Moon and Neptune

We can never just look up in the sky, point to one of the dots of light there, and say, “Oh, yeah — that’s Neptune!” Although it’s the fourth-largest planet in the solar system, Neptune is so far that it’s never visible to the eye alone. Tonight, for example, it’s almost three billion miles away — 30 times the distance from Earth to the Sun. So it’s only about a tenth as bright as it would need to be to see it with your eyes alone.

But we can pinpoint Neptune’s location. That’s easy to do this evening because the planet stands above the crescent Moon. As seen from the East Coast, they’re about six degrees apart — the width of three fingers held at arm’s length. They’re even closer from western parts of the country.

From parts of the southern hemisphere, they’ll be closer still. The Moon will pass in front of the giant planet, briefly blocking it from view. Even then, though, it’ll happen during daylight, limiting the view.

The celestial cover-up isn’t visible from the United States for a few reasons. For one thing, the Moon slides across the sky in a hurry, so it covers the planet for only a short time. And the viewing angle isn’t quite right. From most of the globe, Neptune will pass a little above the Moon. If the Moon was bigger, it would block out the planet from a wider region of Earth. So, when the Moon covers a planet or star, you have to be in the right place at the right time to see it happen.

Script by Damond Benningfield