However, the insides of Great Dark Spots are mostly cloud-free, and unlike Jupiter's spot, which has lasted for hundreds of years, their lifetimes appear to be much shorter, forming and disappearing once every few years or so. Based on pictures taken by Voyager and since then with the Hubble Space Telescope, Neptune appears to spend a little bit more than half its time with a Great Dark Spot.
The dark, elliptically-shaped spot (with initial dimensions of 13,000 × 6,600 km, or 8,100 × 4,100 mi) was about the same size as Earth, and was similar looking to Jupiter's Great Red Spot. Around the Great Dark Spot, winds were measured blowing up to 2,400 kilometers (1,500 miles) an hour, the fastest in the Solar System. The Great Dark Spot is thought to be a hole in the methane cloud deck of Neptune. The spot was seen at different times with different sizes and shapes.
The Great Dark Spot generated large white clouds at or just below the tropopause layer similar to high-altitude cirrus clouds found on Earth. Unlike the clouds on Earth, however, which are made of mostly crystals of ice, Neptune's clouds are made up of crystals of frozen methane. And while Neptune's clouds usually form and then disappear within a period of a few hours, the clouds in the Great Dark Spot were still present after 36 hours, or two rotations of the planet.
Neptune's dark spots are thought to happen in the troposphere at lower heights (or altitudes) than the brighter upper cloud deck features. As they are stable features that can last for several months, they are thought to be vortex structures.
When pictures were going to be taken of the Great Dark Spot again in November 1994 by the Hubble Space Telescope, it had gone away completely, leaving astronomers to believe that it had either been covered up or that it had just disappeared. The persistence of companion clouds shows that some former dark spots may continue to exist as cyclones even though they are no longer able to be seen as a dark feature. Dark spots may disappear when they move too close to the equator or possibly through some other unknown way.
However, a new spot that looked very much like the old spot appeared in Neptune's northern hemisphere. This new spot, called the Northern Great Dark Spot (NGDS), has remained able to be seen for several years.
Supersonic
The term supersonic is used to describe a speed that is over the speed of sound (Mach 1). At a normal temperature like 70 degrees Fahrenheit (21.1 °C), the speed needed for something to be traveling at a faster than sound speed is about 344 m/s, 1,129 ft/s, 770 mph or 1,238 km/h. Speeds faster than 5 times the speed of sound are sometimes called hypersonic. Speeds where only some parts of the air around an object (like the propeller) reach supersonic speeds are called transonic (normally somewhere between Mach 0.8 and Mach 1.2).
Whips have operated supersonically for many centuries. Artillery became supersonic in the 19th century.
It can be very hard to reach supersonic speeds, because drag increases a lot near these speeds. This slows a plane, and for years made control difficult. These problems were called the "sound barrier". Jet engines and other developments solved the problems in the middle 20th century.
Small Dark Spot
The Small Dark Spot, sometimes also called Dark Spot 2 or The Wizard's Eye, was a southern cyclonic storm on the planet Neptune. It was the second strongest storm on the planet in 1989, when Voyager 2 flew by the planet. When first discovered, it was a dark cyclonic storm. As Voyager 2 approached the planet, a bright core of cloud activity developed. It disappeared in 1994.
Aitne (moon)
Aitne or ', is a non-spherical moon of Jupiter. It was found by a team of astronomers from the University of Hawaii led by Scott S. Sheppard, "et al." in 2001, and given the designation '.
Aitne is about 3 kilometres in diameter, and orbits Jupiter at an average distance of 22,285,000 km in 679.641 days, at an inclination of 166° to the ecliptic (164° to Jupiter's equator), with an orbital eccentricity of 0.393.
It was named in August 2003 after Aitna or Aitne, the divine personification of Mount Etna, whose sons by Zeus (Jupiter) are the Palici, the twin sicilian gods of geysers (other authors have them descend from Thalia and/or Hephaistos).
Aitne belongs to the Carme group, made up of non-spherical irregular retrograde moons orbiting Jupiter at a distance ranging between 23,000,000 and 24,000,000 km and at an inclination of about 165°.
William Lassell
William Lassell (June 18 1799 – October 5 1880) was a British astronomer, born in Bolton, Lancashire, England. He died in Maidenhead in 1880.
Roche limit
The Roche limit (), sometimes referred to as the Roche radius, is the distance within which a celestial body, held together only by its own gravity, will disintegrate due to a second celestial body's tidal forces exceeding the first body's gravitational self-attraction. Inside the Roche limit, orbiting material will tend to disperse and form planetary rings, while outside the limit, material will tend to coalesce. The term is named after Édouard Roche, the French astronomer who first calculated this theoretical limit in 1848.
Synchronous orbit
A synchronous orbit is an orbit in which an orbiting body (usually a satellite) has a period equal to the average rotational period of the body being orbited (usually a planet). Or in smaller words, the orbit above and the spinning planet below, go around once in the same amount of time. It orbits in the same direction of rotation as that body. So if you were on the orbiting body, you would always see the same side of the body being orbited. Or if you were on the body being orbited, the orbiting body would stay in the same part of the sky. Geostationary orbit is the most common kind.
François Arago
François Jean Dominique Arago (Catalan: Francesc Joan Dominic Aragó; February 26, 1786 – October 2, 1853) was a French mathematician, physicist, astronomer and politician.
S/2003 J 2
It seems to belong to a group all of its own, with a distant and retrograde orbit.
Santiago Rodríguez Province
Santiago Rodríguez is a province of the Dominican Republic. It is in the northwestern part of the country. Its capital city is San Ignacio de Sabaneta.
The province was created in 1948.
"Santiago Rodríguez" was an officer of the Dominican army when the Dominican-Haitian War. He is one of the founder of the city of Sabaneta. He was an important military leader during the initial stages of the "Restoration War" (1863-1865).
The town of San Ignacio de Sabaneta was founded in 1844 and it was made a municipality of the Santiago province in 1854 and then of the Monte Cristi Province province in 1879. In 1948, it became a province.
Monción was a municipality of Montecristi since 1907. In 1996, Villa Los Almácigos became a municipality.
Santiago Rodríguez is in the region known as "Línea Noroeste" ("Northwestern Line"). The province has the Monte Cristi and Valverde provinces to the north, the Santiago province to the east, the San Juan and Elías Piña provinces to the south and the Dajabón province to the west.
In (last national census), there were people living in the Santiago Rodríguez province, and 27,559 () living in towns and cities. The population density was persons/km².
Its population represents of the total population of the country and the province is ranked as the 30th (out of 31 plus the National District) more populated province.
, the total estimated propulation of the province is 1,015,397 inhabitants.
The largest city of the province is San Ignacio de Sabaneta, its head municipality or capital, with an urban population (in ) of 15,648 inhabitants.
The Santiago province has a total area of . It has of the area of the Dominican Republic and it is ranked as the 22nd (out of 31 plus the National District) largest province.
The altitude of the provincial capital, San Ignacio de Sabaneta, is above sea level.