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Charles Babbage, an Angleščina mechanical engineer and polymath, originated the concept of a programmable computer. Considered the “father of the computer”, [34] he conceptualized and invented the first mechanical computer in the early 19th century. After working on his revolutionary difference engine, designed to aid and navigational calculations, and in 1833 he realized that a much more general design, an Analytical Engine, was possible. The input of programs and data was to be provided to the machine via punched cards, a method being used at the time to direct mechanical looms such as the Jacquard loom. For output, the machine would have a printer, a curve plotter and a bell. The machine would also be able to punch numbers onto cards to be read in later. It employed ordinary base-10 fixed-point arithmetic.

The Engine incorporated an arithmetic logic unit, control flow in the form of conditional branching and loops, and integrated memory, making it the first design for a general-purpose computer that could be described in modern terms as Turing-complete. [35] [ 36]

There was to be a store, or memory, capable of holding 1,000 numbers of 40 decimal digits each (about 16.7 MB). An arithmetical unit, called the “mill”, would be able to perform all four arithmetic operations, plus comparisons and Optionally square roots. Initially it was conceived as a difference engine curved back upon itself, and a generally circular layout, [37] with the long store exiting off to one side. (Later drawings depict a regularized grid layout.) [38] Like the central processing unit (CPU) and a modern computer, the mill would rely upon its own internal procedures, roughly equivalent to microcode and modern CPUs, to be stored in the form of pegs inserted into rotating drums called “barrels”, to carry out some of the more complex instructions the user’s program might specify.

The programming language to be employed by users was akin to modern day assembly languages. Loops and conditional branching were possible, and so the language as conceived would have been Turing-complete as later defined by Alan Turing. Three different types of punch cards were used: one for arithmetical operations, one for numerical constants, and one for load and store operations, transferring numbers from the store to the arithmetical unit or back. There were three separate readers for the three types of cards.

The machine was about a century ahead of its time. However, the project was slowed by various problems including disputes with the chief machinist building parts for it. All the parts for his machine had to be made by hand – this was a major problem for a machine with thousands of parts. Eventually, the project was dissolved with the decision of the British Government to cease funding. Babbage’s failure to complete the analytical engine can be chiefly attributed to difficulties not only of politics and financing, but also to his desire to develop an increasingly sophisticated computer and to move ahead faster than anyone else could follow. Ada Lovelace, Lord Byron’s daughter, translated and added notes to the “Sketch of the Analytical Engine” by Luigi Federico Menabrea. This appears to be the first published description of programming. [40]

Following Babbage, although unaware of his earlier work, was Percy Ludgate, an accountant from Dublin, Ireland. He independently designed a programmable mechanical computer, which he described in a work that was published in 1909.

 

In the first half of the 20th century, analog computers were considered by many to be the future of computing. These devices used the continuously changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved, in contrast to digital computers that represented varying quantities symbolically, as their numerical values change. As an analog computer does not use discrete values, but rather continuous values, processes can not be reliably repeated with exact equivalence, as they can with Turing machines. [42]

The first modern analog computer was a tide-predicting machine, invented by Sir William Thomson, later Lord Kelvin, in 1872. It used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location and was of great utility to navigation in shallow waters. His device was the foundation for further developments in analog computing. [43]

The differential analyzer, a mechanical analog computer designed to solve differential equations by integration using wheel-and-disc mechanisms, was conceptualized in 1876 by James Thomson, the brother of the more famous Lord Kelvin. He explored the possible construction of such calculators, but was stymied by the limited output torque of the ball-and-drive integrators. [44] And a differential analyzer, the output of one integrator drove the input of the next integrator, or a graphing output.

When meteoroids intersect with the Earth’s atmosphere at night, they are likely to become visible as meteors. If meteoroids survive the entry through the atmosphere and reach the Earth’s surface, they are called meteorites. Meteorites are transformed in structure and chemistry by the heat of entry and force of impact. A noted 4-meter asteroid, 2008 TC3, was observed in space on a collision course with the Earth on 6 October 2008 and entered the Earth’s atmosphere the next day, striking a remote area of northern Sudan. It was the first time that a meteoroid had been observed in space and tracked prior to impacting the Earth.[9] NASA has produced a map showing the most notable asteroid collisions with the Earth and its atmosphere from 1994 to 2013 from data gathered by U.S. government sensors (see below).
A meteor, known colloquially as a “shooting star” or “falling star”, is the visible passage of a glowing meteoroid, micrometeoroid, comet or asteroid through the Earth’s atmosphere, after being heated to incandescence by collisions with air molecues in the upper atmosphere,[9][21][22] creating a streak of light via its rapid motion and sometimes also by shedding glowing material in its wake. Meteors typically occur in the mesosphere at altitudes from 76 to 100 km (47 to 62 mi).[23] The root word meteor comes from the Greek meteōros, meaning “high in the air”.[21]

Millions of meteors occur in the Earth’s atmosphere daily. Most meteoroids that cause meteors are about the size of a grain of sand.[citation needed] Meteors may occur in showers, which arise when the Earth passes through a stream of debris left by a comet, or as “random” or “sporadic” meteors, not associated with a specific stream of space debris. A number of specific meteors have been observed, largely by members of the public and largely by accident, but with enough detail that orbits of the meteoroids producing the meteors have been calculated. All of the orbits passed through the asteroid belt.[24] The atmospheric velocities of meteors result from the movement of Earth around the Sun at about 30 km/s (18 miles/second),[25] the orbital speeds of meteoroids, and the gravity well of Earth.

Meteors become visible between about 75 to 120 km (47 to 75 mi) above the Earth. They usually disintegrate at altitudes of 50 to 95 km (31 to 59 mi).[26] Meteors have roughly a fifty percent chance of a daylight (or near daylight) collision with the Earth. Most meteors are, however, observed at night, when darkness allows fainter objects to be recognized. For bodies with a size scale larger than 10 cm to several meters meteor visibility is due to the atmospheric ram pressure (not friction) that heats the meteoroid so that it glows and creates a shining trail of gases and melted meteoroid particles. The gases include vaporised meteoroid material and atmospheric gases that heat up when the meteoroid passes through the atmosphere. Most meteors glow for about a second.
Although meteors have been known since ancient times, they were not known to be an astronomical phenomenon until early in the 19th century. Prior to that, they were seen in the West as an atmospheric phenomenon, like lightning, and were not connected with strange stories of rocks falling from the sky. In 1807, Yale University chemistry professor Benjamin Silliman investigated a meteorite that fell in Weston, Connecticut.[27] Silliman believed the meteor had a cosmic origin, but meteors did not attract much attention from astronomers until the spectacular meteor storm of November 1833.[28] People all across the eastern United States saw thousands of meteors, radiating from a single point in the sky. Astute observers noticed that the radiant, as the point is now called, moved with the stars, staying in the constellation Leo.[29]

The astronomer Denison Olmsted made an extensive study of this storm, and concluded that it had a cosmic origin. After reviewing historical records, Heinrich Wilhelm Matthias Olbers predicted the storm’s return in 1867, which drew the attention of other astronomers to the phenomenon. Hubert A. Newton’s more thorough historical work led to a refined prediction of 1866, which proved to be correct.[28] With Giovanni Schiaparelli’s success in connecting the Leonids (as they are now called) with comet Tempel-Tuttle, the cosmic origin of meteors was now firmly established. Still, they remain an atmospheric phenomenon, and retain their name “meteor” from the Greek word for “atmospheric”
A fireball is a brighter-than-usual meteor. The International Astronomical Union (IAU) defines a fireball as “a meteor brighter than any of the planets” (apparent magnitude −4 or greater).[31] The International Meteor Organization (an amateur organization that studies meteors) has a more rigid definition. It defines a fireball as a meteor that would have a magnitude of −3 or brighter if seen at zenith. This definition corrects for the greater distance between an observer and a meteor near the horizon. For example, a meteor of magnitude −1 at 5 degrees above the horizon would be classified as a fireball because, if the observer had been directly below the meteor, it would have appeared as magnitude −6.[32]

Fireballs reaching apparent magnitude −14 or brighter are called bolides.[33] The IAU has no official definition of “bolide”, and generally considers the term synonymous with “fireball”. Astronomers often use “bolide” to identify an exceptionally bright fireball, particularly one that explodes. They are sometimes called detonating fireballs (also see List of meteor air bursts). It may also be used to mean a fireball which creates audible sounds. In the late twentieth century, bolide has also come to mean any object that hits the Earth and explodes, with no regard to its composition (asteroid or comet).[34] The word bolide comes from the Greek βολίς (bolis) [35] which can mean a missile or to flash. If the magnitude of a bolide reaches −17 or brighter it is known as a superbolide.[33][36] A relatively small percentage of fireballs hit the Earth’s atmosphere and then pass out again: these are termed Earth-grazing fireballs. Such an event happened in broad daylight over North America in 1972. Another rare phenomena is a meteor procession, where the meteor breaks up into several fireballs traveling nearly parallel to the surface of the Earth.

A steadily growing number of fireballs are recorded at the American Meteor Society every year.[37] There are probably more than 500,000 fireballs a year,[38] but most will go unnoticed because most will occur over the ocean and half will occur during daytime.

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