MOA, Minute Of Angle. At 100 yds it's 1.0471996". Rounded off to an inch.
So where'd that come from?
The circle is divided into 360 degrees, and that's derived from early astronomy where movement of stars over time was related to days in a year. We know that there are 365 days in a year, but 360 has the useful feature of being able to be evenly divided by every number between 1 and 9, except 7. And so 360 divisions of a circle provides us with "degrees" which are useful in describing angles and arcs.
Degrees are further divided into "minutes" -- from whence we get "Minute Of Angle," and Seconds. Sixty minutes to a degree. Sixty seconds to a minute.
Writing this out (Use "Alt + 2552 on the ten-key pad for the degree symbol.) we get 00° 00" 00' -- and these designations are used in geometry, trigonometry, surveying, navigation.
A International Nautical Mile (1852 metres, 6076.11549 ft., 1.151 statute miles) is equal to one minute of arc at the meridian of the earth. Seamen use minute of arc, in navigation and so distance between positions can be readily calcuated by adding/substracting difference in minutes.
But getting back to Minute Of Angle -- At 100 yds. it's 1.0471996", and most scopes adjust for MOA. We can use MOA to compute "clicks" at a given distance/range by computing yards and MOA.
So what's that mean in the larger scheme of things -- like artillery, or surveying boundaries?
Compute the distance, Point A to Point B. That provides the radius of a circle. In Trig. it's called a radian. Circumference of a circle equals diameter times Pi.
(Pi = 3.1416) -- C = 3.1416 X D.
To find arc of angle, the tangent between degrees of angle at a given distance, you double the radius, multiply by Pi and divide the product by degrees / 360.
So, arc of angle for one degree at 100 ft. equals 60 MOA or 20.94" -- Or you can do it the "hard way" . . . 200 ft. X Pi divided by 2, divided by 360.
The next time someone talks about "MOA" you can put it in context. Wikipedia has a good discussion of all this. Start w/ MOA and follow the links.
So where'd that come from?
The circle is divided into 360 degrees, and that's derived from early astronomy where movement of stars over time was related to days in a year. We know that there are 365 days in a year, but 360 has the useful feature of being able to be evenly divided by every number between 1 and 9, except 7. And so 360 divisions of a circle provides us with "degrees" which are useful in describing angles and arcs.
Degrees are further divided into "minutes" -- from whence we get "Minute Of Angle," and Seconds. Sixty minutes to a degree. Sixty seconds to a minute.
Writing this out (Use "Alt + 2552 on the ten-key pad for the degree symbol.) we get 00° 00" 00' -- and these designations are used in geometry, trigonometry, surveying, navigation.
A International Nautical Mile (1852 metres, 6076.11549 ft., 1.151 statute miles) is equal to one minute of arc at the meridian of the earth. Seamen use minute of arc, in navigation and so distance between positions can be readily calcuated by adding/substracting difference in minutes.
But getting back to Minute Of Angle -- At 100 yds. it's 1.0471996", and most scopes adjust for MOA. We can use MOA to compute "clicks" at a given distance/range by computing yards and MOA.
So what's that mean in the larger scheme of things -- like artillery, or surveying boundaries?
Compute the distance, Point A to Point B. That provides the radius of a circle. In Trig. it's called a radian. Circumference of a circle equals diameter times Pi.
(Pi = 3.1416) -- C = 3.1416 X D.
To find arc of angle, the tangent between degrees of angle at a given distance, you double the radius, multiply by Pi and divide the product by degrees / 360.
So, arc of angle for one degree at 100 ft. equals 60 MOA or 20.94" -- Or you can do it the "hard way" . . . 200 ft. X Pi divided by 2, divided by 360.
The next time someone talks about "MOA" you can put it in context. Wikipedia has a good discussion of all this. Start w/ MOA and follow the links.
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hold over/under, ballistic charts, the whole shebang. Always good to hear from a different source, though...it may help make sense to someone who doesn't understand some or all of it.
