Uranus at Opposition

Voyager 2 image of Uranus

Viewing the ice giants of our solar system can be a tricky task. They’re visually small, and quite dim because of their immense distance from Earth. Some times are better than others to catch a glimpse of these elusive worlds. Fortunately, such an opportunity presents itself!

On Saturday, October 15, 2016, Uranus will be at opposition. What that means is that Uranus will be directly opposite of the sun in the night sky, and Uranus will reach its zenith around midnight, local time. That also means is that Uranus and Earth will pass at their closest distance, a mere 1.7 billion miles, or 2.6 billion kilometers. Because of this, Uranus will appear the largest and brightest during the year. Under extremely dark skies, with good eyes, you may be able to catch a naked-eyed glimpse of Uranus (if you know where to look). Otherwise, you’ll need binoculars or a telescope to find it.

The Square of Pegasus pointing toward Pisces, and the current location of Uranus

To find Uranus, you first will need to find the Great Square of Pegasus in the night sky. Below Pegasus is the constellation Pisces, which is where Uranus is located. If you spot the square and follow a line from the top right corner to the bottom left corner (northwest to southeast) down into Pisces, it points towards Uranus. Using a star chart will give you a more accurate position. There are many online charts, such as In-The-Sky.org, or apps that will help you pinpoint Uranus’s location.

Image I took of Uranus through my 8 inch telescope with a smartphone camera

If you use binoculars to spot Uranus, you will only see a star-like point of medium brightness. Even using a telescope with low magnification will yield the same results. Keep in mind Uranus escaped discovery until March of 1781, so don’t feel discouraged. In order to see Uranus as a disk, you will need a bare minimum of 100x magnification. Even then, it will appear very small.

The more magnification you use, the larger it will appear. Thankfully, in the northern hemisphere, it is autumn, so there is less humidity and disturbances in the atmosphere during these cool nights. That should let you use more magnification and still see clearly. Even while approaching 400x, you still can’t see much detail on the planet, only that it looks like a cyan-colored disk with some limb darkening along the edge.

With a larger diameter telescope, up to 5 of the moons of Uranus may become visible, as they too become brighter during opposition. Of these moons, Titania, Oberon, and Umbriel are the easiest to spot because they are farther away from Uranus. Ariel and Miranda are fairly close to Uranus, and may be lost in the glare.

As Uranus is tilted on its side as viewed from Earth, Uranus’s moons follow a different path than Jupiter or Saturn’s moons do. Instead of crossing the planet’s face, they circle above and below, allowing them to be seen nightly. If you can view the moons on consecutive nights, you can note this unique motion. Let’s have a look at these 5 moons, which are amongst some of the most unique objects in our solar system.

Voyager 2 image of Titania

Titania is Uranus’s largest moon, and the eighth largest moon in the solar system. Discovered in 1787, 6 years after the discovery of Uranus, it is made of mostly ice and rock, with carbon dioxide ice on the surface. Titania, as with all of Uranus’s moons, remain somewhat of a mystery as they have only been imaged up close by Voyager 2. For upwards of 50 years after William Herschel discovered Titania and Oberon, they could only be viewed in Herschel’s telescope and no other.

Voyager 2 image of Oberon

Oberon is Uranus’s second largest moon, and also its outermost. Also made up of ice and rock, Oberon has a more reddish color than the other moons of Uranus. Oberon has been bombarded by comets and asteroids, and may contain a layer of liquid water between its core and mantle. It was discovered the same night as Titania. Oberon may be the easiest of the moons to spot with amateur telescopes because of its large size and distance from Uranus.

Voyager 2 image of Umbriel

Umbriel is the third farthest moon from Uranus. It has the darkest surface of the Uranian moons, and the second most cratered surface (after Oberon). It wasnt discovered until 80 years after the discovery of Uranus. Umbriel appears to be made up of more rock than ice, and may be more difficult to spot due to its darker surface color.

Voyager 2 image of Ariel

Ariel is the second smallest and second closest of the moons of Uranus. Because of this proximity, Ariel is subject to stronger tidal heating, creating the huge cut-like chasms across its surface. As the same side of Ariel faces Uranus all the time, the seasonal changes on Ariel can be quite extreme. Each pole gets 42 years of sunlight, as Ariel is tilted on its side like Uranus. Because Ariel is so close to Uranus, it can be quite difficult to spot with medium-diameter telescopes. It requires a lot of magnification to seperate Ariel from the glare of Uranus, which effectively makes Ariel dimmer in the eyepiece.

Voyager 2 image of Miranda

Finally, there is Miranda, the smallest moon of Uranus, and the closest moon to the planet. Miranda is one of the smallest objects that is able to form a spherical shape. Miranda has one of the most unique surfaces observed in the solar system. It also contains a cliff that is between 2-5 miles (5-10km) high, which is the tallest found in the solar system. Because of these odd surface features, it is theorized that Miranda was smashed to pieces by a large imapct, then re-formed. Miranda wasn’t discovered until 1948, and catching this moon with a telescope in your backyard is a very difficult, but rewarding challenge!

Uranus being at opposition presents a great opportunity to view this distant planet, along with its unique moons. While not as visually large as the closer planets, it is still an amazing sight to see, and it’s neat to see a planet that was unknown until after the United States became a nation! As long as weather permits, aim your telescope at Uranus, see how many moons you can spot, and enjoy the sight!

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