<< Chapter < Page Chapter >> Page >

But practicing astronomers, that is those who observed the positions of heavenly bodies and calculated their positions, increasingly began to measure the positions of comets. If they were below the Moon, then their parallax    could be no less than the Moon's, about 1 degree (the horizontal parallax, which is the angle subtended at the Moon by the Earth's radius). Why did not a few carefully executed measurements settle this issue quickly?

First, there was in Europe no great tradition of making accurate, or even regular, astronomical observations before about 1500. For that reason, measuring instruments were primitive, not even taking advantage of the capabilities of existing technology. They were simple, hand-held, wooden instruments--little more than roughly calibrated sticks--and their accuracy was perhaps at best 1/4 degree, usually perhaps 1/2 degree. There was little accuracy and even less consistency in the measurements of individual astronomers. When it came to comparing the measurements of practitioners in places all over Europe, the situation became hopeless. The results were parallaxes ranging from 10 degree to negative values.

Second, astronomers and others who practiced the mathematical sciences dealt only with positions and motions. These were accidental properties of bodies and could tell you nothing about their essences. A mathematician could tell you where the apple was and he could describe its motion if it fell. But this information could not tell you what made this body an apple and why it fell. These were questions that belonged to philosophy. It was therefore not at all obvious that the measurements of the astronomers could turn an obviously changing cometary phenomenon into a perfect and immutable heavenly body.

Comet of 1577

By the time Galileo was beginning to turn his attention to the study of mathematics, the science of astronomy was changing. Copernicus's De Revolutionibus (1543) had been around for a generation, and there were other cosmological theories as well that challenged the existing cosmology. When in 1577 a huge comet appeared whose tail spread in a great arc across the sky, observers all over Europe, Tycho Brahe among them, made measurements of its changing positions. The resulting literature was huge, and if the verdict was by no means unanimous, it was clear that the opinion that comets were heavenly bodies had become respectable in learned circles. The rising authority of Tycho Brahe , based on his noble birth and his miraculous instruments, gave added impetus to the change of opinion. Over the next two generations the perfection of the heavens was abandoned, as were the crystalline spheres of which they were supposedly composed.

Comet of 1618

But placing comets in the heavens raised new questions. What were their paths? What was their nature? Through much of the seventeenth century the debate ranged. in his Assayer of 1623 Galileo argued that comets were optical phenomena and that therefore one could not measure their parallaxes. In this opinion he was not followed by others. It was argued that comets moved in straight lines or parabolic arcs. Descartes argued that comets were bodies that traveled from one solar system to another.

The mechanical philosophy of the second half of the seventeenth century had a great bearing on this debate, as we can see in Isaac Newton's conclusions. In his Mathematical Principles of Natural Philosophy of 1687, Newton argued that all matter attracts all other matter. If comets are made of matter, then they are attracted to the Sun just as the planets are. Given rectilinear inertia and a centrally directed force, the moving body's path must be a conic section. Edmond Halley took this notion and drew up a table of the parameters of the twenty-odd brightest comets that had been seen over the previous several centuries. He pointed out that the parameters of the comets of 1533, 1607 and 1682 were the same and concluded that this was a periodic comet. He predicted its return in 1758. In that year (Halley had died in 1742) the comet appeared as predicted and has been called Halley's Comet ever since.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
Practice Key Terms 1

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Galileo project. OpenStax CNX. Jul 07, 2004 Download for free at http://cnx.org/content/col10234/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Galileo project' conversation and receive update notifications?