Tip of the red-giant branch

Ground-based, 8-meter-class telescopes like the VLT are also able to measure the TRGB distance within reasonable observation times in the local universe.

During the core hydrogen burning phase of a Sun-like star's lifetime, it will appear on the HR diagram at a position along a diagonal band called the main sequence.

[2] At a certain point, the helium at the core of the star will reach a pressure and temperature where it can begin to undergo nuclear fusion through the triple-alpha process.

For a star with less than 1.8 times the mass of the Sun, this will occur in a process called the helium flash.

The evolutionary track of the star will then carry it toward the left of the HR diagram as the surface temperature increases under the new equilibrium.

Sun-like stars have a degenerate core on the red-giant branch and ascend to the tip before starting core helium fusion with a flash.
Hertzsprung–Russell diagram for globular cluster M5 . The red-giant branch runs from the thin horizontal subgiant branch to the top right, with a number of the more luminous RGB stars marked in red.