distance = \sqrt{(a_{x} − b_{x})^{2} + (a_{y} − b_{y})^{2}} p_{1} = (α_{1}, δ_{1}) p_{2} = (α_{2}, δ_{2})

α

δ

cos(γ) = cos(90^{∘} − δ_{1}) cos(90^{∘} − δ_{2}) + sin(90^{∘} − δ_{1}) sin(90^{∘} − δ_{2}) cos(α_{1} − α_{2}) γ ≃ \sqrt{((α_{1} − α_{2}) cos(δ_{1}))^{2} + (δ_{1} − δ_{2})^{2}}