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Neptune Is at Opposition Today: Here's How to Spot the Distant Planet

This week is a great time to see the solar system's outermost gas giant planet, if you have a telescope and a little patience.

Planet Neptune is almost directly opposite the sun in the sky today (Sept. 10), according to In-The-Sky.org, which means that the planet will be at its highest point in the night sky around midnight at your local time. Neptune will be visible for most of the night in the constellation Aquarius

Neptune is also bigger and brighter as seen from Earth than any other time of year, thanks to the current cosmic alignment. Yesterday (Sept. 9) the planet passed perigee, or the closest point to Earth in its orbit. And because Neptune is directly opposite the sun in Earth's sky, its Earth-facing side is almost entirely illuminated by sunlight. Much in the same way that our moon has phases, so do the planets, and today we have a "full" Neptune! 

Related: The Brightest Visible Planets in September's Night Sky: How to See them (and When)

On Tuesday, September 10, Neptune will be directly opposite the sun in the sky. At opposition, Neptune will be closest to Earth for the year, slightly brighter and larger in telescopes, and visible all night long. The dim, magnitude 7.8, blue planet will be located among the stars of eastern Aquarius, just 7.5 arc-minutes (approximately one-quarter of the moon's apparent diameter) to the right (or celestial west) of the naked-eye star Phi (φ) Aquarii. Both Neptune and that star will appear together in the field of view of a backyard telescope at medium power.

On Tuesday, September 10, Neptune will be directly opposite the sun in the sky. At opposition, Neptune will be closest to Earth for the year, slightly brighter and larger in telescopes, and visible all night long. The dim, magnitude 7.8, blue planet will be located among the stars of eastern Aquarius, just 7.5 arc-minutes (approximately one-quarter of the moon's apparent diameter) to the right (or celestial west) of the naked-eye star Phi (φ) Aquarii. Both Neptune and that star will appear together in the field of view of a backyard telescope at medium power.

(Image credit: Starry Night)

To find Neptune from the United States, look to the southeast around 10 p.m. local time and find Aquarius. That constellation is a bit below the Great Square of Pegasus. From there, we recommend using a finder chart — such as this free one from astronomical magazine Sky&Telescope — to locate the blue planet. It should be visible all night until just before 4:30 in the morning.

If you're clouded out tonight or otherwise busy, the planet will still be highly visible in the next few weeks. EarthSky.org suggests that you may be able to glimpse the planet in a good set of binoculars, but you will likely have more luck with a telescope. "This world is about five times fainter than the dimmest star that you can see on an inky black night," the website explains. "You'll need binoculars (at least) and a detailed sky chart to see Neptune in front of the constellation Aquarius."

This image of the planet Neptune was obtained during a test of the European Southern Observatory's Very Large Telescope array in northern Chile, in July 2018.

(Image credit: ESO/P. Weilbacher (AIP))

As for what telescope to use, it's possible (but not easy) to spot Neptune in a small, basic telescope. That's because the planet shines just at the threshold of that kind of telescope's capabilities (at around 8.0 magnitude), according to  Sky & Telescope. To see the planet's disk, at bare minimum you will need to use a 6-inch telescope at 200 magnification — but Neptune will be harder to see if the sky conditions are bad, or the telescope is not aligned properly.

Neptune's current distance is about 2.7 billion miles (4.3 billion kilometers) from Earth, according to EarthSky. It's roughly 30 astronomical units, or Earth-sun distances, from the sun.

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