Cross section (geometry) of Earth at right. Cross-sections are often used in anatomy to illustrate the inner structure of an organ, as shown at left. A cross-section of a tree trunk, as shown at left, reveals growth rings that can be used to find the age of the tree and the temporal properties of its environment. Cross section (geometry) In geometry and science, a cross section is the non-empty intersection of a solid body in three-dimensional space with a plane, or the analog in higher-dimensional spaces. Cutting an object into slices creates many parallel cross sections. The boundary of a cross section in
Horizontal branch not horizontal when plotted by bolometric luminosity, with hotter horizontal branch stars being less luminous than cooler ones. The hottest horizontal-branch stars, referred to as extreme horizontal branch, have temperatures of 20,000–30,000K. This is far beyond what would be expected for a normal core helium burning star. Theories to explain these stars include binary interactions, and "late thermal pulses", where a thermal pulse that Asymptotic giant branch (AGB) stars experience regularly, occurs after fusion has ceased and the star has entered the superwind phase. These stars are "born again" with unusual properties. Despite the bizarre-sounding process, this is expected to