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Interstellar Clouds

April 10, 2015

Venus, the “evening star,” blazes in the west as night falls this evening. And if you look carefully, you’ll see another famous celestial object close to its upper right — the Pleiades star cluster.

The eye alone reveals several bright stars that form a tiny dipper. But long-exposure photographs show many more stars, all surrounded by a blue glow — a veil of dust known as a nebula.

There are several kinds of nebulae — vast clouds of gas and dust that fill the space between stars. The Pleiades is surrounded by a reflection nebula. It consists of tiny grains of dust. These grains are the right size to scatter blue wavelengths of light. It’s similar to what happens in Earth’s atmosphere — molecules of air scatter blue light, which is why the sky looks blue.

Another prominent nebula is well to the left of Venus and the Pleiades, a little below the three-star lineup of Orion’s Belt. The Orion Nebula is bright enough to see with the eye alone. It looks like a fuzzy star.

It is an emission nebula — one that produces its own light. It’s part of a giant nursery that’s given birth to thousands of stars. The hottest, brightest stars zap the leftover atoms of hydrogen gas, causing them to glow.

There’s one other type of nebula — a dark one. Its gas and dust are so cold that they don’t produce any visible light. Instead, the dust grains absorb the light of the stars behind them - creating dark “voids” in the night sky.

More tomorrow.


Script by Damond Benningfield, Copyright 2015

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