Astronomy Homework Assignments

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1. Briefly describe the geocentric model of the universe.

Geocentric model states that the Earth is the center of the universe. As a result, all other objects in the Solar System revolve around it. The model was developed in the cosmological system such as in the ancient Greece. The proponents of this theory base their ideas on several observations. Firstly, it was observed that the sun, stars and other planets appear to revolve around the Earth. This makes the Earth the center of the universe. Moreover, each star is usually on a stellar sphere in which the Earth was observed to be at the center and rotated every day. The Earth rotated through the lines that run from the North to the South Pole (Dreyer, 1953). On the other hand, it was observed that the stars that were close to the equator rose and fell from the largest distance as seen from the Earth. Each day, every star circled to its normal point and, as a result, the Earth was seen to be the center of the Solar System. Another dominant notion was developed by the supporter of geocentric theory was that the Earth was not seen to move. This was from an Earth bound observer where there was no observable movement. As a result, the Earth was seen to be more stable and not in motion. This theory was associated with the spherical nature of the Earth by ancient philosophers (Parks, 1991). They believed that the motion of the Earth was circular which was contrary to the Earth-flat model that had been developed earlier. However, the geocentric theory was changed from the 17th century where greater ideas were developed that stipulated that the sun was at the center of the universe.

2. The benefit of our knowledge lets us see flaws in the Ptolemaic model of the universe. What is it basic flaw?

Ptolemaic model of the universe has some basic flaws. Due to the benefit of our knowledge, we are able to see the flaws. The major basic flaw includes the following: the model does not describe the basic movements of the planets. In this case, the model does not describe the motions that are conspicuous with members of the Solar System that are always in motion (Murray, 1999). As a result, this flaw was an avenue for major arguments and further studies that was to analyze the concept of movement of other actors in the Solar System.

3. What was the great contribution of Copernicus to our knowledge of the Solar System?

Copernicus made one of the greatest contributions to the field of astronomy. He developed a theory that stated that the sun is at the center of the Solar System contrary to the previous the theory that had been developed by Ptolemy that stipulated that the Earth is at the center of the universe (Finocchiaro, 2008). This added our knowledge of the Solar System as we developed a new insight into what composes the Solar System and what moves around the other.

4. What was the Copernican revolution?

Copernican revolution is a paradigm that changes from the Ptolemaic to heliocentric model. Notably, the Ptolemaic model stated that the Earth was at the center of the universe. On the other hand, the heliocentric model stipulates that the sun is at the center of the universe. It was one of the major scientific revolutions carried out in the 16th century (Kuhn, 1957). Indeed, Copernicus revolution has greater consequences on the field of astronomy as it gave a new understanding contrary to what had been know there before. His theory was more superior to those that had been developed by scientists such as Ptolemy. In this case, Copernicus challenged later understanding of the universe as he argued the earlier stipulation that the objects at the sky are made of special materials. He maintained that the Earth was just one of the planets (Kuhn, 1957). As a result, all plants are made of the same stuff, and no planet has been made from special materials like earlier studies had shown.

5. Why Galileo is often thought of as the first experimental scientist?

Galileo is known as the first experimental scientists as he originally laid the method of inquiry that was used by later scientists. He was able to reduce problems surrounding a given phenomena into a simple set of basis that made logic. Moreover, he was able to analyze major problems into simple mathematical and physics descriptions (Dreyer, 1953). He successively analyzed the concept of motion, which was the foundation for today’s mathematics among other experiments. Indeed, later scientists such as Isaac Newton used one of his mathematical analyses that involved the law of inertia to come up with the first law of motion. Therefore, he was able to make major experiments that formed the basis for the modern mathematics and physics.

6. Briefly describe Kepler’s three laws of planetary motion?

Kepler gave a concrete description of the motion of the planets as they move around the sun. Firstly, he argued that the orbit of all the planets is in form of an eclipse around the sun. In his law, he argued that the sun is not usually at the center of an eclipse (Murray, 1999). It is actually at the one of the focal points. Indeed, every ellipse has two focal points and a joining segment which coincides with the center

Secondly, he stated that the line that joins the planet and the sun sweeps out at an equal area in every interval of time as the planet moves around the sun. Thus, the time is constant, and it does not vary (Finocchiaro, 2008). Thirdly, he stated that the square of the orbit of a given planet is directly proportional to the cube of its semi major axis of its own orbit.

7. What does it mean to say Kepler’s Laws are empirical in nature?

Kepler’s laws are indeed empirical in nature. This is because they are derived from calculations. Kepler does complex calculation relating to the orbit and the focal points, while, at the same time, considering other related factors (Soden, 2000). Indeed, the formulas are derived from pure mathematics with the understanding that the sun is not usually at the center of an ellipse. It is indeed at one of the focal points. This makes it easy to derive calculations.

8. If radio waves cannot be reflected from the sun, how can radar are used to find the distance from Earth to Sun?

Radar ray would be used to determine the distance between the Earth and the sun in the following manner: according to Kepler’s third law, it can be deduced that the distance from the sun is equal to the square of its orbital period (Bakshi, 2008). In this case, we would get the scale model as the scale factor where we would get the speed of radar signal, which is about 300,000km per sec. As a result, we would be able to determine the distance between the sun and the Earth.

9. List the two modifications made by Newton to Kepler’s laws.

There are two major modifications that were made by Newton to the previously established Kepler’s laws. The first change involved the stipulation that the Earth or the planet does not go round the exact center of the sun. He argued that both the planet and the sun always orbit in responsible to their center of mass (Mantell, 1976). This implies that the Earth and the sun go around on their average position, which is determined by their total composition in terms of matter. Therefore, the first law of Kepler was changed. As a result, it was changed to the state that the orbit of the planet as it moves around the sun is in form of an ellipse. In this case, the planet and the sun are always at the center responsive to their mass, which is at a single focus (Drake, 1957). Today, the law states that the orbit of the planets around the sun is in the form of an ellipse. Newton also changed the third Kepler’s law and added some concepts. He added a concept of combined mass to the formula that has been developed by Kepler’s law earlier. This formula has been developed to measure the time taken by the planet to move around the sun. The changes to Kepler’s law are still in force.

The formula was finally stated as:

(Earth years) 2 = (seminar axis) 3 / (combined mass of the two planets).

  •  Why do we day that the baseball falls to Earth, and not Earth toward the baseball?

The baseball falls to the Earth and not the vice versa because of the force of gravity. Practically, the center of the Earth is continuously pulling objects towards it. As a result, everything that is thrown to the air always comes to the ground (Richard, 1978). Moreover, this force is responsible for keeping objects on the ground and not in the air. In this case, the gravity has the capacity of pulling the baseball to the ground instead of going up or remaining in the air.


  • Define the following wave properties: period, wave length, amplitude, frequency.

Wave period refers to the time that is between the attainment of a given successive maxima. It is measured at a fixed point of a given quantity that characterizes a wave.

Wave length refers to the period of a given wave. It notes the distance in which a wave repeats. The wave length is determined by the distance between two consecutive points which are in the same phase. This may be crests, troughs as well as in zero crossings. Wave length can be measured in both moving as well as in standing waves.

Wave amplitude refers to the number of changes in an oscillation with a given system. For instance, sound waves are always in oscillation in the air (Burmeister, 1993). Their amplitude is always in proportion to the changes in the present pressure in a single oscillation. Thus, a regular oscillation is evident when the pressure is constant.

Wave frequency refers to the number of times a cycle takes. It notes the duration taken by a single cycle in wave light in a repeating event.

2. Compare and contrast the gravitational force with the electric force.

Some of the differences between gravitational and electronic forces include the following: firstly, in the electronic force there are two major forces: the repulsive and attractive, while in the case of gravitational force there are only attractive forces but no repulsive forces between the objects being compared. Secondly, in the electronic force, the force acts between electronic charges, which are the contrary in gravitational force which acts between different masses. Thirdly, in electronic forces, a constant is used, which is referred to as permittivity of a given medium. This notes the amount of electronic forces that can be transferred through a given medium in a given period of time (Archibald, 1973). Thus, the ability of a medium to pass charges enables it to conduct electricity between two points. On the other hand, in gravitational force, there is a universal constant, which is referred to as the gravitational constant which is always used between two masses. Finally, the electronic force is much greater while compared with the gravitational force. The two forces are also similar in that they act between two points or bodies. Moreover, the two forces are able to attract the objects and keep them in that position (Archibald, 1973).

3. What do radio waves, infrared radiation, visible light, ultra-light radiation, X-rays and gamma rays have in common? How do they differ?

The similarity between these rays is that they are all members of electromagnetic spectrum. All radiations have frequency and wavelength although their magnitude makes them different. However, all the radiations have three types: the alpha, the beta as well as the gamma. This also marks another similarly.

Radio wave defines electromagnetic radiation that has wavelengths in a given electromagnetic spectrum (Michael, 2003). They travel at a speed of light and occur naturally. It is made by lightening. However, there are artificially developed radio waves that are used in communication devices such as phones, radios, satellites, computer networks among others

Infrared radiation is a form of an electromagnetic radiation that has a very long wave in comparison with those of visible light. It extends beyond the visible spectrum and includes most of the thermal radiation. They are normally emitted by objects in a room temperature. It is also observed by molecules. However, this only happens when their rotational vibration is changed.

Visible light refers to the light that is visible by the human eye. It is an electromagnetic radiation that leads to the sense of light which is seen by the eye. It has medium wavelengths placed between infrared and ultra-violet.

Ultra-light radiations are electromagnetic radiations that are dangerous to the skin. They are also dangerous to the eye leading to some disorders as well as long-term consequences.

X-rays is a member of electromagnetic radiation. They have short wavelength but longer than those of gamma rays.

Gamma rays are electromagnetic radiations which have high frequency with a lot of energy. They are referred to as ionizing radiation which is biologically dangerous. They are produced from the decay of atomic nuclei know as gamma decay (Feynman, 1963). Therefore, all the waves differ in wavelength and frequency.

4. In what region of the electromagnetic spectrum is the atmosphere transparent enough to allow observation from the ground?

The regions of the electromagnetic spectrum are the radio and infrared rays that allows light to pass through, and as a result it can be observed from the ground (Hogendijk, 2003).

5. If Earth was completely blanketed with clouds and we couldn’t see the sky, could we learn about the realm beyond the clouds? What forms of radiation might penetrate the clouds and reach the ground?

Yes, we could learn about the realm beyond the clouds as there are technologies that could make it possible. Some of the radiations that could pass to the reach the ground include the infrared (Parks, 1991).

6. In terms of its black body curve, describe what happens as a red-hot glowing coal cools.

As the coal gets cool, its peak will go to the left. This is because of the low frequency as well as the increased wavelength (Soden, 2000). Moreover, the total underneath area will also decline.

7. What is a continuous spectrum? An absorption spectrum?

A continuous spectrum is usually divided into three parts which include the following: the point, continuous as well as residual spectrum. They share similar characteristics. Moreover, they do not have lines as well as band. Their radiations are usually distributed over a range that is not interrupted by the wavelengths.

Absorption spectrum is normally produced when an electromagnetic radiation has been absorbed by a certain sample. In this case, the frequencies contained in the radiation are able to excite the atoms as well as molecules of a particular sample (Feynman, 1963). As a result, the atoms change their state from the ground to the excited state. The frequency where a given absorption takes place depends on the differences in energy between the atom in the ground state and in the excited state.

8. What is the normal condition for atoms? What is an excited atom? What are orbital’s?

The normal conditions for atoms refer to the state where the atoms can stick together as a result form a larger and totally different substance.

An excited atom refers to an atom that contains a lot of energy than it does when it is in its typical state or when at the ground. After a given atom is excited, it calms down eventually returning to its original state. This is after it has lost its energy which depends on several related factors.

Orbital’s refers to the path of an electron. In this case, electrons are seen as a wave while in motion. As a result, they take a space in a given shape, which depends on the sort of the orbital. Thus, the electrons move in these paths.

9. Why do excited atoms absorb and reemit radiation at characteristics frequencies?

An excited atom usually absorbs and reemits radiation. As it absorbs energy, it changes its frequency as it becomes more active, because it has a lot of energy (Richard, 1978). This is followed by the loss of energy making it possible to reduce its frequency in its original state.

10. What is the Doppler Effect, and how does it alter the way in which we perceive radiation?

Dropper effect refers to the changes in wavelength as it travels from two objects. Dropper effect is responsible for the received frequencies of a given source. This defines how a wave is perceived when it reaches its destination. On the same, it differs in terms of the frequencies with which it was sent if the motion is increasing or decreasing with the distance between the perceived source and the receiver (Ptolemy & Smith, 1996). The dropper effect is observed on the changes in the pitch of sound between a moving source and a certain observer who is stationary. Therefore, the way we perceive radiation is changed by dropper effect in that the frequencies differ with the motion and the distance of the radiation.

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