Monday, July 23 , 2018, 8:31 am | Fair 74º


Dennis Mammana: Finding Neptune After Dark

Finding Neptune can be a challenge, but is well worth the effort. Click to view larger
Finding Neptune can be a challenge, but is well worth the effort. ( illustration)

Remember a few years back when Pluto was deemed to no longer be a planet? The Internet erupted with protests. People cried: “Why isn’t Pluto a planet? It was a planet when I went to school, and as far as I’m concerned, it still is!”

Well, scientists are in the business of classifying everything, and when new data or understanding becomes available, they must reclassify objects to make them better fit the scheme. So it should have come as no surprise to anyone who follows science that astronomers reclassified Pluto, a tiny ice ball near the edge of our planetary system, as a “dwarf planet.”

And that means that Pluto’s reclassification out of official planet-hood gives Neptune the honor of being the most distant planet from the sun.

Neptune was discovered after astronomers learned that the planet Uranus, which William Herschel had found 6½ decades earlier, didn’t keep to the precise path sky watchers had expected.

A young English astronomer named John Couch Adams calculated that the motion of Uranus was apparently being affected by another world that lay beyond, that its gravitation was tugging on it. Adams even calculated where this unknown planet might be found. Unfortunately, no one in England ever bothered to search for it.

The same was true in France, where Urbain Le Verrier independently made the same calculations. Again, no one seemed to care. But Le Verrier didn’t give up. He showed his calculations to the German astronomer Johann Galle. Galle aimed his telescope skyward and found the new planet (eventually named Neptune) on his very first night of searching!

That was in 1846, and since then, few beginner stargazers have ever even looked for this distant world. Well, now’s a good time to change that because this week Neptune reaches its opposition point when it not only lies as near to the Earth as it ever gets — about 2.69 billion miles — but also shines its brightest.

Finding Neptune among the faint stars of Aquarius isn’t easy, however. Since this distant world is invisible to the unaided eye, you’ll need to utilize the star hopping technique and have a very dark, rural sky, binoculars and patience in order to spot it.

First, find the three faint stars Phi, Gamma and Tau in Aquarius — they form a nice little triangle — and aim your binoculars in their direction. You should spot Neptune as a much fainter star a little more than one degree to the right of Gamma. A small telescope aimed in its direction will show a distinctive bluish-green hue that distinguishes it from neighboring stars.

If you’re not sure you’ve found it, make a sketch of the area, being careful to mark the stars in their exact positions. Then, a week or two later, check out this same region of the sky and see which of the faint objects has changed its position. That’s Neptune!

If needed, click here to create a more detailed finder chart for the planet on the In-the-Sky website.

As challenging as Neptune might be to find, there’s something really cool about seeing the farthest planet of our solar system with our own eyes.

Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at [email protected] and follow him on Twitter: @dennismammana. The opinions expressed are his own.

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