UPrior to the invention of the telescope, five planets were known: Mercury, Venus, Mars, Jupiter and Saturn. Earth, of course, is a planet also, but this was not recognized until the acceptance of the Copernican model of the Solar System. A seventh planet, however, is visible without a telescope: Uranus.

Hubble false-color infrared image of Uranus (Source)

Hubble false-color infrared image of Uranus (Source)

Uranus was not recognized as a planet until telescopes became available because it is so dim relative to the classical planets. In fact, at magnitude between 5 and 6 it is not visible to most people today, simply because artificial light has made truly dark skies hard to find.

The oddest thing about Uranus is that its pole is almost in the plane of the ecliptic. In fact, which is the North Pole depends on how north is defined. On earth, the sun, and every other planet, the right-had rule reigns. If the fingers of the right hand are wrapped around the equator with the finger pointing in the direction of rotation, the thumb points north. On that basis, the North Pole of Uranus is on the wrong side of the ecliptic. On the other hand if the astronomical definition is used, that the North Pole is the pole on the same side of the ecliptic as the Earth’s North Pole, the planet is rotating backward, with the sun rising in the west.

Like the gas giants, Uranus has rings, which being equatorial are nearly at right angles to the Ecliptic*. Its weather is not well understood, and its seasons must be extreme. After all, its Arctic and Antarctic circles are almost at its equator, while its tropics of Cancer and Capricorn are very close to its poles.

Wouldn’t working that weather into a science fiction story be fun?

(If the word Ecliptic is new to you, it is the plane of the earth’s orbit.)

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