The ground is snapping and popping. Ever hear this? On quiet evenings in the country in mid-spring, you can walk up to a roadside ditch along the edge of the forest and listen to green plants pushing up through last year’s leaves and grasses. It sounds like fire consuming tiny twigs. Green fire.
I used to think it was insects but I’ve looked with a flashlight and heard it for so many years I’m certain the sound is from plants on their way up and out. Not even night can hold back the call of the sun.
The sun reached out to Earth this week in the form of the aurora borealis. Uranus also displays auroras but as dots instead of arcs and curtains. Auroras were seen by the Voyager 2 spacecraft during it 1986 flyby of the planet, but this is the first time they’ve been spotted from Earth.
Using the Hubble Space Telescope, astronomers photographed dim dots of aurora glowing above Uranus’ pale blue cloudtops. The Uranian lights last only a few minutes at a time before fading away, making them even trickier to catch than the earthly variety.
Auroras on both Earth and Uranus are produced when charged particles (electrons and protons) from the sun enter a planet’s magnetosphere or protective magnetic envelope, and are guided into the polar atmosphere by the planet’s magnetic field.
Earth’s magnetic field is tipped just 11 degrees relative to the our axis of rotation. When the solar wind hits, the particles travel toward the north and south polar regions, which is why auroras are visible in Earth’s more northern and southern locations than nearer the equator.
Uranus is another place altogether. Its rotational axis is tilted 98 degrees compared to Earth’s modest 23.5. This means the planet literally rotates on its side like a bowling ball rolling down a lane. Its magnetic axis is way out of whack too – not only offset from the planet’s core but tilted 60 degrees relative to the rotation axis. Back during the Voyager 2 flyby, the planet’s south pole was pointed toward the sun with the magnetic poles far off to the sides. Voyager observed auroras on Uranus’ nightside resembling those on Earth.
Uranus has since moved along its orbit so that now its side faces the sun instead of a geographic pole. This happy circumstance means that one of the magnetic poles points directly at the sun.
When a big blast of solar wind left the sun in September 2011, the particles sped past Earth in 2-3 days, blew by Jupiter two weeks later and arrived at Uranus in mid-November, creating the odd dots of aurora that seem to lie near the equator. They’re really near the planet’s magnetic poles!
Uranus, you’re a mixed up planet, but we love you anyway. To read more about the new aurora discovery, click HERE.