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Naked-eye planet

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In astronomy, the naked-eye planets are the five planets of our solar system that can be discerned with the naked eye without much difficulty. Hence, they were the only planets known to the ancients prior to the invention of the telescope. They are Mercury, Venus, Mars, Jupiter, and Saturn, the five planets closest to Earth. The name planet comes from the Greek term πλανήτης, planētēs, meaning "wanderer", as ancient astronomers noted how certain lights moved across the sky in relation to the other stars. In some cultures, the Sun and Moon have also been counted as planets, to make the seven classical planets.

Mercury and Venus are only visible in twilight hours as their orbits are interior to the Earth's orbit. Venus is the most prominent planet, being the third brightest object in the sky after the Sun and the Moon. Mercury is more difficult to see due to its unwavering proximity to the Sun. Mars is at its brightest when it is in opposition to the Earth, which occurs approximately every two years. Jupiter and Saturn are the largest of the five planets, but are further from the sun, and therefore receive less sunlight. Nonetheless, Jupiter is often the next brightest object in the sky after Venus. Saturn's luminosity is often enhanced by its rings, which reflect light back toward the Earth to varying degrees depending on their inclination to the ecliptic; however, the rings themselves are not visible to the naked eye from the Earth. Uranus is visible to the naked eye in principle on very clear nights, but unlike the true naked-eye planets it is always less luminous than several thousands of stars, and as such, does not stand out enough for its existence to be noticed without the aid of a telescope.

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The planets in culture and mythology

In some cultures, the five naked-eye planets are grouped with the Sun and the Moon, called luminaries (meaning "shining object") to form a group of seven heavenly objects (or seven lights of the Earth, starry planets, traditional planets, etc.). Because their existence was known by many cultures throughout the world, since before recorded history, no discoverer is credited for them. The planets were typically named after the gods of their culture. Most Western cultures refer to them by their Latin names in honor of the Roman pantheon and their number probably led to the naming of the seven-day week.

Every culture has woven them into their myths and legends. They are the basis of the practice of astrology. In English, the planets bear names of gods in Roman mythology, a relic of the ancient belief that planets were gods controlling human destiny. They were sometimes considered to be living beings, and myths were created concerning how they came to be, and what they were supposed to be like, based on their movements in the sky, their physical characteristics, and the supposed influences they have on our planet and its inhabitants.

Days of the week

The Ptolemaic system used in Greek astronomy placed the planets in order, closest to Earth to furthest, as the Moon, Mercury, Venus, Sun, Mars, Jupiter, and Saturn. In addition the day was divided into 7-hour intervals, each ruled by one of the planets.

The first hour of each day was named after the ruling planet, giving rise to the names and order of the Roman seven-day week. Modern Latin-based cultures, in general, directly inherited the days of the week from the Romans and they were named after the classical planets—for example in Spanish Miercoles = Mercury, in French Mardi = Mars.

The modern English days of the week were inherited from gods of the old Germanic Norse culture—Thursday = Thor, Friday = Frige (Venus). It can be correlated that the Norse gods were attributed to each of the Roman planets and their gods, probably due to Roman influence rather than coincidentally by the naming of the planets.

In astrology

Astrology was developed when only the naked-eye planets were known. Because they appear to move in cycles about us in the heavens, whereas the "fixed" stars (what we today call the stars) did not, the planets were grouped together with the luminaries and considered to have divinatory significance. At the same time, a distinction was made within this category for the greater importance and brightness of the luminaries (the Sun and the Moon). For more on the significance of naked-eye planets in astrology, see Mercury (astrology), Venus (astrology), Mars (astrology), Jupiter (astrology), and Saturn (astrology).

In Islam

Muslims are encouraged to make a pilgrimage to Mecca at least once in their lifetimes, and during their visit many of them take part in a ritual which includes walking seven times around the Kaaba. According to some, this represents the seven heavenly objects and their revolutions around the Earth.

In Judaism

According to the Jewish Enclopedia and the Jewish historian Josephus, the seven branches of the Jewish Menorah represent the seven heavenly objects.

In East Asia

For the five true planets, their element's Chinese character, kanji, is also part of the names of weekdays in Chinese as well as Japanese, complemented with Sunday and Monday.

In China

The cycles of the Chinese calendar are linked to the orbit of Jupiter, there being 12 sacred beasts in the Chinese dodecannualar geomantic and astrological cycle, and 12 years in the orbit of Jupiter.

In Japan

Trivia

See also

External links

 

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