…continuedObserving Nebulae Season by Season
The Crab Nebula and Other Winter Treats
The Crab Nebula (M1) can be seen in 2-inch finders. Small telescopes reveal only a shapeless 8th-magnitude blur variously sketched as oval, rectangular, or more often something in between. The Crab usually shows in small telescopes as a featureless gray ghost. My 4-inch Clark refractor has revealed hints of the nebula's ragged edge that appears so prominently in photographs. These edge serrations are usually apparent in a 12-inch telescope and easy in a 17-inch. Increased magnification does not seem to change the appearance much. Telescopes of 12-inch aperature and larger often reveal delicate filamentary structure in the nebula.
One object that everyone should enjoy is M76, an unusual planetary nebula on the edge of a dense part of the Milky Way. Often called the Little Dumbbell because it resembles the more-familiar Dumbbell Nebula (M27), to me it always looks more like a dog biscuit. The nebula has a reputation of being hard to find, so here's how best to find it. Start with Phi (φ) Persei. This star and a dimmer one just to the south form a pointer, with Phi at the head, that directs the observer to a diamond of faint stars, within which M76 is dimly perceptible.
With a small aperture or in indifferent sky conditions, M76 shows only a dim irregular oval with ragged edges. But one night, with an 8-inch reflector in the hills north of the Golden Gate in San Francisco, M76 was a most exciting object. High magnifications brought out an intricate network of turbulent celestial clouds.
The California Nebula (NGC 1499) is a vast cloud of glowing hydrogen about 2½° long and ¾° wide. It's known as the California Nebula because its shape, recorded on long-exposure photographs, is similar to that of the western state. Conventional wisdom has long held that the surface brightness of NGC 1499 is too low to be seen against the background sky visually in any telescope. Today the term low surface brightness (LSB) is used to describe large, diffuse objects such as the California Nebula. Their surface brightnesses are so close to that of the sky background that the observer can run his or her eye across the edge of the object without realizing the view has changed from sky to nebulosity. These objects are seen only when the sky is dark and transparent. A low magnification should be used so that the field of view shows plenty of sky to contrast with the object.