General Astronomy Questions - Assignment Example

1.- What is located in the nucleus of the Galaxy? a. a globular cluster, b. a spiral arm, c. a black hole d. the solar system, e. a MACHO Galaxies are formed from smaller ensembles of stars, gas, and dust. The underlying dark matter that clumped together in the young universe drew this matter together, often assisted by a supermassive black hole formed early in the life of the universe. This black hole became the nucleus of the galaxy (Comins 2008, pp 461). 2.- How did Edwin Hubble prove that M31 is not a nebula in our Milky Way Galaxy? Leavitt discovered a direct relationship exists between a Cepheid’s luminosity (absolute magnitude or distance) and its period of oscillation. By observing the star’s period and apparent magnitude, its distance can be calculated. Thanks to this work, Hubble knew that he could use the characteristics of the fluctuating light of Cepheid variable stars to help him calculate the distance to M31. His observations of Type I Cepheids led him to determine that M31 is some 2.2 million lightyears beyond the Milky Way. This proves that M31 is not an open or globular cluster in our Galaxy, but rather an enormous separate stellar system—a separate galaxy. M31, now called the Andromeda Galaxy. (Comins 2008, pp 436) 3.- Why do astronomers believe that vast quantities of dark matter surround our Galaxy? Quite a bit of evidence has accumulated to support the idea of extended halo surrounding our Galaxy. According to Kepler’s third law, the farther a star or cloud is from the center of the Milky Way, the slower it should be moving, just as the orbital speeds of the planets decrease with increasing distance from the Sun. Observations reveal, however, that galactic orbital speeds continue to climb well beyond the visible edge of the galactic disk (The Galaxy’s Rotation Curve is remarkably flat out to surprisingly great distances from the galaxy’s center). This means there must be more gravitational force from the Galaxy acting on the distant stars and clouds than we can see or have taken into account. As with the Milky Way Galaxy, astronomers conclude that a considerable amount of dark matter must extend well beyond the visible portions of most galaxies. (Comins 2008, pp 446 and pp 469) 4.- What are the most massive galaxies in the universe? a. Normal spirals, b. barred spirals, c. giant ellipticals d. Dwarf ellipticals, e. irregulars (Comins 2008, pp 461) 5.Which of the following statements about the motion of galaxies is correct? a. All galaxies are moving apart. b. Superclusters of galaxies are all moving apart. c. Superclusters of galaxies are all moving toward each other. d. The Milky way Galaxy is at the center of the Universe. e. All clusters of galaxies in each supercluster are moving toward each other (Comins 2008, pp 470) 6.- Some galaxies in the Local Group exhibit blue-shifted spectral lines. Why are these blue shifts not Violations of the Hubble law? All galaxies have their own motion relative to each other due to their mutual gravitational force. For nearby galaxies, the speed of the Hubble flow is smaller than these intrinsic velocities. Hence, some of the nearest galaxies are actually approaching us and have blueshifts instead of redshifts. (Comins 2008, pp 471) 7. Explain how the rate of variability of a source of light can be used to place an upper limit on the size of the source. ? By physical arguments, if an energy source of a certain size is to exhibit a well defined period in its luminosity, some signal must travel through the object to "tell" it to vary. Since such a signal can travel no faster than light velocity, the maximum size of an object varying with some characteristic time is the distance that light could have traveled during that time. For example, if a source is observed to vary its light output substantially over a period of a week, this implies that the spatial extent of the energy producing region can be no larger than the distance light can travel in a week (Ewert, 2013). 8.. Inflation most directly explains which of the following? a. Why the universe is homogeneous b. Why the universe is expanding c. Why the universe is going to last forever d. why the universe has a background Temperature e. Why the universe has particles (Comins 2008, pp 520) 9. Explain the difference between a Doppler redshift and a cosmological redshift. The redshift that Hubble observed, caused by the expansion of the universe, is properly called the cosmological redshift. In other words, the photons that we observe from galaxies in other superclusters are all redshifted because space is expanding. The Doppler redhisft results from the relative motion of the light emitting object and the observer. If the source of light is moving away from you then the wavelength of the light is stretched out, i.e. it has redshift. (Comins 2008, pp 446 and pp 469) 10. Give examples of the actions or roles of each of the four basic physical forces in the universe. Properties of the Fundamental Forces The strong interaction is very strong, but very short-ranged. It acts only over ranges of order 10-13 centimeters and is responsible for holding the nuclei of atoms together. It is basically attractive, but can be effectively repulsive in some circumstances. It is presents inside atomic nuclei. The electromagnetic force causes electric and magnetic effects such as the repulsion between like electrical charges or the interaction of bar magnets. It is long-ranged, but much weaker than the strong force. It can be attractive or repulsive, and acts only between pieces of matter carrying electrical charge. The weak force is responsible for radioactive decay and neutrino interactions. It has a very short range and, as its name indicates, it is very weak. It is presents inside atomic nuclei. The gravitational force is weak, but very long ranged. Furthermore, it is always attractive, and acts between any two pieces of matter in the Universe since mass is its source. Ewert M. “Astronomy 162. Stars, Galaxies, and Cosmology”, http://csep10.phys.utk.edu/astr162/lect/cosmology/forces.html [Accessed on March 5, 2013] 2.- Which element serves as the foundation or "backbone" of life? a. oxygen, b. carbon, c. silicon, d. hydrogen, e. nitrogen Carbon is the backbone of life on Earth. The humans are made of carbon, they eat carbon and furthermore, the civilization is built on carbon. Carbon’s ability to form four bonds simultaneously means that it can be combined with itself and other elements to make a huge number of different molecules (Przyborski, 2013). 3.- What arguments could you make against sending messages via radio or spacecraft into interstellar Space? Radio communication: We need to think of the intended receptor has discovered radio waves and been able to make a transmitter and a receiver. Also, the intended recipient has to know how to demodulate the incoming radio wave. Spacecraft: It takes a long time to get anywhere, even to Moon. Fuel would be another big problem. People aboard the spacecraft need plenty of food. References: Comins N. F., Kaufmann III W. J., 2008 “Discovering the Universe”, 8th Edition, Clancy Marshall Publisher. Ewert M. “Astronomy 162. Stars, Galaxies, and Cosmology”, http://csep10.phys.utk.edu/astr162/lect/active/compact.html [Accessed on March 5, 2013] Ewert M. “Astronomy 162. Stars, Galaxies, and Cosmology”, http://csep10.phys.utk.edu/astr162/lect/cosmology/forces.html [Accessed on March 5, 2013] Przyborski P. “The Carbon Cycle”,http://earthobservatory.nasa.gov/Features/CarbonCycle/ [Accessed on March 5, 2013] Read More