a
\({1^{ \circ \,}}\, = \,60'\,\,\,\,({\text{minute}}),\,\,\,\,1'\, = \,60\,{\text{(second)}}\,\,\,\)

\(\therefore {1^ \circ }\, = \,3600\,\,\,\,\,\therefore \,\,1\, = {\left( {\frac{1}{{3600}}} \right)^ \circ }\)

\(But,\,\,\,{1^{ \circ \,}}\, = \,\frac{\pi }{{180}}\,\,rad\,\,\,\)

\(\therefore \,\,\,1\, = \,\left( {\frac{1}{{3600}}} \right) \times \,\frac{\pi }{{180}}\)

\(\,\, = \,\,\,\frac{{3.14}}{{3600 \times 180\,}}\,\, = \,\,\,4.85 \times {10^{ - 6}}\,rad\)