A 3.8-metre 150-inch infrared telescope, located at the Mauna Kea Observatories in Hawaii. It is operated from the Joint Astronomy Center in Hilo, Hawaii, for the UK Particle Physics and Astronomy Research Council. It is the largest telescope dedicated solely to infrared astronomy and operates in the wavelength band between 1 and 30 microns.

A 1.2-metre 48-inch Schmidt camera located at the Anglo-Australian Observatory and currently administered by the Anglo-Australian Telescope Board. It was opened in 1973 and for a time administered by the Royal Observatory, Edinburgh.

A US government observatory in Washington, DC, the main purpose of which is to provide the astronomical data required to support Navy and other Department of Defense activities. These include astrometry, the preparation of almanacs, time measurement and the maintenance of the Master Clock for the USA. It has astrographic telescopes located at Anderson Mesa, near Flagstaff, Arizona, and Black Birch, New Zealand, as well as in Washington. The observatory was founded in 1830 and given the title US Naval Observatory in 1844. For fifty years it was located at the site now occupied by the Lincoln Memorial. It was moved to its present site, next to the official residence of the Vice President, in 1893. The largest telescope at the site is the 66-centimetre 26-inch refractor, dating from 1873, with which Asaph Hall discovered the moons of Mars, Phobos and Deimos, in 1877. Other instruments there include a 30-centimetre 12-inch Alvan Clark refractor, two 61-centimetre 24-inch reflectors and a 15-centimetre 6-inch transit circle. The largest telescope belonging to the observatory is the 1.5-metre 61-inch astrometric reflector at Flagstaff. Using this instrument, James Christy discovered the moon of Pluto, Charon, in 1978. At the Arizona site, the observatory has also constructed an optical interferometer, the Navy Prototype Optical Interferometer, which was the largest of its kind when it came into operation in 1995. The US Naval Observatory also houses one of the world’s leading astronomical libraries.

A measure of time that relates closely to the Sun’s daily apparent motion and serves as the basis for civil timekeeping. It is formally defined by a mathematical formula that links it to sidereal time, and is thus determined from observations of the stars. The timescale taken directly from the stars, designated UT0, depends slightly on the place of observation. UT0 corrected for the shift in longitude of the observing station caused by polar motion is known as UT1. The use of the abbreviation UT normally implies UT1. Coordinated Universal Time UTC is the time used for broadcast time signals. It differs from International Atomic Time TAI by an integral number of seconds, and is maintained to within ±0.90 second of UT1 by introducing when necessary one-second steps - leap seconds.

The entirety of all that exists. The size of the observable universe is limited to the distance light has had time to travel since the Big Bang. See also: particle horizon.

A photographic technique used for processing images to reveal fine detail. A positive contact copy of a glass photographic plate is made on low-contrast film. The copy is blurred because of the glass between the film and the image on the plate. This blurred image contains the large-scale structure of the image and constitutes the unsharp mask. When replaced in contact with the back of the original plate, it effectively cancels out the large-scale structure, leaving fine detail to be seen much more easily.

Asteroid 30, diameter 94 km, discovered in 1854 by J. R. Hind.

The observatory of Tycho Brahe 1546-1601 on the island of Hven, north of Copenhagen. It was completed in 1580 and used by Brahe to make accurate astronomical observations for twenty years. Only ruins now remain.

A star atlas compiled by Johann Bayer 1572-1625, published in 1603. In this atlas Bayer introduced the system of labelling stars with Greek letters which is still in use.

A largely obsolete term for positional astronomy or astrometry.

The seventh major planet of the solar system in order from the Sun, discovered by William Herschel in 1781. It is just bright enough to be seen by the naked eye under good observing conditions. From the Earth, it appears as an almost featureless greenish disc, in even the largest telescope. In 1986, the space probe Voyager 2 passed close to Uranus and its satellites, providing close-up images of them. Ten small satellites were discovered by Voyager 2; five larger satellites were already known: Miranda, Ariel, Umbriel, Titania and Oberon. Uranus is one of the four gas giant planets of the solar system, with a diameter four times the Earth’s and a mass fifteen times greater. It is composed almost entirely of hydrogen and helium. It is generally believed that there is a small rocky core at the centre of the planet, which is surrounded by a thick icy mantle of frozen water, methane and ammonia. The outermost layer is an atmosphere of hydrogen and helium, with small quantities of some molecular compounds. Even in the Voyager close-ups, Uranus presents a bland, nearly featureless appearance, though there is some evidence for faint bands parallel to the equator. A curious feature of Uranus is that its rotation axis lies almost in the plane of the solar system, rather than being nearly perpendicular to it, as is the case for the other planets. The internal rotation period is 17 hours 14 minutes. In 1977, a series of narrow rings was discovered around Uranus in its equatorial plane. The rings are each only a few kilometres wide and not visible from Earth. The discovery occurred when Uranus occulted an eighth magnitude star. The rings caused small dips in the observed brightness of the star just before and just after the occultation by the disc of the planet. Later occultations, of Beta β Scorpii and Sigma σ Sagittarii, confirmed the result. The ring system was subsequently imaged by Voyager 2 in 1986, when two further rings were discovered, bringing the total to eleven.

A rare and unusual type of meteorite belonging to the achondrite class. The space between silicate grains is filled by a carbon-rich material, which in some examples has been transformed into diamond.

One of the most familiar constellations of the northern sky and the third largest in area. It contains nineteen stars brighter than fourth magnitude. The seven main stars of the constellation form an asterism known variously as the Plough, the Big Dipper and Charles’s Wain. The two stars Merak and Dubhe in the Plough are known as the Pointers since the line between them is effectively an arrow to Polaris, the Pole Star. Ursa Major is one of the ancient constellation listed by Ptolemy c. AD 140. It contains a group of galaxies belonging to the Local Supercluster, including the relatively bright spiral galaxy, M81.

The northern constellation in which the north celestial pole lies. The brightest star of Ursa Minor, the second magnitude Polaris, is within 1° of the pole. The constellation was among those listed by Ptolemy c. AD 140. Though fainter and smaller than the plough in Ursa Major, its main pattern of seven stars is somewhat similar and is known as the Little Dipper.

United States Naval Observatory.