50 Fun Facts About Stars

About how many stars are visible to the naked eye?

All of them are inside the Milky Way.

Stars and their remnants create almost all elements heavier than which element?

Hydrogen, helium and a little lithium came from the Big Bang; the rest was cooked in stars.

The word "star" shares an ancient root meaning "to burn" with which English word?

Asterisk, asteroid and Esther are cousins too.

The oldest accurately dated star chart, from 1534 BC, comes from which civilisation?

The earliest known catalogues came from Babylonian astronomers a little later.

Which astronomers were the first to record a supernova, in 185 AD?

The brightest stellar event in history, SN 1006, came eight centuries later.

The supernova of 1054 gave birth to which famous object?

Chinese and Islamic astronomers both recorded the event.

Who wrote the Book of Fixed Stars in 964?

He recorded star clusters and the Andromeda Galaxy.

Who suggested in 1584 that stars were suns that might have their own planets?

Democritus and Epicurus had floated the idea in antiquity.

Who discovered that some paired stars are true physical companions, or binaries?

He also counted stars in 600 directions to map their distribution.

Who made the first direct measurement of a star's distance, in 1838?

He used parallax on 61 Cygni, 11.4 light-years away.

Edward Pickering found the first spectroscopic binary in 1899 in which star?

Its spectral lines split and merged on a 104-day cycle.

Who made the first measurement of a star's diameter, in 1921?

He used an interferometer on the Hooker telescope at Mount Wilson.

In which year was the Hertzsprung–Russell diagram developed?

It plots stars by luminosity and temperature and drove the study of stellar evolution.

Whose 1925 PhD thesis first proposed that stars are mostly hydrogen and helium?

Quantum physics later made sense of stellar spectra in detail.

Which astronomer labelled stars in each constellation with Greek letters around 1600?

Flamsteed numbers, based on right ascension, came with his 1712 catalogue.

Which of these is a well-known example of a star-forming molecular cloud?

Such clouds are mostly hydrogen with 23 to 28 percent helium.

Dense collapsing knots of dust and gas in a cloud are called what?

A protostar forms at the core once hydrostatic equilibrium is reached.

What fraction of its life does a star spend on the main sequence?

Such stars are called dwarfs, whatever their size.

By about how much has the Sun brightened since reaching the main sequence?

That was 4.6 billion years ago.

How long is the Sun expected to live in total?

It is roughly halfway through.

The lightest red dwarfs, at 0.08 solar masses, may last about how long?

Far longer than the universe's current 13.8 billion years.

Astronomers call all elements heavier than helium what?

A star's metallicity affects its lifespan and magnetic field.

When the Sun becomes a red giant, it will swell to about how many times its present size?

Its radius will reach roughly 1 astronomical unit.

What is the explosive onset of core fusion in a low-mass red giant called?

The star then shrinks and moves to the horizontal branch of the HR diagram.

A dying low-mass star ejects its outer layers to form what?

Despite the name, it has nothing to do with planets.

Very massive stars that shed their outer layers become what kind of star?

Alnilam in Orion's Belt is one candidate, being too massive to become a red supergiant.

Fusion stops releasing energy once a massive star's core starts producing which element?

Iron nuclei are the most tightly bound, so fusing them consumes energy.

Which star's 19th-century "Great Eruption" was a supernova impostor event?

With 100 to 150 solar masses, it is one of the most massive stars known.

A stellar remnant below about 1.4 solar masses becomes what?

It is roughly the size of Earth and eventually fades to a black dwarf.

What is the nearest star to Earth after the Sun?

At Space Shuttle speed the 4.25-light-year trip would take about 150,000 years.

Stellar collisions in dense clusters can produce which unusually hot stars?

They sit where standard evolution says they should already have left the main sequence.

The oldest known star, HD 140283, is nicknamed after which long-lived biblical figure?

Its estimated age of 14.46 billion years has a large enough error bar not to predate the universe.

New stars in the Milky Way today are about what percentage hydrogen by mass?

Helium makes up about 27%, with a small fraction of heavier elements.

Other than the Sun, which star has the largest apparent size in our sky?

Even so, its angular diameter is only 0.057 arcseconds.

Betelgeuse's diameter is about how many times the Sun's?

Neutron stars, at the other extreme, are only 20 to 40 km across.

Which B-class star spins so fast its equator bulges more than 50% wider than its poles?

Its equatorial speed of about 225 km/s is just below break-up velocity.

How often does the Sun rotate?

It spins faster at the equator than near the poles.

The pulsar left by the 1054 supernova rotates how many times per second?

Its spin gradually slows as it radiates energy away.

A one-step difference in magnitude equals a brightness ratio of about how much?

Five magnitudes is exactly a factor of 100.

What is the faintest magnitude visible to the naked eye in good conditions?

Smaller numbers are brighter; the brightest objects go negative.

Absolute magnitude is the brightness a star would have at what distance?

That is about 32.6 light-years.

Which spectral class contains the hottest stars?

The sequence in order of decreasing temperature runs O, B, A, F, G, K, M.

What is the Sun's full spectral classification?

It is a main-sequence yellow dwarf of ordinary size.

Which long-period pulsating variable gives its name to a class of stars?

Cepheids are the other famous pulsators.

What is the visible surface layer of a star called?

It is where the plasma becomes transparent to light, and where sunspots appear.

The Sun's outermost atmosphere, seen during eclipses, is called what?

Despite its extreme temperature it emits little light because the gas is so thin.

By which reaction does the Sun fuse hydrogen in its 16-million-kelvin core?

More massive stars use the carbon-catalysed CNO cycle instead.

The triple-alpha process turns helium into carbon via which intermediate element?

It needs core temperatures around 100 million kelvin.

In solar masses, what is the rough upper limit for stars forming in today's universe?

A few stars in the R136 cluster exceed it, probably via mergers.

What is the name for the 70-year spell with almost no sunspots in the 17th century?

Slowly rotating stars like the Sun can shut down their activity for long periods.