The problem with absolutes is that they can be disproven by a single exception. Many ancient philosophers and theologians deemed the heavens to be perfect; uncorrupted and unchanging. The problem was, even they knew there were exceptions.
Now, the ancients of course knew of changes in nature. There were cyclical changes, like the turn of the seasons, the phases of the Moon and the progress of the constellations through the year. There were also the omens and portents, such as comets and "guest stars." Those, however, were seen as divine exceptions, special events used to send a message. Unfortunately, there were also things in the heavens which didn't quite fit the dogma.
The name Algol comes from the Arabic "ra's al-ghoul" (head of the ogre) which was derived from its position in the constellation Perseus. In that constellation it represented the head of the Gorgon Medusa. Demon Star and Blinking Demon or Winking Demon are other English versions of ancient names for Algol. In Hebrew folklore it was known as "Satan's Head," and was also traditionally linked with Lilitu. A Latin term for Algol from the 16th century was Caput Larvae (Spectre's Head). Algol is known as "The Fifth Star of the Mausoleum" in Chinese astronomy, and also bears the grim name "Tseih She" (meaning "piled up corpses") in Modern Pinyin. Perhaps the oldest name is Sibi (Double-eye). Are you starting to get the feeling that the ancients thought there was something wrong with this star?
Why all the fuss? Algol can be seen to change brightness with a very regular period. Those references to winking and blinking and the fact that so many different cultures thought there was something evil and unholy about Algol tends to make modern folks think the ancients did, indeed, notice the cyclic dimming. That odd behavior made for some uncomfortable questions. When the ancients couldn't answer those questions, they blamed Algol. "Oh, it's evil. It defies the will of Heaven."
The variability of Algol was first officially recorded in 1667 by Geminiano Montanari. In May 1683 he presented his findings to the Royal Society, suggesting that the periodic variability was caused either by a dark body passing in front of the star, or else that the star itself had a darker region which periodically turned toward the Earth. For his report he was awarded the Copley Medal. In 1881, the Harvard astronomer Edward Charles Pickering presented evidence that Algol was, indeed, an eclipsing binary. This was confirmed a few years later, in 1889, when the Potsdam astronomer Hermann Carl Vogel found periodic doppler shifts in the spectrum of Algol. He determined that these changes resulted from variations in the radial velocity of this binary system, caused by the tug of one star on another. (A modern version of this process is used to find extrasolar planets.) Thus Algol became one of the first known spectroscopic binaries. Algol is now known to be a three-star system, with two stars very close together, their orbital plane lined up with Earth. The third star orbits the other two at a distance about two and two-thirds as far as Earth is from the Sun.
By the time the reason behind Algol's winking was determined, of course, science - and many religions - had accepted that the Earth was not the center of the universe. This very strong evidence that one star was orbiting another confirmed what most educated people already understood; that the Sun wasn't the center of the universe, either.
Even after the telescope was used to open the universe, many beliefs now known to be untrue persisted. Galileo, himself, thought that comets were atmospheric phenomena. The very word "meteor" comes from the ancient belief that those objects were due to some weird weather effect. We snicker at the ignorance of the ancients, now, but they really had no reason to think differently until more data was gathered. That was a process which took centuries.
Of course, even if they'd had more data they also had a mindset which could very well have prevented them from interpreting it correctly. You can see this in such things as Galileo's misconception of the nature of comets, and the refusal of people who looked through his telescope to accept what they saw. Change takes time.
Still, as people continued looking, they continued to find more and more things which contradicted the static view of the universe. Change became the accepted standard. Though not easily, and not universally.
Part of the problem - even today - is that people have trouble understanding just how old the Earth is. As well as the fact that the universe is about three times as old. Actually, that's looking at things backwards. All of human history occupies such a small slice of time that we are essentially looking at a snapshot. Over and over again, you find examples of humans making decisions and taking action based on the situation as it has been for the past few decades... then learning, to their distress, that those decades were atypical. Change is everywhere, and happens at many rates. Also, some changes are one-time events, while others are cyclic or even continuous but very slow.
Even once the mutability of the universe was accepted, how often changes take place and how quickly remained serious questions.
The Earth's axis has a slow wobble, which produces a phenomenon known as the precession of the equinoxes. Because of this wobble, the equinox and solstice points have each moved westward about 30 degrees in the last 2,000 years. Thus, the zodiacal constellations named in ancient times no longer correspond to the segments of the zodiac represented by their signs. One of the differences between astrology and astronomy is that the latter recognizes this change. Astrological charts based on ancient sky maps are literally thousands of years out of date. Connected to this, when the Great Pyramid was built there was no North Star, because the Earth's axis was pointing towards a different part of the sky, one where - from our viewpoint - there was no distinctive star. At that time Polaris was well away from the north pole. Buildings which needed a particular alignment got that from repeated observations of sunrises and sunsets. That gave an east-west baseline. (Note that away from the Equator these observations would only give true east and west twice a year.)
Besides that, constellations can change due to relative movements of stars and alterations in the brightness and color of some stars. Some stars change color cyclically, at various rates, something which the ancients may have known. Others change color slowly and progressively, due to aging. Some stars change due to one-time events, such as capturing a smaller star or going supernova. During the course of history, a few stars even disappeared altogether, at least to the unaided eye. This reshapes constellations, until modern students of astronomy wonder just how you can possibly get a goat or a fish out of that. (Not that the constellations have ever been particularly literal representations of whatever.) The Seven Sisters may be an example of a constellation named at a time when some of the stars looked different than they do today.
The idea that constellations change over thousands of years would have outraged most of the ancients. Any difference in observations must be the result of someone making a mistake. Today, the field of paleoastronomy is used - among other applications - to date ancient structures and artwork. By comparing alignments of structures and the positions of stars in paintings and carvings with where the stars are today, we can get a very good estimate of when the ancient creation was made. Because the heavens do change, and in several ways.
For these records to be properly appreciated, a change in thought was required. For most of history, any difference between ancient records and what could actually be observed were blamed on bad observations by the original author... or that modern observers were making mistakes. ("Why did you bother to go look?! It's right here, on this scroll!!") However, we now know that many of those early writers were accurately relating what they observed. Only when we understood that stars can change were we able to use the information in the old records properly. Today, those records which are thought to be accurate (determining which differences are due to time and which to bad observations isn't always easy) give us indications of how specific stars have changed through time.
The heavens are not the only parts of nature which change. On Earth, as above, the ancients accepted that there were both natural cycles and special events. These latter were things like storms, sent to punish the wicked (well, that was a common explanation, especially when it was someone else hurt). However, there are continuous and incremental changes which are not so obvious as seasons and Moon phases. Earthworms slowly build soil from organic debris, causing objects resting on the surface to be submerged. Year after year, decade after decade, century after century, the worms work. There are other mechanisms which create soil layers, of course. Floods wash soil in, or remove it. Wind blows dust in or away. These processes give a combination of steady and intermittent changes, with occasional reversals.
Water features also change, both slowly and steadily and sometimes dramatically. Ponds fill with washed-in silt. Rivers wear away at their banks, changing their own courses. (If those rivers were property boundaries in ancient times, disputes resulted. Because those boundaries were set with the understanding that they would be permanent and unchanging.) Floods may fill in ponds, and breach banks to change the course of a river or create a new lake.
One of the many revelations (and revolutions) in geology occurred when someone realized that an active and still growing volcano rose on top of distinct geological layers which could be found all around it. That meant they also ran under it. This in turn meant the volcano came later... yet it was ancient in human terms. Those sedimentary rocks below it were therefore older still. Said rocks containing thousands of layers and being vastly thick. Yet there were fossils in the layers, and the fossils changed with depth. Those fossils in the upper layers were often indistinguishable from current living creatures, but many from deeper were unlike anything ever seen alive (though there were also familiar creatures). If the deeper rocks were older, that meant life - at least some of it - had changed through time. This realization of the concept of stratigraphy provided one of the first hard clues as to the real age of the Earth. Understanding this required accepting the concept of change in nature.
Even into the Twentieth Century the idea of sudden change was resisted. (See my previous JOHT on the Channeled Scablands.) As we enter the Twenty-First, however, the concept of punctuated equilibrium has been accepted not just in evolutionary theory, but far more broadly. Simply stated, this accepts that in nature there is a mixture of slow, steady change and quick, short-term - and often random - changes.
Recognizing and accepting that changes occur and finding explanations for those changes drove human understanding of the universe. In fact, it continues to drive it.
One of the accepted truths of modern science is that the physical laws we know on Earth operate the same throughout the universe. However, evidence has recently led to a sneaking suspicion that this may not be completely true. MOND (MOdified Newtonian Theory) theory posits that gravity becomes slightly less powerful with increasing distance. (This is in addition to the long-known inverse square law.) Other new hypotheses formed in an attempt to explain things seen at great astronomical distances contemplate that the differences are not due to linear distance but time, since the further away something is the older our view of it is (due to speed of light lag).
This brings us to the biggest change of all. Early in the Twentieth Century astronomers measuring the movement of galaxies noticed that - overall - they seemed to be moving uniformly away from us. This was quickly understood to mean that the universe as a whole is expanding. That is, expanding from a single point of origin. From the rate of expansion, we can calculate backwards to get the age of the universe. (Naturally, the situation wasn't that clear cut, nor as easy to understand, but that's the basic idea.)
There's a reason scientists are always qualifying their statements, even about things long known to be absolutely true. That reason is the repeated lessons in humility reality has dealt when we assume we know something for certain. This caution, and the accompanying self-checking mechanisms of the scientific method, are what makes science our best tool for understanding the physical universe.
One of the more interesting re-evaluations of what science has long thought true is a possible change in decay rate of radioactive substances here on Earth. A stringent statistical analysis of measurements of decay rates found a correlation with the distance from the Sun through the year. So far the jury is still out as to whether this is even happening. If it is, the difference is infinitesimal. Also, since the change occurs on a yearly cycle, it doesn't have any effect on radioactive dating methods. Those generally are used to measure intervals of at least decades, so any annual change in decay rate averages out.
The real significance is that if this effect is real, and we can figure out what is causing it, we may be able to use it to design inherently safe fission power plants. Just build a core which is normally subcritical, and turn on a device which increases the decay rate. If anything goes wrong, turn off the device.
So, to commit good science, check your assumptions at the door. Maybe you'll learn something.
This document is Copyright 2011 Rodford Edmiston Smith. Anyone wishing to repost it must have permission from the author, who can be reached at: firstname.lastname@example.org