- #1

ckirmser

- 97

- 3

One of the measurements used is the Semi-major Axis, 'a.' Unfortunately, this measurement is not always given in a standard unit of length. In fact, most of the time it is given in " (seconds of arc) and, occasionally, in ' (minutes of arc).

My problem is - what's the arc?

I get that a minute is 1/60th and that a second is 1/3600th, but of what? What is the baseline that I use to determine the size of the semi-major axis?

Thanx in advance for any help!