Lab Exercises in Astronomy: The Crab Nebula

Students will take on an in-depth investigation of the beautiful Crab Nebula, learning its history before calculating the nebula's age, expansion, and distance.

Owen Gingerich begins this five-page, fully illustrated exercise with a historical overview of observations of the Crab Nebula. Then, on large-scale photographs taken 34 years apart, proper motions of knots and filaments are measured to find its rate of expansion across the sky. Radial velocities (line-of-sight motions) of the filaments are obtained from a high-dispersion spectrogram showing red and blueshifted lines. The combined measurements yield the nebula’s size and distance, as well as the year the expansion began.