Uranus Reading Comprehension Lesson

Reading Passage

Uranus

Uranus is the seventh planet from the Sun and the third-largest planet in our solar system by diameter. It is classified as an ‘ice giant’ — a type of planet whose interior is composed largely of icy materials (water, methane, and ammonia) mixed with rock, as opposed to the gas giants Jupiter and Saturn, which are mainly hydrogen and helium. Uranus has a diameter of about 31,518 miles (50,724 km) — about four times the diameter of Earth — and a mass about 14.5 times Earth’s. Despite being visible to the naked eye under good conditions, Uranus was not recognized as a planet until 1781, because it moves so slowly that earlier observers had catalogued it as a star.

Uranus was the first planet to be discovered with the aid of a telescope. British astronomer William Herschel first identified Uranus as a planet on March 13, 1781, while systematically surveying the sky from his backyard in Bath, England. Initially Herschel thought it might be a comet, but further observation confirmed it was a planet. The discovery doubled the known size of the solar system. Herschel wanted to name the planet ‘Georgium Sidus’ (George’s Star) after King George III, but the astronomical community eventually settled on Uranus — the ancient Greek god of the sky and father of Saturn — following the tradition of naming planets after Roman and Greek gods.

The most distinctive feature of Uranus is its extreme axial tilt: Uranus rotates on its side, with its axis tilted about 98 degrees relative to its orbit. This means that, unlike any other planet, Uranus essentially rolls around the Sun on its side. The origin of this extreme tilt is believed to be a collision with an Earth-sized object early in the solar system’s history. This tilt has dramatic seasonal consequences: each pole receives about 42 years of continuous sunlight followed by 42 years of total darkness. A Uranian year (one orbit around the Sun) takes about 84 Earth years. Curiously, despite its extreme tilt, Uranus’s poles are not significantly hotter than its equator.

Uranus has a ring system — less famous than Saturn’s but real. The rings were discovered in 1977 when Uranus passed in front of a star and the star’s light dimmed just before and just after the planet blocked it, revealing rings. Voyager 2 (which flew past Uranus in January 1986) discovered additional rings and confirmed 10 that had been identified from Earth; later observations have found 13 rings in total. The rings are narrow, dark, and composed of large particles. Uranus also has 27 known moons, all named after characters from the works of William Shakespeare and Alexander Pope — including Titania, Oberon, Miranda, Ariel, Umbriel, Puck, and Caliban.

Uranus has a faint blue-green color, caused by methane in its upper atmosphere absorbing red wavelengths of sunlight and reflecting blue-green wavelengths. The atmosphere is composed of about 83% hydrogen, 15% helium, and 2% methane. Uranus is the coldest planetary atmosphere in the solar system, with a minimum temperature of -371°F (-224°C), despite not being the farthest planet from the Sun (Neptune is farther). Scientists are not entirely sure why. Only one spacecraft has ever visited Uranus: Voyager 2, which flew past in 1986 at a distance of about 50,600 miles. The flyby revealed a featureless, nearly cloud-free planet with little visible weather activity. Scientists hope that a future dedicated mission to Uranus will reveal far more about this mysterious, underexplored world.

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