Uranus at Opposition 2024: Did we visit it on bad day?

If you head outside this coming weekend with a small telescope or even a decent pair of binoculars and know where to look, you'll be able to spot the ice giant planet Uranus throughout all of the night. Larger telescopes will show it as a small pale green or blue ball.

Where Uranus will be in the sky as seen from Sydney on the 17th of November 2024 around 8.30 pm local time. Please note the illustrations show where astro objects will be in the night sky, not their actual size or appearance. Produced via Stellarium.

This is the 7th planet from the Sun and the first one to be discovered in more recent times. Uranus is bright enough to be seen with just your eyes magnitude 5.8, but its faintness and very slow motion against the background stars meant that it wasn't recorded by ancient cultures unlike closer and brighter members of the Solar System.

It was discovered by astronomer William Herschel in 1781 when he noticed Uranus looked a bit different and found it to move compared to background stars.  He'd originally wanted to call it "George" after the king at the time and a name maybe they should have stuck with!

The telescope used by William Herschel to discover the planet Uranus from his garden on the 13th March 1781, alongside a modern Dobsonian. Image via the Herschel Museum of Astronomy.

The planet also orbits the Sun almost on its back, inclined some 98 degrees. (The Earth by comparison orbits the Sun at a season inducing 23.5 degrees.) 

There's some debate about why Uranus orbits the Sun at such a tilt. One suggestion is that an impact with an Earth sized object in the distant past during the formation of the Solar System effectively knocked it sideways. The Earth's tilt of 23.5 degrees produces the seasons we experience. Many other planets orbit the Sun with varying degrees of tilt - Mars at around 25 degrees, Saturn at a bit over 26 degrees and Neptune at 28 degrees. Even exoplanets outside our Solar System have been found to orbit their host stars at a tilt. 

The large tilt of Uranus also means its season are long and extreme. 

Uranus has only been visited once by humans when NASA's Voyager 2 flew within about 80,000km in January of 1986. What it found there was strange in many ways. Apart from new moons and a ring system, it also found no plasma in the magnetosphere around Uranus and intensely charged electron belts, second only to Jupiter - but with no source of high energy particles to charge those belts.

Uranus as imaged by Voyager 2 in 1986. Image via NASA

Is Uranus really that strange or was it just having a bad hair day?

It seems Voyager 2 arrived at Uranus when there some strange things going on.

A recent study published in Nature a couple of days ago showed that when Voyager 2 arrived at Uranus, it encountered conditions that occur only about 4% of the time and were far from typical. By analysing decades old data, they found an intense Solar wind had arrived at the planet only days before and this compressed the region dominated by the magnetic field, or magnetosphere, around Uranus. 

The first panel of this artist’s concept depicts how Uranus’s magnetosphere — its protective bubble — was behaving before the flyby of NASA’s Voyager 2. The second panel shows an unusual kind of solar weather was happening during the 1986 flyby, giving scientists a skewed view of the magnetosphere. Credit: NASA/JPL-Caltech

"If Voyager 2 had arrived just a few days earlier, it would have observed a completely different magnetosphere at Uranus," said Jamie Jasinski of NASA's Jet Propulsion Laboratory in Southern California and lead author of the new work published in Nature Astronomy. "The spacecraft saw Uranus in conditions that only occur about 4% of the time."

There is good news however - not only did this even help solve the anomalies found by Voyager 2 in 1986, but it means we can detect underground oceans on a planet's moons if they're within its magnetosphere. A larger and more normal  magnetosphere around Uranus might mean we can hold out hope for finding them on Titania and Oberon.

What can I see on Uranus?

Due to its remoteness and lack of surface detail, it's not as jaw dropping in a telescope unlike Saturn or Jupiter, but it's always inspiring to know you're viewing with your eyes such a distant object. 

Cheers,

Earl White

BINTEL

12th November 2024