Facts
Thirty-four verified facts. Eight are disputed or commonly repeated wrong, and that is stated on them.
33 facts
Scale
The Planck length is 1.616255 × 10−35 m
The scale where our present description of space and time is expected to break down. That it is the smallest possible distance is often repeated, but the source does not say so: CODATA gives a value, not a lower bound on length.
Disputed
Source: NIST CODATA 2022
Show at scaleScale
An atom is almost entirely empty
If an atom were a stadium, the nucleus would be a pea at the centre. The ratio is roughly 1 to 63,000.
Source: NIST CODATA 2022
Show at scaleScale
The Milky Way is about 100,000 light years across
Light needs a hundred thousand years to cross it.
Source: NASA Imagine the Universe
Show at scaleScale
Laniakea, our home supercluster, is 500 million light years across
It holds around a hundred thousand galaxies, and we sit near its edge.
Source: Tully et al. 2014, Nature
Show at scaleScale
The observable universe is 94 billion light-years across
The most distant objects are 47 billion light-years away, even though the universe is 13.8 billion years old. Space itself expanded in the meantime.
Source: ESA Planck 2018
Show at scaleLight
Sunlight takes 8 minutes 20 seconds to reach Earth
If the Sun vanished, we would not know for over eight minutes.
Source: IAU 2012 Resolution B2
Send lightLight
Voyager 1 will soon be one light day from Earth
Its signal takes roughly twenty-four hours to arrive.
Source: NASA JPL, Where Are Voyager 1 and 2 Now
Send lightLight
The light from Andromeda left before modern humans existed
It has been travelling for two and a half million years.
Source: NASA/ESA Hubble, M31
Send lightLight
In space we never see now, only the past
The further you look, the deeper into the past you see.
Source: Special relativity, delay = distance divided by c
Send lightTime
The universe is 13.787 billion years old
With an uncertainty of twenty million years.
Source: ESA Planck 2018
Time
In about 6 billion years the Sun will become a red giant
It will swallow Mercury and Venus. Earth’s fate is still an open question in the literature.
Time
The last black holes evaporate around 10100 years
A theoretical extrapolation, not an observation. Adams and Laughlin put the boundary between the Black Hole Era and the Dark Era at 10100 years; it rests on proton decay and Hawking radiation, neither of which has been measured.
Disputed
Numbers
The Milky Way has 100 to 400 billion stars
Nobody knows more precisely, and that range is the honest answer.
Source: NASA Imagine the Universe
Numbers
More stars than grains of sand? It depends on your assumptions
Estimates on both sides are so uncertain that sand may win. It is not a settled fact, however often it is repeated as one.
Disputed
Source: Scientific American
Extremes
The highest measured temperature is trillions of kelvin
Quark-gluon plasma: ALICE measured 297 MeV in lead collisions, that is 3.45 trillion kelvin, PHENIX measured 221 MeV in gold collisions, that is 2.56 trillion. It is a temperature read off the slope of the direct-photon spectrum, so the numbers differ by collider and by method. The popular “5.5 trillion” comes from a press release, not a peer-reviewed paper.
Disputed
Source: ALICE Collaboration 2016, Phys. Lett. B 754, 235 (přímé fotony v Pb-Pb)
Extremes
The coldest spot at NASA’s JPL is 200 nanokelvin
Two hundred billionths of a kelvin on the Cold Atom Lab ground testbed.
Source: NASA JPL Cold Atom Lab
Extremes
A sugar cube of neutron star matter weighs about a billion tonnes
Roughly as much as a mountain.
Source: NASA Imagine, Neutron Stars
Extremes
Nobody knows which star is the largest
Stephenson 2-18 works out at 2150 to 2583 solar radii, but no paper states the radius itself: it is derived from temperature and luminosity. It is also disputed whether the star belongs to the Stephenson 2 cluster at all, and without that the distance is not settled either. The measured record holder is UY Scuti at 1708 ± 192 radii.
Disputed
Source: Published radius estimates, mutually overlapping
Show at scaleExtremes
The fastest known spinning star turns 716 times per second
About 43,000 revolutions per minute.
Extremes
The most distant confirmed galaxy existed 290 million years after the Big Bang
JADES-GS-z14-0, redshift 14.32.
Source: NASA JWST, 2024
Black holes
The black hole in our galaxy has 4 million solar masses
Four million solar masses at the centre of our Galaxy, 27,000 light-years away.
Source: EHT / ESO 2022
Black holes
The event horizon in M87 is larger than the whole solar system
Six and a half billion solar masses.
Source: EHT 2019
Show at scaleBlack holes
Falling into a black hole spaghettifies you
To a distant observer your clock slows down and freezes at the horizon.
Strange
On exoplanet HD 189733b it rains molten glass sideways
The wind blows at around two kilometres per second.
Source: NASA/Hubble, HD 189733b
Strange
The Boötes Void is a hole 62 megaparsecs in radius
A 1987 survey confirmed a roughly spherical void of radius 62 Mpc, about 200 million light-years. It holds far fewer galaxies than the distribution of matter would predict.
Source: Kirshner et al. 1981, ApJ
Show at scaleStrange
The whole Local Group is falling towards the Great Attractor
The Local Group is falling towards it at around 600 km/s. It sits behind the plane of the Milky Way, so it is hard to observe, and newer surveys lowered its mass estimate by about 14 % against the original 1988 prediction.
Disputed
Strange
The cosmic microwave background is real, the television static claim is not
The CMB is 2.725 K and well measured. The claim that it made up 1 % of the static on an old television has no serious source.
Disputed
Strange
Rogue planets without a star exist, but we do not know how many
Estimates differ by orders of magnitude and are not settled, so we quote no ratio.
Disputed
Source: Microlensing surveys, estimates differ by orders of magnitude
Perspective
The solar system is overwhelmingly empty
At one pixel per Moon diameter, there are hours of scrolling between the planets.
Source: Josh Worth, If the Moon Were Only 1 Pixel
Show at scalePerspective
Voyager 1 is the most distant human-made object
About 25 billion kilometres, deep in interstellar space, and still transmitting.
Source: NASA JPL
Send lightPerspective
In the Pale Blue Dot photograph, Earth is smaller than a single pixel
Taken from six billion kilometres on 14 February 1990.
Source: NASA, Pale Blue Dot
Strange
55 Cancri e is not a diamond planet
The 2012 hypothesis was superseded by later spectroscopy favouring a rocky world with lava.
Disputed
Numbers
A day on Venus lasts 243 Earth days, not 234
Venus turns on its axis once every 243 days, and backwards. A solar day there, from one sunrise to the next, takes 117 days, which is shorter than the 225-day year.
Disputed
Source: NASA Science, Venuše - fakta