Are you real? What about me?
These used to be questions that only philosophers worried about. Scientists just got on with figuring out how the world is, and why. But some of the current best guesses about how the world is seem to leave the question hanging over science too.
Science calls it "Pangaea Proxima". You might prefer to call it the Next Big Thing. A supercontinent is on its way that incorporates all of Earth's major landmasses, meaning you could walk from Australia to Alaska, or Patagonia to Scandinavia. But it will be about 250 million years in the making.
"Let us go rambling about the Universe." This is the invitation that American astronomer Harlow Shapley gave to an audience in Washington DC in 1920. He was taking part in the so-called Great Debate with fellow scientist Heber Curtis on the scale of the Universe.
It was September 2011 and physicist Antonio Ereditato had just shocked the world. The announcement he had made promised to overturn our understanding of the Universe. If the data gathered by 160 scientists working on the OPERA project were correct, the unthinkable had been observed.
The Moon is Earth's only permanent natural satellite, as well as the only celestial body besides Earth to have been visited by humans. It is the fifth largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits (its primary). It is the second-densest satellite among those whose densities are known (after Jupiter's satellite Io).
The Moon is thought to have formed approximately 4.5 billion years ago, not long after Earth. There are several hypotheses for its origin; the most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia.
The Moon is in synchronous rotation with Earth, always showing the same face, with its near side marked by dark volcanic maria that fill the spaces between the bright ancient crustal highlands and the prominent impact craters. It is the second-brightest regularly visible celestial object in Earth's sky after the Sun, as measured by illuminance on Earth's surface. Its surface is actually dark (although it can appear a very bright white) with a reflectance just slightly higher than that of worn asphalt. Its prominence in the sky and its regular cycle of phases have made the Moon an important cultural influence since ancient times on language, calendars, art, and mythology.
The Moon's gravitational influence produces the ocean tides, body tides, and the slight lengthening of the day. The Moon's current orbital distance is about thirty times the diameter of Earth, with its apparent size in the sky almost the same as that of the Sun, resulting in the Moon covering the Sun nearly precisely in total solar eclipse. This matching of apparent visual size will not continue in the far future. The Moon's linear distance from Earth is currently increasing at a rate of 3.82 ± 0.07 centimetres (1.504 ± 0.028 in) per year, but this rate is not constant.
The Soviet Union's Luna programme was the first to reach the Moon with unmanned spacecraft in 1959; the United States' NASA Apollo program achieved the only manned missions to date, beginning with the first manned lunar orbiting mission by Apollo 8 in 1968, and six manned lunar landings between 1969 and 1972, with the first being Apollo 11. These missions returned over 380 kg (840 lb) of lunar rocks, which have been used to develop a geological understanding of the Moon's origin, the formation of its internal structure, and its subsequent history. After the Apollo 17 mission in 1972, the Moon has been visited only by unmanned spacecraft.
Using a new high-speed camera, lightning researcher Ningyu Liu of the Florida Institute of Technology managed to film a lightning storm in slow motion. The footage, captured on 20 May, was recorded at 7,000 frames per second. For the video, Liu plays it back at 700 frames per second so you can savour every little detail.
The famous White Sands National Monument is made of gypsum, a mineral that normally dissolves in water. But here the climate is so dry that the grains have been preserved
Is our Universe one of many? The idea of parallel universes, once consigned to science fiction, is now becoming respectable among scientists – at least, among physicists, who have a tendency to push ideas to the limits of what is conceivable.
The recent film The Theory of Everything tells the story of Stephen Hawking, who managed to become a world-famous physicist despite being confined to a wheelchair by a degenerative disease. It's mostly about his relationship with his ex-wife Jane, but it does find a bit of time to explain what Hawking has spent his career doing.
Sailors out at sea would sometimes see a bluish glow seeming to shoot out of the ends of the masts of ships at night. The light wasn't hot and wouldn't burn anything on board. They took it to be a good omen and called it St Elmo's fire.