Assignment 3Chapters 5 & 6Thomas Edison State College

Introductory AstronomyAST-101-GS002Semester - October 2013

1.) The Seeds textbook states, To an astronomer, nothing is so precious as starlight. Today we recognize that this starlight is electromagnetic radiation. List the following: A. Each part of this radiation used by an astronomer. The parts of electromagnetic radiation utilized by an astronomer are x-rays, gamma rays, ultraviolet radiation, visible light, infrared radiation, and radio waves. One cannot see infrared radiation, but a persons skin senses it as heat. In the electromagnetic spectrum, electromagnetic waves shorter than violet are known as ultraviolet, the ones shorter than those are known as X-rays, and the shortest of the three are known as gamma rays.

B. What instrument (telescope, etc.) works best with each type of radiation.The instrument that works best for radio waves is a radio telescope. Astronomers use a radio telescope to study celestial objects such as clouds of gas and erupting stars. Due to never reaching the Earths surface infrared radiation, ultraviolet, X-Rays, and gamma ray are used with instruments such as the infrared telescopes. Astronomers have used many infrared telescopes to study star formation; planets are orbiting other stars, distant galaxies, and more. Some of these telescopes are known as the Spitzer Space Telescope, Hubble Space Telescope, Ariel 1, and the Chandra X-Ray Observatory. C. What celestial objects we study and what we learn about them from the radiation they emit.All astronomical objects, except for black holes, emit at least some light. Many objects emit more radiation in some parts of the electromagnetic spectrum than in others while others emit strongly across the entire spectrum. Each part of the spectrum reveals information not found at other wavelengths. Light is a form of electromagnetic radiation. Visible light is a narrow range of wavelengths of the electromagnetic spectrum. By measuring the wavelength or frequency of light coming from objects in the universe, we can learn something about their nature. Since we are not able to travel to a star or take samples from a galaxy, we must depend on electromagnetic radiation to carry information to us from distant objects in space.

D. What special instruments work in conjunction with telescopes to advance our studies of starlight. The unique instruments that work together with telescopes to promote our studies of starlight are charge-coupled devices and spectrographs. Charge-coupled devices are specialized chips that detect both bright and faint objects in a single exposure, and the chip could be placed into a computer for later analysis. Spectrographs are used to analyze light in detail. They spread the light out according to wavelength to form a spectrum. 2. The ultimate key to our understanding the universe is our knowledge of the atom. A. Illustrate with an example the difference between an atom and an ion. The ultimate key to understanding the universe is our knowledge of the atom. Atoms are the basic units of matter made up of three particles; protons, neutrons, and electrons. The atom is also a defining structure of an element. A typical atom has a neutral charge with the same number of protons and electrons. An ion is an atom that has lost one or more electrons and now either has a net positive or a net negative charge.

B. Describe two ways an atom can be excited. There are two ways to excite an atom. These two ways are either absorbing a proton or moving an electron from a low energy level to a high energy level. An atom can only absorb a proton with the right amount of energy if the proton has too much or too little energy the atom would not be able to absorb it. When moving an electron from a low energy level to a high energy level, the atom now has added energy. C. Why should photons emitted by a hotter material have an average shorter wavelength?The amount of energy a photon carry is inversely proportional to its wavelength. The temperature of an object is a measure of how much energy its atoms have. Since atoms in hotter objects have more energy, they can emit photons with more energy than cooler objects can So hot objects emit high-energy photons or short wavelength light. They also emit more photons that cooler objects do. The rule is the amount of power emitted (energy emitted each second) is P emitted T4 D. Atoms produce spectra. Distinguish between a continuous, a bright-line, and an absorption spectrum by describing how each is formed. There are two ways to excite an atom. These two ways are either absorbing a proton or moving an electron from a low energy level to a high energy level. An atom can only absorb a proton with the right amount of energy, if the proton has too much or too little energy the atom will not be able to absorb it. When moving an electron from a low energy level to a high energy level, the atom now has added energy. Photons emitted by a hotter material have an average of a shorter wavelength. This is because they have a high energy level and the higher the energy level the shorter the wavelength. Atoms produce spectra. There are three different types of spectra the continuous, bright-line, and absorption spectra. Continuous spectrum is formed by gas emitted electromagnetic radiation at all wavelengths. Excited low-density gas is containing produces an emission/ bright-light spectrum containing emission lines. Absorption spectrum is formed by a light source viewed through low-density gas containing absorption lines.3. How was the spectral classification system arrived at? Relate its construction to the Balmer series and explain how a stars spectral class can give us clues to its temperature, motion, and chemical composition. In 1802, William Wollaston noted that the spectrum of sunlight did not appear to be a continuous band of colors, but rather had a series of dark lines superimposed on it. Wollaston attributed the lines to natural boundaries between colors. Joseph Fraunhofer made a more careful set of observations of the solar spectrum in 1814 and found some 600 dark lines, and he specifically measured the wavelength of 324 of them. Many of the Fraunhofer lines in the solar spectrum retain the notations he created to designate them. In 1864, Sir William Huggins matched some of these dark lines in spectra from other stars with terrestrial substances, demonstrating that stars are made of the same materials of everyday material rather than exotic substances. This paved the way for modern spectroscopy. The Balmer absorption lines help to find temperatures of the stars more accurately. Calculations can predict how strong Balmer lines will be for stars. When a star of particular strength can either be a star with a high temperature or a low-temperature one must examine other spectral lines to choose the correct temperature. A stars spectral class can give us clues to its temperature, motion, and chemical composition. The seven spectral classes are O, B, A, F, G, K, M known as the spectral sequence that is the temperature sequence. O is the hottest temperature and M is the coolest temperature. By dividing the seven spectral classes into ten subclasses in each division, it accurately identifies the temperature within about 5 degrees. The strength of the spectral lines depends on the temperature of the star. By identifying the lines in the stars spectrum, one can identify the elements that are present in the star. It is important to know though that if spectral lines characteristics of an element are missing, one cannot accurately conclude that the element is absent. For example hydrogen, Balmer lines are weak in the suns spectrum even though 90% of the atoms in the sun are hydrogen. A stars spectral class can give us clues to its motion by looking at the Doppler Effect. One can measure the wavelengths of the lines in a stars spectrum and find the velocity of the star by using the Doppler Effect. The Doppler Effect is the apparent change in wavelengths of radiation caused by the motion of the source. One will observe a blueshift when a star is approaching and produces shorter wavelengths. On the other hand, one will observe a redshift when the star is moving away creating longer wavelengths.