, but the camera turns upward by that point and the line of lights along the coast (our reference point, though i mistakenly said "horizon") isn't visible, so I have to settle for the angle at this earlier point in its ascent.

 

[Ann K]

You can estimate an angle by holding your hand out at arms length, but of course that doesn't help when you're looking at a video. I think you'd have to have some things of known size and distance (or known subtended angle) in the video.

• The Moon subtends an angle of 1/2°.
• When you look at the Big Dipper, the angular separation of the pointer stars is 5°.
• You can use your hands, held out at arms length, to estimate angles in the sky. Your smallest finger subtends an angle close to 1°. If you spread your fingers and thumb out, the distance between your smallest finger and your thumb subtends an angle close to 20°.

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https://sites.ualberta.ca/~pogosyan/teaching/ASTRO_122/lect2/lecture2.html#:~:text=You can use your hands, held out at,thumb subtends an angle close to 20 o.

 

[Mendel]

If you can determine the FOV of the camera, that would give you the data necessary to compute the angle. However, that often depends on the level of zoom, and is most practical when you have access to the camera.

As Ann noted, if the images can be processed to make celestial objects visible, that is often your best bet, especially when you have time & location. A planetarium software such as Stellarium can help you locate your target in the sky.

Do you know the camera position, and can you identify objects on the coastline? With a map, this would translate to angles.

 

[Null]

Thank you guys, that was very helpful. I've just seen the other thread about this incident, so I'll continue over there.