Horizontal Branch morphologies in the age of multi-band photometry

The Horizontal Branch (HB) stars have always played a crucial role in the study of the galactic globular clusters (GC). They are the direct offspring of the low mass, Red Giant Branch (RGB) stars and the final product of the helium flash taking place at the Tip of the RGB. The colour and the luminosity of a HB star are tied to its mass which, in turn, is tied to the mass of the star undergoing the flash. The sensitivity of this value to the chemistry of the cluster allows for a large variety of HB morphologies which is one of the culprits that led to the discovery of the multiple populations phenomenon. A leap forward in our understanding of GCs has been made when recent works, based on a large collection of HST data, measured, albeit indirectly, the helium abundance in a large collection of GCs, allowing the characterization of these old stellar populations in unprecedented ways. In spite of this richness of information, however, we still lack the key to fully understand the populations hosted along the HB, especially due to the complex interplay between the parameters regulating their evolution. In this talk, I will provide a review of the current state of the HB study and discuss how the synergy with the recent advancements in the field of multi-band photometry can provide solutions to some new and decades-old problems.