What is the mathematical relationship used to calculate the numerical designation for an elliptical galaxy based on major axis ($a$) and minor axis ($b$)?

Answer

$10 \times (1 - b/a)$

The numerical index for the E classification is mathematically derived using the formula $10 \times (1 - b/a)$, where $a$ is the major axis and $b$ is the minor axis.

What is the mathematical relationship used to calculate the numerical designation for an elliptical galaxy based on major axis ($a$) and minor axis ($b$)?
galaxieselliptical galaxiesshape