Many works of science fiction talk about the “galactic rim” — the outer edge of the Milky Way Galaxy. And the Moon points toward the rim the next couple of evenings. It will pass the star El Nath — the tip of one of the horns of Taurus, the bull. El Nath will stand above the Moon this evening, with the bull’s bright eye — the star Aldebaran — about the same distance below the Moon. El Nath will huddle closer to the Moon tomorrow night.

El Nath is near the galactic anti-center — the point opposite the Milky Way’s heart. So it points the way to the galactic rim and beyond.

The Milky Way forms a wide, flat disk. It’s more than a hundred thousand light-years in diameter. The solar system is roughly half way out from the center to the rim.

The center is thicker than the rest of the galaxy. It’s packed with stars, gas clouds, and black holes. As you approach the rim, though, things are much more open — like the deserts of the southwest compared to the city of Los Angeles. There are fewer stars, and less gas and dust. There’s no precise boundary that marks the edge, though — the galaxy just fades away.

The rim forms a ring around the entire sky. The circumference of that ring is hundreds of thousands of light-years. But El Nath points the way to the rim’s closest point.

There are still a few stars and puffs of gas and dust outside the rim. But they’ve escaped from the Milky Way — flying beyond the edge of the galaxy.
 

Script by Damond Benningfield

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