Q 01/05

Roughly what range of initial masses, in solar masses, produces a red giant?

A) About 8 to 40

B) Over 100

C) Under 0.1

D) About 0.3 to 8

Answer · why

D) About 0.3 to 8

Anything more massive becomes a supergiant instead, and the very smallest red dwarfs never puff up at all.

Q 02/05

What is the surface temperature of a typical red giant?

A) Around 25,000 K

B) Around 5,000 K or lower

C) Around 10,000 K

D) Around 50,000 K

Answer · why

B) Around 5,000 K or lower

The Sun's photosphere is nearly 6,000 K; a red giant's inflated envelope is cooler but so vast that the star is far more luminous.

Q 03/05

A star becomes a red giant when it has exhausted which fuel in its core?

A) Hydrogen

B) Helium

C) Carbon

D) Iron

Answer · why

A) Hydrogen

Fusion then continues in a shell around the inert core, and the outer layers balloon outward.

Q 04/05

Which spectral classes do most red giants belong to?

A) W and L

B) A and F

C) O and B

D) K and M

Answer · why

D) K and M

Some are class G, and the carbon stars and class S stars also count; colours run from yellow-white to reddish-orange.

Q 05/05

What are stars on the red-giant branch fusing, and where?

A) Hydrogen into helium in the core

B) Carbon into oxygen in a shell

C) Hydrogen into helium in a shell around an inert helium core

D) Helium into carbon in the core

Answer · why

C) Hydrogen into helium in a shell around an inert helium core

Red-clump stars have moved on to core helium burning; AGB stars burn helium and hydrogen in two shells.