Cabeza Prieta Natural History Association
Astronomy
Understanding the Universe: a Short History
We owe our description of the night sky to the ancients of 1300-1000 BC. The Mesopotamians and Sumerians established the characterizations that make up the constellations. Babylonians, established the measure of time and angle using the units 60 and 360 derived from the count of days in a year.
About 500 BC the greeks borrowed much of this knowledge and added the Zodiac to the sky, and more constellations. Aristarchus of Samos (BC 310-BC 230) and Ptolemy (AD 90-AD 168),began a controversy over the morphology of the solar system. Ptolemy felt:
- The Earth was composed if 4 elements: Earth, Water, Air and Fire. The Celestial objects were composed of a fifth: "Quint Essence." Aether.
- The Universe appears to be a sphere upon which the stars are affixed and inside of which the planets (and the Sun being one) revolve about the Earth which appears to be at its center. The Earth appears fixed. There are Biblical references to this.
- Five of the "planetes" (wanderer in Greek) move among the stars occasionally reversing motion and the Sun precesses about the Earth along the same imaginary line in the heavens we call the ecliptic.
In AD 391 the Library at Alexandrea burned along with the collected works of Greek mathematics and science, this loss occurred following several earlier fires one perhaps set by Caesar. Following this catastrophe Europe enters the middle ages, when knowledge and science languish and where advances are few and higher education is focused on Alchemy, Astrology, and ardent Christianity.
Johannes Gutenberg (1389-1469) changed all this with a printing press. When it was invented the making of copies of many rare and singular books became possible. The Middle Ages had been a time bereft of the knowledge of the ancients due to the Roman collection of books and the subsequent burning of Alexandrea. What knowledge was left was again available.
In 1453 the sacking of Constantinople and the slow Reconquista of the Iberian peninsula resulted in the return of some of the surviving Greek texts which had since been translated into Arabic and now into Latin, Greek, and other romance languages. Books fueled the Renaissance. To this day many Star names remain Arabic, while the constellations and their names remain mostly Greek with some Roman and a few are Babylonian.
The structure of the universe is challenged when Galileo (1564-1642) uses a telescope to view the phases of Venus, the mountains and plains of the Moon, satellites of Jupiter, and sunspots. None of these discoveries are consistent with the Ptolemaic Universe. He is tried and convicted of making claims that the Earth moves, in conflict with biblical passages and for degrading the quintessence. Interestingly he was vindicated by the Catholic Church in 1992 some 359 years after his judgement.
It was Nicholaus Copernicus,(1473-1543) who set forth the modern view of the motion of the solar system and by so doing relegated the sphere of stars to a vast distance as they did not display relative motion due to the Earth revolved about the Sun. In this new enlightened age Johanas Kepler (1571-1630) used mathematics to calculate the orbit of Venus, and show that it was an ellipse with the Sun at one center. Isaac Newton (1642-1727) soon invented the mechanism of gravity that kept the planets in these ellipses and raised the tides as well. His contributions to mathematics, physics and the British monetary system are legendary. Albert Einstein (1879-1955) succeeded in replacing Newton's mysterious gravity which seemed to act at a distance with a set of fields in which the planets traveled in response to a curvature of space. Mass curves space, massive objects travel along these curvatures in elliptical orbits.
Edwin Hubble (1889-1953) enlarged the scope of space by the discovery of Cepheid variable stars in Nebulae believed at the time to be clusters of gas in our galaxy the Milky Way, which was generally thought to be the entire Universe. These varying stars were the key to knowing the star's actual brightness and thus, depending on its apparent glow could be used to determine its distance. The universe became millions of times larger than previously thought. The myriad of Nebulae were then seen to be other external galaxies. In addition Hubble showed through the red-shifting of light from galaxies that space was expanding in all directions. The Universe had once been much smaller and perhaps even tiny. It would have expanded into the space we know today. Fred Hoyle derisively dubbed this expansion's beginning- the Big Bang.
If such a cataclysmic event in fact had occurred its remnant energy would still exist throughout space as a low level microwave length signal. The theoretical work predicting this was done and published about 1950. In 1964, Arno Penzias and Robert Wilson two technicians with Bell Labs were experimenting with a supersensitive, antenna originally built to detect radio waves bounced off Echo balloon satellites. Despite their best efforts to eliminate it they found a persistent signal pervading space which proved to be the product of the energy of Fred Hoyle's Big Bang. Calculations have since shown the Universe is 13.4 billion years old, and it's current diameter is 91 billion light years.
The stars we see in the night sky all belong to our Galaxy, the Milky Way, a significant but ordinary particle in the vastness of space. Good vision, binoculars, or even a small telescope will easily show many other galaxies, in fact many galaxies can be seen without assistance.
Planets Visible in the Night Sky in Tucson, Arizona, USA
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