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Barnard's Star is a very low-mass star in the constellation Ophiuchus which was discovered by the astronomer E. E. Barnard in 1916. Barnard measured its proper motion to 10.3 arcseconds per year, which remains the largest known proper motion of any star relative to the Sun. Lying at a distance of about 1.8 parsecs or 5.96 light-years, Barnard's Star is the second closest known star system to the Sun and the fourth closest known individual star after the three components of the Alpha Centauri system.
Barnard's Star is a relatively well-studied astronomical object, and has likely received more attention than any other M dwarf star given its proximity and favourable location for observation near the celestial equator. It has also been the subject of some controversy. For a decade from the early 1960s onward, an erroneous discovery of a planet or planets in orbit around Barnard's star was accepted by astronomers. It is also notable as the target for a study on the possibility of rapid, unmanned travel to nearby star systems. Research has focused on stellar characteristics, astrometry, and refining the limits of possible planets.
A black hole is an object predicted by general relativity with a gravitational field so strong that nothing can escape it — not even light.
A black hole is defined to be a region of space-time where escape to the outside universe is impossible. The boundary of this region is a surface called the event horizon. This surface is not a physically tangible one, but merely a figurative concept of an imaginary boundary. Nothing can move from inside the event horizon to the outside, even briefly.
The existence of black holes in the universe is well supported by astronomical observation, particularly from studying X-ray emission from X-ray binaries and active galactic nuclei. It has also been hypothesized that black holes radiate energy due to quantum mechanical effects known as Hawking radiation.
The Cat's Eye Nebula (NGC 6543) is a planetary nebula in the constellation of Draco. Structurally, it is one of the most complex nebulae known, with high-resolution Hubble Space Telescope observations revealing remarkable structures such as knots, jets and sinewy arc-like features.
It was discovered by William Herschel on February 15, 1786, and was the first planetary nebula whose spectrum was investigated, by the English amateur astronomer William Huggins in 1864.
Modern studies reveal several mysteries. The intricacy of the structure may be caused in part by material ejected from a binary central star, but as yet, there is no direct evidence that the central star has a companion. Also, measurements of chemical abundances reveal a large discrepancy between measurements done by two different methods, the cause of which is uncertain.
Comet Hyakutake (Japanese: 百武彗星 Hyakutake suisei, IPA [çakɯtake sɯiseː]; formally designated C/1996 B2) is a comet that was discovered in January 1996, and passed very close to the Earth in March of that year. It was dubbed The Great Comet of 1996, and was one of the closest cometary approaches to the Earth in the previous 200 years, resulting in the comet appearing very bright in the night sky and being seen by a large number of people around the world. The comet temporarily upstaged the long-awaited Comet Hale–Bopp, which was approaching the inner Solar System at the time, although Hyakutake was at its brightest for only a few days.
Scientific observations of the comet led to several notable discoveries. Most surprising to cometary scientists was the discovery of X-ray emission from the comet, the first time a comet had been found to be emitting X-rays. This emission is believed to be caused by ionised solar wind particles interacting with neutral atoms in the coma of the comet. The Ulysses spacecraft also unexpectedly crossed the comet's tail at a distance of more than 500 million km from the nucleus, showing that Hyakutake had the longest tail yet known for a comet.
Hyakutake is a long-period comet. Before its most recent passage through the Solar System, its orbital period was about 15,000 years, but the gravitational influence of the giant planets has now increased this to 72,000 years.