40 years ago, the English rock band Joy Division released their debut album, Unknown Pleasures. The cover of the album is now iconic, and features a series of lines that indicate radio emissions from a pulsar, PSR B1919+21. It was the first radio pulsar ever discovered. Pulsars are incredibly massive objects, and the remnants of dead stars much more massive than the Sun. After the star goes nova, it leaves behind a dense core, known as a neutron star. A spinning neutron star is called a pulsar. Each of the 80 lines on the album cover featuring measurements of PSR B1919+21 corresponds to a turn in the pulsar. Think of it like a lighthouse, where the beam crosses an observer periodically. Only, the light is not always of the same brightness, and is in the radio spectrum. These differences in brightness cause the wavy lines in the measurement. The pulsar made 80 turns over a period of 107 seconds. The original observation was published in a PHD thesis by Harold Craft. It found its way to an encyclopedia read by Joy Division lead guitarist Bernard Sumner. The band's graphic designer, Peter Saville based the album cover on this image.
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