10 Strange Facts and Cosmic Mysteries That Sound Completely Made Up
Space is far stranger than even the most imaginative science-fiction story.
There are planets where a single day lasts longer than an entire year, stars so dense that a spoonful of their material would weigh billions of tonnes, and mysterious signals that can release enormous amounts of energy in less than the blink of an eye.
Some of these cosmic curiosities are well understood. Others continue to puzzle the world’s greatest astronomers. Here are ten strange facts and unsolved mysteries that reveal just how wonderfully weird our universe really is.
1. A Day on Venus Is Longer Than Its Year
Venus takes approximately 225 Earth days to complete one orbit around the Sun. However, it takes around 243 Earth days to rotate once on its axis.
That means a single Venusian day is longer than a Venusian year.
Things become even stranger when you consider the direction in which Venus rotates. Most planets turn anticlockwise when viewed from above the Solar System’s north pole, but Venus rotates in the opposite direction. If you could somehow stand on its surface and see through its thick clouds, the Sun would appear to rise in the west and set in the east.
Why Venus rotates this way remains uncertain. A huge collision early in the planet’s history may have knocked it over, or interactions between its atmosphere, interior and the Sun may have gradually altered its rotation.
Discover more about this fascinating world in our Planet Profile of Venus.
2. Neutron Stars Are Almost Unimaginably Dense
When a sufficiently massive star reaches the end of its life, it can explode as a supernova. The remaining core may collapse into a neutron star—an object that can contain more mass than the Sun inside a sphere roughly the size of a city.
The material within a neutron star is packed so tightly that a teaspoonful would weigh around a billion tonnes on Earth.
Some neutron stars also rotate hundreds of times every second. When beams of radiation from one of these stars repeatedly sweep across Earth, astronomers detect regular pulses and call the object a pulsar.
Imagine an object heavier than the Sun spinning faster than the blades of a kitchen blender. The universe does not do subtlety.
3. We Do Not Know What Most of the Universe Is Made From
Everything we can directly see—including planets, stars, galaxies, people and telescopes—accounts for only around 5% of the universe.
Approximately 27% appears to be dark matter. We cannot see dark matter because it does not appear to emit, reflect or absorb light, but astronomers can detect its gravitational influence on stars and galaxies.
The remaining 68% is thought to be dark energy, the name given to whatever is causing the expansion of the universe to accelerate.
In other words, scientists have detailed theories explaining the behaviour of just a small fraction of the cosmos. The overwhelming majority appears to consist of things we cannot directly see and do not yet fully understand.
4. Black Holes Can Distort Time
A black hole contains so much mass in such a small region that it severely distorts the space and time around it.
To a distant observer, an object approaching a black hole’s event horizon would appear to slow down. Its light would become increasingly stretched, red and faint until the object effectively disappeared from view.
The falling object would experience events differently. It would cross the event horizon without seeing itself freeze at its edge—although it would then be unable to escape.
Near a small black hole, the difference in gravity between one part of an object and another could stretch it into a long, thin strand. Astronomers have given this rather unpleasant process the surprisingly playful name “spaghettification”.
5. Some Planets May Wander Through Space Without a Star
Not every planet belongs to a Solar System.
Astronomers believe there are rogue planets travelling through the darkness between stars. Some may have formed alone, while others were probably thrown out of their original planetary systems through gravitational encounters with larger planets or passing stars.
These lonely worlds would have no sunrise, sunset or familiar seasons. Their surfaces could be extraordinarily cold, although some might retain internal heat beneath thick atmospheres or layers of ice.
We still do not know how many rogue planets exist. There could be billions of them wandering through the Milky Way—silent worlds hidden in the darkness.
6. Space Is Not Completely Silent—But You Could Not Hear It Normally
You may have heard that there is no sound in space. This is mostly correct because sound waves require particles through which to travel, and space is far too empty for ordinary sound to move through it effectively.
However, space is not entirely empty. Gas, plasma and charged particles can carry waves and vibrations in certain environments.
Spacecraft and telescopes also collect information such as radio waves, X-rays and changes in brightness. Scientists can convert these measurements into audible frequencies through a process called data sonification.
The resulting sounds are not recordings made with an ordinary microphone floating in space. They are an audible representation of scientific data—and they can sound wonderfully eerie.
7. Mars Has Blue Sunsets
On Earth, sunsets usually appear orange or red because our atmosphere scatters shorter blue wavelengths of light more effectively, leaving warmer colours to reach our eyes directly.
Mars reverses the effect.
Fine dust suspended in the Martian atmosphere allows blue light to remain more concentrated around the Sun, while the surrounding sky can take on reddish or brownish tones. As a result, a sunset on Mars may display a cool blue glow close to the Sun.
It is a strangely familiar scene with the colours rearranged—as if someone had applied the wrong filter to the sky.
Learn more about the Red Planet and how to find it from the UK in our Planet Profile of Mars.
8. Mysterious Radio Signals Flash Across the Universe
Fast radio bursts, or FRBs, are extremely brief flashes of radio energy arriving from deep space. Many last for only a few milliseconds, yet they can release an extraordinary amount of energy.
Some FRBs have been observed repeating, while others have appeared only once. Astronomers have linked at least some of them to magnetars—highly magnetic neutron stars—but this may not explain every burst that has been detected.
Because radio telescopes observe enormous areas of sky, locating the exact source of a split-second signal can be extremely difficult.
They are not evidence of extraterrestrial messages, despite what an exciting headline might suggest. Nevertheless, their tremendous energy, short duration and varied behaviour make them one of modern astronomy’s most fascinating puzzles.
9. Looking Into Space Means Looking Back in Time
Light travels incredibly quickly, but the universe is incredibly large.
Light from the Moon takes approximately 1.3 seconds to reach Earth. We therefore see the Moon as it appeared just over a second ago. Sunlight takes roughly eight minutes to reach us, so we always see the Sun as it was eight minutes in the past.
The effect becomes far more dramatic beyond our Solar System.
When you look at the Andromeda Galaxy, you are seeing light that began its journey around 2.5 million years ago. Powerful observatories can detect galaxies whose light has travelled for more than 13 billion years.
A telescope is therefore more than a device for seeing distant objects. It is also a kind of time machine, allowing us to observe earlier chapters in the history of the universe.
Want to discover what is within reach from your own garden? Read our guide to what you can see with a telescope.
10. We Still Do Not Know Whether Anyone Else Is Out There
The Milky Way contains hundreds of billions of stars, and observations have shown that planets are common. With such an enormous number of possible worlds, it seems reasonable to wonder whether life has developed elsewhere.
Yet we have found no confirmed evidence of extraterrestrial civilisation.
This apparent contradiction is known as the Fermi paradox: if intelligent life is common, why have we not detected it?
Possible explanations range from the simple to the unsettling. Technological civilisations may be extremely rare, too distant, short-lived or difficult for us to recognise. They may communicate in ways we cannot detect, or our searches may simply have covered too little of the sky for too short a time.
We have only recently developed the ability to search for signs of life beyond Earth. In cosmic terms, humanity has barely opened its eyes.
The Universe Is Stranger Than It Looks
The most exciting thing about astronomy is not simply how much we have discovered—it is how much remains unknown.
You do not need a space telescope to begin exploring, either. The Moon, planets, double stars, star clusters and distant galaxies can all be observed from the UK with the right conditions and equipment.
Start by learning a few recognisable patterns with our Complete Guide to Constellations. A pair of astronomy binoculars can reveal far more stars than the unaided eye, while a telescope can bring craters, planetary detail and deep-sky objects into view.
Every mystery begins with someone looking up and asking a question. What might you discover tonight?
