Q 01/05

Which of these nearby stars is too small ever to swell into a red giant?

A) Sirius A

B) Proxima

C) Procyon A

D) Vega

Answer · why

B) Proxima

Proxima is the Sun's nearest neighbour among the stars, yet it is so small and dim that it is too faint to see with the naked eye.

Q 02/05

Why do red giants glow orange or red rather than white?

A) They are rushing away from us

B) Their surfaces are fairly cool

C) Their hydrogen glows red

D) Their gravity reddens light

Answer · why

B) Their surfaces are fairly cool

Their surfaces are fairly cool: the star gets brighter, but its size grows faster still, so each patch of its surface ends up cooler.

Q 03/05

The brightest red giants in a galaxy all top out at about the same brightness, so astronomers use them to measure what?

A) The galaxy's age

B) The galaxy's mass

C) The galaxy's distance

D) The galaxy's spin

Answer · why

C) The galaxy's distance

The galaxy's distance: set against how bright those stars really are, their dimness gave an independent check on how fast the universe is expanding.

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

K and M come from Annie Jump Cannon's O, B, A, F, G, K, M scheme, which was built on spectral lines but turned out to be sorting the stars by temperat...

Q 05/05

Stars can fuse elements up to which metal, leaving red giants to build heavier ones by slowly capturing neutrons?

A) Magnesium

B) Calcium

C) Titanium

D) Iron

Answer · why

D) Iron

Iron: slow neutron capture in red giants builds elements as heavy as bismuth, but anything heavier needs the far faster neutron floods of violent cosm...