The brownish staining of a child's tooth enamel is due to excessive ingestion of fluoride. Fluoride is a mineral compound that is useful in preventing dental caries. It is thought to work by strengthening the mineral composition of tooth enamel making it more resistant to acid attacks. It may also reduce the acid-producing ability of microorganisms in dental plaque. The water supply may naturally provide fluoride, or it may be added. Mild fluorosis causes white mottling of the teeth; severe cases show brown staining and usually occur in areas where the level of fluoride in the water is many times greater than the recommended level of 0.7 to 1.2 parts per million. ...

"The ISS is the largest man made object in space. Here's how it compares to other notable objects, both real and fictional, all drawn to scale."

The ISS isn't just the largest space craft ever built, it's also the world's most expensive object. According the Government Accountability Office, it cost upwards of 100 billion dollars to complete.

I learned about something called axial precession in astronomy class several years ago, which is the idea that as something rotates along its axis, it will slowly trace out a cone if the weight of the object isn't equally distributed. In the case of Earth, Earth isn't a perfect sphere as many of us may think it is -- it actually bulges out in the middle enough for it to allow this phenomenon to occur. At the time, all I really took from this concept was how fascinating it is for the north axial pole to move 1° every 72 years from where it is now, and complete one full cycle every 26 000 years. However, I never managed to understand how this concept could fit in to my understanding of why ice ages[1] occur, and why they too follow a specific ...

This is Urechis unicinctus, a species of marine spoon worm. It is also know as the fat innkeeper worm or (I bet you'll never guess why) the penis fish. They live in burrows of sand and mud and are commonly eaten raw with salt and sesame oil in Korea and parts of Japan.

This is the Northrop Grumman B-2 Spirit (stealth bomber). This machine is capable of pin-point strikes on most any hardened target available such as underground bunkers. Needless to say, it is also capable of delivering nuclear weapons.

This stealthy aircraft was designed in a way that enemies could not anticipate its arrival, but its 22,600 Kg bomb load and a multitude of nuclear missiles would ensure they'd know when it had arrived. Named the B-2 Spirit, its advantage in battle is derived from its designation spirit; it operates like a ghost.

Engines: Four General Electric F118-GE-100 turbofans of 17,300 lbs. thrust each
Wingspan: 172 ft.
Length: 69 ft.
Height: 17 ft.
Speed: High subsonic
Takeoff weight: 336,500 lbs. ...

Dolphins are regarded as the second smartest animal alive, and are only outwitted by humans. Compared to other animals their size, dolphin brains are five times larger. Dolphins have been shown to be self-aware, and are capable of a wide range of emotions.

How this bicycle got up in the tree has been the subject of plenty of local legend around Washington’s Vashon Island. The real story involves a boy in the 1950s who left his bike in the woods while playing with friends, because he didn’t like it. The bike was placed about two meters high in the tree, which eventually grew around it.