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Billy Henry
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Neptune at Opposition
A hidden giant lurks between the Moon and the bright planet Saturn tonight. Neptune is the fourth-largest planet in the solar system, and it’s putting in its best showing of the year this week. But it’s so far away that you need help to see it. Neptune is about four times the diameter of Earth. But it’s the Sun’s most-remote major planet – 30 times farther from the Sun than Earth is. As a result, it looks faint. It’s so faint, in fact, that it wasn’t discovered until September of 1846. And it was found because astronomers calculated that another planet was pulling on Uranus, the most-distant planet known at the time. This week, Neptune is at opposition – it lines up opposite the Sun in our sky. That means it rises around sunset and is in view all night. The planet’s also closest to us for the year, so it shines at its brightest. It peaks at a magnitude of about 7.7. That sounds bright. But in the magnitude scale, brighter objects have lower numbers. So Neptune would have to be several times brighter to be visible to the unaided eye even under the absolute best viewing conditions. Under moonlight or city lights, it would have to be even brighter. Tonight, Neptune is to the upper right of the Moon at nightfall. It’s about half way along toward Saturn, which looks like a bright star. Neptune is a big but faint target for good binoculars or a small telescope. More about Neptune tomorrow. Script by Damond Benningfield
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