The unit of time is the second. The minute (60 seconds) and hour (60 minutes or 3600 seconds) are larger units. A day is defined as 24 hours, but the Earth’s rotation has slowed. The difference is corrected at the end of some years with what is called a leap second. A week (7 days) and month are also standard units.
A unit of measurement that applies to money is called a unit of account. This is normally a currency issued by a country. For instance, the United States use dollars. Each dollar is 100 cents. The United Kingdom uses pounds. Each pound is 100 pennies or pence. The European Union uses the Euro. There are 100 cents in the Euro.
The units for electricity, magnetism and radiation were mostly invented in the 19th century when scientists learned how to measure them. Most were originally given imperial systems, but it is usual to use metric systems for them today.
United States customary units
U.S. customary units is the system of units of measurement used to measure things in the United States. The system of Imperial units is similar and in some parts identical.
Length or distance units include the inch, foot, yard and mile.
Land units include square miles (2589998.47032 square meter) and acres (4046.8726 square meter).
Common volume units are the teaspoon, tablespoon (3 teaspoons), fluid ounce (two tablespoons), cup (8 ounces), pint (2 cups, or 16 fluid ounces), quart (2 pints, or 32 fluid ounces), US gallon (16 cups, 128 fluid ounces, or 3.8 liters).
A barrel is the unit to measure oil.
Temperature is measured in degrees Fahrenheit (°F). Here is a formula to convert from °C to °F: formula_1
Units of weight and mass include the pound (453.6 grams), which contains 16 ounces. This should not be confused with the British pound which is a type of money. The different uses of the word "pound" can cause confusion. Different sizes of ounce are also in use.
Some people have been trying to replace these units with the metric system since the 1820s. Much infrastructure in the United States and British Empire was built in past centuries using the old measures. During the 20th century some sectors such as science, medicine and the military of the United States converted to metric but Americans still use the old units for daily purposes. On the other hand, world trade is conducted using the metric system and except for the US, the world uses the metric system for almost all purposes.
Uranus
Uranus is the seventh planet from the Sun in the Solar System. It is an ice giant. It is the third largest planet in the solar system.
The planet is made of ice, gases and liquid metal. Its atmosphere contains hydrogen (H), helium (He) and methane. The temperature on Uranus is near the top of its atmosphere, but its small solid core (about 55% the mass of Earth) is probably about .
The planet is tilted on its axis so much that it is sideways. It has five big moons, many small ones, and a small system of 13 planetary rings.
The distance between Uranus and the Sun is about 2.8 billion km. Uranus completes its orbit around the Sun in 84 earth years. It completes a spin around itself in 17 hours and 14 minutes. This means there are about 43,000 Uranian days in one Uranian year.
Uranus was discovered in 1781. This planet can be seen with the naked eye under perfect conditions. John Flamsteed saw it decades earlier but mistook it for a star (34 Tauri).
Uranus is named after Uranus, the Greek name of the Sumerian god Anu, who was a god of the sky.
Uranus has 27 known moons. They are named for characters from the works of Shakespeare and Alexander Pope. The five biggest moons are Miranda, Ariel, Umbriel, Titania and Oberon. Many moons have yet to be discovered.
In 1986, NASA's "Voyager 2" visited Uranus. This is the only space probe that tried to investigate the planet from a short distance.
Uranus is covered in blue clouds. The top clouds, made of methane, are difficult to see. Lower clouds are thought to be frozen water. There are also violent storms. Wind speeds can reach . Scientists are studying the clouds to try to understand the storms on the planet.
The planet Uranus has a system made of 13 rings which is far fewer than the rings of Saturn but more than those around Jupiter and Neptune. The rings of Uranus were discovered in 1977. More than 200 years ago, William Herschel also reported observing rings, but modern astronomers do not believe that he saw them, because they are very dark and faint. Two additional rings were discovered in 1986 in images taken by Voyager 2, and two outer rings were found in 2003–2005 by the Hubble Space Telescope. The rings are probably mainly composed of frozen water.
The rings of Uranus are thought to be relatively young, not more than 600 million years old. The Uranian ring system probably began from the collisional fragmentation of moons that once existed around the planet. After colliding, the moons probably broke up into many particles, which survived as narrow, optically dense rings only in zones of maximum stability.
The ring system of Uranus has thirteen distinct rings. In order of increasing distance from the planet they are: 1986U2R/ζ, 6, 5, 4, α, β, η, γ, δ, λ, ε, ν, μ rings. They can be divided into three groups: nine narrow main rings (6, 5, 4, α, β, η, γ, δ, ε), two dusty rings (1986U2R/ζ, λ) and two outer rings (μ, ν). The rings of Uranus consist mainly of macroscopic particles and little dust, although dust is known to be present in 1986U2R/ζ, η, δ, λ, ν and μ rings.
In addition to these well-known rings, there may be numerous optically thin dust bands and faint rings between them. These faint rings and dust bands may exist only temporarily. Some of them became visible during a series of ring plane-crossing events in 2007. A number of dust bands between the rings were observed in forward-scattering geometry by "Voyager 2". All rings of Uranus show azimuthal brightness variations.
The rings are made of an extremely dark material. The rings are slightly red in the ultraviolet and visible parts of the spectrum and grey in near-infrared. They show no identifiable spectral features. The chemical composition of the ring particles is not known. However, they cannot be made of pure water ice like the rings of Saturn because they are too dark, darker than the inner moons of Uranus. This shows that they are probably a mixture of the ice and a dark material. The nature of this material is not clear, but it may be organic compounds considerably darkened by the charged particle irradiation from the Uranian magnetosphere. The rings' particles may consist of a heavily processed material which was initially similar to that of the inner moons.
As a whole, the ring system of Uranus is unlike either the faint dusty rings of Jupiter or the broad and complex rings of Saturn, some of which are composed of very bright material—water ice. However, there are similarities with some parts of the latter ring system; the Saturnian F ring and the ε ring are both narrow, relatively dark and are shepherded by a pair of moons. The newly discovered outer rings of Uranus are similar to the outer G and E rings of Saturn. Narrow ringlets existing in the broad Saturnian rings also resemble the narrow rings of Uranus. In addition, dust bands observed between the main rings of Uranus may be similar to the rings of Jupiter. In contrast, the Neptunian ring system is quite similar to that of Uranus, although it is less complex, darker and contains more dust. The Neptunian rings are also positioned further from the planet.