Naked eye planets
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In astronomy, the naked eye planets are the five planets of our solar system that can be seen with the naked eye. 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 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.
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 lumonisity 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.
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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, etc.),
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.
The days of the week are named after them in many cultures. 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.
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. 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.