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If the Sun–Neptune distance is scaled to 100 metres (330 ft), then the Sun would be about 3 cm (1.2 in) in diameter (roughly two-thirds the diameter of a golf ball), the giant planets would be all smaller than about 3 mm (0.12 in), and Earth's diameter along with that of the other terrestrial planets would be smaller than a flea (0.3 mm or 0. ...
The definition of the term planet has changed several times since the word was coined by the ancient Greeks. Greek astronomers employed the term ἀστέρες πλανῆται (asteres planetai), 'wandering stars', for star-like objects which apparently moved over the sky.
One of the oldest fields in astronomy, and in all of science, is the measurement of the positions of celestial objects. Historically, accurate knowledge of the positions of the Sun, Moon, planets and stars has been essential in celestial navigation (the use of celestial objects to guide navigation) and in the making of calendars. [67]: 39
The closest approach of one celestial object to another, as viewed from a third body. apsis In the orbit of a planetary body, one of the two extreme points of distance between the body and its primary – either the point of minimal distance, called the periapsis, or the point of maximal distance, called the apoapsis. The term may also be used ...
This was an area where only one planet had been expected, and they were much smaller than all other planets; indeed, it was suspected that they might be shards of a larger planet that had broken up. Herschel called them asteroids (from the Greek for "starlike") because even in the largest telescopes they resembled stars, without a resolvable disk.
One of the oldest stars with a multiplanetary system, although it is still more metal-rich than the Sun. None of the known planets is in the habitable zone. [30] 61 Virginis: Virgo: 13 h 18 m 24.31 s: −18° 18′ 40.3″ 4.74: 28: G5V: 0.954: 5531: 8.96: 2 (1) Planet d remains unconfirmed, [31] and a 2021 study found that it was likely a ...
The term is also used to describe situations when all the planets are on the same side of the Sun although they are not necessarily in a straight line, such as on March 10, 1982. [ 8 ] Apparent planetary alignment involving Mercury, Venus, Mars, and Jupiter; the Moon is also shown, as the brightest object.
Hot Neptune – an exoplanet in an orbit close to its star (normally less than one astronomical unit away), with a mass similar to that of Uranus or Neptune. Pulsar planet – a planet that orbits a pulsar or a rapidly rotating neutron star. Rogue planet (also known as an interstellar planet) – a planetary-mass object that orbits the galaxy ...