historical figures

Aristarchus of Samos, who lived from about 310-230 B.C. is often referred to as the Copernicus of antiquity, as he laid the foundation for much scientific examination of the heavens. According to his contemporary, Archimedes, Aristarchus was the first to propose not only a heliocentric universe, but also one larger than any of the geocentric universes proposed by his predecessors. He was a brilliant but little-known natural philosopher, a master of geometry and a devout watcher of the skies.

Aristarchus hit the truth when he had the courage, against the mystical tastes of his time, to suggest that it was the Earth that moved around the Sun. There is a reference in the writings of Plutarch not only to Aristarchus's theory, but also to the way it was received by his contemporaries who in general held the geocentric view of the universe. Accepted opinion appeared to be:

“We must suppose the Earth to remain fixed, and the planets with the whole embracing heaven to move, and we reject with abhorrence the view of those who have brought to rest the things which move, and set in motion the things which by their nature and position are unmoved, such a supposition being contrary to the hypotheses of mathematics."

As we can imagine, this did not look good for Aristarchus, and was probably one of the main reasons the heliocentric hypothesis did not re-emerge until the middle of the 15th century with the Copernican revolution, 2,000 years later.

Though some of his reasoning was out of place in his time, Aristarchus nevertheless was able to adapt to the conventions of society and use the methods of known geometry to explain other phenomena. His treatise On the Sizes and Distances of the Sun and Moon , written from a geocentric point of view, was a breakthrough in finding distances to objects in the universe, and his methods were used by later astronomers and mathematicians through the time of Hipparchus and Ptolemy.

Aristarchus introduced six hypotheses, from which he determined first the relative distances of the sun and the moon, then their relative sizes:

1) The moon receives its light from the sun.

2) The earth is positioned as a point in the centre of the sphere in which the moon moves.

3) When the moon appears to us halved, the great circle, which divides the dark and bright portions of the moon, is in the direction of our eye.

4) When the moon appears to us halved, its [angular] distance from the sun is 87 degrees.

Although his geometry was perfect, Aristarchus's methods of measurement were extremely inaccurate, as the requisite instrumentation for giving precise angular measurements did not exist. However his basic value for the angle from Sun to Earth to Moon was off by only a few degrees (the actual value is 89 degrees, 50 minutes).

5) The breadth of the earth's shadow is that of two moons.

We now know that the width of the earth's shadow cone at the moon is actually three rather than two moon diameters.

6) The moon subtends one-fifteenth part of a sign of the Zodiac. (The 360 degrees of the celestial sphere are divided into twelve signs of the Zodiac each encompassing 30 degrees, so the moon, therefore, has an angular diameter of 2 degrees.)

Although he proved many propositions (eighteen to be exact), the three most well-known are the following:

1) The distance of the sun from the earth is greater than eighteen times, but less than twenty times, the distance of the moon from the earth.

2) The diameter of the sun has the same ratio (greater than eighteen but less than twenty) to the diameter of the moon.

3) The diameter of the sun has to the diameter of the earth a ratio greater than 19 to 3, but less than 43 to 6.

In order to determine the values for the sizes of the sun and moon, Aristarchus used two observations: first, the disc of the moon normally just covers the sun during a total solar eclipse, and second, that during a lunar eclipse the shadow of the earth appears to be twice as large as the moon at the moon's distance. Despite inaccuracies he discovered that the sun is many times larger than the earth and many times further away from the moon.

Using improved values, today we can show that the sun is about 400 times farther from the earth than the moon, and that the sun’s diameter is approximately 109 times greater than that of the earth.

Aristarchus contributed a great deal to both geometry and astronomy, and his methods, as adapted by Hipparchus and others, were used well into the 17th century. In 1681 Aristarchus was recognised as one of the greatest astronomers in history, when Giovanni Riccioli named the brightest crater on the moon, in the Ocean of Storms, after him. This crater was on the NASA list of possible landing sites for Apollo, and is particularly subject to the reddish glows and obscurations known as ‘trans-lunar phenomena’ which may suggest gaseous emissions from the moon’s crust.

Overall, Aristarchus was a pioneer both in his depiction of the universe and his geometric approach to the measurement of the heavenly bodies. He was a man of perception and genius who deserves at least the recognition awarded to Ptolemy, Brahe, Keplar, Newton and Herschel.

(Article submitted by Colin Brett)

REGIOMONTANUS

Johann Muller, who was born in Germany on the 16th June 1436, was a central figure in the scientific renaissance, which took place in the 15th century. The renaissance (translation re-birth), was named by its main protagonists who saw it as a return to the newly rediscovered teachings of ancient Greece and Rome. Johann Muller in affectatiously taking the name Regiomontanus, a Latin form of his own home-town Konigsberg ‘Kings Mountain’, shows just how important this movement encompassing the study of Latin and Greek had become.

Regiomontanus was a brilliant scholar from a very young age, enrolling in the University of Leipzig when he was twelve. At the University he was able to produce more accurate calculations of planets positions than those produced by the college. At the age of fourteen he moved to the more prestigious Vienna University, where after finishing his studies, he joined the faculty and he collaborated with Georg Peuerbach (real name) who was the leading astronomer of his day. Evidence shows that in 1457, when Regiomontanus was twenty-one, they worked together on recording an eclipse of the moon.

Their collaboration was so close that in 1461, on his deathbed, Peuerbach extracted a promise from that Regiomontanus that he would continue his unfinished translation of Ptolemy’s Almagest. The subsequent publication, “Epitome” a multi-volume translation, was largely produced by Regiomontanus. It was a model of clarity, which involved him in rewriting whole sections of the ancient book to make them conform to the contemporary scientific thought of the day. He also produced an extensive book on triangles, which required him to produce for the first time accurate sine and cosine tables to 6 decimal places. The sine tables, that you possibly used at school, use the same figures except for a few minor corrections from the ones produced by Regiomontanus.

From 1467 Regiomontanus worked under the patronage of King Mathias, (with no teaching duties) first at the University of Pressburg then in Nuremberg. In Nuremberg he did extensive observations that were more accurate than anyone had done before. He recorded the passage of a comet, this was some 200 years before it was named after Halley, and was the first person to suggest that latitude could be calculated by accurate observations of the Moon (which he had started).

He started collaboration with the merchant Bernard Walther (1430-1504) which enabled him to set up his own printing press on which the first scientific publications were produced. On the presses he also made popular calendars, these included charts for predicted sunrise, sunset, conversions of planetary hours to terrestrial hours, and predicted eclipses. The prediction of the lunar eclipse on 29 February 1504 were said to have been used by Christopher Columbus on his fourth voyage, 30 years after its first publication, to frighten natives in Jamaica.22

The calculations of the correct date of Easter made by Regiomontanus brought him to the attention of the church and he was summoned to a conference in Rome on the reform of the calendar in July 1476. There is no reliable information about what happened to him on his arrival in Rome, where he may have been made a bishop, some accounts state that he was poisoned but it is more likely that he died of the plague aged forty.

It is very likely that Regiomontanus with his prodigious intelligence and capacity for hard work had he lived could have made a more significant contribution to astronomy and mathematics. One of his main contributions to astronomy were his accurate observations, continued after his death by Bernard Walther which were the basis on which others such as Copernicus and Kepler made their discoveries.

by C.Maskill

References:

“Revolutionising The Sciences” by Peter Dear.

Bernhard Walther (1430 - 1504)

Bernhard Walther was a Nuremberg merchant who formed an early collaboration with Regiomontanus in astronomical observations. It was however only after Regiomontanus did not return from his fateful trip to Rome in 1476 that Walther started lifelong observations of the night sky.

Walther is now regarded as the first “modern day” observer. He made systematic observations that where later used to form the backbone of a catalogue published by Schoener in 1544. These observations where republished by Snell in 1618 and in that form have remained the earliest observations used in this era.

Being a merchant Walther was able to afford the cost of a variety of instruments with which he observed the movements, of the Sun, Moon, and planets.

He used a modification of Ptolemy’s parallactic rulers to measure hundreds of solar zenith distances and so provide accurate observations of the Suns movement. A rectangulum instrument, like a cross staff was used for measuring hundreds of angular distances between planets and fixed stars until 1488. In 1488 he acquired an armillary with which he was able to make hundreds of direct observations of the longitude and latitude of planets. He died aged 74 on the Nineteenth of June 1504 (one of his busiest years of observations).

Copernicus who relied heavily on the observations of others, including Walther to produce “Revolution of the Heavenly Spheres” started his own observations around 1504.

I have not been able to find much personal information on Walther, he is now a largely forgotten figure. However he has been well enough regarded to have a 100 km lunar crater named after him

By Colin Maskill

References

N.M. Swerdlow "Astronomy in the Renaissance in Astronomy before Telescope,"

Cambridge History of Astronomy

Updated 10 February 2002 Next Page