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

α δ

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