Man Behind the Comet - Edmund Halley

Meet the Man Behind the Comet

Edmund Halley is famous the world over for the work he did to identify Comet Halley from orbital measurements. For his labors, his is name attached to this famous comet.  Who was he?

Edmund Halley's official birth date is November 8, 1656. At the age of 17, he entered Queen's College Oxford, already an expert astronomer. He carried with him a wonderful collection of astronomical instruments purchased for him by his father.

Halley Makes a Name for HimselfHe worked for John Flamsteed, the Astronomer Royal and was so useful that when Flamsteed published his findings inPhilosophical Transactions of the Royal Society in 1675, he mentioned his protegé by name. On August 21, 1676 Halley observed an occultation of Mars by the Moon, and published his findings.

Halley put his Oxford career on hold to go map the southern skies. He cataloged 341 southern stars and discovered a star cluster in the constellation Centaurus. He also made the first complete observation of a transit of Mercury across the face of the Sun. 

Halley returned to England in 1678 and published his catalogue of southern hemisphere stars. King Charles II decreed that the University of Oxford confer a degree on Halley, without his having to take exams. He was also elected a member of the Royal Society at 22, one of its youngest members. All these honors did not sit well with John Flamsteed. Despite his earlier liking of Halley, Flamsteed came to consider him an enemy.

During his travels, Halley observed a comet. He worked with Giovanni Cassini to determine its orbit.  tha the inverse square law of attraction. He discussed Kepler's third law as a possible way of understanding that orbit with his colleagues Christopher Wren and Robert Hooke.Travels and Observations

He visited Isaac Newton and urged him to publish his Principia Mathematica, which discussed the same issues of planetary orbits.

In 1691, Halley applied for the Savilian Chair of Astronomy at Oxford, but Flamsteed blocked the appointment. So, Halley edited Philosophical Transactions, published the first actuarial tables, and made careful studies of comets. In 1695, when Newton accepted the position of Master of the Mint, he appointed Halley deputy controller of the mint at Chester.

Heading out to Sea and Into Academia

Halley accepted command of the ship Paramour, on a scientific expedition. He studied the variation between magnetic north and true north, and published a map showing isolines, or points of equal value of deviation.

In 1704, he was finally appointed Savilian Professor of Geometry at Oxford, which upset Flamsteed. When Flamsteed died, Halley succeeded him as Astronomer Royal. Flamsteed’s widow was so angry she had her late husband’s instruments sold so Halley could not use them.

Discovering Comet Halley

Halley turned his attention to work he had started in 1682. Armed with Kepler’s Laws of Planetary Motion, and Newton’s theories of elliptical orbits, Halley recognized that the comets of 1456, 1531, 1607, and 1682 all followed similar paths. He then that these were all the same comet. After publishing his theory, Synopsis on Cometary Astronomy in 1705, it was simply a matter of waiting for the next return to prove his theory.

Edmund Halley died January 14, 1742 in Greenwich, England. He did not survive to see the return of his comet on Christmas day in 1758.

Father of modern astronomy-Tycho Brahe

Tycho Brahe has often been called the Father of modern astronomy, and for good reasons. However, I think that title really belongs to Galileo Galilei for his pioneering use of the telescope to magnify the view of the sky. However, Brahe did advance the science more than anyone in the past, simply by using his senses, rather than philosophy to study the sky.

The work that Brahe began was continued and expanded by his assistant, Johannes Kepler, whose laws of planetary motion are among the foundations of modern astronomy.

Sir William Herschel (1738-1822), though born in Germany, was a British astronomer. He discovered Uranus in 1781 coined the word "asteroids". He also cataloged about 2,000 nebulae, discovered several satellites of Uranus and Saturn, studied the rotation of planets. Discovered and studied binary stars. He discovered two satellites each orbiting Uranus and Saturn. He studied the rotation period of many planets, the motion of double stars, and nebulae. He cataloged more than 800 double stars and contributed new information on the constitution of nebulae. Herschel was the first to propose that these nebulae were composed of stars. He is considered the founder of sidereal astronomy.There are many other astronomers since Galileo, Brahe, and Kepler who have advanced the science:  Here, in brief, are some of the other bright lights who helped bring astronomy to its current place.

• Edmund Halley (1656-1742) was a British astronomer who was also a big fan of Sir Isaac Newton. After encouraging Newton to write his Principia, Halley then published it at his own expense. Not stopping to rest on the fame of another, he went on to calculate the orbits of comets, including the one named after him.

• Albert Einstein (1879-1955) was a German-born American physicist and Nobel laureate. He may be the most well-known scientist of the 20th century. In 1915, he developed his general theory of relativity, which states that the speed of light is constant and that the curvature of space and the passage of time are linked to gravity. Thinking the universe was unchanging, he inserted a  cosmological constant "fudge factor" into his calculations to make them fit his viewpoint.

• 
  Edwin P Hubble (1889-1953), American Astronomer. In the 1920s, Albert Einstein stated, "I have made my greatest blunder." This pronouncement came when Hubble demonstrated that the universe was not static and Einstein's cosmological constant was not necessary. Utilizing improved telescopic devices, he was also able to confirm that those "fuzzy" objects astronomers had seen for years were in fact other galaxies.Willem de Sitter: (1872 - 1934), a Dutch astronomer, removed Einstein's cosmological constant from his calculations and used the theory of relativity to show that the universe may always be expanding.
• Georges-Henri Lemaitre: (1894 - 1966) was not only a Belgian astronomer, he was also a Jesuit priest. Discovering the writings of Russian mathematician, Alexander Friedmann, Lemaitre took his solution for an expanding universe and theorized that if the universe is expanding, if we follow it back to the starting point, then our universe began as a great "cosmic egg" which exploded and expanded outward. Lemaitre is often referred to as the father of the Big Bang theory.

• Thomas Gold (1920 - 2004) was an American astronomer. Though it is generally believed that Gold's "steady state" theory of the universe is incorrect, he made many major contributions to our knowledge of the universe, including the nature of pulsars as rotating neutron stars, and the origin of planetary hydrocarbons.

These are just a few of the astronomers and their findings in the pre- and early 20th century history of astronomy. There have been and are many other great brains in the field of astronomy, but it's time to get away from history for now. We'll meet some of these other astronomers throughout the rest of our lessons. Next, we'll look at numbers.

The Rise of Rational Thought in Astronomy

                                                     

Throughout history, astronomers have come up with, studied, and refined their theories of how the universe and the objects in it came to exist and how they behave. The early theories of the universe and astronomy, while very clever, all had the same problem. They were all based on incorrect information and beliefs.

The way science works, you need actual data (from experiments and observations).  To make the best possible conjectures about what you observe and measure, you need a LOT of data.

The more you have, the better your eventual explanation of phenomena will be. Data help shape the theory, not the other way around. This is at the heart of the scientific method. 

The Rise of Rational Thought in Astronomy

Thanks to the observations of Tycho Brahe, his assistant Johannes Kepler was able to determine that the circle was not the correct geometric form to explain planetary motions.

If planets moved in pure circles, their observed motions in the sky would not look the way they do. So, he applied mathematics and geometry to the problem of understanding orbits. As a mathematician, Kepler knew that a circle is just a specializedellipse. Utilizing non-circular ellipses, he was able to calculate orbits, which correctly predicted planetary positions. He couldn’t directly measure a planet's exact orbital sizes, but he was able to measure the ratio by using his equation and Brahe's observations.

Kepler had explained how planets moved, but he still couldn’t explain why. Up till that time, scientists believed that objects tended to stay at rest. Observation had shown that all motion eventually ceases and unmoving objects did not begin to move on their own.

So, why would planets?

In the early 17th century, Galileo Galilei used surfaces of varying smoothness to slide blocks across them to understand effects on a body's motion. He found that rough tables made objects slow down at a faster rate than smooth ones. Extrapolating from these observations, he theorized that if a surface were completely smooth, objects would continue moving forever.

If you’ve studied physics, you’ll recognize this as the basis for the theory of inertia. Objects in motion tend to stay in motion in a straight line, and objects at rest tend to stay at rest, unless acted upon by an external force.

Using these experiments, astronomers could figure out WHY the planets were moving, but why did they stay in elliptical orbits? Why didn't they keep traveling in straight lines and fly off into deep space?

That question was answered by Sir Isaac Newton through a great many experiments that he wrote up in his publication Philosophiae Naturalis Principia Mathematica. He theorized that the external force that keeps the planets in orbit is the pull of gravity. According to Newton, the same force that causes an apple falls to the ground also explains why the moon continually "falls" around the Earth. Newton's discoveries began to revolutionize our thoughts about motions of objects in space.

Meanwhile, humanity's view of the universe kept evolving. While Tycho Brahe’s attempt to compromise with the Copernican theory and the Ptolemaic model led to an awkward mess, his observations helped Johannes Kepler calculate his three laws of planetary motion, which gave a more accurate picture. Galileo’s discovery of the moons of Jupiter with the newly invented telescope lent credence to the sun-centered model of the solar system.

Starting with Brahe’s years of observation, the work of Kepler, Galileo, and Newton were part of a new era of science, where observation, not philosophy was king. Scientists no longer tried to match data to theory. Instead, they took data and used it to help them shape their theories of the universe. This would lead to a real renaissance in astronomy and cosmology. Directly and indirectly, their work brought us to the brink of space travel and exploration. 

Nicolaus Copernicus

On February 19, 1473, Nicolaus Copernicus entered a world that was considered to be the center of the universe. By the time he died in 1543, he had succeeded in changing our views of Earth's place in the cosmos.

Copernicus was a well-educated man, studying first in Poland and then in Bologna, Italy. He then moved to Padua,where he undertook medical studies, and then focused on law at the University of Ferrara. 

He received a doctorate in canon law in 1503. 

Soon afterward, he returned to Poland, spending several years with his uncle, assisting in the administration of the diocese and in the conflict against the Teutonic Knights. During this time, he published his first book, which was a Latin translation of letters on morals by 7th-century Byzantine writer, Theophylactus of Simocatta.

While studying in Bologna, Copernicus was greatly influenced by professor of astronomy Domenico Maria de Ferrara, Copernicus was especially interested in Ferrara's criticism of the “Geography” of Ptolemy. On March 9, 1497 the men observed the occultation (eclipse by the moon) of the star Aldebaran (in the constellation Taurus). In 1500, Nicolaus lectured on astronomy in Rome. So, it should have been no surprise that while performing his ecclesiastical duties and practicing medicine, he also returned his attention to astronomy.

Copernicus wrote a short astronomical treatise, De Hypothesibus Motuum Coelestium a se Constitutis Commentariolus (known as the Commentariolus). In this work he laid down the principles of his new heliocentric astronomy.

Essentially, this was an outline of his later-developed ideas about Earth and its position in the solar system and universe. In it, he suggested that Earth was NOT the center of the cosmos, but that it orbited the Sun. This was not a widely held belief at the time, and the treatise almost disappeared.

A copy of his manuscript was found and published in the 19th century.

In this early writing Copernicus suggested seven ideas about objects in the sky:  

• celestial bodies do not all orbit a central point in the sky;
• the Moon orbits Earth;
• the planets all orbit the Sun (which he thought might be the center of the universe);
• the distance between the Sun and Earth is a very small fraction of the distance from the Sun to the stars. Thus, he thought that parallax is not observed in the stars;
• the apparent motion of the stars stems from the fact that Earth rotates on its axis:
• Earth orbits the Sun, which explains the apparent annual motion of the Sun;
• Earth's orbit around the Sun sometimes make it look as if some planets are moving backwards. 

Not all of these precepts are true or completely accurate, particularly the one about the Sun being the center of the universe. However, Copernicus was at least applying scientific analysis to understanding the motions of distant objects.

In this same period, Copernicus took part in the Fifth Lateran Council's commission on calendar reform in 1515.He also wrote a treatise on monetary reform, and shortly thereafter, began his major work, De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres).

Expanding vastly on his earlier work, the Commentariolus, this second book was in direct opposition to Aristotle and to the 2d-century astronomer Ptolemy. Instead of the geocentric system based Ptolemaic model that was approved of by the Church, Copernicus proposed that a rotating Earth revolving with the other planets about a stationary central Sun provided a much simpler explanation for the same observed phenomena of the daily rotation of the heavens, the annual movement of the Sun through the ecliptic, and the periodic retrograde motion of the planets.

Although completed by 1530, De Revolutionibus Orbium Coelestium was first published by a Lutheran printer in Nürnberg, Germany in 1543. It changed the way people looked at Earth's position in the universe forever and influenced later astronomers in their studies of the heavens. One often-repeated Copernican legend claims that he received a printed copy of his treatise on his deathbed. Nicolaus Copernicus died on May 24, 1543.

developing theories about the design of the universe (early science of astronomy)

The study of our universe is not new and it's actually our oldest science. People have been looking up, trying to explain what they saw for as long as there have been people. The earliest astronomers were priests, priestesses, and other "elites" who  studeied the movement of celestial bodies to determine celebrations and planting cycles. With their ability to observe and even forecast celestial events, these people held great power among their societies.

However, their observations were not always as scientific as they are today, and people often imagined that the stars could "foretell" their own futures, which led to the now-discounted practice of astrology. 

The ancient Greeks were the first to start developing theories about the design of the universe (early science of astronomy), and there's much evidence that early Asian societies also relied on the heavens as a sort of calendar.

Certainly navigators and travelers used the positions of the Sun, Moon, and stars to find their way around the planet. 

Previous observations of the Moon had already taught observers that Earth was round. When coupled with Plato’s assertion that the sphere was the perfect geometrical shape, the original geocentric, or Earth-centered view of the universe seemed like a natural fit. 

While many earlier observers in history believed the heavens were a giant bowl covering the Earth, this new philosophy, expounded by astronomer Eudoxus and philosopher Aristotle in the 4th century BC, said the Sun, Moon, and planets hung on concentric spheres, all surrounding Earth.

Although helpful to ancient people trying to make sense of an unknown universe, this model did not help in properly tracking the motions planets, the moon, or stars as seen from Earth's surface.

Still, with few refinements, it remained the predominant scientific view of the universe for another 600 years.

In the 2nd century BC, Claudius Ptolemaeus (Ptolemy), a Roman astronomer working in Egypt, added a curious invention of his own, called epicycles, to the geocentric model. He said that the planets moved in perfect circles, attached to perfect spheres, that all rotated around the Earth.

While it was wrong, this theory could, at least, predict the paths of the planets fairly well. Ptolemy's view remained the "preferred explanation for another 14 centuries!

That all changed in the the 16th century, when Nicolaus Copernicus, a Polish astronomer, tiring of the cumbersome and imprecise nature of the Ptolemaic Model, began working on a theory of his own. He thought there had to be a better way to explain the perceived motions of planets and the Moon in the sky. He theorized that the Sun was at the center of the universe, and that Earth and other planets revolved around it. The fact that this idea conflicted with the Holy Roman church's idea (which was largely based on the "perfection" of Ptolemy's theory), caused him some trouble. That's because in the Church's view, humanity and its planet were always and only to be considered the center of all things. But, Copernicus persisted.

The Copernican Model of the universe, while still incorrect, did three main things. It explained the prograde and retrograde motions of the planets. It took Earth out of its spot as the center of the universe. And, it expanded the size of the universe. (In a geocentric model, the size of the universe is limited so that it can revolve once every 24 hours, or else the stars would get slung off due to centrifugal force.)

While it was a major step in the right direction, Copernicus’ theories were still quite cumbersome and imprecise. His book, On the Revolutions of the Heavenly Bodies, which was published as he lay on his deathbed, was still a key element in the beginning of the Renaissance and the Age of Enlightenment. 

course in astronomy

How to Take This Course

This course in astronomy is for you to take at your own speed. The suggested time is ten weeks, one week per lesson.You can, of course, move through the material at a faster or slower pace, it is all up to you. You're learning new and interesting things, and there are many paths to take as you move through the material.

Here's the best path through the lessons:

• Read through each lesson.
• Follow the links within the lesson to find more in depth information
• Study the related definitions.
• Complete the associated assignment.
• Optional: Read some of the Related Resources articles.
• Move on to the next lesson at your own pace.
• Once you have completed all ten lessons, take the final quiz and see how you did! 

We'll start with a look into the past. Astronomy is the oldest science, so let’s take a quick look at its history and the remarkable people who brought us to the understanding of the cosmos that we have today.

Why Study Astronomy?

Why Study Astronomy?

Why should we study the universe? As it says above, everything is part of the universe, and that includes us. That's right. You are part of the universe along with the planets, stars, and galaxies.

We live on a planet, Earth, which circles the Sun, which is a star called Sol. Just like all the other stars, it's part of the Milky Way Galaxy, and the Milky Way is just one of billions of galaxies in the cosmos. 

Astronomy is also much more than the scientific study of the objects and processes in the universe. It embodies many aspects of human history and culture. People first began to "use" the sky for navigation and calendar-making thousands of years ago. Over time, they began to wonder about those distant objects, and speculate about what they were and their origins. You find a lot of astronomy and mythology entertwined together throughout history. Over time, as people became more technologically oriented, they could build instruments to study the stars, planets, and galaxies. That's when the study of the sky moved from philosophy and the realm of myth to the realm of science and mathematics