Three sources of scintillation of radio sources:
terrestrial ionosphere
interplanetary gas
ionised interstellar medium
Studying interplanetary scintillation at Cambridge
Hewish and Bell [14] observed the recordings
shown in Figure 2, period = 1.337 seconds.
human made?
from a spacecraft?
extraterrestrial civilisation?
Figure 2: Discovery observations of the first pulsar. (a) The first recording
of PSR 1919+21; the signal resembled the radio interference also seen on
this chart. (b) Fast chart recording showing individual pulses as downward
deflections of the trace. From Lyne & Graham-Smith 1990 [23].