Lenticular galaxies look like Spiral galaxies, but without the spiral arms. Because of this, they are sometimes referred to as S0 galaxies. Elliptical galaxies are galaxies that are shaped like ellipses. Irregular galaxies are galaxies with an irregular shape, and therefore don't fit into any of the above categories. Elliptical NGC 205 Lenticular Irregular Large Magellenic Cloud Classification of Nebulae Nebulae are large clouds of gas.
Reflection nebulae reflect the light from nearby stars.
Planetary nebulae are created when a light red giant throws off it's outer layers. They come in a variety of colors. Our sun will create a planetary nebula in billions of years. Dark nebulae are just that - dark. The gas that makes them up is dense and does not allow light to pass through.