ng. What could it mean?

Taking it for granted, on Hansen's authority, that his tables
represented the motions of the moon perfectly since 1750, was there no
possibility of learning anything from observations before that date?
As I have already said, the published observations with the usual
instruments were not of that refined character which would decide
a question like this. But there is another class of observations
which might possibly be available for the purpose.

Millions of stars, visible with large telescopes, are scattered
over the heavens; tens of thousands are bright enough to be seen
with small instruments, and several thousand are visible to any
ordinary eye. The moon, in her monthly course around the heavens,
often passes over a star, and of course hides it from view during
the time required for the passage. The great majority of stars
are so small that their light is obscured by the effulgence of
the moon as the latter approaches them. But quite frequently the
star passed over is so bright that the exact moment when the moon
reaches it can be observed with the utmost precision. The star then
disappears from view in an instant, as if its light were suddenly
and absolutely extinguished. This is called an occultation.
If the moment at which the disappearance takes place is observed,
we know that at that instant the apparent angle between the centre
of the moon and the star is equal to the moon's semi-diameter.
By the aid of a number of such observations, the path of the moon in
the heavens, and the time at which she arrives at each point of the
path, can be determined. In order that the determination may be of
sufficient scientific precision, the time of the occultation must be
known within one or two seconds; otherwise, we shall be in doubt how
much of the discrepancy may be due to the error of the observation,
and how much to the error of the tables.

Occultations of some bright stars, such as Aldebaran and Antares,
can be observed by the naked eye; and yet more easily can those of
the planets be seen. It is therefore a curious historic fact that
there is no certain record of an actual observation of this sort
having been made until after the commencement of the seventeenth
century. Even then the observations were of little or no use,
because astronomers could not determine their time with sufficient
precision. It was not till after the middle of the century, when the
telescope had been ma