Light crosses the Milky Way's disc of stars from one edge to the other. How many years does that trip take?
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Answer
About 100,000 years
The Sun sits roughly 26,000 light-years from the galactic centre and needs about 230 million years to complete a single lap around it.
How to estimate it
Light covers one light-year per year, so the answer equals the disc's width in light-years. Take 100 billion stars, each claiming about 100 cubic light-years as near the Sun: 10 trillion cubic light-years. A disc 1,000 light-years thick then has an area of 10 billion square light-years, which means a diameter near 110,000 light-years. The accepted crossing time is about 100,000 years.
Source: NASA
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