Our galaxy, the Milky Way, is about 100,000 light-years (946,073,047,000,000,000 km) across. In comparison, the diameter of our Sun is a mere 1,392,000 km, almost 12 orders of magnitude smaller. There is no way to make someone easily visualize this difference in length. This would be roughly the same to a 0.5-mm sugar molecule being compared to the Sahara Desert or Canada!
Our Sun is 1,392,000 km in diameter. This is roughly 109 times the diameter of the Earth, which is on average 12,742 km. This would be roughly proportionate to a 0.5-cm pea compared to a pillow 55-cm long. The largest known star is a red hypergiant called UY Scuti, with a diameter of about 1,700 times the Sun’s. This could be represented as a 0.9-cm wide marble compared to a 15-meter-long house.
The largest GALAXY, though, is another matter altogether. You’ll need light-years to measure the lengths of these behemoths. The largest one found so far, called IC 1101, is 5.5 MILLION light-years long, compared to the Milky Way’s 100,000. This means that at lease 50 Milky Ways would be necessary to reach a combined length similar to IC 1101’s.
This could be represented as a 0.7-cm marble compared to a regular 12-inch ruler.
Hopefully this helped!