spectral arguments claiming that the "evidence admits, but does not prove, the conclusion that the south preceding star is the central star of the nebula". In late 1968, David H. Staelin and Edward C. Reifenstein III reported the discovery of two pulsating radio sources "near the crab nebula that could be coincident with it" using the Green Bank radio antenna. They were given the designations NP 0527 and NP 0532. The period and location of the Crab Nebula pulsar NP 0532 was discovered by Richard V. E. Lovelace and collaborators on November 10, 1968, at the Arecibo radio observatory. A subsequent study by them, including William D. Brundage, also found that the NP 0532 source is located at the Crab Nebula. A radio source was also reported coincident with the Crab Nebula in late 1968 by L. I. Matveenko in Soviet Astronomy. Optical pulsations were first reported by Cocke, Disney, and Taylor using the telescope on Kitt Peak of the Steward Observatory of the University of Arizona. Their discovery was confirmed by Nather, Warner, and Macfarlane. Jocelyn Bell Burnell, who co-discovered the first pulsar PSR B1919+21 in 1967, relates that in the late 1950s a woman viewed the Crab Nebula source at the University of Chicago's telescope, then open to the public, and noted that it appeared to be flashing. The astronomer she spoke to, Elliot Moore, disregarded the effect as scintillation, despite the woman's protestation that as a qualified pilot she understood scintillation and this was something else. Bell Burnell notes that the 30 Hz frequency of the Crab Nebula optical pulsar is difficult for many people to see. The Crab Pulsar was the first pulsar for which the spin-down limit was broken using several months of data of the LIGO observatory. Most pulsars do not rotate at constant rotation frequency, but can be observed to slow down at a very slow rate (3.7 Hz/s in case of the Crab). This spin-down can be explained as a loss of rotation energy due to various mechanisms. The spin-down limit is a theoretical upper limit of the amplitude of gravitational waves that a pulsar can emit, assuming that all the losses in energy are converted to gravitational waves. No gravitational waves observed at the expected amplitude and frequency (after correcting for the expected Doppler shift) proves that other mechanisms must be responsible for the loss in energy. The non-observation so far