Caption: "Comparison of the current-day Sun and the Sun as a red giant in the future."

Features:

1. The Sun's red giant phase is estimated to begin in ∼ 5.4 Gyr (see Wikipedia: Sun: After core hydrogen exhaustion).

2. Now the estimated diameter as a red giant is ≅ 2 astronomical units (AUs) implying an estimated radius of ≅ 1 AU.

   So it is uncertain if the Sun will envelop the Earth (mean orbital radius 1.00000261 AU) then---maybe yes, maybe no.

   Note the orbital radius of the Earth might increase if the Sun loses significant mass (and therefore gravitational force) via stellar winds in the Sun's red giant phase.

3. If the Earth does get inside the red giant Sun's atmosphere, there will be drag force that will cause the Earth to spiral into deeper layers and there it will be vaporized. The time scale after envelopment is ∼ 200 years (Ze2002-344)---a sad case of orbital decay.

4. Note that no matter what happens to the Earth in the Sun's red giant phase, Mercury (mean orbital radius 0.387098 AU) and Venus (mean orbital radius 0.723327 AU) are toast.

5. If the Earth survives the Sun's red giant phase, it will then survive horizontal branch phase. But then it is doomed. In asymptotic giant branch (AGB) phase (which comes after horizontal branch phase), modeling circa 2008 predicts the Earth's orbit will shrink due to tidal forces and lower chromosphere drag force and the Earth will be enveloped by the AGB Sun (which may or may NOT be larger than in its red giant phase) and vaporized (see Wikipedia: Sun: After core hydrogen exhaustion).

6. What happens to the Earth happens to the Moon.

7. "So the glory of this world passes away: sic transit gloria mundi."