Why do chemists use alpha and beta symbols when describing steroid structures?

Chemists use the symbols $\alpha$ and $\beta$ to specify the three-dimensional orientation of atoms or substituent groups attached to the steroid nucleus. Because steroids are three-dimensional structures, these symbols are essential for defining the stereochemistry of the molecule.1

• $\beta$ (beta): Indicates that a substituent or hydrogen atom is oriented above the plane of the steroid diagram. In structural drawings, this is typically represented by a full line.1
• $\alpha$ (alpha): Indicates that a substituent or hydrogen atom is oriented below the plane of the diagram. This is typically represented by a broken line.1

This notation is critical for identifying specific stereoisomers, as the biological activity and chemical reactivity of a steroid are often determined by the precise spatial arrangement of its functional groups. If the orientation of a substituent is unknown, the symbol $\xi$ (xi) is used instead.12