Selected Topics
in History of Science
Some history of astronomy and calendar
Lecture 2
7 March 2024
Astronomy – highly sophisticated
an allowing mathematization
●
Subject matter: Sun, Moon, planets, stars
●
Stable and simple – compared to physics, biology, chemistry
●
Early observations: Bronze Age – images of the Sun and the Moon,
perhaps also some stars
●
Evidence: Stonehenge – principal axis in the direction of sunrise at
summer solstice (winter s.; vernal / spring and autumn equinox)
●
(churches in Europe: altar facing East)
Astronomy in Babylonia
●
Pattern of celestial omens (bad signs): harvest, epidemic, …
●
By 2000 BCE („before Christian era“) - established (pre-astrology)
●
Social function of astronomy in Babylonia – stability in taking and
keeping the records (clay tablets – copied, when broken)
●
Observations by temple astronomers – visible to the naked eye
– „re-emergence“ of Venus (not too close to the Sun)
– „retrograde“ motion of Jupiter
●
Sophisticated prediction of planetary motions: 300 BCE
Astronomy in Ancient Greece
●
Recorded in literature, e.g. Homer
●
Constellations: Orion, the Great Bear (Velký vůz), Pleiades
●
Lunar eclipse: observation that the Earth's shadow is round, hence
Earth is a sphere (Aristotle, On the Heavens, 350 BCE)
●
Measuring the circumference of the Earth: 72 thousand kilometers,
but given in stadia (now: 40 thousand km), Eudoxos of Cnidus
●
Eratosthenes: measuring the the circumference of the Earth at
summer solstice (Aswan / Syene and Alexandria): 45 thousand km
https://www.nagwa.com/en/videos/287108723870/
Ancient observations: studying the planets
Planets known from
Ancient times:
●
Mercury
●
Venus
●
Mars
●
Jupiter
●
Saturn
discovered since the 18th century:
Uranus:
1781
Neptune:
1846
Pluto:
1930 (until 2006)
Claudius Ptolemaeus, Almagest (2nd
c. BCE)
●
geocentric model: the Sun, the Moon, and
all planets orbit a stationary Earth
●
heavenly bodies must move in the most
perfect possible fashion – circles
●
retain such motion and still explain the
erratic apparent paths of the bodies: shift
the centre of each body's orbit (deferent)
from Earth—accounting for the body's
apogee and perigee—and add a second
orbital motion (epicycle) to explain
retrograde motion.
Regiomontanus, 1496, Epitome
●
Johannes Müller von Königsberg (1436-1476)
●
Cardinal Bessarion asked R.'s teacher Peuerbach to
remedy the problems in the translation of Almagest by
George of Trebizond (1450)
●
Regiomontanus finished the work 1462 (print: 1496)
●
An alternative to Ptolemy's model of the orbits of
Mercury and Venus – the „geometric key“ for Nicolaus
Copernicus (1473-1543) to reorient planetary motions
around the Sun (not the Earth)
Calendar and its reforms
●
Solar calendar: in step with the seasons
●
Lunar calendar: movable religious feasts (Easter etc.)
●
Roman republican calendar: probably only 10 months / 304 days
●
Martius, Aprilis, Maius, Juniiue, Quintilis, Sextilis, September,
October, November, December (M, A, M, J, 5, 6, 7, 8, 9, 10)
●
Adding January and February (7th
c. BCE, changed 5th
c. BCE)
●
Continuing confusion; Julian calendar: 46 BCE (Julius Caesar)
●
Tropical year: 365 and ¼ of a day – nowadays: leap year
Further calendar reforms
●
Julian calender: 365.25 days, but correct value: 365.242199
●
error 11 minutes 14 seconds per year → ¾ of a day in 100 years, and
by 1545, the vernal equinox (20 or 21 March) was 10 days later
●
1572: Pope Gregory XIII agreed to the proposal of Christopher
Clavius (1537-1612)
●
24 February 1582: bull issued determining that 5 October became
15 October that year; accepting 365.2422 days
●
Introduction of a leap year: every 4 years, but not in the years
divisible by 100, unless divisible by 400 (1900 not, 2000 leap)
Adoption of Gregorian calendar
●
Draft of the bull: an astronomer and scientist, Christopher Clavius,
who also introduced decimal comma
●
Accepted by Kepler and Brahe (science)
●
Accepted by Catholics – issued by Pope
●
Not accepted by Protestants; only gradually
●
Jacob Bernoulli: born late December 1654, or early January 1655
●
All of Europe eventually accepted, Russia only in 1918
– (Great October Revolution – 7 November 1917)
Johannes Kepler (1571-1630) astronomer
Laws of planetary motions:
●
Planets move in elliptic orbits
●
„area law“
●
„harmonic law“
made his living as an astrologer
●
Snowflakes
●
Tycho Brahe
Mysterium Cosmographicum
Five regular solids:
●
Tetrahedron (4 triangles)
●
Cube (6 squares)
●
Octahedron (8 triangles)
●
Dodecahedron (12 pentagons)
●
Icosahedron (20 triangles)
What do we want to achieve?
Harmony – easy model
- four or five elements;
everything
in small numbers
-
…
Predictions
- regularities
occuring
again
predicting
eclipses (lunar / solar)
Another take on cosmology
-
Spheres
„cloud
nine“
Heaven
beyond these spheres
Going beyond the sphere