Getting your questions ready
Getting your questions ready
Beat the crowd
10 questions No timer
50 free Red Giants trivia questions with answers — science & nature quiz, new questions added Aug 2026.
This red giants trivia quiz covers the late-life stage that awaits most stars, including our own Sun. It explains what actually happens when a star runs out of core hydrogen: the shell burning that inflates it to hundreds of solar radii, the helium flash in the degenerate cores of Sun-like stars, the red-giant branch, the red clump and the asymptotic giant branch, dredge-ups and carbon stars, and the planetary nebula and white dwarf that end the story. It then tours the famous examples in the night sky: Arcturus (whose light opened the 1933 Chicago World's Fair), Aldebaran, Pollux and its planet Thestias, Gacrux, Mira the 'wonderful' variable with its 13-light-year tail, and the red supergiants Betelgeuse and Antares, including the Great Dimming of 2019-20 and how bright a Betelgeuse supernova would be. It finishes with the Sun's own future, five billion years out, when it swells to about 256 solar radii and swallows Mercury and Venus. Every answer is checked against Wikipedia's articles on red giants, stellar evolution and the individual stars, and each explanation adds one further fact. Good for astronomy students, stargazers and science quiz nights.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Roughly what range of initial masses, in solar masses, produces a red giant?
About 0.3 to 8
Anything more massive becomes a supergiant instead, and the very smallest red dwarfs never puff up at all.
Q 02What is the surface temperature of a typical red giant?
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 03A star becomes a red giant when it has exhausted which fuel in its core?
Hydrogen
Fusion then continues in a shell around the inert core, and the outer layers balloon outward.
Q 04Which spectral classes do most red giants belong to?
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 05What are stars on the red-giant branch fusing, and where?
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.
Q 06What is the sudden ignition of the second-lightest element in the degenerate core of a Sun-like red giant called?
Helium flash
It happens at roughly 100 million kelvin; stars above about 2 solar masses start helium fusion smoothly and skip it.
Q 07By what reaction do red-clump stars fuse helium into carbon?
Triple-alpha
Three helium nuclei (alpha particles) combine to make one carbon nucleus.
Q 08What is the second swollen phase, after core helium is exhausted, called?
Asymptotic giant branch
AGB stars have a helium-burning shell around a degenerate carbon-oxygen core, with a hydrogen shell farther out.
Q 09What are the convective episodes that carry carbon to a red giant's surface called?
Dredge-ups
The first happens on the red-giant branch; the second and third, on the AGB, are what make a star visibly carbon-rich.
Q 10How does a low- or intermediate-mass star's red-giant phase usually end?
Planetary nebula, then white dwarf
Stars below about 8 solar masses never ignite their carbon-oxygen cores.
Q 11How long does the whole red-giant phase last for a star of one solar mass?
About a billion years
Almost all of it is spent on the red-giant branch; the horizontal and asymptotic branches go by tens of times faster.
Q 12How much larger than the Sun can the radius of a red-giant-branch star get?
Up to about 200 times
Their luminosities reach nearly 3,000 times the Sun's despite surface temperatures of only 3,000-4,000 K.
Q 13How does the surface of a red giant differ from the Sun's in its pattern of convection?
A few huge cells
Q 21What fraction of its mass will the Sun lose as it swells into a red giant?
38%
It will then contract into a white dwarf; some studies suggest a habitable zone at 7-22 AU could persist for a billion years afterwards.
Q 22For how long might a planet at Jupiter's distance sit in a Sun-like star's habitable zone during its red-giant phase?
370 million years
For a 0.5-solar-mass star the same orbit stays habitable for 5.8 billion years.
Q 23By one hypothesis, why might giant planets around red giants be more massive?
They gain mass from the star via Roche lobe overflow
Those giant cells are what make the brightness of red giants and red supergiants vary so much.
Q 14What is the 'mirror principle' in red-giant evolution?
Core contracts, outer layers expand
The hydrogen-burning shell divides the star; the physics is complex but follows from conserving gravitational and thermal energy.
Q 15On which classic astronomers' chart do red giants occupy the upper-right region?
Hertzsprung-Russell
It was created independently by Ejnar Hertzsprung in 1911 and Henry Norris Russell in 1913.
Q 16Which stars, in the 0.2-0.5 solar mass range, become red giants but never manage to ignite helium?
Small red dwarfs
They never reach the tip of the red-giant branch; they simply puff off their outer layers and become white dwarfs.
Q 17What do the very lowest-mass stars eventually become instead of red giants?
Helium white dwarfs
Being fully convective, they burn nearly all their hydrogen and grow hotter and up to ten times brighter before fading.
Q 18How do very-high-mass stars typically end their lives instead of becoming red giants?
Type II supernovae
The most massive of all can become Wolf-Rayet stars without ever becoming giants or supergiants.
Q 19In roughly how many years will the Sun leave the main sequence and begin to become a red giant?
About 5 billion
Its main-sequence lifetime is about 10 billion years in total.
Q 20When the Sun becomes a red giant, roughly how large will it grow?
About 256 times its present radius
That is about 1.2 AU, enough to engulf Mercury, Venus and probably Earth; it will lose 38% of its mass in the process.
Several hundred giant planets had been found around giant stars by 2023, and their masses do not track their stars' masses.
Q 24Which red giant in Bootes is the brightest star in the northern celestial hemisphere?
Arcturus
It is the fourth-brightest star in the whole night sky, and you find it by following the arc of the Big Dipper's handle.
Q 25Light from which red giant was used to switch on the 1933 Chicago World's Fair?
Arcturus
Organisers thought the light had left the star during the previous Chicago fair in 1893; at 36.7 light-years it actually set off in 1896.
Q 26Which red giant is the 'eye' of Taurus, with a name meaning 'the follower' in Arabic?
Aldebaran
It seems to follow the Pleiades across the sky, and merely lies in front of the Hyades cluster, which is more than twice as far away.
Q 27Which defunct probe is drifting toward Taurus's bright red giant, due for its closest approach in about 2,000,000 years?
Pioneer 10
Aldebaran itself is about 67 light-years away with a radius roughly 45 times the Sun's but about the same mass.
Q 28Which red giant in Gemini hosts an exoplanet named Thestias by the IAU in 2015?
Pollux
The planet had been announced in 2006 as Pollux b; the star is the brightest in its constellation despite being Beta Geminorum.
Q 29Which star in the Southern Cross is the nearest M-type red giant to Earth, about 88 light-years away?
Gacrux
It is the third-brightest star in Crux; Arcturus, a K-type giant, is closer at 36 light-years.
Q 30Which red giant in Cetus, recorded as variable in 1596, has a Latin name meaning 'wonderful'?
Mira
David Fabricius first noted its variability; Johannes Hevelius named it in 1662, and it is now the prototype of the Mira variables.