How big is the sun? Well, that depends on when you’re measuring.
The sun slightly shrinks and expands as it goes through a solar cycle, a roughly 11-year period of high and low magnetic activity, a new study finds. When the sun is the most active, its radius decreases by 1 or 2 kilometers, two researchers report in a paper accepted in the Astrophysical Journal. Given that the sun’s full radius is about 700,000 kilometers, that’s a tiny change.