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Big Questions If astronomers measure an objects apparent brightness (flux), what do they need to know to figure out how far away that object is? Why are astronomers interested in different parts of the electromagnetic spectrum? How do an objects size and temperature affect the light it emits, both the quantity and the color? How can astronomers take a stars temperature from so far away? Slide 2 Below are four Honda Civics driving toward you at sunset with their headlights turned on. Each car is equipped with identical headlights. Rank the distance that each car is from you from greatest to least. Slide 3 Below are four Honda Civics driving toward you at sunset with their headlights turned on. Each car is equipped with identical headlights. Rank the apparent brightness (flux) of each cars headlights from greatest to least. Slide 4 Below are four Honda Civics driving toward you at sunset with their headlights turned on. Each car is equipped with identical headlights. Rank the absolute brightness (luminosity) of each cars headlights from greatest to least. Slide 5 The figure below shows five stars (A-E) as they appear in the night sky from Earth. A darker shade is used to indicate the appearance of a dimmer star. The distances to each star are unknown. Rank the flux of each star from greatest to least. 1 2 3 5 4 Slide 6 Rank the luminosity of each star from greatest to least. The figure below shows five stars (A-E) as they appear in the night sky from Earth. A darker shade is used to indicate the appearance of a dimmer star. The distances to each star are unknown. 1 2 3 5 4 Slide 7 Slide 8 Slide 9 Visible Rusty Slide 10 Infrared Rusty Slide 11 Slide 12 USA - Visible Slide 13 USA - IR Slide 14 USA - gamma Slide 15 USA - radio Slide 16 The Whirlpool Galaxy, M51 Radio: cold gas & magnetic fields Ultraviolet: young stars Visible: stars Infrared: warm dust X-ray: black holes and neutron stars Slide 17 Atomic H gas GMCs dust Forming stars Stars Hot gas & binaries Cosmic rays colliding with the interstellar meduim Slide 18 Infrared light has 1-greater 2-less energy than ultraviolet light Slide 19 X-ray photons have 1-longer 2-shorter wavelengths than gamma ray photons Slide 20 Visible electromagnetic radiation has a 1-higher 2-lower frequency than radio wave electromagnetic radiation Slide 21 Infrared light has a 1-faster 2-slower speed than microwave light Slide 22 Of all the types of light the sun gives off, it emits the greatest amount of light at visible light wavelengths. If the sun were to cool off dramatically and as a result start giving off mainly light at wavelengths longer than visible light, how would the frequency, energy and speed of this light given off by the sun also be different? Frequency : Energy: Speed: Slide 23 Slide 24 AB C D E The hot plates are shaded according to temperature (darker shading means colder). Rank the hotplates in order by how much light they emit. Emits most light ___ ___ ___ ___ ___ Emits least light Slide 25 Below is the information about several stars. Rank the stars in order by the total amount of light they emit. StarRadius [R sun ]Temperature [K]Distance [lyr] alpha14,00025 beta12,00078 gamma28,00013 delta416,000104 epsilon22,00057 Emits most light ___ ___ ___ ___ ___ Emits least light Slide 26 Slide 27 Color Temperature! Which stars are hottest? Coolest? Which stars are hottest? Slide 28 The figure below is a graph of luminosity and temperature. Which group of stars is the red giants? 1 2 3 4 Slide 29 The figure below is a graph of luminosity and temperature. Which group of stars is the white dwarfs? 1 2 3 4 Slide 30 The figure below is a graph of luminosity and temperature. Which group of stars is the red dwarfs? 1 2 3 4 Slide 31 Flux Wavelength (nm) BlueRed Slide 32 Star 1 Star 2Star 3 Which star is the hottest? Slide 33 Star 1 Star 2Star 3 What color is Star 2? (The visible part of the spectrum goes from 4000 to 7000 on this scale). Slide 34 Big Questions How does light interact with matter? How does quantum mechanics affect these interactions? How do the spectra of opaque and non-opaque objects differ? When do astronomers observe absorption lines vs emission lines? What information can astronomers learn directly from the spectrum of an object? Slide 35 Slide 36 Slide 37 Slide 38 Slide 39 Slide 40 Slide 41 Slide 42 Questions about Emission and Absorption: The picture to the right is of the Ring Nebula -- a bubble of gas surrounding a small star. If you aimed the Hubble Space Telescope at box A and took a spectrum, what would you expect to see? 1- Emission lines 2- Absorption lines 3- Blackbody continuum 4- None of the above A B Slide 43 Questions about Emission and Absorption: The picture to the right is of the Ring Nebula -- a bubble of gas surrounding a small star. If you aimed the Hubble at box B and took a spectrum what would you expect to see? (Note - box B contains a star) 1- Emission lines 2- Absorption lines 3- Blackbody continuum 4- None of the above A B Slide 44 Slide 45 Below is the spectrum for the planet Mars from UV to IR. Which portion of the spectrum is created by reflected sunlight? 1 2 345 Slide 46 Below is the spectrum for the planet Mars from UV to IR. Which portion of the spectrum is created by hot carbon dioxide gas in the upper atmosphere of Mars? 1 2 345 Slide 47 Below is the spectrum for the planet Mars from UV to IR. Which portion of the spectrum is created by Mars own blackbody radiation? 1 2 345 Slide 48 Below is the spectrum for the planet Mars from UV to IR. What color does Mars appear? 1 2 345 Slide 49 Below is the spectrum for the planet Mars from UV to IR. Which portion of the spectrum is created by absorption by the red soil of Mars? 1 2 345 Slide 50 Slide 51 The visible light emitted by hydrogen is caused by transitions from higher energy levels down to the 1st excited state. Below is the emission spectrum of hydrogen gas. Draw an atom, including a nucleus and five energy levels. Using a dot to represent the electron and an arrow to represent its motion, sketch and label what happens to the electron to create the red emission line. On the same drawing, sketch what happens to the electron to create the blue emission line.