November 28, 1967

PSR B1919+21

Jocelyn Bell records the first resolved pulses from the first known pulsar

Bell had to inspect 96 feet of chart paper a day. Hidden in it was an intermittent mark she called scruff — and on 28 November 1967 it resolved into pulses.

Pulses forming under the pen

On 28 November 1967, at Cambridge's Mullard Radio Astronomy Observatory, the postgraduate researcher Jocelyn Bell put a fast chart recorder on a previously intermittent radio trace. It resolved into a regular string of pulses roughly one and one-third seconds apart — 1.33730 seconds.

Bell was operating the telescope and reading its paper output herself. She recognized the pulse train as the chart moved beneath the pen, took the chart off, and confirmed the spacing was even.

A telephone call to a man teaching a class

Bell telephoned her supervisor, Antony Hewish, who was teaching in Cambridge. He was not beside her at the recorder. His first reaction was that the signal had to be human-made.

Hewish came back at the source's transit the next day and saw the pulses recur. From the earlier charts he established that the source kept sidereal rather than civil time — strong evidence it was celestial, though its natural origin was not yet proved.

What the chart did not yet settle

The instrument was a 4.5-acre array built from more than 1,000 posts, more than 2,000 dipoles and roughly 120 miles of wire and cable, designed to study interplanetary scintillation in compact radio sources. Its decisive output was ink on moving paper.

Nothing was announced that day. The five-author Nature paper was received on 9 February and published on 24 February 1968, and the source appeared as CP 1919 — the coordinate-based name PSR B1919+21 came later.

Sources

Researched 23 Aug 2026 9 sources 2 audit passes

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

What the sources leave uncertain

November 28 is well supported as the date of the decisive high-speed recording that resolved individual pulses. It was not necessarily the first appearance of the source: low-resolution “scruff” had appeared on charts months earlier.
Cambridge captions and secondary accounts differ by a day over whether the surviving early ordinary-speed trace dates from August 5 or August 6. Bell’s own retrospective account gives no exact August date.
Attribution depends on what “discovery” denotes. Bell personally noticed and recorded the signal; Hewish designed and supervised the project and led subsequent analysis. Calling the November 28 act something Bell and Hewish physically did together obscures that sequence.
PSR B1919+21 is a later coordinate-based designation. The source was initially published as CP 1919; it was not assigned the modern name on November 28.