4 Ancient Astronomy & Trigonometry
Astronomy is one of the most important drivers of mathematical development; early trigonometry
(literally triangle-measure) was largely developed in order to facilitate astronomical computations, for
which there are many practical benefits.
Calendars The phases of the moon (whence month), the seasons, and the solar year are paramount.
Without accurate calendars, food production, gathering and hunting are more difficult: When
will the rains come? When should we plant/harvest? When will the buffalo return?
Navigation The simplest navigational observation in the northern hemisphere is that the stars appear
to orbit Polaris (the pole star), thus providing a fixed reference point/direction in the night sky.
As humans travelled further, accurate computations became increasingly important.
Religion and Astrology In modern times, we distinguish astronomy (the science) from astrology
(how the heavens influence our lives), but for most of human history the two were inseparable.
In our light-polluted urban world, it is hard to imagine the significance the night sky held for our
ancestors, even 100–200 years ago. Almost all religions imbue the heavens with meaning, which
historically provided a huge religious/astrological imperative for mathematical and technological
development. Here are just a few examples of the relationship between astronomy, astrology and
culture.
• The concept of heaven as the domain of the gods, whether explicitly in the sky or simply atop a
high mountain (e.g., Olympus in Greek mythology, Moses ascending Mt. Sinai, etc.).
• Many ancient structures were constructed in alignment with heavenly objects:
– Ancient Egyptians viewed the region around Polaris as their heaven; pyramids included
shafts emanating from the burial chamber so that the deceased could ‘ascend to the stars.’
– Several Mayan temples and observatories appear to be oriented to the solstices (see be-
low). Such alignments can be found elsewhere in the Americas and throughout the world.
– Venus and Sirius, respectively the brightest planet and star in the night sky, were also
important objects of alignment.
• The modern (western) zodiac comes from Babylon, dating to before 1000 BC. A tablet dated
to 686 BC describes 60–70 constellations and stars with aspects that are familiar to modern as-
trologers, including Taurus, Leo, Scorpio and Capricorn. During the same time-period Chinese
and Indian astronomers developed different systems of constellations.
16
• Calendars mark religious festivals, practices and even the age of the world.
– The traditional Hebrew calendar dates the beginning of the world to 3760 BC.
– The Mayan long count calendar dates the creation of the world to 3114 BC.
– The modern Gregorian calendar arose to facilitate an accurate determination of Easter.
• The star in the east is associated to the birth of Jesus in Christianity.
• Muslims orient themselves towards Mecca when at prayer; we’ll see later how this direction
(the qibla) may be computed, but the required data is astronomical.
16
Chinese astronomy has 28 constellations (or mansions). As a point of comparison, Taurus corresponds roughly to the
Chinese ‘White Tiger of the West’ (Baihu, and similar terms in various East-Asian languages).
36