Time-lapse Photography


Time-lapse Photography

Time-lapse Photography

The purpose of using time­-lapse photography is to speed up events that normally take considerable time. A simple example is the opening of a flower. In a sense, it is just the opposite of the process used in creating slow ­motion pictures. Both processes involve a technique for intentionally altering a normal duration of time in order to learn more about the subject by closer examination.

But, whereas slow­-motion focuses only on the specific subject being filmed at the time, time-lapse photography can record processes that in real time take or months or years to be completed. With both techniques, humans are able to effectively manipulate time for their own practical or artistic purposes.

In time­-lapse photography, the photographer takes a sequence of pictures at a slower rate than the standard 24 frames per second used by the movie industry. The special skills needed to perform time-­lapse photography include being able to discern how much time should be allowed to lapse between each photograph being taken, so as to record discernable changes that are occurring.

movie industry

movie industry

Time intervals may need to be adjusted depending on the particular changes the subject is undergoing, but the process will usually involve taking individual pictures over 24­hour periods for as long as is needed to record the entire process. The effects of both temperature and light must also always be considered.

John Ott is generally considered a pioneer in time­lapse photography. What began as a hobby in his high school days in the late 1920s developed into a career in which his skills became influential.

Because this type of photography was relatively unexplored, he had to use whatever equipment was available and to devise improved equipment himself until he was satisfied that he was photographing subjects in their most realistic setting.

high school

high school

Starting with a Brownie camera and a timer made from kitchen clock works, he eventually built an automatic plastic greenhouse. He developed the ability to take microscopic pictures, as well as a process known as “total spectrum lighting.”

Ott witnessed growing interest in uses of timelapse photography beyond entertainment and advertising, such as applications in horticulture and medicine. He received numerous honors, including an honorary degree from Loyola University, and eventually became a faculty member in the Department of Horticulture at Michigan State University. He worked as a researcher for various companies, including Quaker Oats and General Electric.

In working with Walt Disney on the film Secrets of Life, which was to include a segment on the growth of an apple, Ott discovered that ordinary glass would not transmit all the ultraviolet and shorter wavelengths needed to accurately record the normal process. He was finally able to complete the assignment by substituting special plastic materials.

Walt Disney

Walt Disney

In his film Our Changing World, he wanted to depict the orderly progressions of earth and the creation of life and its development. The power of the single cell had always impressed him. He noted that humankind has been on earth a much shorter time than plants and that plants and animals tend to respond similarly to light.

Though Ott had said that his work was often slow and discouraging, his pioneering efforts were very impressive. His advances encouraged others to devise and use more sophisticated techniques and equipment. Those working with the process continued to emphasize the importance of correct lighting and determining the most appropriate time intervals between pictures.

Time­lapse photography has been used in many scientific studies, such as research on glacier motion in Glacier National Park, studies of sleep patterns, studies of slow­acting geologic processes in natural settings, studies of movement in plants, and studies of weather phenomena.

Glacier National Park

Glacier National Park

In addition to exploring the natural world, there are also many other potential applications of time­lapse photography with respect to human activities, such as monitoring business projects and procedures, and studying the urban environment and urban renewal.

An example of a successful project related to the urban landscape can be found in the work of Camilio Jose Vergara, a photographer, sociologist, and ethnographer. For 30 years he recorded the changes in inner­city neighborhoods in New York, Newark, Chicago, Detroit, and Los Angeles.

Perhaps one of the most dramatic uses has occurred at Ground Zero, the site of the World Trade Center disaster. Documentary filmmaker Jim Whitaker initiated Project Rebirth in the spring of 2002, with the goal of recording what was happening in this area. As the project continued, cameras were installed at all four corners and at ground level.

Ground Zero

Ground Zero

Some results of the ongoing process are available on the Project Rebirth Web site. The process involves taking one frame every 5 minutes for 7 days a week; the final result will be viewable within a span of 20 minutes.

Photosynthesis


Photosynthesis

Photosynthesis

Photosynthesis is the process by which organisms convert light energy into chemical energy in the form of carbohydrates. The inputs of the chemical reaction are light energy, carbon dioxide, and water; the outputs are carbohydrates and oxygen. The overall reaction, which has many intermediate steps, is written as follows:

Light energy + CO2 + H2O => (CH2O) + O2

The sun is the main source of light for the process. Photosynthetic organisms break down the bonds in the resulting carbohydrates to obtain the necessary energy for life­sustaining functions.

Plants, algae, and some bacteria are the known organisms capable of photosynthetic activity. They all produce pigments, specialized proteins that capture energy when exposed to light.

photosynthetic activity

photosynthetic activity

Numerous photosynthetic organisms have developed adaptations to regulate the timing of photosynthesis. By lengthening the time spent in photosynthesis per day or changing the time of day when photosynthesis occurs, organisms improve the efficiency of photosynthesis and their ability to survive.

Locations and Functions of Pigments

The location of pigments in photosynthetic organisms depends on whether the organism is prokaryotic (does not have a cell nucleus or organelles) or eukaryotic (has cell nucleus and organelles). The prokaryote Halobacterium halobium and other photosynthetic bacteria have pigments embedded in their cell membranes.

Prokaryotic blue­green alga has pigment proteins inserted in a more complicated system of stacked membranes interior to the cell wall. Higher plants, such as needle­leaved plants and flowering plants, have a specialized organelle for photosynthesis within the plant cell, the chloroplast. The double­ membraned organelle contains photosynthetic membranes that are embedded most commonly with the pigments, chlorophyll­-a and chlorophyll­-b.

Locations and Functions of Pigments

Locations and Functions of Pigments

Pigments are essential to photosynthesis, because they can absorb energy from photons, the units of light energy. Each pigment absorbs a characteristic wavelength, which is a stream of photons. For example, chlorophyll­a absorbs wavelengths in the range between 550 and 700 nanometers (nm, 1 x 10–9 meter), and bacteriochlorophyll­a in bacteria absorbs wavelengths between 470 and 750 nanometers.

Pigments efficiently absorb energy because they contain chemical bonds that accommodate fluctuating levels of energy. The characteristic carbon rings in pigments include many double bonds.

Carbon atoms joined by double bonds share their electrons; thus the electrons are not strongly attracted to a particular carbon nucleus and move in a loose cloud around the entire molecule. When photons strike a pigment, their energy is accepted by the pigment’s electrons, which can easily move from a lower energy level to a higher one in the cloud of electrons.

energized electrons

energized electrons

Chlorophyll­a has five carbon rings with a total of 10 double bonds, making it an excellent acceptor of energy from light. The pigment can either donate the energized electrons to other molecules or release the energy from the electrons as longer wavelengths than those the pigment absorbed.

Structures in Photosynthesis

Organisms have structures in their photosynthetic membranes called reaction centers and antennae, respectively, both of which are necessary for photosynthesis to occur.

The reaction center is composed of the unique pigments capable of initiating the chemical reactions of photosynthesis by donating electrons to molecules within cells; the pigments are bacteriochlorophyll­a in bacteria and chlorophyll­a in algae and plants. Scientists have identified special forms of these chlorophylls that are responsible for the actual work of changing light energy into chemical energy in the reaction centers.

Structures in Photosynthesis

Structures in Photosynthesis

The chlorophylls are P870 in bacteria and P700 and P680 in algae and plants, where P stands for pigment and the number refers to an absorption wavelength. However, the specialized chlorophylls cannot absorb enough light energy on their own to drive photosynthesis; they are fed energy by the antennae.

The antenna structure in membranes is the locus of light energy absorption and concentration. It is composed of accessory pigments that generally can absorb shorter wavelengths than P680, P700, and P870 can. Examples of accessory pigments are bacteriochlorophyll­b (absorbs 400 nm–1020 nm wavelengths) in purple bacteria and chlorophyll­b (absorbs 454 nm–670 nm wavelengths) in higher plants.

Accessory pigments capture light energy and then release it to other accessory pigments or chlorophylls in the antennae as longer wavelengths, but these accessory pigments are not capable of donating electrons to other molecules. The accessory pigments pass along longer wavelengths to each other until the waves reach a length that can be absorbed by the specialized chlorophylls in the reaction center.

pigment proteins

pigment proteins

A substantial number of accessory pigment proteins are needed to feed a reaction center with enough light energy to drive photosynthesis. Over 300 molecules of chlorophyll­b are needed to funnel enough light energy to activate one molecule of chlorophyll­a in the reaction center of a typical higher plant.

Adaptations in Photosynthesis

Photosynthetic organisms are capable of making photosynthesis more efficient by regulating the time spent in photosynthesis per day or changing the time of day when photosynthesis occurs. Some higher plants can change their leaf position over the course of a day to track the sun’s movement.

This adaptation allows the plants to increase the number of hours per day spent in direct sunlight and maximum light absorption. Experiments have confirmed that this behavior, called diaheliotropism, increases the efficiency of photosynthesis.

Adaptations in Photosynthesis

Adaptations in Photosynthesis

Plants that live in hot, dry climates, such as cacti, have developed an adaptation of photosynthesis that allows parts of the process to occur at a different time of day than in the majority of plants.

Generally, all steps of photosynthesis occur during daylight, including the intake of carbon dioxide through stomata, which are openings in the leaves of plants. The majority of plants take in carbon dioxide and initially fix the carbon into a compound called 3­phosphoglycerate.

However, plants in hot, arid regions lose water at a high rate when the stomata are open, so many have developed crassulacean acid metabolism (CAM) to avoid dehydration. CAM plants open their stomata only at night, initially fix carbon dioxide into malic acid, and then store the acid.

carbon dioxide

carbon dioxide

During the day, CAM plants close their stomata, break down the malic acid to release the carbon dioxide, and then proceed with photosynthesis. The CAM adaptation makes it possible for plants to withstand long periods of drought.

Phylogeny


phylogeny

phylogeny

A phylogeny is an evolutionary history of an organism or group of organisms; it may be interpreted as a genealogical tree, an ancestor and descendant lineage, or as systematic relationships of form within a classification scheme. Phylogenies are studied principally in the fields of phylogenetics and systematics.

History of Phylogenetics

Phylogeny was discussed in detail by the 19th-­century German morphologist Ernst Haeckel, who proposed a biogenetic law (or the law of recapitulation). The biogenetic law states that phylogeny, or the evolutionary history of an organism, is recapitulated through its ontogeny, or the development of an individual organism in embryo.

The subsequent rejection of Haeckel’s law was a significant move away from using mechanical explanations or causes, such as embryonic development, to explain the relationship between organisms. Haeckel’s most significant contribution was that of the phylogenetic tree (Phylogenetisches Stambaum), the now universally accepted way to depict genealogical relationships.

History of Phylogenetics

History of Phylogenetics

A phylogenetic tree may depict hypothetical ancestor­descendant relationships, sometimes called a transformation series, between groups of organisms (species, genera, and families) or their characteristics, through time. Such phylogenetic trees have been popular tools of paleontologists who use them to establish so­called ghost lineages between similar­looking fossils throughout the stratigraphic record.

Phylogenetic trees were challenged in the early 20th century by the German­speaking systematic morphologists, led by Adolf Naef. The evolutionary relationships that phylogenetic trees were claimed to depict were based on linking similar­looking organisms that overlapped through time, rather than considering relationships of form.

The systematic morphologists considered homologues (different manifestations of the same morphological structure) to be a sounder basis for the discovery of relationship than the assembly of ghost lineages. If organisms are related, their characters are homologous, that is, the same; as opposed to analogous, that is, similar but not the same.

hypothetical lineages

hypothetical lineages

Naef’s trees related organisms only at the terminal branches, rather than depicting hypothetical lineages, with organisms (hypothetical or real) at both the nodes and tips. Homologous organisms belonged to “natural groups or classifications” that share a greater relationship among themselves than they do to any other group.

The rejection of phylogenetic trees and the concomitant support for natural groups was criticized by Anglo American phylogeneticists such as George Gaylord Simpson and Ernst Mayr, who defended the depiction of lineages in phylogenetic trees rather than the discovery of natural groups, which challenged some traditional taxonomic groups.

Anglo American phylogenetics, however, changed considerably in the latter half of the 20th century when the work of Willi Hennig, a German entomologist, was translated into English.

Phylogenetic Systematics

Phylogenetic Systematics

Phylogenetic Systematics

Hennig’s Phylogenetic Systematics attempted to resurrect Haeckel’s systematic phylogenetics by reintroducing the causal mechanisms that had been rejected by Adolf Naef.

Hennig’s phylogenetic systematics combined Haeckel’s transformational viewpoint—but at the level of character rather than taxon—with Naef’s trees of relationships to form ancestor­descendant schemes of relationship with organisms only at the tips, and character transformations leading from the nodes to the tips.

The resulting trees attempted to group homologous organisms into “natural” or monophyletic classifications based on a causal mechanism, thus combining Haeckel’s phylogenetic tree with Naef’s systematic morphology.

numerical method

numerical method

Phylogenetic systematics developed into a numerical method by incorporating the principal notion of phenetics, that is, similarity concepts, with a causal mechanism to find optimal trees.

Phylogenetic systematics, later referred to as cladistics, underwent a revolution in the work of Gareth Nelson by returning to systematic morphology. Pattern cladistics rejected causal homologies and ancestor­descendant relationships as uninformative and misleading, because they introduced bias into phylogenetics.

The pattern cladists, led by Ronald Brady and Gareth Nelson, considered monophyly to indicate “natural groups,” which can be used to test existing taxonomies rather than to identify causal relationships (a common ancestor). The resulting diagrams, called cladograms, could represent numerous lineages but only a single classification.

Colin Patterson

Colin Patterson

Hennig’s elimination of paraphyly and its connection made with ancestry by cladists such as Colin Patterson helped to define phylogenetics as a science of classification based on the relationships of form.

Molecular Phylogenetics

Molecular phylogenetics is the study of amino acid or DNA sequences and how they may be related among different organisms. The field has grown exponentially and amassed a significant volume of data.

Unlike phylogenetic systematics, molecular phylogenies tend to consist of individual character trees (relationships between organisms based on a single character) and are used to hypothesize recent genealogies in populations as well as ancestor­descendant relationships in species.

DNA sequences

DNA sequences

Despite its popularity, very little theoretical work has been done on the relevance of homology of DNA sequences. Molecular phylogenetics, however, has progressed methodologically and technologically in such issues as alignment of sequences and in mapping the similarity distances in phenetic methods.

Phylogenetic Classification

Phylogenies may be interpreted as explicit evolutionary pathways, natural groups (classifications), or a combination of both. The latter has caused the most controversy in its claim for phylogenetic classifications.

Recent debate has focused on defend­ ing lineages rather than classifications in taxonomy. A nonmonophyletic group (also known as a paraphyletic or polyphyletic group) is an artificial or incongruous set that shares greater relationship to other groups than to its own.

Phylogenetic Classification

Phylogenetic Classification

A proposed lineage may be paraphyletic and therefore contradict any given natural classification. Reptiles are an example of a paraphyletic group that exists in name only, not within a natural classification.

The defense of paraphyletic groups in classification reflects the battle between the Anglo American paleontologists and systematic morphologists in the early 20th century, during which classification and hypothetical lineages were confused.

Phylogenetic Biogeography

Phylogenies have been used in biogeography (the study of biotic distributions) during three periods: in the late 19th century, with the advent of natural selection as a viable mechanism for species evolution (e.g., Haeckel); in the 1960s, with the onset of Hennig’s phylogenetic systematics; and in the late 20th century, with the use of molecular phylogenies.

Phylogenetic Biogeography

Phylogenetic Biogeography

The same method has been used in each of these periods, namely that of proposing a center of origin and drawing the direction of dispersal and/or vicariance events (allopatry) on a phylogenetic tree.

Since the late 19th century, fossils were used to date such events within any given phylogenetic tree. The method is still widely practiced today (i.e., using a molecular clock). The only difference between these periods is the data used.

Nineteenth­-century phylogeneticists relied on fossils, mid­-20th-­century phylogeneticists on the morphology of extant taxa, and 21st-­century molecular systematists on molecular data.

molecular systematists

molecular systematists

Jean Piaget


Jean Piaget

Jean Piaget

Jean Piaget was a Swiss philosopher and psycholo­gist whose principal research interests were in epistemology and developmental psychology. He believed that to understand knowledge, one must look at its psychological origins and how it evolves as children become adults. His research led him to the epistemological stance he deemed constructivism—the posi­tion that knowledge is constructed from experience over time.

During work in Alfred Binet’s lab at the Sorbonne, Piaget noticed that children of the same age consistently made the same mistakes on intelligence tests.

Later, after very careful observations of children during which he would ask questions or assign tasks to elicit behaviors that would give him insight, Piaget noted that children were organizing and reorganizing the world as they gained more experience.

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Piltdown Man Hoax


Piltdown Man Hoax

Piltdown Man Hoax

In 1912, fragments of a skull and jawbone were found in a gravel pit at Piltdown, a village in East Sussex, England. When assembled, scientists believed the specimen to be the “missing link” between ape and human, providing solid proof of the theory of evolution. Forty years after its discovery, Piltdown man became exposed as the Piltdown hoax, one of the most notorious frauds in the history of science.

The Find

A laborer working in the Piltdown gravel pit in the early 1900s claimed to have found a piece of a skull. He passed it on to Charles Dawson, a local solicitor and well­known amateur archaeologist. Dawson found additional fragments at the site in 1911, and presented them to Sir Arthur Smith Woodward, keeper of geology at the British Museum.

Interested in the finds, Woodward returned to the site with Dawson, where they recovered additional skull fragments and half of a lower jawbone. The same pit also produced a few fossil animal bones and a tooth. In December 1912, they presented their reconstructed skull to the Geological Society of London as a new type of early human, Eoanthropus dawsoni, or “Dawson’s Dawn Man.”

English paleontologists

English paleontologists

The bone of the skull was unusually thick and stained with age, implying primitiveness, while having the shape and larger size of a modern braincase. However, the mandible associated with it was far more simian than human. This apparent ape­man found with the bones of extinct mammals in a Pleistocene gravel bed was exciting news for English paleontologists.

Until that point, all fossil human remains had been found in various locations on the Continent, especially Germany and France. England could now claim a place on the evolutionary tree even earlier than these other hominids.

Additional finds were made at Piltdown through 1915, including additional animal bones, stone tools, and a second skull (also found by Dawson) 2 miles away from the original site. Interestingly, no more finds were made after Dawson’s death in 1916.

Franz Weidenreich

Franz Weidenreich

The reconstruction of Piltdown man was challenged from its introduction. The hinge joining the jaw to the skull was conveniently missing, causing some experts to doubt that the skull and jaw were from the same individual. Others developed a completely different model from the pieces.

In the 1920s, Franz Weidenreich, an anatomist, examined the specimen and reported that it was a modern human cranium and an orangutan jaw with filed teeth. He was correct, but it took 30 years for paleontologists to admit it.

As more and more hominid finds were made around the world in the following years, including Homo erectus and Australopithecus, Eoanthropus was pushed aside. Not only did it not fit into the increasingly clear evolutionary tree, but also no other specimen was ever found resembling it.

Exposure of the Hoax

Exposure of the Hoax

Exposure of the Hoax

Joseph Weiner, an anthropology professor at Oxford University, has been given credit for exposing the hoax. In the early 1950s, he attended a paleontology congress in London. Piltdown man was hardly mentioned once again, for not “fitting in.” The possibility of fraud dawned on him.

After meticulously gathering evidence, conducting interviews, and using recently developed tests on the bones themselves, he exposed the forgery in 1953. A new dating technique, the fluorine absorption test, was developed to determine age and had been applied to the Piltdown fossils in 1949.

The results established that the remains were, in fact, relatively modern, but they were still assumed to be genuine. In 1953, with the fluorine test more advanced, the Piltdown remains were retested. It was determined that the cranium was from the Upper Pleistocene and approximately 50,000 years old, while the mandible and tooth were modern.

hominid evolution

hominid evolution

Another new test devised by American scientists analyzed nitrogen content to determine age and corroborated these results. In 1959, however, the recently discovered carbon­14 dating technique was applied to the bones. The skull was shown to be between 520 and 720 years old, and the jawbone a bit younger.

Eventually it was proven that the Piltdown site had been salted with bones and artifacts from a variety of sources. The hoax had succeeded for 40 years due to a variety of circumstances. The find gave experts evidence supporting a theory they believed to be true at the time.

The scientists closest to Piltdown were experts, but not in hominid evolution. In the early 20th century, there were no chemical tests or dating techniques. Analytical tools were primitive by today’s standards.

earliest Neanderthal

earliest Neanderthal

At the time of the find, there were no hominid fossils other than the earliest Neanderthal remains for comparison. Finally, the Piltdown bones were kept locked away in the British Museum as valuables, so most scientists wishing to study them had to rely on pictures, sketches, or poor­quality X­rays.

Identity of the Forger

The identity of the perpetrator has never been proven. The reason for the entire hoax is also debated. This hoax was deliberately and systematically carried out over a number of years with no obvious motive. About two dozen suspects have been suggested over the intervening years, and there is plenty of circumstantial evidence implicating several of them.

The most obvious suspect is Dawson himself. He had no formal training but a lot of luck at finding unique artifacts. He was present at Piltdown when all the major finds were made. Once Piltdown was exposed, scientists reexamined his other finds, and 46 objects credited to him turned out to have questionable backgrounds or were outright forgeries.

the Forger

the Forger

He appears to have appropriated the finds of others as his own, and many of his writings were plagiarized. Most people agree he was involved, but question the presence of an accomplice. Woodward is also suspect.

He was Piltdown’s strongest supporter and refused to allow some of the simplest scientific tests to be given to the specimens, which would have exposed the forgery immediately. Sir Arthur Conan Doyle, author of the Sherlock Holmes stories, is often presented as a suspect.

He was a neighbor of Dawson, an amateur fossil hunter, and a participant in the digs at Piltdown. It has been argued that his novel, The Lost World, has clues referring to the hoax. Pierre Teilhard de Chardin has also been accused.

Martin Hinton

Martin Hinton

He was a Jesuit, a theologian, and an anthropologist. As Dawson’s friend, he participated in the work and was present for many of the key discoveries. He had traveled to locations in Africa where some of the frauds originated, and his later recollections of the events at Piltdown were very vague.

The most recent accusations, however, have been against Martin Hinton, zoology curator at the Natural History Museum in London. He worked under Woodward at the time of the hoax and had a public conflict with him over salary.

There was also professional rivalry between the two, and Hinton may have perpetrated the hoax to embarrass his colleague. He was known for creating elaborate practical jokes. In the mid­1970s a trunk was found in a loft of the museum with Hinton’s initials on the lid.

scientific paper

scientific paper

Among other things, there were a variety of bones and teeth stained with chemicals identical to those used on the Piltdown finds. The chemical recipe was apparently created by Hinton and presented in an 1899 scientific paper.

The identity of the culprit and the reasons for creating such an elaborate scheme may never be proven, but there is an important lesson to be learned. The hoax was successful for decades, owing to inconsistent examination and analysis.

Once an expert had established the importance of the find, it was accepted uncritically. Scientists embraced the Piltdown find because it supported the prevailing beliefs of the time. Scientists are still human, and ambition, pride, and rivalry can all come into play.

still human

still human

Planetariums


Planetariums

Planetariums

A planetarium is a device for artificially depicting the night sky, showing the relative positions and motions of the sun, moon, and planets. Modern planetariums are theaters, usually dome shaped, that employ elaborate equipment, including projector systems and lasers, for educating and entertaining the public about astronomy and for training nautical and military personnel in celestial navigation.

The lineage of the planetarium can be traced back to ancient Greece. An ancient mechanical calculator used to accurately determine astronomical positions was found in 1900 by sponge divers in what is now referred to as the “Antikythera wreck,” off the Greek island of the same name (located between Kythera and Crete) and has been dated to about 150–100 BCE.

This technology was extraordinarily complex for the time, and it has no known precursor and no successor or equivalent until the 18th century CE. This movement, or one similar, with its high level of sophistication for that and most other eras, is widely believed to have been used in Archimedes’ construction of a primitive equivalent to the modern planetarium.

Archimedes

Archimedes

Rather than providing public entertainment or instruction to navigators in training, the creation of Archimedes was used to predict the movements of the sun, moon, and planets as known at that time and also to approximate their relation to each other at various phases and points in time.

Giovanni Campano, more readily identified as Johannes Campanus, was an Italian astrologer, mathematician, and astronomer of the 13th century. In his Theorica Planetarum, Campano describes, and, more importantly, provides direction on how to assemble, a planetarium incorporating the astronomical knowledge at that time.

Given the instructions left on how to build this piece, it can be stated that there is a very high correlation between the “planetarium” of Campano and the orrery of today. (The orrery is so named for the Earl of Orrery; Orrery is a location within Ireland, and an 18th­century Earl of Orrery had one constructed.)

mechanical device

mechanical device

An orrery is a three­dimensional mechanical device that depicts the relative positions and motions of the planets and moons in the solar system, as well as their relation to each other, as based upon the presumption of Copernican heliocentrism.

These pieces usually owe their movement to a large clockwork mechanism with a sphere (representing the sun) at its core and with a distinct and specific representation of a particular planet at the end of each of its arms.

Given the small size of orreries as constructed by Campano and his predecessors, it appears that these devices were mostly used for personal curiosity, knowledge, and recreation, as they were not large enough to be of any true service to a crowd. One obvious limitation of this form of representation is its complete inability to replicate or depict the backdrop of stars and constellations.

Adam Walker

Adam Walker

Early 19th­century England provided the backdrop for Adam Walker and his Eidouranion, the name given his very large orrery, approximately 20 to 25 feet in height, with a proportionate width.

Walker’s Eidouranion provides the first documented usage of an orrery for either educational or entertainment purposes, with his lecture incorporating both facets into a simulated presentation on the heavens. While not extremely precise in its representation, this show provided the audience an opportunity to encounter elements of time beyond an immediate number, day, and date.

In relaying the parallels of heavenly occurrences such as a lunar phase, or planetary alignment, with definite cycles and events (e.g., seasonal change resulting from the earth’s positioning and alignment in relation to the sun), Walker can be seen as one of many to have helped establish the depth and permanence of events of this world by incorporating the heavens as support.

William Kitchener

William Kitchener

As Walker’s popularity, and presumably wealth, began to grow, others such as William Kitchener and his Ouranologia began to take their rather inaccurate orreries on the road, forgoing scientific display for sensationalism and the awe of large crowds.

The preeminent German optics firm of Carl Zeiss found itself in a unique situation at the turn of the 20th century. Working within the firm’s compound in Jena, Germany, were astronomer Max Wolf, former director of Heidelberg’s Baden Observatory, and Franz Meyer, chief engineer of optical works for Zeiss.

Both men, in conjunction with Oskar von Miller of Munich’s Deutsches Museum, looked to create a representation of the night sky free of movement created by overt force (e.g., the mechanically driven arms of an orrery). The result of their ingenuity and labor was a projector that produced the movements of planets and stars, without aid from bulky and visually obtrusive rails, supports, and the like.

Zeiss building

Zeiss building

Instead, once centrally mounted, their optical projector was capable of projecting images upon the surface of a hemispherical ceiling, and in 1923 the first modern­day planetarium projected its representation of the heavens upon the inside of a dome erected on the roof of the Zeiss building.

Given the complexities associated with production of a planetarium (named for the device used to project images, and not necessarily the hemispherical room or building in which the projector is housed; commonly the entire unit—projector[s]— and dome, are referred to as a planetarium) and the sterling reputation of Carl Zeiss, most every planetarium produced or in use upon the globe prior to World War II could be directly traced to the Zeiss factory of Jena.

Projectors such as those introduced by Zeiss use a hollow sphere with a light contained within as their primary means of projecting the appearance of the heavens. This “ball of stars” contains a tiny hole for each star being represented, with the location and relation of “star holes” being computed to near perfection when compared with their authentic form in the true night sky. To simulate the planets and their movements, another projector is commonly used to superimpose these images upon the starry backdrop.

digital projectors

digital projectors

Currently, digital projectors are beginning to appear in more and more planetarium settings. The cost of upkeep is considerably less than that of the traditional “star ball” models, and synchronization of various projectors (e.g., a star projector and a separate planet projector) is not required, as all solar/celestial data are stored and represented by one computer and its corresponding digital projector.

Much like digital projectors in a lecture hall or elsewhere, images of the night sky are displayed as pixels, with higher pixilation resulting in a better viewing accuracy.

Planets


Planets

Planets

Astronomy, one of the oldest sciences of humankind, always provided orientation in space and time: Cardinal directions (east, north, west, south) are defined and obtained by basic astronomical measurements.

Time and calendar issues are also definable and measurable by astronomical observations: One “year” is the period the earth needs for one full revolution around the sun (originally, before the Copernican revolution, it was seen the other way around), and one “month” is roughly the time our moon needs to orbit the earth.

The currently most widely used calendar system, the Christian calendar in use in Europe, North and South America, and many other parts of the earth, is based mainly on the motion of the earth with respect to the sun. Other cultures have developed slightly different calendars based either on the moon (e.g., the Moslem calendar) or a combination of sun and moon (e.g., the Jewish calendar).

ancient cultures

ancient cultures

We count seven days per week because, a long time ago, people considered “seven” objects as “planets” or “planet­like objects,” namely the real planets, which could be observed by the naked eye before the invention of the astronomical telescopes: Mercury, Venus, Mars, Jupiter, and Saturn, as well as the other two large visible bodies in the solar system, the sun and our moon, together seven objects, hence also the names of the seven days of the week:

Sunday, as the original first day of the week, is the day of the sun, the brightest object in the sky, often even worshipped as a god in several ancient cultures.

The word Monday obviously refers to the moon.

god of War

god of War

Tuesday is named after Mars, the god of War (notice in French, Italian, and Spanish, the words for Tuesday are still close to that for the Roman God Martius (for Mars), namely Mardi, Martedi, and Martes, respectively) and it originally comes from Tiwes dag or Tyr dag, from the old Teutonic word Tyr for Mars.

Wednesday is named after the Roman God Mercury (in Romanian, the day is still known as Miercuri), and the word Wednesday itself comes from Wodan dag for the Teutonic god Wodan.

In Roman times, the fifth day of the week (Thursday) was known as dies Jovis, after their god of thunder and chief of the gods, Jupiter, where Thursday itself comes from Thunor dag, the day of the Teutonic God Thor.

astronomical observations

astronomical observations

The Romans named another day after their goddess of beauty, Venus, and called it dies Veneris (still similar in French). When Germanic tribes invaded England more than 500 years ago, they imposed their goddess upon that day and called it Frigedaeg, now Friday.

And finally, Saturday is obviously called after Saturn.

Nowadays, both time and the unit second are defined by the speed of light. Previously, a second was defined by the atomic clocks, and also earlier as one certain small part of a day, that is, one small part of a revolution of the earth. Still, astronomical observations are important for fixing “time”: Due to tidal interaction among the sun, earth, and moon, the rotation period of the earth is very gradually slowing down.

Historical Background

Historical Background

Historical Background

The definition of a planet has changed over the centuries, always following new astronomical observations and new understanding. The word planet comes from the Greek word for wanderer, meaning a wandering or fast­moving starlike object (e.g., the old Arabic name for the Egyptian capital Cairo is “Al Qahira” for “the backwards wandering,” meaning Mars).

As mentioned above, a few hundred to 3,000 years ago, people could see, by the naked eye, seven objects apparently moving fast in the sky (compared to the “fixed stars”), incorrectly thought to orbit around the earth in the center, namely the sun, Mercury, Venus, the moon, Mars, Jupiter, and Saturn.

The next planet known today behind Saturn, called Uranus, is also visible to the naked eye during clear and dark nights, and may be visible when Uranus is close to the sun and the earth is roughly in between the sun and Uranus. This is called opposition: when an outer planet like Uranus is brightest as seen from the inner planet like Earth, but no such reports are known so far , possibly because Uranus moves only slowly and is quite faint.

Galileo Galilei

Galileo Galilei

During the Renaissance period in general and the so­called Copernican revolution in particular, it became clear, through a number of new observa­ tions, that the old theory placing the earth in the center of the universe was not perfect.

Those observations became possible with the invention of the astronomical telescope. In 1609, Galileo Galilei observed the phases of Venus and craters on our moon and discovered moons around Jupiter (first called “Medici planets” or “Medici stars” after his supporters of the Italian Medici family, and now known as “Galileian moons”).

All this together favored an alternative explanation, putting the sun in the center of our solar system and having the planets orbiting around the sun. At this moment, it also became clear that the earth is orbiting the sun and, hence, was now seen as a planet. Later, two more planets were discovered beyond Saturn, namely Uranus and Neptune.

solar disk

solar disk

While it was always possible to estimate the orbital periods of planets around the sun by their periodic appearance and disappearance in the sky, it was originally difficult to measure distances between the planets, or from Earth to either its moon or the sun. The distance between Earth and the sun is now called the astronomical unit, which is about 150 million kilometers.

The first good estimates of such distances were obtained a few centuries ago by observing eclipses of the sun by the inner planets Venus and Mercury, which happen only very rarely (usually only once or a few times per century): One has to measure exactly either the angular distance between the apparent path of the planet across the solar disk, as seen from two different locations on Earth, or the exact times of ingress and egress of the planet moving in front of the sun.

These four so­called contacts must be observed and measured from different locations on Earth with as large as possible a distance in between them, for example from South Africa and Europe. A few centuries ago, it was still difficult to coordinate such efforts and also to run precise clocks. A first observation was done in 1639, a Venus transit.

Johannes Kepler

Johannes Kepler

After several attempts, the first good values for the distance between Earth and the sun were obtained in 1761 and 1769—these values also giving evidence about the size of the sun. Together with the laws of gravity just determined by Isaac Newton and their application to the solar system by Johannes Kepler, these values immediately yielded all distances between each of the planets and the sun.

Toward the end of the 18th century, the socalled Titius­Bode law was found and discussed: According to this law, the distance from planet to planet roughly doubles with each planet reached as one moves further away from the sun; for example, Saturn is roughly twice as distant from the sun as Jupiter, Uranus is roughly twice as distant as Saturn, and so on.

However, from Mars to Jupiter, the distance increases roughly by a factor of four, so that there would be space for one more planet. Even the famous philosopher G. W. F. Hegel wrote his dissertation about this problem at the University of Jena in Germany.

Pluto

Pluto

Many astronomers were already hunting for this new planet. Then, in January 1801, an object was found at the expected distance from the sun, called Ceres, and celebrated as a new planet. However, soon afterward, more similar objects were found, all at a similar distance; a few decades later, the solar system had more than 20 “planets.”

It was also found that these new objects were smaller than all other previous planets, so it was decided to call them “minor planets” (a new class of objects). Hence, objects celebrated and counted as planets were removed from the list of planets by a new definition.

Early in the 20th century, another new object was discovered and celebrated as a new, ninth planet, called Pluto, located most of the time beyond Neptune, but sometimes crossing its orbit.

The Solar System

solar system

solar system

There are now eight planets in the solar system.

Mercury, the innermost known planet, is also the smallest known planet in our solar system with a diameter of less than 5,000 kilometers. (Pluto is smaller, but it is not a planet anymore according to the new definition.)

It has a rotation period of 59 days, which is about two thirds of its orbital period around the sun (88 days); hence one “Mercury­day” is equal to two “Mercuryyears.” Mercury does not have an atmosphere that is comparable to that of Earth, and its surface is similar to that of the moon. Two thirds of its material and mass is made of iron.

According to Einstein’s general theory of relativity, the orbit of Mercury should change slowly: The location of the perihelion (the point in the planet’s orbit at which it is the smallest distance from the sun) moves by a small angle of 43 seconds or arc per century, which has been confirmed observationally.

theory of relativity

theory of relativity

Venus needs 225 days for orbiting the sun (compared to 365 days for one Earth orbit around the sun). The rotation of Venus around its own axis is retrograde, that is, in the rotational direction opposite to the direction in which it revolves around the sun, and one such “Venus­day” lasts 243 days; that is, it is longer than one “Venus­year.”

Venus has a dense atmosphere consisting mostly of carbon dioxide and nitrogen, and it has strong pressure on the surface, from where one would never be able to see the stars in the night sky through the dense clouds.

Mercury and Venus, as planets inside the earth’s orbit, orbit the sun faster than the earth does and are often close to the sun, as seen from Earth. Hence, they are observable either in the evening sky just after sunset or in the morning sky just before sunrise; that is, Venus is also called the “morning star” or the “evening star.” The Greeks called Mercury “Hermes” when it appeared as the evening star and “Apollo” when it appeared as the morning star; Venus was similarly called either “Hesperus” or “Phosphorus,” respectively.

thin atmosphere

thin atmosphere

Earth is the third planet from the sun; it needs 365 days for a complete orbit around the central star and 24 hours for one rotation. Its atmosphere consists mainly of oxygen and nitrogen. This planet is the only one known so far to harbor living beings like plants, animals, and intelligent life.

The fourth planet is called Mars. It has an orbital period of 687 days and a rotation period of 24.6 hours, so that a “Mars­day” is only slightly longer than a day on Earth. Its thin atmosphere consists mostly of carbon dioxide and nitrogen, but this atmosphere is not identical to that of Earth.

There is frozen carbon dioxide and water ice at the poles, but no fluid water has yet been detected. However, some surface structures look like dry river beds and may indicate that fluid water was present some billions of years ago. It is not impossible that life has formed on Mars, too, but no clear evidence for life on Mars has been found yet.

Phobos and Deimos

Phobos and Deimos

Mars is orbited by two small moons, called Phobos and Deimos, with 8­hour and 30­hour orbital periods, respectively. Like the moon of Earth, their rotation is bound: Their orbital period equals their rotational period; they are rotating around themselves only by orbiting their planet and always show the same side to their planet.

The innermost four planets are also called terrestrial planets, as they are all made mostly of solid material like Earth (terra). Between Mars, the fourth planet, and Jupiter, the fifth planet, there is a large gap where many small bodies are orbiting the sun. These are called minor planets or sometimes planetoids, because they are physically like terrestrial planets; that is, they are rocky objects.

They are also called asteroids, because in the sky they look like the stars looked when they were discovered, namely pointlike (as opposed to the planets of our solar system, which appeared to be extended on the sky even in naked­eye observations, because of their larger size and smaller distance from observers).

terrestrial planets

terrestrial planets

The four outermost known planets (Jupiter, Saturn, Uranus, and Neptune) all are larger in size than the terrestrial planets, mostly because of their large atmospheres and only small solid or fluid cores. (In the case of Jupiter, there may not even be a core at all.) Hence, they are called the “gaseous giant planets.”

Jupiter is the largest planet in our solar system; it has a diameter of 143,000 kilometers and a mass of 318 times the mass of Earth. It needs almost 12 years for one orbit around the sun, but only 10 hours for a rotation around itself, as can be observed with even a small telescope because of the moving large red spot in its outer atmosphere.

Given its diameter, mass, and composition (mostly molecular hydrogen), it is not absolutely clear whether it has a solid or fluid core or possibly even no core, that is, no solid surface. If it has a core, the core could have a mass of a few or maybe 10 Earth masses. Due to contraction, Jupiter is still radiating more energy to outer space than it is receiving from the sun.

four moons

four moons

This giant planet also has a small ring system and a large number of moons, probably a few dozen; new small moons are still being discovered. The four largest moons were originally discovered by Galileo, when he observed Jupiter for the first time with a telescope. These four moons (Io, Europa, Ganymede, and Callisto) are called the Galileian satellites.

Saturn is twice as far from the sun as Jupiter is. Saturn is known mostly for its large ring system. It also has a large number of moons. Saturn needs 29.5 years to orbit the sun and has a rotation period of 10 hours and 40 minutes.

It has a solid core of a few Earth masses and a large atmosphere made mostly of molecular hydrogen gas. Saturn is the second largest planet (120,000 kilometers in diameter) and the second most massive (95 times the mass of Earth) in our solar system.

gas giants

gas giants

All planets from Mercury to Saturn (including Earth) have been known for several thousand years to most cultures on Earth, because they can be observed by the naked eye. The outermost planets, Uranus and Neptune (as well as Pluto), were discovered after the invention of the telescope. While Jupiter and Saturn are called “gas giants,” Uranus and Neptune are also gaseous planets that can be seen as “ice giants.”

Uranus was discovered (and recognized as a planet) in 1781 by William Herschel. Others had observed it before but did not recognize that it as a planet. Uranus is also a gaseous planet with a central solid core, but in total it is only 15 times as massive as Earth.

Uranus needs 84 years to circle around the sun, and one “day” on Uranus lasts around 17 hours. Uranus’s atmosphere consists of 83% hydrogen, 15% helium, and 2% methane. So far, 21 moons have been discovered (and astronomers are still counting). Uranus also has a small ring system as discovered by the Voyager satellites.

Neptune

Neptune

Neptune is the outermost known (and accepted) planet. It was observed by Galileo in 1612, but he did not recognize it as a planet. Because of apparent deviations in the orbit of Uranus, both John Couch Adams and Urbain Le Verrier predicted the existence of another planet theoretically and tried to forecast its rough location in the sky.

Later, in 1846, the observer Johann Gottfried Galle in Berlin, Germany, searched that area of the sky for a small moving object and discovered Neptune within a few hours. Neptune needs 165 years for one full circle around the sun.

One “day” on Neptune lasts 16 hours. Neptune has a small solid core, a large gaseous atmosphere composed mostly of molecular hydrogen, and a total mass of 17 times the mass of Earth. Neptune, like all gaseous planets in our solar system, has moons and rings.

Astronomical Union

Astronomical Union

The object Pluto was discovered in 1930 and celebrated as a new planet, but it was deleted from the list of planets in the 2006 definition of planet by the International Astronomical Union.

The new definition of planet is formulated for the solar system, but it can and should be applied analogously to other planetary systems around other stars. However, there is as yet no consensus or definition for the upper mass limit of planets. Such an upper mass limit, however, would be very important for extrasolar planets, to be able to decide whether they are planets or so­called brown dwarfs.

In history, the two definitions for a planet worked for about 200 years: The first definition worked from the Copernican revolution to the discovery of Ceres and other minor planets (which now form the asteroid belt between Mars and Jupiter); the second definition, excluding the minor planets, was in effect again for about 200 years until 2006.

general assembly

general assembly

Both the problem regarding Pluto and the missing upper mass limit for planets may very well lead to a new definition at one of the next meetings of the International Astronomical Society, which holds a general assembly every three years.