Friday, 17 November 2017

Uranus

Uranus is the seventh and before-last known planet of our Solar System and was the first to be discovered in recent history. Although it is just visible to the naked eye under dark skies, it has always been mistaken for a star until William Herschel realised it was a planet, back in 1781. 

Uranus is the third-largest planet of our Solar System, being only slightly larger than Neptune, but contrary to its more distant cousin it has no internal heat source. This makes it an extremely cold planet, with temperatures varying around -220°C in its outer layers (being a gas giant it doesn't have a solid surface). Its featureless, blue-greenish colour is caused by the large presence of methane in its atmosphere.

As dull as Uranus may look through earthbound telescopes, it is definitely very interesting in a lot of ways. First of all, it is the only planet that's severely tilted with respect to its orbit. Scientists believe that it may have been knocked over in a collision with another planet, early in its history. Also the orbits of the 27 known moons exhibit the same 97° tilt as the planet, compared to the system's orbit around the Sun. 

In 1977 a very faint system of rings was discovered, which is of course way beyond reach of amateur telescopes. However, in infrared they appear surprisingly prominent.

During my observation yesterday I was able to make out three of its moons: Titania on the top-left, Oberon on the left and probably Ariel (very faint) nearer to the planet on its bottom-right. Titania is with its diameter of 1,580km the eight-largest moon in our Solar System. Its surface has been dramatically carved in the past and one of its canyons is over 1,600km long, dwarfing the Grand Canyon! Oberon's slightly smaller and contrary to its sister shows little evidence of interaction, apart from being covered in craters. It's also the most distant moon to Uranus. Ariel is number four in size, but usually appears as brightest because of the high reflectivity of its surface. It looks covered in river beds, probably caused by a mixture of liquid ammonia, methane and carbon monoxide that shaped them during the moon's primeval history. There is a lot of water on Ariel but this couldn't have contributed because at the extremely low temperatures on its surface water ice is as hard as steel.

I did "believe" to have seen a sort of darker band on the planet during my observation. At first I wasn't sure if it was real or just the fruit of my imagination after having stared through the binoscope for a considerable time. But when I did some research afterwards, it appeared that the "band" indeed followed the planet's rotational axis as it should have been through my binoscope's view. Therefore the observation may have been correct. I've included a more detailed (and perhaps slightly exaggerated) enlarged inset to give you a better idea.

Uranus lies 19 times further away from the Sun than the Earth, at a distance of 2.9 billion kilometres, and completes its orbit in 84 Earth years. And... no, dear astrology believers, you won't find it in Aries. It's in Pisces at the moment. :-)
 

 

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