Poor Uranus. So dim it barely gets noticed. A lost soul. But every year at opposition, it’s nice to give the 7th planet its due. Uranus will be closest to the Earth on Tuesday October 7 at “just” 1.8 billion miles (2.9 billion km) or 19 times the Earth’s distance from the sun.
Understandably, the naked eye planets get most of our attention. They’re brighter, closer and bigger. We can follow them without optical aid, and when viewed through a telescope, there’s usually cool stuff to see. Mars wows with polar caps and dust storms, Jupiter shows his stripes, Venus and Mercury’s phases look like miniature versions of the moon and Saturn spins a hula-hoop.
Uranus at magnitude +5.7 can be seen with the naked eye just like the others if you know exactly where to look. This season it tracks slowly across the middle of Pisces the Fish below the bright fall asterism, the Square of Pegasus. Finding and following this tiny blue orb will be easier than usual thanks to a lucky alignment.
Draw a line from Beta Pegasi, the upper right star in the Square, diagonally to Gamma Pegasi and continue in that direction until you bump into Delta Piscium. Uranus lies about 3º to its south in the same binocular field of view. To pinpoint the planet, use the binocular map. Right now, the planet lies about a degree to the east of a 5.7 magnitude star, its twin in brightness. Using this star as a reference, you’ll easily see Uranus’ slow westward crawl over the next three months.
With a diameter of 31,518 miles (50,724 km) Uranus is the third largest planet in the solar system after Jupiter and Saturn. Being so far away it takes 84 years to revolve once around the sun, 4 years longer than the average life expectancy of a U.S. citizen. One of my goals in life is to celebrate one complete Uranian year. Maybe even a little more.
Uranus has 27 moons named after characters from the works of William Shakespeare and Alexander Pope and 13 known rings, the first of which was discovered only in 1977. NASA’s Voyager 2 spacecraft visited the planet in January 1986 and discovered 10 new moons and two new rings. A day on Uranus lasts just 17 hours 14 minutes. But the planet’s oddest trait is that it rotates on its side.
All the other planets have tilted axes but they rotate right side-up generally perpendicular to the plane of the solar system. Not wayward Uranus. With an axis tilted at 98º, it rotates on its side like a bowling ball! This makes for curious seasons. Since Uranus takes 84 years to orbit the sun, each of the planet’s poles gets 42 years of continuous sunlight during the summer season followed by 42 years of winter darkness.
Seen from Uranus (its cloudtops at least – below that it’s permanently overcast), as northern spring progresses toward summer, you’d see the sun the move in ever tighter circles toward the planet’s north celestial pole. On the solstice, the sun would be just 8º from the celestial pole and circle it once every Uranian day (17-plus hours). Then the sun would spiral out from the pole over the next 21 years until it finally set, not to return to view for another 42 years. Bizarre.
Astronomers think that long ago Uranus was struck by an Earth-sized planet at an angle that effectively tipped it over on its side like a well-placed football tackle.
The best time to view Uranus is without a bright moon nearby. Since the moon is now near full, you’ll want to wait a few nights to make your first observation. But Wednesday morning’s total eclipse offers an exceptional opportunity.
Because the moon’s light will be quenched during total eclipse, you’ll be able to spot Uranus with ease in binoculars about a degree to the left or east of the moon.