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CHAPTER 9 notes.docx

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York University
Natural Science
NATS 1745
Robin Metcalfe

CHAPTER 9: 1. All attempts to detect stellar parallax failed until the 1830s because people believed that the brightest stars in the sky were the nearest stars to the Earth. 2. He announced that the stars have their own unique motions across the sky, but because the stars are so distant, their motion appears so tiny that we can't easily perceive it. The stars move in their own direction with different speed. Stellar parallax was finally seen in the nearest stars, now chosen for their brightness and large motion- Instead of assuming the brightest star are the nearby stars, the brightness requirement was combined with the requirement that the stars had large motion. REASON: if a star has no noticeably motion after a century of tracking it then this star is probably very far away. 3. Alpha Centauri is the nearest star Distance of 270,000AU [4.4 ly (light years) or 1.3 pc (parsecs)] 4. The definition of a light year is the distance that light travels in one year. Aparsec is the distance of an object with a parallax of 1 arcsecond. Aparsec is bigger than a light year.Aparsec is roughly 206,000AU (31 billion km) and a light year is about 63,000AU (9.5 billion km). 5. All light waves travel like waves; they are waves of oscillating electric and magnetic fields. 6. Describe how a wave from a bright blue light source is different from a wave from a faint red light source. Abright blue light source will have a high amplitude and a small wavelength. Afaint red light source will have a small amplitude and a high wavelength. 7. Blue light is the shortest in wavelength. Red light is the longest in wavelength. Blue light has the highest frequency; red light has the lowest frequency. 8. Gamma waves have the shortest wavelength, but have the highest frequency. Radio waves have the longest wavelength, but have the smallest frequency. 9. What is a spectroscope? Aspectroscope is a scientific instrument that splits light into its different wavelengths, which humans see as different colors. Violet has the shortest wavelength that people can see and red the longest. This instrument can also identify wavelengths that humans cannot see, such as infrared and ultraviolet radiation. Invented in 1814 by Joseph von Fraunhofer. 10. Fraunhofer passed sunlight through glass and observed the spectrum through a telescope. He saw roughly 600 thin dark lines and labeled them with letters to designate their wavelength. It contained absorption lines. 11. Through Spectroscopy: which is the analysis of the spectrum of a light source for the purpose of determining its chemical composition (the study of light spectrum in order to determine the chemical composition of a light source). The unique spectra of known substances could be used to identify the spectra of an unknown substance- e.g. unknown substance- meteoroid u want to know what its composed of, you would have to heat up a sample of it and disburse the light from its flame and examine the pattern of coloured lines in the flames spectrum then you can match the wavelengths of the coloured lines that you see with the wavelengths of lines in known substances. We can collect a stars light. 12. They found the darker lines got thicker. They concluded, the Sun’s core, which produced the full spectrum of light, is surrounded by a gas layer (an atmosphere). Molecules in the Sun’s atmosphere absorb light at their signature wavelengths, producing the dark lines (absorption lines). During the solar eclipse, the spectrum of the Sun’s atmosphere was produced, revealing the “emission lines” predicted by Bunsen and Kirchhoff. 13. Norman Lockyer discovered an absorption line that had never been detected before. He suggested that it must be produced by a new element. He named it ‘helium’, after ‘Helios’the greek god of the sun. 14. In a graphical spectrum, emission lines appear as peaks in the graph.Absorption lines appear as dips. 15. The spectra of a gas cloud is made up of emission lines.Astar cluster is made up of continuum emission and absorption lines. Gas/star systems are made up of continuum emission, emission lines and absorption lines. 16. Huggins produces the spectrum of a planetary nebula and found unidentified emission lines. These emission lines were for the element Oxygen, but because he found them within planetary nebula, he named it Nebulium. 17. OnAugust 29, 1864, Huggins was the first to analyze the spectrum of a planetary nebula. His observations of stars showed that their spectra consisted of a continuum of radiation with many dark lines superimposed on them. He later found that many nebulous objects had spectra that were quite similar. Planetary nebulae are usually identified by their emission-line spectrum. These nebulae were later shown to be galaxies. 18. Radial motion is the approaching or receding motion. If I am giving out light waves as I move towards you, the light waves are going to get compressed, as I move away from you the light waves are going to get stretched. This i
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