Sun vs Cairo

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The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy mainly as light and infrared radiation. It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometres (864,000 miles), or 109 times that of Earth, and its mass is about 330,000 times that of Earth. It accounts for about 99.86% of the total mass of the Solar System. Roughly three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.The Sun is a G-type main-sequence star (G2V) based on its spectral class. As such, it is informally and not completely accurately referred to as a yellow dwarf (its light is closer to white than yellow). It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core. It is thought that almost all stars form by this process.

In its core the Sun currently fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result. This energy, which can take between 10,000 and 170,000 years to escape the core, is the source of the Sun's light and heat. When hydrogen fusion in its core has diminished to the point at which the Sun is no longer in hydrostatic equilibrium, its core will undergo a marked increase in density and temperature while its outer layers expand, eventually transforming the Sun into a red giant. It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus, and render Earth uninhabitable – but not for about five billion years. After this, it will shed its outer layers and become a dense type of cooling star known as a white dwarf, and no longer produce energy by fusion, but still glow and give off heat from its previous fusion. The enormous effect of the Sun on Earth has been recognized since prehistoric times. The Sun has been regarded by some cultures as a deity. The synodic rotation of Earth and its orbit around the Sun are the basis of solar calendars, one of which is the predominant calendar in use today.

Source: Wikipedia

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Cairo ( KY-roh; Arabic: القاهرة‎, romanized: al-Qāhirah, pronounced [ælˈqɑːhɪɾɑ] (listen), Coptic: ⲕⲁϩⲓⲣⲏ) is the capital of Egypt and the largest city in the Arab world. Its metropolitan area, with a population of over 20 million, is the biggest in Africa, the Arab world, and the Middle East, and the 6th-largest in the world. Cairo is associated with ancient Egypt, as the famous Giza pyramid complex and the ancient city of Memphis are situated in its geographical location. Located near the Nile Delta, Cairo was founded in 969 AD by the Fatimid dynasty, but the property composing the present-day city was the site of early national capitals whose descendants stay visible in parts of Old Cairo. Cairo has long been a centre of the region's cultural and political life, and is titled"the city of a thousand minarets" for its preponderance of Islamic architecture. Cairo is considered a World City with a"Beta +" classification based on GaWC.Cairo has the oldest and largest film and music industries in the Arab world, as well as the world's second-oldest institution of higher learning, Al-Azhar University.

Many international media, businesses, and organizations have regional headquarters in the city; the Arab League has had its headquarters in Cairo for the majority of its existence. With a population of over 9 million spread over 3,085 square kilometers (1,191 sq mi), Cairo is definitely the largest city in Egypt. An additional 9.5 million individuals reside in close proximity to the city. Cairo, like many other megacities, suffers from high levels of traffic and pollution. The Cairo Metro is one of the only two subway systems in Africa (the other being in Algiers, Algeria), and ranks amongst the fifteen busiest in the world, with over 1 billion annual passenger rides. The market of Cairo was ranked first in the Middle East in 2005, and 43rd internationally on Foreign Policy's 2010 Global Cities Index.

Source: Wikipedia