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Tuesday, December 11 , 2018, 1:20 am | Fair 46º


Dennis Mammana: How to Find the Farthest Planet From the Sun

Find the planet farthest from the sun this week. Click to view larger
Find the planet farthest from the sun this week. (Creators.com illustration)

Scientists are in the business of classifying things. They classify everything from butterflies to rocks to clouds to stars.

And sometimes, when new understanding becomes available, they must go back and reclassify things to make them better fit the scheme.

So, it should come as little surprise to anyone who follows science that a few years ago, astronomers reclassified Pluto, that tiny ice ball near the edge of our planetary system, as a dwarf planet.

I’ve been rather amused by the outrage expressed by some — even some scientists — about this reclassification. Their cry is “Pluto was a planet when I was a kid and, as far as I’m concerned, it still is.”

I suspect that, if the Internet had existed back when people figured out that whales were mammals instead of fish, folks would have been upset about that, too.

But this is how science works, and Pluto’s reclassification from official planethood means that the honor of being the solar system’s most distant planet belongs to Neptune (for now). Neptune was discovered after astronomers learned that the planet Uranus — which William Herschel had found 6½ decades earlier — exhibited some odd orbital behavior. In other words, Uranus 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 and that its gravitation was tugging on it. He even figured out where this unknown planet might appear; unfortunately, no one in England ever bothered to look 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, who 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 beginning stargazers have ever even looked for this distant world. Well, now’s a good time to change that because during early September, Neptune will reach 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 at its brightest.

Finding Neptune with a bright moon in the sky this week isn’t easy, so give it a few days until moonlight is no longer a nuisance. Even without moonlight, it’ll be tough. But fortunately, the planet now lies near the visible star Lambda Aquarii.

Aim binoculars in the star’s direction. You should find Neptune as a much fainter “star” less than 1 degree to its lower left. A small telescope aimed in its direction will show a bluish-green hue that distinguishes it from neighboring faint stars.

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

If needed, click here for a more detailed finder chart for the planet.

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. Click here to read previous columns. The opinions expressed are his own.

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