Neptune: The Other Blue Planet
June 6, 2016
This week, planet Neptune hovers at its nearest to Earth for the whole year. This giant blue gas planet will also be at its brightest, with its face fully illuminated by the Sun and out all night long. The only major planet we cannot see with the naked eye, it’s actually an amazing place. Let me prove it.
Neptune is the most distant planet in our Solar System—2.8 billion miles from Earth!
How Neptune Was Discovered
In 1845, the French astronomer Le Verrier realized that planet Uranus—discovered 60 years earlier—was not moving in a normal way. Something was mysteriously tugging at it. He calculated where this unseen planet should be located and tried to get someone to aim a telescope at the spot. No one was interested.
Meanwhile an English astronomer had the same idea and was meeting with similar indifference. Finally, Le Verrier convinced someone at the Berlin observatory to point their small 9 inch telescope at his calculated position. Bingo. Within one hour, Neptune was found within a single degree of the predicted spot. That was September, 1846.
Credit: NASA Voyager 2. Taken August, 1989.
Just 17 days later, a giant moon was seen orbiting it. It strangely had no name for 75 years, but in the 1930s people started calling it Triton after the 3-pronged staff held by the god of the sea. A second satellite was found in 1949, and the Hubble telescope eventually discovered a bunch more.
Planet Neptune’s moons are bizarre. Triton is the only major satellite that orbits its planet in the wrong direction (to which Neptune orbits). Backward! And its orbit is a perfect circle.
Credit: NASA. Composite illustration of Neptune as seen from its moon, Triton, using images from Voyager spacecraft.
Neptune’s tiny moon Nereid is the opposite, with an weirdly squashed elliptical path that brings it SEVEN times closer to Neptune on some occasions than others. Imagine if our own moon sometimes got seven times larger than before?
Other newly found moons are also weird, because two of them orbit at the astonishing distance of 30 million miles—the most faraway satellites from their planet in the known universe. That’s farther than Venus is from us. It’s hard to imagine such moons even being gravitationally connected with mysterious Neptune.
So it’s a strange place, that huge blue world, so enormous that 58 Earths could fit inside. Even if we can’t see it floating halfway up the southern sky, among the dim stars of Aquarius.
About This Blog
Welcome to “This Week’s Amazing Sky,” the Almanac’s hub for everything stargazing and astronomy. Bob Berman, longtime and famous astronomer for The Old Farmer’s Almanac, will help bring alive the wonders of our universe. From the beautiful stars and planets to magical auroras and eclipses, he covers everything under the Sun (and Moon)! Bob, the world’s mostly widely read astronomer, also has a new weekly podcast, Astounding Universe!