PSR B1919+21

PSR B1919+21 is a pulsar with a period of 1.3373 seconds, and a pulse width of 0.04 second. It was the first radio pulsar discovered (on November 28, 1967 by Jocelyn Bell Burnell and Antony Hewish). The power and regularity of the signals was thought to resemble a beacon, so for a time the source was nicknamed "LGM-1" (for "Little Green Men").

The original designation of this pulsar was CP 1919 which stands for Cambridge Pulsar at R.A. 19^h 19^m. It is also known as PSR J1921+2153 and is located in the constellation of Vulpecula.

Discovery

In 1967, a radio signal was detected using the Interplanetary Scintillation Array of the UK Mullard Radio Astronomy Observatory by Jocelyn Bell and Antony Hewish. The signal had a 1.337302088331 second period and 0.04 second pulsewidth. It originated at celestial coordinates 19^h 19^mright ascension, +21° declination. It was detected by individual observation of miles of graphical data traces. Due to its almost perfect regularity, it was at first assumed to be spurious noise, but this hypothesis was promptly discarded. After that, the discoverers proposed an alternative explanation that the signal might be a beacon or a communication from an intelligent extraterrestrial civilization and named it Little green men 1 (LGM-1).