Mirabile dictu is a Latin phrase meaning "wonderful to tell". This page is a list of sourced facts I find particularly wonderful. (Feel free to tell me or correct any mistakes if I'm wrong about any of this!) Also, feel free to contribute your own interesting facts, just please cite them if possible.
Saturn's moon Titan is the only body other than Earth known to have stable pools of liquid on it's surface. It is hypothesized that these pools of hydrocarbons evaporate and condense in Titan's atmosphere, raining down to the surface in one inch diameter drops that fall at the speed of snow flakes.
Light can travel around the world about seven and a half times in one second, but it takes a little more than eight minutes to travel from the Sun to the Earth — and estimates for how long it takes light to get from the center of the Sun out to the surface range from 17,000 to 50 million years.
The vast majority of the heavier elements were created through stellar nucleosynthesis and supernova nucleosynthesis, finding their way into planetary systems (like Earth) only after the parent star exploded. Christopher Hitchens (possibly quoting someone else), described this poetically as, "the stars had to die so that we could live." Lawrence Krauss went further and pointed out that not only are we born from stars, the number of stars that contributed to our makeup is so great that the matter in your left hand probably isn't from the same star as the matter in your right hand.
When you flip a coin you have a 50/50 chance of getting heads or tails—now imagine that if you flipped the coin a second time without looking at the result of the first flip, that you always got the opposite of what you started with. (So if it started on tails, it always came up heads after the second flip, and vice versa.) This is one of the inherent properties of quantum mechanical objects. (Sadly it doesn't work with "large" objects like coins, but it is common behavior for small objects like photons, electrons, and atoms.) This is the nature of reality, (and one of the central reasons quantum mechanics causes such a fuss).
Due to tidal locking, the Moon is actually getting further away from the Earth. The tidal bulges seen in the oceans of Earth are being "pulled" forwards by the rotation of the Earth beneath them, which then "drags" the Moon forwards. This process would eventually lead to the same side of Earth always facing the Moon (this is the same reason the Moon always faces the same way towards us). This is equivalent to saying the length of a day will equal the length of a month, (though in reality the process is happening far too slowly with Earth to ever play out completely).
No matter how quickly or slowly you are moving, you will always measure light to be moving at 299,792,458 meters per second (in a vacuum). Nature distorts the passage of time, the length of space, and the mass of objects to correct for the discrepancy that two observers (in different reference frames) would measure the speed the same c, (despite the relative motion between them); in physics this subtle counter-intuitive trick of nature is called Special relativity.
James Clerk Maxwell derived the speed of light ab initio from his eponymous equations, leading him to question whether light could be a form of electromagnetic wave. He also found that the equations suggested the speed of electromagnetic waves was invariant under Lorentz transformations.
In 2008, a gamma ray burst called GRB 080319B was briefly visible with the unaided eye, setting the record for the most distant visible object to about 7.5 billion light years, about half the age of the universe.
The sum of all the positive integers, 1+2+3+4+... to infinity, is equal to -1/12. (See this or this proof.)
The P versus NP problem in computer science asks about certain kinds of common problems for which a solution is easily verified whether or not there is also an easy way to find solutions. It is connected to the question of whether or not one-way functions exist, which has important implications for cryptography. It is considered an extremely difficult problem, and most of what we know about it is that most of the methods we use in proofs will not work here. One of the more interesting features of the problem is that if a proof were found that P is equal to NP it would be rather easy to verify it, whereas if they are not equal, the very fact that P is not equal to NP would imply the proof could be extraordinarily difficult to find, so the answer has strong implications to solving the question itself.
Of all the cells in your body, the ones containing your DNA are outnumbered by the ones that do not, by a factor of 9 to 1—that is, 90% of "you" isn't you. Consequently, the bacteria in your gut also out number all the humans who have ever lived. WARNING: newer research has revised this estimate down, from 9-to-1 or 10-to-1 to just 3-to-1 or even just 1-to-1. In part this is due to the estimate of the number of cells in a human (not including the microbiota) being revised upwards from 10 trillion to 37.2 trillion. It's also been claimed that a person has about 5 pounds of bacteria living in/on them, but I have yet to see a good source for that.
Turritopsis nutricula is a potentially biologically immortal jellyfish capable of returning to a sexually immature state after reaching adulthood—possibly repeating the cycle of maturation indefinitely. (Though this has currently been observed in the lab only.)
A number of ant species farm fungus, thought to have discovered agriculture 50-65 million years ago, long before humans. The most advanced ant farmers (leaf cutter species) farm a fungus that exists no where on Earth besides their farms, an example of mutualism. There are also species of ants who "milk" aphids, and protect the aphids while they feed.
The Y chromosome can be used to trace paternal ancestral lines, as the Y chromosome is unique to the paternal lineage. Mitochondrial DNA can be used to trace the maternal lines, as it is only passed through the ovum.
Horizontal gene transfer—the transfer of genetic material into an organism in any way other than inheritance from it's parents—is now thought to play an important role in prokaryotic evolution (bacteria mostly), and though it's role in the evolution of multicellular life is less clear, it has been confirmed to occur.
Bacteriophages—viruses that infect bacteria—are among the most common "biological entities" on Earth, with as many as 900 million phages per cubic centimeter in mats of bacteria living on the surface of seawater.
Endosymbiotic theory suggests that mitochondria, chloroplasts and other organelles originated as individual life forms that were later taken into other organisms, becoming endosymbionts. Viral Eukaryogenesis suggests that this same process was responsible for the cell nucleus of eukaryotes. (Taking these theories together with the development of multicellular life and social structures it seems that cooperation is a very valuable tool for survival on many levels!)
Nylonase is a set of enzymes recently evolved in bacteria found in the waste water ponds of nylon factories allow the bacteria to digest the recently invented human-made molecules.
Your body produces approximately your entire body weight in adenosine triphosphateevery day. Alhough the body only contains about 250 grams on average, ATP is constantly being recycled in a loop, being broken down in metabolic processes and reassembled by your mitochondria.
Your eyes subtract the amount of green light they detect from the amount of red light they detect, so you can't tell the difference between a 100% red + 25% green detection versus a 75% red + 0% green detection. (Check out Opponent process for more information, or for even more information read this post on how the filters work; or for the most information check out this in depth treatise on color vision.)
There are individual living trees nearly as old as written history (~3200 BC vs ~2832 BC).
Your brain can triangulate an estimated position for a noise source based on the delay of arrival to your ears, with delays as small as 9 millionths of a second.
A quaking aspen named Pando in Utah is thought to be the heaviest known organism, estimated to weigh about 6 million kilograms, spanning an estimated 106 acres and having around 47,000 trunks or stems. The root system is thought to be 80,000 years old, making it among the oldest known living organisms.
A verbatim quote, from Richard Dawkins' book, A Devil's Chaplain, “Molecular evidence suggests that our common ancestor with chimpanzees lived, in Africa, between five and seven million years ago, say half a million generations ago. This is not long by evolutionary standards ... in your left hand you hold the right hand of your mother. In turn she holds the hand of her mother, your grandmother. Your grandmother holds her mother's hand, and so on ... How far do we have to go until we reach our common ancestor with the chimpanzees? It is a surprisingly short way. Allowing one yard per person, we arrive at the ancestor we share with chimpanzees in under 300 miles.”
Most mammals have a vestibulo-ocular reflex which allows allows us to see even when our heads are moving, (which is why we don't have to bob our heads when we move around).
Pencils never contained lead. When graphite was first discovered it was mistaken for lead, and the mistake stuck.
Define "maximal terrestrial separation" to be the distance between two humans on opposite sides of the planet (antipodal points). The twelve men who landed on the moon, (along with the twelve who orbited but didn't set foot on it), were about five times further away from all life we know of, than any other life we have ever been aware of. As far as we know, they are the only living things to spend time on an astronomical object other than Earth.
The state of the art human technology from 2.6 million years ago (mya) to 1.7 mya was the Oldowan. About 1.7 mya the Acheulean displaced the Oldowan as the state-of-the-art, lasting another 1.6 mya (to about 0.1 mya).
Atoms are so small that if you were to shrink every page of the 1950 Encyclopedia Britannica down by a factor of 25,000, there would still be hundreds of atoms per dot of ink, and yet the entire set would still fit comfortably on the head of a pin.
In the six and a half decades since Lego began manufacturing toy bricks they've produced around 560 billion Lego parts, which is probably somewhere between 0.08%-0.5% of the number of atoms in a single human cell, or about 0.16% of the number of cells in a typical human body.
There is no "now" in two different senses; in the special theory of relativity which dismantles traditional notions of simultaneity (in much the same way discovering the Earth was spherical dismantled traditional notions of "up"); and in the fact that our conscious brains are delayed to allow all the various sensory signals to be aligned with one another, to be experienced as one coherent picture, even though it's a few dozen milliseconds behind when those senses were originally triggered.
I plan on growing this list significantly over time, and increasing the number and veracity of sources (both internal to wikipedia and external links). Feel free to contribute!
Fizeau-Foucault apparatus for measuring the speed of light. (In college I reproduced this experiment with my boss and got about 4% error; in class I was supposed to re-demonstrate the experiment but got something like 20% error.)
Millikan's oil drop experiment which measured the charge of the electron. (In college I reproduced this experiment and got 1.38% error(!), but in class demonstrating the experiment most students didn't seem to grasp what we were doing, and I don't think we got useful results. Students struggled to observe the drops.)
LIGO has now confirmed twice, detection of gravitational waves, in both instances seemingly caused by the merging of distant black holes, approximately 1.3 and 1.4 billion light years distant (and in the past).
^About 1.4 x 1018 tonnes of water on Earth (1 tonne = 1,000 kg) and 236 mL in a cup equals 5.9 x 1021 cups. Whereas 18 g/mol for water gives 13 mol times 6.02 x 1023 molecules per mole gives 7.8 x 1024 molecules of water—a factor of more than 1,000!