This image shows the recovered nova of March 11, 1437 and its ejected shell. It was taken with the Carnegie SWOPE 1-meter telescope in Chile using a filter that highlights the hot hydrogen gas of the shell. The now-quiescent star that produced the nova shell is indicated with red tick marks; it is far from the shell's center today. However, its measured motion across the sky places it at the red '+' in 1437. The position of the center of the shell in 1437 is at the green plus sign. The agreement of the 1437 positions of the shell center and of the old nova are the 'clock' that demonstrates that the old nova of 1437 A.D. really is the source of the shell.