From the Greeks to Newton
earliest efforts to understand astronomical events were to make predictions
and appease various gods. Little attention to an explanation of celestial events
was made since such was considered too lofty for human understanding. The first
attempts to explain astronomy were made by the Greeks,
such as Aristotle, Aristarchus, Erasthothones, and Ptolemy. Rival solar system
models of a geocentric and heliocentric nature were proposed and discarded,
as well as an accurate understanding of the very shape, movement, and size of
our planet. By clicking on the image of Aristotle to the left, you can get a
nice look at his contributions to the early natural explanation of astronomical
events. Aristotle (384-322 B.C.) was the first to propose that the earth is
round. While he still maintained the view that the Earth occupies a central
stage amidst the celestial objects, he did not believe the Earth to be flat.
Two lines of evidence supported his claim. While witnessing a lunar eclipse,
Aristotle noticed that the shadow on the moon was curved. Believing that the
earth was blocking the light of the sun toward the moon, he concluded that the
curved shadow represented a curved earth surface. He also cited the fact that
Egyptians could not see all of the same stars as those living in Greece because
they lived further south and were curved away from the most northern star groupings.
While Aristotle was far more a philosopher, his ideas of a round earth still
proved helpful in gaining a true picture of our world.
The Greeks were also the first to really organize a weekly calendar, giving
names to the days of the week according to their views of the relative motions
of the planets in the sky. To learn about the development of the days of the
week, please visit the Calendar
Development page in this course. If you want to know more about the "Days
of Our Lives," then you will have to skip school to watch the soaps, or
tape it and watch later :)
To the Greeks, philosophy and science ran hand in hand, and thus their view
of the universe was a combination of the natural and perceived spiritual realms.
The Greek cosmos is shown to the left, and demonstrates the idea of rotating
spheres within which celestial bodies as well as the elements of earth, wind,
water, and fire existed.
(276-192 B.C.) applied his considerable mathematical skills to a study of Astronomy,
and he was the first to set a circumference figure for the Earth. While in Syene,
Egypt on a midsummer day, he noticed that the sun shone directly to the bottom
of a well. During another midsummer day in Alexandria, which is practically
north, the sun did not shine directly to the bottom of the well, but was off
by about 7 degrees. Since this represents one fiftieth of a circle, then the
distance between Syene and Alexandria should represent one fiftieth of the circumference
of the earth. By using an astronomical technique in measuring angles between
stars, Eratosthenes determined that the earth was 250,000 stadia around. This
would make the measure about 46,000 km, which is too great, but still represents
an interesting idea and intuition on his part.
(310-230 B.C.) who was a contemporary with Eratosthenes was the first to suggest
that the earth revolved around the sun. While Aristotle and most others held
to the traditional "Geocentric Model," Aristarchus went against all
with his "Heliocentric Model." His mathematics were horribly off the
mark, but his idea was true. Unfortunately, no one accepted his model for sun-centeredness.
(writing between 134 and 124 B.C.) was a brilliant Greek astronomer who made
very accurate determinations of the length of the year, and he devised a simple
system of classifying stars according to their brightness. His star-brightness
method is still used today, where the more dim stars visible to the naked eye
are 100 times more dim than the brightest stars. We will learn more about star
magnitudes later. Most importantly, Hipparchus recognized the precession of
the Earth ... the slow wobble while the earth rotates, that causes the north
star to be different. Presently, Polaris is aligned with the northward point
of the earth's axis. But since the earth slowly spins in a wobbled circle, the
north pole of our axis will slowly make a circle against the stars. To Hipparchus,
the celestial sphere is rotating. He also noted that this precession would cause
the constellations to move slowly, the result of which is that some Zodiac constellations
are not in the ecliptic, or plane of the sun's motion.
Please move next to a look at this history by clicking
on Ptolemy, or return to the Introduction
for this History Unit, the Syllabus,
or the Home page.
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