There are between 700 and 1,000 species of leeches throughout the world. Most prey on insects, snails and other small creatures. Some swallow their prey whole. Others have an extendible proboscis, which they use to spear their prey and suck up their juices.
And then there are the “bloodsuckers.” These sanguivorous (blood-feeding) leeches feed on fish, reptiles, waterfowl, small mammals, earthworms (their closest biological relatives) and, yes — humans. Sanguivorous leeches generally have either two or three jaws, which contain small teeth or a sharp cutting edge. A bite from a two-jawed leech leaves a V-shaped bite, while that of the three-jawed variety results in a Y-shaped one.
As proof that first impressions can be misleading, one need not look further than Uranus. After the spacecraft Voyager 2 visited Uranus in 1986, it was dubbed “the most boring planet” in the Solar System. But recent photos from the Hubble Telescope reveal that Uranus is not as dull as once imagined.
For one thing, Uranus is the only planet other than Venus with a retrograde (i.e., clockwise) orbit. Unlike the other planets of the solar system, however, Uranus is tilted almost all the way over on its axis. Essentially, it orbits the sun on its side. Astronomers hypothesize that this unusual orientation might be due to a collision with a planet-sized body soon after Uranus was formed.
Because of its unusual axial tilt, each pole gets around 42 years of continuous sunlight, followed by 42 years of darkness. (A year on Uranus is equal to 84 years on Earth). Bizarrely, however, even though the poles receive more sun than the equator, Uranus is – for unknown reasons — hotter at its equator than at its poles. Continue reading →
Medieval alchemists were concerned with discovering the “philosopher’s stone,” a hypothetical substance they believed could convert base metals into gold. Though usually held to be a solid, sources sometimes describe it as a liquid also capable of curing diseases and/or staving off death — hence its alternative name, the “elixir of life”.
The first known references to alchemy exist in myths and legends about ancient China. Alchemy in the Western world seems to have originated in Egypt, though early records were destroyed around the year 300. The Roman emperor Diocletian was concerned that alchemically obtained gold and silver could be used to fund a revolt. So Diocletian issued a decree ordering the destruction of all books on the subject.