Finding the Outer Planets

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Outer Planets Uranus and Neptune

Spotting the other worlds contained within our solar system can be a fairly easy task. The 5 inner planets are fairly bright and are usually unmistakable. Saturn can prove to be slightly tricky, as it is sometimes only as bright as the stars that surround it. Mars is plainly red, Venus is extremely bright, and Jupiter is bright too, although not quite as bright as Venus. Mercury is never far from the Sun and isn’t too hard to find.

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Hubble Space Telescope view of Uranus

But what about Uranus and Neptune? They prove to be tricky to find, as they are much farther away, which makes them appear much smaller and dimmer than the other planets. Thankfully, this time of year, spotting these ice giants is a little easier, as both planets are out just after dark in the evening. With a little patience and luck, you too can see these elusive planets!

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

First, we’ll take a look at Uranus. Uranus is just barely bright enough to be seen in an extremely dark sky with the naked eye. However, most of us don’t have access to such a dark sky. So, we’ll have to rely on the constellations. High in the east in the evening is the Great Square of Pegasus. As it is rising, it appears more like a diamond. Below Pegasus is Pisces, which is where Uranus is currently located. To find Uranus, spot the Square of Pegasus, then find the corner that points toward Pisces (bottom of the diamond, or lower left corner of the Square if Pegasus is higher in the sky). Using a telescope or binoculars, follow the corner of Pegasus straight down and look for a group of three stars close together. Uranus will be the bluish “star” slightly offset from the others.

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Image of Uranus taken with an 8-inch telescope. Image taken by me

Seeing Uranus in binoculars isn’t all that impressive. Using a telescope with at least 100x magnification is recommended to make Uranus appear as a disk. Uranus appears as a grayish-blue, featureless disk with a little limb-darkening near it’s edge. It looks quite similar to Hubble and Voyager 2 images, just a lot smaller. Even with 250x magnification, it’s small as compared to the other planets. It is unmistakably identified with magnification though, and doesn’t have the glare that other stars have. With a larger diameter telescope, and if viewed near its opposition, 2 or 3 dim moons can even be made out nearby.

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Hubble Space Telescope image of Neptune

Finding Neptune is much more of a challenge! Neptune is more than 2.5 billion miles away, but is the same size as Uranus. That makes Neptune even smaller in a telescope, approximately 1/2 the size of Uranus. Neptune is also dimmer due to its distance from the sun. Still, with patience and effort, you too can find Neptune.

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Constellation of Aquarius where Neptune can be found

To find Neptune, we have to find the constellation Aquarius. In the evening, just after dark, Aquarius is high in the south. It’s not a bright constellation, so darker skies are a huge help. Once Aquarius is spotted, follow the “line” at the top. On the left edge of the top is a group of three offset stars. From the left-most star of that group, go straight down to the next bright star (indicated by the Greek letter “lambda” in the image above). That star will appear as an orange-like color. From there, you will want to move to the right, and slightly below. In that region, you’ll want to look for a bluish-gray star. That is where you’ll find Neptune.

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Image of Neptune taken through an 8-inch telescope. Image taken by me

Neptune can also be spotted with binoculars as a star-like object. 250x magnification or more with a telescope will be needed to see Neptune as a small disk. No features can be made out, but Neptune appears more blue than Uranus. Even at 250x, not much limb-darkening can be noticed. Also, upper-atmosphere distortion can hamper getting a clear view. As with Uranus, with a larger-diameter telescope, you can catch a glimpse of Neptune’s largest moon, Triton. Triton is best seen during Neptune’s opposition, as it is near the limit of what an 8-inch diameter telescope can see.

It can be somewhat of a chore to find the outer planets. A good star map and familiarity with the constellations will help immensely. The effort is worth it, as getting to see these distant worlds is a treat, and will give you bragging rights since you will have seen all of the planets of our solar system with your own eyes. Keep in mind that no amateur telescope will offer the views of the Hubble Space Telescope or Voyager 2. There is, however, a certain satisfaction in getting to see these planets from your backyard with your own eyes in your own equipment. So on a clear, early evening here in late fall/early winter, head out and see if you can spot Uranus and Neptune and see the outer planets of our solar system!

Don’t forget to share us with your stargazing friends on Facebook and Twitter!

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2 thoughts on “Finding the Outer Planets

  1. Even reading about outer planets give me goosebumps. Last summer I saw Saturn and Jupiter along with its moons for the first time ever. Great blog.

    spacevash.com

    Like

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