"In
the upper left-hand corner is an easily recognized drawing
of the phonograph record and the stylus carried with it.
The stylus is in the correct position to play the record
from the beginning. Written around it in binary arithmetic
is the correct time of one rotation of the record, 3.6 seconds,
expressed in time units of 0,70 billionths of a second,
the time period associated with a fundamental transition
of the hydrogen atom. The drawing indicates that the record
should be played from the outside in. Below this drawing
is a side view of the record and stylus, with a binary number
giving the time to play one side of the record - about an
hour.
"The
information in the upper right-hand portion of the cover
is designed to show how pictures are to be constructed from
the recorded signals. The top drawing shows the typical
signal that occurs at the start of a picture. The picture
is made from this signal, which traces the picture as a
series of vertical lines, similar to
ordinary television (in which the picture is a series of
horizontal lines). Picture lines 1, 2 and 3 are noted in
binary numbers, and the duration of one of the "picture
lines," about 8 milliseconds, is noted. The drawing
immediately below shows how these lines are to be drawn
vertically, with staggered "interlace" to give
the correct picture rendition. Immediately below this is
a drawing of an entire picture raster, showing that there
are 512 vertical lines in a complete picture. Immediately
below this is a replica of the first picture on the record
to permit the recipients to verify that they are decoding
the signals correctly. A circle was used in this picture
to insure that the recipients use the correct ratio of horizontal
to vertical height in picture reconstruction.
"The
drawing in the lower left-hand corner of the cover is the
pulsar map previously sent as part of the plaques on Pioneers
10 and 11. It shows the location of the solar system with
respect to 14 pulsars, whose precise periods are given.
The drawing containing two circles in the lower right-hand
corner is a drawing of the hydrogen atom in its two lowest
states, with a connecting line and digit 1 to indicate that
the time interval associated with the transition from one
state to the other is to be used as the fundamental time
scale, both for
the time given on the cover and in the decoded pictures.
"Electroplated
onto the record's cover is an ultra-pure source of uranium-238
with a radioactivity of about 0.00026 microcuries. The steady
decay of the uranium source into its daughter isotopes makes
it a kind of radioactive clock. Half of the uranium-238
will decay in 4.51 billion years. Thus, by examining this
two-centimeter diameter area on the record plate and measuring
the amount of daughter elements to the remaining uranium-238,
an extraterrestrial recipient of the Voyager spacecraft
could calculate the time elapsed since a spot of uranium
was placed aboard the spacecraft. This should be a check
on the epoch of launch, which is also described by the pulsar
map on the record cover."