13
160 0 bce. Some of the constellations
(groupings of stars) we know today
have come from Mesopotamian
mythology going back even earlier,
to before 2000 bce.
Astronomy and astrology
The Babylonians of Mesopotamia
were greatly concerned with
divination. To them, planets were
manifestations of the gods. The
mysterious comings and goings of
the planets and unusual happenings
in the sky were omens from the
gods. The Babylonians interpreted
them by relating them to past
experience. To their way of
thinking, detailed records over long
periods were essential to establish
connections between the celestial
and the terrestrial, and the practice
of interpreting horoscopes began in
the 6th century bce. Charts showed
where the sun, moon, and planets
appeared against the backdrop of
the zodiac at some critical time,
such as a person’s birth.
For some 2,000 years, there was
little distinction between astrology,
which used the relative positions of
celestial bodies to track the course
of human lives and history, and the
astronomy on which it relied. The
needs of astrology, rather than pure
curiosity, justified observation of
the heavens. From the mid-17th
century onward, however,
astronomy as a scientific activity
diverged from traditional astrology.
Today, astronomers reject astrology,
because it is unfounded in scientific
evidence, but they have good reason
to be grateful to the astrologers of
the past for leaving an invaluable
historical record.Time and tide
The systematic astronomical
observations once used for astrology
started to become increasingly
important as a means of both
timekeeping and navigation.
Countries had highly practical
reasons—civil, as well as military —
to establish national observatories,
as the world industrialized and
international trade grew. For many
centuries, only astronomers had
the skills and equipment to preside
over the world’s timekeeping.
This remained the case until the
development of atomic clocks in
the mid-20th century.
Human society regulates itself
around three natural astronomical
clocks: Earth’s rotation, detectable
by the apparent daily march of the
stars around the celestial sphere to
give us the day; the time our planet
takes to make a circuit around the
sun, otherwise known as a year;
and the monthly cycle of themoon’s phases. The combined
motion in space of Earth, the sun,
and the moon also determines
the timing and magnitudes of the
oceanic tides, which are of crucial
importance to coastal communities
and seafarers.
Astronomy played an equally
important role in navigation, the
stars acting as a framework of
reference points visible from
anywhere at sea (cloud permitting).
In 1675, British King Charles II
commissioned an observatory, the
Royal Observatory at Greenwich,
near London. The instruction to
its director, the first Astronomer
Royal, John Flamsteed, was to
apply himself diligently to making
the observations needed “for the
perfecting of the art of navigation.” ❯❯INTRODUCTION
You have to have the
imagination to recognize a
discovery when you make one.
Clyde Tombaugh