Wandering Star

Wandering Star

In antiquity the classical planets were the non-fixed objects visible in the sky, known to various ancient cultures. The classical planets were therefore the Sun and Moon and the five non-earth planets of our solar system closest to the sun (and closest to the Earth); four of which are easily visible without a 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 with the other stars. They called these objects asteres planetai, or wandering stars. Together they form the seven classical planets, as well as the names of the seven days of the week - Sun-day, Moon-day, Saturn-day, and in Latin, 'Martis' (Mars, Tuesday), 'Mercurii' (Wednesday), 'Iovis' (Jupiter, Thursday) and 'Veneris' (Venus, Friday).

Mercury and Venus are only visible in twilight hours as their orbits are interior to the Earth's orbit. The third brightest object in the sky, Venus is the most prominent planet. Mercury is more difficult to see due to its proximity to the Sun. Lengthy twilight and an extremely low angle at maximum elongations make optical filters necessary to see Mercury from extreme northerly locations like Scandinavia or Alaska. Mars is at its brightest when it is in opposition, which occurs approximately every twenty-five Earth-months. Jupiter and Saturn are the largest of the five planets, but are farther 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 and sometimes the asteroid Vesta are visible to the naked eye in principle on very clear nights, but unlike the true naked-eye planets they are always less luminous than several thousands of stars, and as such, do not stand out enough for their existences to be noticed without the aid of a telescope.