[Tom]

As I am starting up the process of long distance observations, please help me with a formula.

If I measure from the beach a ship at sea from the front to the back and it is 10 cm long for me and I know the ship is 100 meters long, what then is the distance between me and the ship?

[Pete Svarrior]

If I measure from the beach a ship at sea from the front to the back

How do you intend to accomplish that?

[Thork]

As I am starting up the process of long distance observations, please help me with a formula.

If I measure from the beach a ship at sea from the front to the back and it is 10 cm long for me and I know the ship is 100 meters long, what then is the distance between me and the ship?

10cm long how? 10cm if you hold your arm straight out, 10cm if you hold a ruler 6 inches from your face or 10 cm as measured by your friend stood 20 feet in front of you?

Assume the top of a triangle is your retina, your ruler makes the base of the triangle. Work out how far from your eye the ruler is. Now you have the base (10cm) and the height (distance from your eye). Then extrapolate that triangle as though the base is 100m and work out the new height.

[Tom]

As I am starting up the process of long distance observations, please help me with a formula.

If I measure from the beach a ship at sea from the front to the back and it is 10 cm long for me and I know the ship is 100 meters long, what then is the distance between me and the ship?

10cm long how? 10cm if you hold your arm straight out, 10cm if you hold a ruler 6 inches from your face or 10 cm as measured by your friend stood 20 feet in front of you?

Assume the top of a triangle is your retina, your ruler makes the base of the triangle. Work out how far from your eye the ruler is. Now you have the base (10cm) and the height (distance from your eye). Then extrapolate that triangle as though the base is 100m and work out the new height.

Thank you for your response, but I don't understand it.

I know the ship is 100 meter long.
I see it as 10 cm long from the beach. I can measure it with my thumb and finger.

I guess the ship is 5 kilometers far away, but I am not sure about it.
I would like to know the exact distance between me and the ship.

As I am looking at the ship on the beach I cannot move to a different position for a new different size measurement.
 

[Pongo]

Couldn't your arm length be the "screen" distance?  That's how we used to do it in Boy Scouts.  There was a shortcut table and you measured how many thumb lengths something was.  Plug in the variables and get a rough distance.

[Tom]

Couldn't your arm length be the "screen" distance?  That's how we used to do it in Boy Scouts.  There was a shortcut table and you measured how many thumb lengths something was.  Plug in the variables and get a rough distance.

The scout thing is interesting. I found the info on the internet.

Thank you for the hint!