Famous Astronomers | List of Great Scientists in Astronomy
When most people believed the world was flat, the notable Greek mathematician, astronomer and geographer Eratosthenes (276–195 B.C.) used the sun to measure the size of the round Earth. His measurement of 24,660 miles (39,690 kilometers) was only 211 miles (340 km) off the true measurement.
In ancient Greece, astronomer and mathematician Claudius Ptolemy (A.D. 90–168) set up a model of the solar system in which the sun, stars, and other planets revolved around Earth. Known as the Ptolemaic system, it remained in place for hundreds of years, though it turned out to be flat wrong. According to NASA, "Ptolemy represents the epitome of knowledge of Grecian astronomy."
Persian astronomer Abd al-Rahman al-Sufi (903–986), known as Azophi to Westerners, made the first known observation of a group of stars outside of the Milky Way, the Andromeda galaxy.
Nicolaus Copernicus
Credit: Public Domain
In 16th century Poland, astronomer Nicolaus Copernicus (1473–1543) proposed a model of the solar system that involved the Earth revolving around the sun. The model wasn't completely correct, as astronomers of the time struggled with the backwards path Mars sometimes took, but it eventually changed the way many scientists viewed the solar system.
Using detailed measurements of the path of planets kept by Danish astronomer Tycho Brahe, Johannes Kepler (1571–1630) determined that planets traveled around the sun not in circles but in ellipses. In so doing, he calculated three laws involving the motions of planets that astronomers still use in calculations today. However, closed minds put Kepler's work at risk.
"The era in which Kepler lived was one of tremendous upheaval and change," said Dan Lewis, curator of the history of science and technology at the Huntington Library in San Marino, Calif. "Religious leaders were reluctant to relinquish their ideas about the heavens. Talk by astronomers of a sky filled with objects moving in non-circular orbits and other phenomena that went against an Earth-centric model threatened their beliefs. As a result, Kepler and his first wife, Barbara, created a code with which to write letters to each other so that their correspondence would not put them at risk of persecution."
Galileo Galilei is credited with discovering the first four moons of Jupiter.
Credit: NASA
Born in Italy, Galileo Galilei (1564–1642) is often credited with the creation of the optical telescope, though in truth he improved on existing models. According to the Rice University's Galileo Project, "Galileo made his first telescope in 1609, modeled after telescopes produced in other parts of Europe that could magnify objects three times. He created a telescope later that same year that could magnify objects twenty times."
The astronomer (also mathematician, physicist and philosopher) turned the new observational tool toward the heavens, where he discovered the four primary moons of Jupiter (now known as the Galilean moons), as well as the rings of Saturn. Though a model of the Earth circling the sun was first proposed by Copernicus, it took some time before it became widely accepted. Galileo is most widely known for defending the idea several years after Kepler had already calculated the path of planets, and Galileo wound up under house arrest at the end of his lifetime because of it.
Italian astronomer Giovanni Cassini (1625–1712) measured how long it took the planets Jupiter and Mars to rotate. He also discovered four moons of Saturn and the gap in the planet's rings. When NASA launched a satellite to orbit Saturn and its moons in 1997, it was fittingly dubbed Cassini.
Dutch scientist Christiaan Huygens (1629–1695) proposed the earliest theory about the nature of light, a phenomenon that puzzled scientists for hundreds of years. His improvements on the telescope allowed him to make the first observations of Saturn's rings and to discover its moon, Titan.
English astronomer Sir Isaac Newton (1643–1727) is most famous for his work on forces, specifically gravity. Building on the work of those who had gone before him — he is quoted as saying, "If I have seen further, it is by standing upon the shoulders of giants" — he calculated three laws describing the motion of forces between objects, known today as Newton's laws.
Edmond Halley (1656–1742) was the British scientist who reviewed historical comet sightings and proposed that the comet that had appeared in 1456, 1531, 1607, and 1682 were all the same, and would return in 1758. Although he died before its return, he was proven correct, and the comet was named in his honor.
French astronomer Charles Messier (1730–1817) composed a database of objects known at the time as "nebulae," which included 103 objects at its final publication, though additional objects were added based on his personal notes. Many of these objects are often listed with their catalog name, such as the Andromeda Galaxy, known as M31. Messier also discovered 13 comets over the course of his lifetime.
British astronomer William Herschel (1738–1822) cataloged over 2,500 deep sky objects. He also discovered Uranus and its two brightest moons, two of Saturn's moons, and the Martian ice caps. William trained his sister, Caroline Herschel (1750–1848), in astronomy, and she became the first woman to discover a comet, identifying several over the course of her lifetime.
Henrietta Swann Leavitt (1868–1921) was one of several women working as a human "computer" at Harvard College, identifying images of variable stars on photographic plates. She discovered that the brightness of a special flashing star known as a Cepheid variable was related to how often it pulsed. This relationship allowed astronomers to calculate the distances of stars and galaxies, the size of the Milky Way, and the expansion of the universe.
Albert Einstein at the blackboard.
Credit: NASA
In the early 20th century, German physicist Albert Einstein (1879–1955) became one of the most famous scientists ever after proposing a new way of looking at the universe that went beyond current understanding. Einstein suggested that the laws of physics are the same throughout the universe, that the speed of light in a vacuum is constant, and that space and time are linked in an entity known as space-time, which is distorted by gravity.
In a lecture given in 1966, fellow scientist Robert Oppenheimer said, "Einstein was a physicist, a natural philosopher, the greatest of our time."
At the same time Einstein was expanding man's view of the universe, American astronomer Edwin Hubble (1899–1953) calculated that a small blob in the sky existed outside of the Milky Way. Prior to his observations, the discussion over the size of the universe was divided as to whether or not only a single galaxy existed. Hubble went on to determine that the universe itself was expanding, a calculation which later came to be known as Hubble's law. Hubble's observations of the various galaxies allowed him to create a standard system of classification still used today.
American astronomer Harlow Shapley (1885–1972) calculated the size of the Milky Way galaxy and general location of its center. He argued that the objects known as "nebulae" lay within the galaxy, rather than outside of it, and incorrectly disagreed with Hubble's observations that the universe boasted galaxies other than the Milky Way.
Frank Drake with a young observer at the Lick Observatory.
Credit: SETI Institute
Frank Drake (born 1930) is one of the pioneers in the search for extraterrestrial intelligence. He was one of the founders of the Search for Extraterrestrial Intelligence (SETI) and devised the Drake equation, a mathematical equation used to estimate the number of extraterrestrial civilizations in the Milky Way galaxy able to be detected.
American astronomer Carl Sagan (1934–1996) may not have been a great scientist in comparison to some on this list, but he is one of the most famous astronomers. Sagan not only made important scientific studies in the fields of planetary science, he also managed to popularize astronomy more than any other individual. His charismatic teaching and boundless energy influenced people around the world as he broke down complicated subjects in a way that interested television viewers even as he educated them. Sagan founded the Planetary Society, a nonprofit organization devoted to advancing space science and exploration.
Professor Stephen Hawking speaks about "Why We Should Go into Space" for the NASA Lecture Series, April 21, 2008.
Credit: NASA/Paul Alers
American astronomer William K. Hartmann (born 1939) put forth the most widely accepted theory on the formation of the moon in 1975. He proposed that, after a collision with a large body scooped, debris from the Earth coalesced into the moon.
Stephen Hawking (born 1942) has made many significant insights into the field of cosmology. He proposed that, as the universe has a beginning, it will likely also end. He also suggested that it has no boundary or border. Despite being viewed as one of the most brilliant minds since Einstein, many of Hawking's books and lectures are steered toward the general public as he seeks to educate people about the universe they live in.
https://www.space.com/16095-famous-astronomers.html
Biology
Characteristics of Life - Advanced
What do a bacterium and a whale have in common?
Do they share characteristics with us? All living organisms, from the smallest bacterium to the largest whale, share certain characteristics of life. For example, all living things are made of cellsand they must reproduce to make the next generation. Without these characteristics, there is no life.
Characteristics of Life
Biology examines the structure, function, growth, origin, evolution, and distribution of living things. It classifies and describes organisms, their functions, how species come into existence, and the interactions they have with each other and with the natural environment. Four unifying principles form the foundation of modern biology: cell theory, evolution, genetics and homeostasis.
Most biological sciences are specialized areas of study. Biology includes biochemistry, cell biology, microbiology, immunology, genetics, physiology, zoology, ecology, evolutionary biology, and botany. Biochemistry is the study of the chemicals that make up life. Cell biology is the study of life at the level of the cell. Microbiology is the study of microscopic organisms. Immunology is the study of an organism's resistance to disease. Genetics is the study of how organisms pass traits to their offspring. The study of how the human body works is called physiology. Zoology is the study of animals. The study of how organisms interact with their environment and each other is called ecology. Evolutionary biology is the study of how populations and species change over time. Botany is the study of plants. The four unifying principles are important foundations for each and every field of biology. Applied fields of biology such as medicine and genetic researchinvolve many specialized areas of study.
What Is Life?
Not all scientists agree exactly about what makes up life. Many characteristics describe most living things. However, with most of the characteristics listed below we can think of one or more examples that would seem to break the rule, with something non-living being classified as living or something living being classified as non-living.
There is not just one distinguishing feature that separates a living thing from a non-living thing. A cat moves but so does a car. A tree grows bigger, but so does a cloud. A cell has structure, but so does a crystal. Biologists define life by listing characteristics that living things share. Something that has all of the characteristics of life is considered to be alive. The duck decoy in Figure below may look like a duck, act like a duck in that it floats about, but it is not alive. The decoy cannot reproduce, respond to its environment, or breathe.
An individual living creature is called an organism. There are many characteristics that living organisms share. They all:
- respond to their environment
- grow and change
- reproduce and have offspring
- have a complex chemistry
- maintain homeostasis
- are built of structures called cells
- pass their traits onto their offspring
Responding to the Environment
All living organisms respond to their environment. If you step on a rock, it will just lie there, but if you step on a turtle, it may move or even snap at you. Living things know what is going on around them, and respond to changes in the environment. An adaptation refers to the process of becoming adjusted to an environment. Adaptations may include structural, physiological, or behavioral traits that improve an organism's likelihood of survival, and thus, reproduction.
Growth and Change
All living organisms have the ability to grow and change. A seed may look like a pebble, but under the right conditions it will sprout and form a seedling that will grow into a larger plant. The pebble of course will not grow. Even the smallest bacteria must grow. This bacteria will reproduce by dividing into two separate bacterium. If the parent bacterium does not grow, then each subsequent generation will just be smaller then the previous generation. Eventually the bacteria will be too small to function properly.
Tadpoles, like those shown here, go through many changes to become adult frogs.[Figure3]
Reproduction
All living organisms must have the ability to reproduce. Living things make more organisms like themselves. Whether the organism is a rabbit, or a tree, or a bacterium, life will create more life. If a species cannot create the next generation, the species will go extinct. Reproduction is the process of making the next generation and may be a sexual or an asexual process. Sexual reproduction involves two parents and the fusion of gametes, haploid sex cells from each parent. Sexual reproduction produces offspring that are genetically unique and increases genetic variation within a species. Asexual reproduction involves only one parent. It occurs without a fusion of gametes and produces offspring that are all genetically identical to the parent.
Have Complex Chemistry
All living organisms have a complex chemistry. A flower has a complicated and beautiful structure. So does a crystal. But if you look closely at the crystal, you see no change. The flower, on the other hand, is transporting water through its petals, producing pigment molecules, breaking down sugar for energy, and undergoing a large number of other biochemical reactionsthat are needed for living organisms to stay alive. The sum of all the chemical reactions in a cell is metabolism.
Maintain Homeostasis
A human body has a temperature of 37 degrees Celsius, (about 98.6 degrees Fahrenheit). If you step outside on a cold morning, the temperature might be below freezing. Nevertheless, you do not become an ice cube. You shiver and the movement in your arms and legs allows you to stay warm. Eating food also gives your body the energy it needs to keep warm. Living organisms keep their internal environments within a certain range (they maintain a stable internal condition), despite changes in their external environment. This process is called homeostasis, and is an important characteristic of all living organisms.
Built of Cells
If you look closely at any organism you can see that it is made of structures called cells. Organisms that are very different such as ferns, fish, and elephants all look similar at the cellular level. A cell is the basic unit of structure and function of all living organisms. All living organisms are made of one or more cells: a simple bacterium will consist of just one cell, whereas you are made of trillions of cells.
Representations of human cells (left) and onion cells (right). If you looked at human and onion cells under a microscope, this is what you might see.[Figure4]
Organisms are organized in the microscopic level from atoms up to cells. The matter is structured in an ordered way. Atoms are arranged into molecules, then into macromolecules, which make up organelles, which work together to form cells. Beyond this, cells are organized in higher levels to form entire multicellular organisms, as shown in Figure below. Cells together form tissues, which make up organs, which are part of organ systems, which work together to form an entire organism. Of course, beyond this, organisms form populations which make up parts of an ecosystem. All of Earth's ecosystems together form the diverse environment that is Earth.
@@license="(a) CC-BY 2.0; (b) Public Domain; (c) Public Domain; (d) Public Domain; (e) Public Domain; (f) Public Domain"
Levels of organization in a tree. (a) The tree is the organism; (b) a leaf is an organ, (c) a leaf tissue is made up of different types of cells; (d) a plant cell; (e) chloroplast is an organelle inside a plant cell; (f) chlorophyll is the photosynthetic molecule that is found in chloroplasts.
Summary
- The seven characteristics of life include:
- responsiveness to the environment;
- growth and change;
- ability to reproduce;
- have a metabolism and breathe;
- maintain homeostasis;
- being made of cells; and
- passing traits onto offspring.
Review
- What are the four unifying principles that form the foundation of modern biology?
- Identify three of the seven characteristics of living things.
- What is adaptation?
- Distinguish between metabolism and homeostasis.
- What is a cell?
https://www.ck12.org/biology/Characteristics-of-Life/lesson/Characteristics-of-Life-Advanced-BIO-ADV/
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