Practical Exercise 5:

A thin, spherical envelope named Oort cloud with approx. 200 000 au in diameter is sometimes considered as a boundary of our Solar system. How many times would the Solar system „fit“ into the diameter of our Galaxy?

Answer: The calculation can be performed almost by heart because the Galaxy diameter is 100 000 ly, the diameter of the Solar System is 200 000 au and 1 ly ≈ 63 000 au. As a result, we get n = 100 000 · 63 000 au/ 200 000 au = 63 000 / 2 = 31 500×

Dimensions of the Oort cloud are only approximate, the outer boundaries of the Solar System are not uniquely determined. If we imagined the Solar System as a sphere with 1 m in diameter (the size of a human), the diameter of our Galaxy would correspond to the distance of 31.5 km, a route from the centre of Bratislava to Blatné.