Editing Openai/6946e998-79f0-8007-9a65-19828450838d (section)

=== Assistant: The Sun’s red-giant stage is relatively short compared to its total lifetime. ===
The Sun’s red-giant stage is relatively short compared to its total lifetime.

Technical summary:

• The Sun is ~4.57 Gyr old.
• It will leave the main sequence at ~10–11 Gyr.
• After hydrogen exhaustion in the core, it enters the subgiant and then red-giant branch (RGB) phases.

The true red-giant interval—where the Sun has a hydrogen-shell–burning core, greatly expanded radius, and luminosity rising from tens to thousands of L☉—lasts approximately:

===== More detailed breakdown (rounded): =====
# Subgiant phase: ~0.5 Gyr Hydrogen-shell burning begins, radius expands modestly.
# Red-giant branch: ~0.8–1.0 Gyr This is the classic “red giant” Sun: • radius increases from ~2–3 R☉ to ~200 R☉ near the tip • luminosity rises from ~2–3 L☉ to ~2000 L☉ • helium core contracts until it reaches degeneracy
# Helium flash → horizontal branch: very rapid transition; Sun becomes a helium-burning red clump star for ~0.1 Gyr. This is not usually lumped into the “red giant phase,” because the Sun stabilizes at a smaller radius.
# Asymptotic giant branch (AGB): ~10–20 Myr A second giant phase, much shorter, where the Sun becomes huge and luminous again before losing its envelope.

===== That interval (near the tip of the RGB + AGB) is much shorter, of order: =====

• ~100–200 million years at very large radii
• the final AGB high-radius episodes last only a few million years

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===== The Sun will spend roughly 1 billion years in the “classical red-giant” state, with only the final ~100 million years being the extreme, planet-engulfing phase. =====

If you want a timeline diagram or want to know specifically when Earth gets destroyed vs only sterilized, I can provide that as well.