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The seven days of the week and the astronomical objects they honor.
According to ancient literature, the days of the week represent different astronomical objects. Monday represents the moon while Tuesday represents the planet Mars. Wednesday represents planet Mercury, Thursday represents planet Jupiter while Friday, Saturday, and Sunday represent planet Venus, planet Saturn, and the sun respectively. The above astronomical objects have maintained their names for centuries and are still associated with the days of the week. The names symbolize the names of gods in ancient literature, and the cycle has never been broken even today.
Eratosthenes measures the side of the earth.
Eratosthenes is known for his calculation of the earth’s circumference which he estimated using the overhead position of the sun in an Egyptian town called Syene and the distance between Syene and Alexandria in Egypt. Syene is located very close to what is in modern science known as Tropic Cancer. Using data on the distance between Syene and Alexandria, Eratosthenes was able to estimate the angle of the rays of the sun as 7.5 degrees and the circumference of the earth was known to be 360 degrees. Dividing 360 degrees with the 7.6 degrees, according to him would equal the division of the circumference of the earth with the distance between Syene and Alexandria. Eratosthenes found out, through his calculations, that the circumference of the earth was roughly 40,000 kilometres, a largely correct estimate compared to recent data that estimate the circumference of the earth to be 40,000 kilometres.
Geocentric model- Ptolemaic model (A.D. 100-170)
The geocentric model developed by Ptolemaic has its base on the belief that the earth was the center of the universe. Ptolemaic also argued that the earth was round and existed in a celestial sphere where all the stars rotated around it. Ptolemaic also asserts that the stars rotated around the earth which was static in circles he called epicycles. However, his assumption that the earth and not the sun is the center of the universe makes his model incorrect. However, the geocentric model was the best during its time.
How does the Ptolemaic model explain retrograde motion?
Ptolemaic used two circles, the epicycle (smaller circle) and the deferent (larger circle) to explain the retrograde motion of the planets. He determined that planets moved in a backward looping motion and then they would adopt their original movement around the earth. As an asteroid rotates around its epicycle, the deferent moves around the Earth. When the planet’s motion brought it inside the deferent circle, then the retrograde motion would take place. However, the use of epicycles failed to explain the concept of retrograde motion clearly.
How did Copernicus, Tycho, and Kepler challenge the Earth-centered idea?
Copernicus, Tycho, and Kepler challenged the idea that the earth was the center of the solar system. They replaced it with the idea that the sun, not the earth was the center of the solar system. Whereas Copernicus’s model still used circles to explain planetary motions, Tycho Brahe determined naked eye measurements of positions of planets. Kepler did away with the circles and instead adopted orbits to describe planetary motions although a discrepancy resulted in his discovery and use of ellipses. Later, Kepler came up with three laws of planetary motion that later proved that indeed the earth, like other planets orbited the sun.
Tycho Brahe (1546–1601) – Johannes Kepler (1571–1630)
Tycho Brahe was a Denmark born astronomer. During his education, Tycho developed an interest in Astronomy, an interest that led him to his observations on planets and their associated characteristics and motions as well rejecting the geocentric model in favor of the sun-centered model. Johannes Kepler was a German-born astronomer who made considerable contributions to the scientific revolution. Kepler’s works created the three laws of planetary motion and set the stage for the discovery of gravitational force by Isaac Newton. Both Tycho and Kepler challenged the earth-centered model and helped in the later scientific insights on the solar system and geography.
What are Kepler’s three laws of planetary motion? Kepler’s Second Law: As a planet moves around its orbit, it sweeps out equal areas in equal times.
Kepler’s first law of planetary motion states that the orbit around the sun of every planet is an ellipse with the sun at one focus. The second law says that as a planet moves around its orbit, it sweeps out equal areas in equal times. The second law means that when nearer to the sun, planets move faster and they are slower when farther away from the sun. Therefore, the closer a planet is to the sun, the faster it moves and vice versa. The third law states that the more distant a planet is from the sun, the slower its orbiting average speeds. The third law shows the relationship p²=a³ where p represents the orbital period, and a represents the average distance from the sun.
An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun?
If p²=a³, and a=4 AU, then we can find the value of p. Recall that Kepler’s third law’s foundation is on the relationship p²=a³. In this case, a is given as 4 AU, and we are required to find the number of orbital years represented by p. From the relationship formula, we can determine the value of a³ by cubing four which gives us 64. Given that p² is equal to a³, we can determine that p²=64. Therefore, p is given by the square root of 64 which give us eight orbital years.
Galileo’s observations of all phases of Venus proved that it orbits the Sun and not Earth (Venetian’s view of Earth?).
Galileo was an Italian born astronomer who discovered that the moon had mountains and rifts on it and that the planet Jupiter had moons orbiting it. However, Galileo’s biggest achievements were that he was the first to use a telescope to observe the solar system during which he discovered that planet Venus had different phases, a proof that the planets orbited the sun and not the earth. The phases of the planet Venus led Galileo to conclude that the planet could have only been travelling around the sun for it to have phases as it went behind and beyond the sun, just as the moon does. Therefore, Galileo was the first astronomer to observe with evidence that the sun was the center of the universe and not the earth as it had been believed, and by so doing, Galileo confirmed as true the observations of Copernicus.
How Long Is a Day?
A day refers to the time it takes the earth to complete one rotation around its axis relative to the sun. A typical day is 24 hours long. Converting the hours of a day into minutes gives a total of 1440 minutes. If the 24 hours of a day are converted to seconds, then a day has a total of 86,400 seconds, the SI unit for measuring time. However, when the time it takes the earth to rotate around its axis relative to far away stars other than the sun is measured, a day is found to have 23 hours and 56 minutes. Scientists measure the time it takes the earth to rotate around its axis relative to the sun, and thus a day is exactly 24 hours using this approach.
Solar day = 24 hours (rotation + orbit about the Sun). Sidereal day (Earth’s rotation period) = 23 hours, 56 minutes
A solar day is the most common measurement of the length of a day used on earth. The solar day is measured as the time it takes the earth to rotate on its axis with reference to the sun. The time it takes the earth to rotate around its axis with reference to the sun is exactly 24 hours. The earth rotates on its axis while at the same time orbiting around the sun. A sidereal day, on the other hand, refers to the time it takes the earth to rotate around its axis with reference to distant stars. These stars are assumed to be fixed, that is, not moving. A sidereal day, therefore, is the period between the first and the next overhead positions of the distant stars relative to the earth. A sidereal day is 23 hours and 56 minutes long, a time that is four minutes shorter than the solar day.
The idealized scientific method: • Based on proposing and testing hypotheses • Hypothesis = educated guess
Modern science is based on the testing of hypothesis to determine if they are correct or not and if they can be applied or they should be discarded. A hypothesis is an educated guess that is open to testing to determine validity or invalidity. The proposing and testing of the hypothesis has come to define modern science and mathematics, and indeed almost all scientific researches. When an educated guess is made, it is a statement or idea that is not yet scientifically proven, and its concepts cannot, therefore, be adopted, unless they are proved to be correct beyond reasonable doubt. Determining whether or not a hypothesis is correct or incorrect calls for a valuable and careful collection of relevant data, the application of both scientific and mathematical skills where applicable to analyze the data and the drawing of conclusions. The conclusions drawn determine the truthfulness or wrongness of the hypothesis.
What is a scientific theory?
A scientific theory can be defined as a scientifically tested, proven, and widely accepted explanation for a specific phenomenon. Therefore, a scientific theory evolves in different stages from a hypothesis to an accepted explanation tested using the scientific method. The scientific method involves the collection of data, the analysis of data, and the drawing of conclusions from the analyzed data. A scientific theory is therefore considered to be an acceptable position on any given matter unless other data is analyzed through the scientific method that proves the theory wrong. Science is made up of numerous scientific theories that explain the numerous scientific concepts that define the modern world. Scientific theories have and continue to play a key role in furthering scientific knowledge in all areas of human endeavor. Scientific theories employ inductive and deductive reasoning to offer explanations to certain phenomena that are of importance to human life.
How do we describe motion? – The acceleration caused by Gravity
Motion is the state of moving or being moved. Motion can be described through speed, velocity, and acceleration. Even though the three concepts are related, they are entirely different and have different methods of calculating them. Acceleration by gravity explains the power of the force of gravity that pulls objects towards the surface of the earth. Acceleration due to the force of gravity can be observed in the falling of objects when they are thrown vertically upwards, released vertically downwards or thrown horizontally. In all of these instances, the objects are pulled towards the surface of the earth. Acceleration due to gravity is 9.8m/s². The acceleration due to gravity is deemed to be constant for all bodies falling freely, in spite of their mass, other factors like buoyancy and air resistance held constant.
Momentum and Force
Momentum can be defined as an object’s quantity of motion. The quantity of motion of an object is given by multiplying its velocity by its mass. Therefore, mass and velocity are strong determinants of the momentum of an object. Since all objects have mass, then all moving objects have momentum. Therefore, the larger the mass and velocity of a body, the higher the momentum. On the other hand, force can be defined as simply a push or pull. Force is measured in Newton.
How is mass different from weight?
Mass is the measure of the amount of matter contained in an object while weight is the measure of the pull of gravity on an object. Another difference is that mass is measured in kilograms while weight is measured in Newton, a measure of force. Another difference is that mass can never be zero since all objects have matter, but weight can be zero if there is no gravitational force. Furthermore, mass is a scalar quantity while weight is a vector quantity. Mass is measured using the ordinary scale while weight is measured using the spring scale.
Why are astronauts weightless in space?
Astronauts are weightless in space. The reason for this is that there is very little force of gravity in space. Science does note that the farther away from the earth one goes, the lower the force of gravity becomes. Astronauts are usually very far away from the earth, making the force of gravity there almost negligible. As a result of the reduced or negligible gravitational pull, astronauts can float in space. Given that weight is given by mass multiplied by gravitational pull denoted by g, the fact that g is zero in space makes the weight of the astronauts zero. The above statement explains why astronauts are weightless in space.
What are Newton’s three laws of motion- explain all 3 in detail.
Newton’s first law of motion, also the law of inertia states that every object will remain in a constant state of rest or uniform motion unless it is acted upon by an external force. The first law means that if all the external forces acting on an object are zero or they cancel each other out, then the velocity of an object remains constant. Therefore, if the velocity of an object is zero, then it is in a constant state of rest. Newton’s second law of motion states that the force applied on an object to cause it to change its velocity is given by the mass times the acceleration of that body. This law allowed Newton and other scientists to analyze the effects of applying force on an object at rest or in motion and the changes in velocity (acceleration) that would follow. The third law of motion states that for every action, there is an equal and opposite reaction. That is to say that every action force generates another reaction force from the object on which the action force is applied. The third law has been used in the development of jet fighter engines, and other scientific innovations.
Conservation of Angular Momentum- Angular momentum conservation also explains why objects rotate faster as they shrink in radius: (example: the collapse of stars)
Angular momentum refers to the velocity with which an object rotates around an axis. The conservation of angular momentum is the property of a spinning body to keep spinning unless it is acted upon by an external force. As a planet orbiting around the sun gets closer to the sun, more of its angular momentum is conserved thereby increasing its orbiting speed. Therefore, unless a spinning body is acted upon by an external force, other factors held constant, the body continues to spin without stopping. Gyroscopes are an example of innovations based on the conservation of angular momentum.
Basic Types of Energy
- Kinetic (motion) • Radiative (light) • Stored or potential
Kinetic energy refers to the energy a body possesses due to its motion. Therefore, kinetic energy is simply energy in motion. Radiative energy is the energy that is transmitted by electromagnetic radiation. An example of radiative energy is the warmth that is felt from the sun or a nearby burning candle. Stored or potential energy is the energy that is stored in an object relative to its position. For instance, positioning the ball of a demolition machine at a high position stores potential energy that is released when the ball is released to hit a target structure.
Thermal Energy
Thermal energy is also referred to as heat energy. Thermal energy refers to the energy that results from the increased collision of molecules and atoms of an object due to an increase in temperature. As temperature increases, the rate of collisions also increases thereby releasing thermal energy. Therefore, thermal energy is induced by an increase in the temperature of a body. The hot an object is, the faster the vibrations of its atoms and molecules, and therefore the more the thermal energy generated.
Gravitational Potential Energy, Mass-Energy
Gravitational potential energy is the energy an object possesses as a result of its location in a gravitational field. Gravitational potential energy is derived from the law of gravity. The higher the position of an object, the more the gravitational potential energy it has. An example is placing a car at a higher sloping ground. At a higher position, the car has more gravitational potential energy.
Conservation of Energy
The law of conservation of energy states that the energy of an object is constant. The law, therefore, suggests that energy is neither created nor destroyed. Since energy can neither be created nor destroyed, it can only be transferred from one form to another. For instance, energy can be transferred from potential energy to kinetic energy and vice versa. Chemical energy can also be converted into kinetic energy and many other examples. The law of conservation of energy has failed to change over time due to the consistent nature of other scientific laws.
The Force of Gravity, what determines the strength of gravity?
The force of gravity is affected by two main factors. The first factor is the mass of an object. The more the mass of an object, the more the gravitational force. Recall that gravity is a force given by multiplying mass and acceleration. Therefore, the higher the mass of a body, the higher the force of gravity. The second factor affecting gravity is the distance between objects. The longer the distance between two bodies, the lower the force of gravity, and the shorter the distance between two bodies, the higher the force of gravity between them.
Tidal Friction
The tidal frictions can be defined as the frictions that deform the earth’s oceans due to the frictions of the moon as it spins around its axis. The frictions result in tidal bulges that slow down the speed of the earth’s rotation. In reality, tidal friction can be conceptualized as a force that brakes the speed of the earth’s rotation. Tidal frictions affect the earth’s ocean beds as a result of the braking effect they have on the rotation of the earth. However, this process takes a lot of time and may take millions of years to have a real impact. Astronomers argue that the earth’s rotation has been slowing down, a phenomenon that could result in increased lengths of days.