Let’s now have a closer understanding of the planet Uranus.
Uranus is the seventh planet from the Sun and the third-largest and fourth-most massive planet in the solar system. Its distance from the Sun is about 1.8 billion miles. It is named after the ancient Greek deity of the sky (Uranus, the father of Kronos (Saturn) and grandfather of Zeus (Jupiter).
Uranus was the first planet discovered in modern times. Though it is visible to the naked eye like the five classical planets, it was never recognized as a planet by ancient observers due to its dimness.
Sir William Herschel a British astronomer announced its discovery on March 13, 1781, expanding the known boundaries of the solar system for the first time in modern history.
Uranus and Neptune have internal and atmospheric compositions different from those of the larger gas giants Jupiter and Saturn. As such, astronomers sometimes place them in a separate category, the “ice giants“.
Uranus’s atmosphere, while similar to Jupiter and Saturn is said to be composed primarily of hydrogen and helium, contains a higher proportion of ices such as water, ammonia and methane, along with the usual traces of hydrocarbons.
It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of (−224 °C). It has a complex, layered cloud structure, with water thought to make up the lowest clouds, and methane thought to make up the uppermost layer of clouds.
Like the other giant planets, Uranus has a ring system, a magnetosphere (An asymmetrical region surrounding a planet, extending from about one hundred to several thousand kilometres above the surface, in which charged particles are trapped and their behaviour is dominated by the planet’s magnetic field), and has numerous moons (it has at least 27 known moons).
The system has a unique configuration among the planets because its axis of rotation is tilted sideways, nearly into the plane of its revolution about the Sun; its north and south poles lie where most other planets have their equators.
Seen from Earth, Uranus’ rings can appear to circle the planet and its moons revolve around it like the hands of a clock, though in 2007 and 2008 the rings appeared edge-on.
In 1986, images from Voyager 2 space craft showed Uranus as a virtually featureless planet in visible light without the cloud bands or storms associated with the other giants.
However, terrestrial observers have seen signs of seasonal change and increased weather activity in recent years as Uranus approached its equinox (either of two moments in the year when the Sun is exactly above the Equator and day and night are of equal length all over the planet). The wind speeds on Uranus can reach 250 meters per second.
Uranus has a diameter of 51100 km (4 times that of Earth).
Its mass is 14.5 Earth’s mass. Uranus has a rotation period of 17.2 hours around its own axis and the time for one revolution around the Sun (Uranus year) is 30,799 Earth days or about 84.3 Earth years.
Just like Jupiter and Saturn, Uranus’s atmosphere rotates differently. However, its rotation speed is faster at the poles than at the Equator.
One unusual fact about Uranus is that its spin axis is 98 degrees to the perpendicular – it appears that Uranus lies on its sides. Scientists have not yet known why Uranus came to have such an unusual spin axis. Some have hypothesized that it may have resulted from a grazing collision with another large-sized body.
In 1977, the first nine rings of Uranus were discovered. During the Voyager 2 spacecraft encounters, these rings were photographed and measured, as were two other new rings and ringlets.
Uranus’ rings are distinctly different from those at Jupiter and Saturn. The outermost epsilon ring is composed mostly of ice boulders several feet across. A very tenuous distribution of fine dust also seems to be spread throughout the ring system.
There may be a large number of narrow rings, or possibly incomplete rings or ring arcs, as small as 50 meters in width. The individual ring particles were found to be of low reflectivity. At least one ring, the epsilon, was found to be grey in colour.
Seasons in Uranus
Imagine what the seasons are like in Uranus with its axis tilted about 90°. Since the orbital period is about 84 years, the north and south poles alternate between periods of 42 years of light and 42 years of darkness.
The summer happens when the north or south poles point directly towards the sun, while the winter occurs when they point away from the sun.
During the spring and autumn equinoxes, the equator faces the sun directly. Each season on Uranus lasts 21 years.