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 ne
