= Discovery of the first pulsar
<Jocelyn Bell Burnell> helped build <Antony Hewish>'s <radio telescope> for finding compact sources through <interplanetary scintillation> in the <solar wind>. Operating it and inspecting its <chart recorder> output in 1967, she recognized an unusual recurring trace, checked earlier charts, and obtained fast recordings resolving pulses in late November. Her observation, recognition and persistent analysis were indispensable.<Little Green Men, White Dwarfs or Pulsars? by Jocelyn Bell Burnell>[Little Green Men, White Dwarfs or Pulsars?, construction through November recordings]{ref}
The 1968 paper by <Antony Hewish>, <Jocelyn Bell Burnell> (bylined S. J. Bell), <J. D. H. Pilkington>, <P. F. Scott> and <R. A. Collins> reported $1.337\,\mathrm{s}$ spacing and proposed compact-star oscillations. Its <radio telescope> had 2,048 full-wave <dipole antennas> in sixteen rows. Four receivers selected declinations; two array halves formed an east-west <interferometer>. The $81.5\,\mathrm{MHz}$ receivers passed $1\,\mathrm{MHz}$. Observations used $0.05\,\mathrm{s}$ receiver time constant and Rapidigraph <chart recorder> with $0.03\,\mathrm{s}$ time constant; radio second pips calibrated timing.<Observation of a Rapidly Pulsating Radio Source by Antony Hewish and others>[Observation of a Rapidly Pulsating Radio Source, Nature 217, p. 709, opening and Position and Flux Density]{ref}
<Antony Hewish> checked <sidereal time> recurrence. <Jocelyn Bell Burnell> recalls that <P. F. Scott> and <R. A. Collins> reproduced the pulses with another telescope and receivers, while <J. D. H. Pilkington> measured <pulsar dispersion delay>: independent checks of instrument independence and intervening <plasma>.<Little Green Men, White Dwarfs or Pulsars? by Jocelyn Bell Burnell>[Little Green Men, White Dwarfs or Pulsars?, follow-up controls]{ref}
A useful numerical comparison uses the approximate <sidereal time> day of $1436.07\,\mathrm{min}$. Relative to a $1440\,\mathrm{min}$ schedule, the same sky direction transits about $3.93\,\mathrm{min}$ earlier each day, or $39.3\,\mathrm{min}$ after ten days. This compares successive passages through the receiving beam; it is a different clock from the roughly $1.3\,\mathrm{s}$ pulse spacing within one passage. Sky recurrence alone cannot rule out every transmitter or reflection, and <pulsar dispersion delay> alone does not uniquely establish an emission mechanism. Their strength lies in independent constraints agreeing.
\Image[/pulsar-discovery-array-timing.png]
{title=From a scintillation survey to two distinct timing tests}
{id=pulsar-discovery-array-timing}
{description=Original functional schematic, not an engineering drawing or a reconstruction of a discovery chart. The illustrative fast signal has a chosen 1.4 second period. The lower panel compares sidereal recurrence with a 24 hour schedule using an approximate sidereal day.}
The discovery lesson is that an unexpected signal must survive changes of readout, instrument and observing date. Increasing <chart recorder> speed exposed structure hidden in a compressed trace; it did not make the source begin pulsing. The <pulsar> interpretation now separates the rotating clock, beam geometry, <pulsar magnetosphere> emission and <pulsar dispersion delay>. The initial observation established periodic arrival, not a direct measurement of the <neutron star>'s surface motion or radius.
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