Above the solar chromosphere and solar corona there is a transition region. The temperature here rises from 20000 to ~ 1-2 millions of K. Below the transition region, gravity dominates the shape of mo
st features, so that the Sun may be described in terms of layers and horizontal features (like sunspots); above the transition region, dynamic forces dominate the shape of most features, so that the transition region itself is not a well- defined layer at a particular altitude.
An event where one astronomical object appears to move across the face of another. As seen from Earth, the planets Venus and Mercury are seen to transit the Sun. We can also observe natural satellites
transit the face of their host planet. Similarly exoplanets have been observed to transit their host stars.