MOA question

[danprkr]

I know that Minute of Angle = 1" group @ 100 yards. 2" @ 200 etc, and I know that I usually shoot about 4 MOA since I'm a lousy rifle shot. What I don't know is how the term MOA came into being. Any ideas?

Just curious.

Dan

 

[youngda9]

MOA is not 1" at 100 yds, it is 1.0471996"

 

[mitch127]

360 degrees in a full circle, 60 minutes per degree

1 MOA = 0.0046% of a circle

 

[taliv]

or asked a different way, why do we say "one quarter MOA" instead of "15 SOA" ?

 

[Vern Humphrey]

A circle is divided into 360 degrees -- this was developed by the ancient Babylonians.

Later as more precision was required, Europeans divided a degree into 60 tiny parts, calling them partes minutes -- hence our term "minute." Hours of time were also divided that way, so we make sure people understand we are talking about angular measurement by using the term "minute of angle."

There are 21,600 (360 X 60) minutes of angle in a circle.

Since the circumfrence of a circle is calculated by the formula C = Pi * D, if we take a circle with a 100 yard radius (200 yard diameter) and convert that to inches (200 * 36 = 7,200), we get a circumfrence of 3.1416 * 7,200 = 22,620 inches.

So we see a minute of angle subtends about 22,620/21,600 or 1.0472 inches.

(just in passing, I might note that both minutes of time and minutes of angle were further divided into 60 partes minutes secondes, or "seconds.")

 

[benEzra]

What I don't know is how the term MOA came into being. Any ideas?

It stands for Minute Of Arc, or alternatively Minute Of Angle, which is an old term for an arcminute. 1 arcminute/1 MOA equals 1/60th of a degree, and is fairly widely used in astronomy and optics, although radians/milliradians are gradually overtaking it, I think.

http://en.wikipedia.org/wiki/Minute_of_arc

 

[danprkr]

Very interesting and informative. Not sure I could do the math, but I do now understand the concept better.

Thank you folks.

Dan