Ancient Greek philosophers considered stars planets. Modern scientists call them stars, but the question remains: are stars planets? As far as mass and apparent motion goes, planets do not meet the criteria for stars. They are less massive than planets, but are still heavenly bodies. In this article, we’ll examine some of the astronomical evidence that supports the planets’ status as planets. After all, the Ancient Greeks did call them planets.
Ancient Greek philosophers called stars planets
Greek philosophers called the stars planets because they believed the earth was stationary in the universe. This made them think that the motions in the heavens were caused by the motion of the earth, a view that is not compatible with modern science. This also leads to the confusion over why ancient philosophers called the stars planets. During this time, the Greeks did not study the origin of the sun or the moon, but concentrated on the motion of the planets in their nightly course around the Earth.
The ancient Greeks also named the five stars that we can see with our naked eyes: Venus, Mars, Saturn, and Jupiter. The first three planets were named after their respective gods, which were called ASTRA PLANETA. The second planet, Saturn, was named Phaethon, because it was the son of Sol. This mythical god, a mischievous youth, foolishly drove the chariot of his father and subsequently set fire to the earth. Jove then struck him, conveying him to the constellations. The third planet, Mars, was named after Aphrodite, the goddess of love and fire.
In the 4th century BCE, the Greeks introduced the concept of physics and initiated scientific thought. They asked questions about the nature of matter. They believed that planets and moons move around the sun at a constant rate, but without any experimental basis. Their belief in constant motion had a profound effect on attempts to understand the movements of planets for the next two thousand years. This belief helped them make sense of the universe.
Ptolemy was another ancient Greek philosopher who was interested in the motion of celestial bodies. He was an Alexandrian and published a 13-volume summary of Greek astronomy. The Almagest, which is considered the first star catalogue, described the positions of more than 1,000 stars in constellations. Ptolemy was a great believer that all celestial bodies revolved around the earth, but he also discovered fixed stars in the sky. The Almagest also discussed the motion of the sun and the length of the year.
Brown dwarfs do not meet the criteria for stars or planets
As their name suggests, brown dwarfs are not stars but are in the same class as stars. Their formation is similar to that of stars, except that they are much less massive and have weaker gravitational pulls. This helps them hold on to lighter elements better than planets, such as hydrogen. They are also not massive enough to begin stellar fusion. Unlike planets, however, brown dwarfs are able to sustain deuterium fusion, which is necessary for stellar formation.
The mass of brown dwarfs falls between the heaviest gas planets and the lightest stars. This mass is more than 13 Jupiter masses, but less than 80 Jupiter masses. They can orbit each other and even travel through the galaxy on their own. Because of their small mass, they are easily studied using infrared wavelengths. The difference between gas giants and brown dwarfs makes it difficult to differentiate them, but they are similar in structure.
Although brown dwarfs are not planets, they do have atmospheres. They were originally referred to as black dwarfs, but the term is now used to describe the last stage of stellar evolution. Once a white dwarf has radiated its entire heat, it becomes a brown dwarf. They eventually cool to below the main sequence stellar temperature of about 1,800 K. At this point, they are too dim to detect.
Although the mass of brown dwarfs is small, their presence in the sky confirms their existence. Using Hubble, scientists have identified 21 candidates that contain optical proplyds. The presence of such objects confirms their membership in a cluster and their substellar nature. One such cluster is the Trapezium Cluster, which contains about a hundred of them. This is an example of a brown dwarf’s potential to be a planet.
Some of the candidates were reported soon after the discovery of GD 165B. But these stars failed to live up to the brown dwarf criteria and did not have lithium in their atmospheres. Lithium is a crucial ingredient for brown dwarfs to achieve substellar status. They will not burn lithium within the first 100 Myr of their existence and thus will not achieve the core temperatures required for star formation.
They do not have enough mass to ignite nuclear fusion
Stars are much larger than planets. Stars undergo nuclear fusion to create energy. This process is what allows them to burn hydrogen. Planets, on the other hand, do not have enough mass to ignite fusion. They usually orbit around a star. In order to ignite nuclear fusion, a star must have a mass that is 75 times that of Jupiter.
While some brown dwarfs have been discovered to act like stars, they do not have enough mass to trigger fusion. Even with 13 times Jupiter’s mass, they can ignite a limited type of fusion. Once the deuterium supply is exhausted, nuclear fusion will stop and the object will revert to glowing, contracting, and cooling. But there is another possibility.
The process of nuclear fusion is a complex process. If a planet had enough mass to ignite nuclear fusion, it would be a star. It is hard to find a stable planetary orbit in a binary star system. A planet would have to be a giant, dense mass, and have sufficient mass to withstand the pressure and heat of nuclear fusion.
In a singlet star, the process of fusion is predictable. Once the star ignites nuclear fusion, the central star will burn through the hydrogen fuel in its core. This process will continue until the core hydrogen is depleted. At this point, the rate of fusion decreases because the outward radiation pressure is no longer strong enough to hold the central star in place against gravity.
Besides being rocky, these objects have a massive core. Stars with a high mass undergo nuclear fusion. This fusion requires a high pressure of 2×1011 atm. But stars with a lower mass will not initiate nuclear fusion. This process occurs when the temperature of hydrogen is high enough. A star’s core contains enough hydrogen to ignite nuclear fusion.
How is this process possible? The Sun undergoes nuclear fusion to generate energy. At its core, the sun is a nuclear fusion machine. The sun’s core is 74% hydrogen, with about 620 million tons of hydrogen fusing into helium every second. As a result, the sun creates a vast amount of heat and light. However, this process is far from complete.
They have less mass than planets
The question arises, why do stars have less mass than planets? Planets are formed by accreting leftovers from a primordial cloud. Because planets have a lower mass than stars, they experience weaker gravitational pulls. Because of this, they can contain high amounts of metal and are typically near a star. This means they orbit their host star and clear debris from their orbits.
However, stars are still the largest objects in the universe. Jupiter, for example, has a mass of 2.5 times the mass of the planets combined, and it has a density less than one gram per cubic centimetre. In fact, if we were to walk on a star the size of Jupiter, we would be unable to. And so, star-like objects that are much smaller than planets are called brown dwarfs.
There are a few ways to detect planets around stars. One way is to steal mass from planets nearby. A star can lose mass if the mass of its outer layers is too low to fuse carbon into heavier elements. This process can stop nuclear reactions. But stealing mass from a planet can only go so far, which means the planet has to be close to the star. And that’s not a very good way to discover planets.
A binary system with two gas giants will rotate around a common center of gravity. This binary system will be able to orbit around a common center of gravity. However, this doesn’t mean that they will ever be able to orbit one another. The binary system will not contain a planet that is more massive than the other. In fact, two objects orbit each other, but at a distance of seventy-five million km.
Another way of finding planets is by searching for binary star systems. Approximately 50 percent of all stars are binary, which is when two stars orbit each other. Some even have three or more binary star systems. Both ways are similar, though locating planets in these systems is more challenging. They can orbit many stars, but are not as dense. So how do we discover them? This is the key to understanding how planets form and their relationship with their stars.