Planets

A planet is an astronomical object orbiting a star or stellar remnant that
* is massive enough to be rounded by its own gravity,
* is not massive enough to cause thermonuclear fusion, and
* has cleared its neighbouring region of planetesimals.

The term planet is ancient, with ties to history, astrology, science, mythology, and religion. Several planets in the Solar System can be seen with the naked eye. These were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate obj A planet is an astronomical object orbiting a star or stellar remnant that
* is massive enough to be rounded by its own gravity,
* is not massive enough to cause thermonuclear fusion, and
* has cleared its neighbouring region of planetesimals.

The term planet is ancient, with ties to history, astrology, science, mythology, and religion. Several planets in the Solar System can be seen with the naked eye. These were regarded by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the International Astronomical Union (IAU) officially adopted a resolution defining planets within the Solar System. This definition is controversial because it excludes many objects of planetary mass based on where or what they orbit. Although eight of the planetary bodies discovered before 1950 remain "planets" under the modern definition, some celestial bodies, such as Ceres, Pallas, Juno and Vesta (each an object in the solar asteroid belt), and Pluto (the first trans-Neptunian object discovered), that were once considered planets by the scientific community, are no longer viewed as such.

The planets were thought by Ptolemy to orbit Earth in deferent and epicycle motions. Although the idea that the planets orbited the Sun had been suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei. At about the same time, by careful analysis of pre-telescopic observation data collected by Tycho Brahe, Johannes Kepler found the planets' orbits were not circular but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some shared such features as ice caps and seasons. Since the dawn of the Space Age, close observation by space probes has found that Earth and the other planets share characteristics such as volcanism, hurricanes, tectonics, and even hydrology.

Planets are generally divided into two main types: large low-density giant planets, and smaller rocky terrestrials. ...more

Planets Books

A Fire Upon the Deep (Zones of Thought, #1)

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Space with aliens or viruses. Thriller and horror.

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14 books — 3 voters

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Science Fiction
Science
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Earth
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Planet

Solar System
Planetary Science
Scieñce
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Quotes Tagged “Planets”

“ To catch a wild animal, you have to use the right bait. What happens to the bait? I haven't decided yet. ...more ”
― March Lions, The Last Sunset

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“ ‘That has to be Mr Davis,’ Semilla said with an air of complete confidence as she stared at the inferno rising above the roof tops. ‘How can you be so certain?’ Burt questioned looking slightly pensive. Semilla gave a shrug. ‘Let’s face it he’s been in the vicinity of one or two little disasters lately. ”
― A.R. Merrydew, Our Blue Orange

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