Rikunarita-ORG/Wikinium huggingface dataset:
# Longitude

Map of Earth showing some major latitudes
**Longitude** is a way to say where a place is on the Earth. It is measured starting from an imaginary north–south line called the Prime Meridian. (A meridian is an imaginary line drawn from the North Pole to the South Pole.) Longitude says how far east (positive numbers) or west (negative numbers) of the Prime Meridian any place is.

Longitude is measured using degrees, the same way an angle is. The Prime Meridian is 0° (zero degrees), and the farthest away is +180° eastward and -180° westward. Unlike latitude, which has the equator as a natural starting position, there is no natural starting position for longitude. Other meridians have been used in the past, but most scientists now agree to use the Prime Meridian.

For centuries, navigators at sea were seldom able to know their longitude. The problem was solved by making better clocks (chronometers) in the early 19th century.

Unlike latitude, longitude does not maintain a constant distance between degrees since meridians all come together at the poles and are far apart at the equator. This means people near the North or South Pole can cross many degrees of longitude by travelling a short distance. The time difference between longitudes is 4 minutes per degree. The distance between degrees of longitude is maximum at the equator.

## Related pages

* Latitude

What are the lines latitude and longitude Archived 2021-09-27 at the Wayback Machine
# Meridian

A **meridian** is an imaginary line of longitude drawn along the surface of the earth from the North Pole to the South Pole.

Geographers today measure these lines from what they call the Prime Meridian. It is the line of longitude that goes through the Royal Greenwich Observatory in Greenwich, England. They decided this at the 1884 *International Meridian Conference*.

Meridians, as lines of longitude, are measured in degrees. The Prime Meridian, as the starting point, is 0 (zero) degrees. Lines west of the Prime Meridian are either called *west*, as in "the longitude of Los Angeles, California is 118 degrees west", or as a negative number: "the longitude of Los Angeles, California is -118 degrees". Going the other direction, east of the Prime Meridian is always said as a positive number: "The longitude of Mecca is about 40 degrees east," or just "The longitude of Mecca is about 40 degrees."

## Related pages

* Eastern Hemisphere
* Western Hemisphere
* International Date Line
# Sundial

A sundial
A garden sundial at 9:30am
A **sundial** shows the current solar time during the day. It does this because the sun appears to move through the sky. At different times in the day when the sun is shining, a shadow is cast in different places on the dial. A person marks the dial with the time at a certain shadow. This lets users easily see the time. There are a few commonly seen designs, such as the 'ordinary' or standard horizontal garden sundial. However, sundials can be designed for any surface where a fixed object casts a predictable shadow. They may be horizontal or vertical or tilted.

Ancient Egypt had sundials. Other cultures developed them further, including the Greeks and Romans.

## Related pages

* Time
* Water clock
* Clock

## Other websites

* Sunbeams and Sundials Children's guide to the sun, the seasons and sundials.
* There is a book from 1319 that talks about sundails
* There is another old book from the 1500's that talks about how to make a sundial. It's written in the Arabic language
# Celestial equator

The celestial equator is inclined by 23.5° to the ecliptic plane. The image shows the relations between Earth's axial tilt (or *obliquity*), rotation axis and plane of orbit.
The **celestial equator** is a term in observational astronomy. It is a great circle on the imaginary celestial sphere, in the same plane as the Earth's equator. In other words, it is a projection of the terrestrial equator out into space. As a result of the Earth's axial tilt, the celestial equator is inclined by 23.4° with respect to the ecliptic plane.

An observer standing on the Earth's equator visualizes the celestial equator as a semicircle passing directly overhead through the zenith. As the observer moves north (or south), the celestial equator tilts towards the southern (or northern) horizon. At the poles, the celestial equator is parallel to the horizon.

The observer always sees the ends of the semicircle disappear over the horizon exactly due east and due west, regardless of the observer's position on Earth.
# Rail transport

Rail transport.
Train station in the city of Mumbai. Railways in India carry about 17 million passengers every year and are one of the busiest in the world
**Rail transport** is the movement of passengers and goods using wheeled vehicles called trains, made to run on railway tracks. In most countries, this transportation method helps trade and economic growth. Railways (British English) or railroads (American English) provide an energy-efficient way to transport material over land. The railway tracks are a large part of the system and provide smooth and hard surfaces on which the wheels of the train roll with a little friction. Also, the track spreads the weight of the train which means larger loads can be carried than with trucks on roads.

Rail transport started to be important in the Industrial Revolution. In France the areas that adopted steam-power quicker in the mid-1800s got more jobs (122% more) and higher wages than other areas which were slower.

The first railroads were built in England.

Rolling stock on rails generally encounters lower frictional resistance than rubber-tyred road vehicles, allowing rail cars to be coupled into longer trains. Power is usually provided by diesel or electrical locomotives. While railway transport is capital-intensive and less flexible than road transport, it can carry heavy loads of passengers and cargo with greater energy efficiency and safety.

Modern rail transport began with the invention of the steam locomotive in Great Britain around 1800. The first passenger railway, the Stockton and Darlington Railway, opened in 1825. The quick spread of railways throughout Europe and North America, following the 1830 opening of the first intercity connection in England, between Liverpool and Manchester, was a key part of the Industrial Revolution. Rail transport lowered shipping costs compared to water transport, leading to "national markets" in which prices varied less from city to city.

In the 1880s, railway electrification began with tramways and rapid transit systems. Starting in the 1940s, steam locomotives were replaced by diesel locomotives. The first high-speed railway system was introduced in Japan in 1964, and high-speed rail lines now connect many cities in Europe, East Asia, and the eastern United States. Following some decline due to competition from cars and fixed-wing aircrafts, rail transport has had a revival in recent decades due to road congestion and rising fuel prices, as well as governments investing in rail as a means of reducing CO2 emissions.

## Related pages

* Level crossing
* Railway station
* Train
# Rotation

A sphere rotating around its axis
**Rotation** is the movement of an object in a circular motion.

A two-dimensional object rotates around a *center* (or *point*) *of rotation*. A three-dimensional object rotates around a line called an *axis*. If the axis of rotation is within the body, the body is said to rotate upon itself, or *spin*– which implies relative speed and perhaps free-movement with angular momentum. A circular motion around an external point (for example the Earth around the Sun) is called an *orbit* or more properly *orbital revolution.* As an extension, 4d rotations are around planes. Every rotation can also be described as in a plane and around a point.

## Types of rotation

The Clockwise direction
Rotation around a point in one plane can be in a clockwise direction or an anticlockwise direction.

### Aviation

In flight dynamics, the principal rotations are known as *yaw* (left/right), *pitch* (up/down), and *roll* (rolling). The term rotation is also used in aviation to refer to the upward pitch of an aircraft, particularly when starting the major climb for takeoff. The same terms are used for fish moving through water.

### Amusement rides

Many amusement rides provide rotation. A Ferris wheel and observation wheel have a horizontal central axis, and parallel axes for each gondola, where the rotation is opposite, by gravity or mechanically.

### Sports

Rotation, usually called *spin*, plays a role in many sports. *Topspin* and *backspin* in tennis. *English*, *follow* and *draw* in billiards and pool. Curve balls in baseball and spin bowling in cricket. Table tennis paddles are specialized to allow players to spin the ball as they hit it.

## Related pages

* Earth's spin
* Precession
* Torque

## Other websites

* Product of Rotations at *cut-the-knot*
* When a Triangle is Equilateral at *cut-the-knot*
* Rotation (Interactive Animation) at Math is Fun
* Rotate Points Using Polar Coordinates Archived 2007-02-20 at the Wayback Machine
# Ceres (dwarf planet)

Ceres | Ceres, photographed by the *Dawn* mission |
| Discovery |
| Discovered by | Giuseppe Piazzi |
| Discovery date | January 1, 1801 |
| Designations |
| MPC designation | **1 Ceres** |
| Alternative designations | A899 OF; 1943 XB |
| Minor planet category | dwarf planet main belt |
| Orbital characteristics |
| Epoch November 26, 2005 (JD 2453700.5) |
| Aphelion | 447,838,164 km 2.987 AU |
| Perihelion | 381,419,582 km 2.544 AU |
| Semi-major axis | 414,703,838 km 2.765 956 424 AU |
| Eccentricity | 0.07976017 |
| Orbital period | 1679.819 days 4.599 years |
| Average orbital speed | 17.882 km/s |
| Mean anomaly | 108.509° |
| Inclination | 10.586712° |
| Longitude of ascending node | 80.40696° |
| Argument of perihelion | 73.15073° |
| Physical characteristics |
| Mean radius | 473 km |
| Flattening | 0.067 ± 0.005 |
| Mass | 9.46 ± 0.04×1020 kg |
| Mean density | 2.08 g/cm3 |
| Equatorial surface gravity | 0.27 m/s² 0.028 g |
| Equatorial escape velocity | 0.51 km/s |
| Sidereal rotation period | 0.3781 d 9.074 h |
| Geometric albedo | 0.113 (geometric) |
|

| Surface temp. | min | mean | max |
| --- | --- | --- | --- |
| Kelvin |  | ~167 K | 239 K |

 |
| Spectral type | G |
| Apparent magnitude | 6.7 to 9.32 |
| Absolute magnitude *(H)* | 3.34 |
| Angular diameter | 0.84" to 0.33" |
|  |

**Ceres**, also known as **1 Ceres** (symbol: ), is the smallest dwarf planet in the Solar System and the only one in the main asteroid belt.

It was discovered on 1 January 1801, by Giuseppe Piazzi, and is named after the Roman goddess Ceres, as the goddess of growing plants, the harvest, and motherly love. After about 200 years from its discovery, the International Astronomical Union decided to upgrade Ceres from an asteroid (or minor planet) to dwarf planetary status in 2006.

With a diameter of about 950 km, Ceres is by far the largest and most massive object in the asteroid belt, and has about a third of the belt's total mass. It was once thought to be smaller than Vesta, which is brighter. The asteroid is spherical, unlike the irregular shapes of smaller bodies with lower gravity. At its brightest it is still too dim to be seen with the naked eye. Ceres is located at 2.8 AU (257 million miles) from the Sun, which makes it the closest dwarf planet to the Sun. It is also the only dwarf planet in the Solar System that has no moons.

On September 27, 2007, NASA launched the Dawn space probe to explore Ceres and Vesta. In 2015, Dawn became the first spacecraft to visit a dwarf planet, arriving at Ceres a few months before NASA's New Horizons spacecraft visited Pluto, another dwarf planet.

Ceres has an unusual crater, Occator which contains bright salts.

## Images

Close up image of bright salts, imaged by the Dawn spacecraft, in the crater Occator on Ceres.
## Related pages

* Ceres
* List of planets