The Sun
The Sun can be split into two regions:
The interior is a sphere with radius R = 7x108m
The atmosphere lies on top and has the following layers (from innermost to outermost):
The photosphere is about 300 km thick. Most of the Sun's visible light that we see originates from this region.
The chromosphere is about 2000 km thick. We only see this layer and the other outer layers during an eclipse.
The corona extends outwards for more than a solar radius.
The size of the atmosphere compared to the Earth.