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Galaxies Exam 1
| Question | Answer |
|---|---|
| What was the first observational evidence that the geocentric model of the Solar System was wrong? | Some planets were observed to undergo retrograde motion in the sky. |
| Galileo used a telescope to prove the heliocentric nature of the solar system by observing: | Venus goes through all of the phases (crescent, gibbous, etc.) |
| How do astronomers use spectroscopy to measure the rotation rates of stars (i.e. how fast stars are spinning)? | They measure the widths of emission and/or abortion lines in a star's spectrum. |
| What types of telescopes are used to detect low-energy light emitted by rotating molecules in outer space? | Radio telescopes |
| If you were to double the size (diameter) of a telescope's primary mirror, its diffraction-limited angular resolution would . | get better by a factor of 2 |
| What does light consist of ? | electric & magnetic fields |
| The regions of the light spectrum, in order of highest to lowest energy, are: | Gamma Rays → X Rays → Ultraviolet → Visible → Infrared → Radio |
| Understanding the nature of black-body radiation allows astronomers to measure the ________ of a star. | temperature |
| If the temperature of an object were to triple, the total power (energy per unit area) radiated by the object will __________. | increase by a factor of 81 (81x) |
| An electron that transitions from a higher energy state to a lower energy state ___________________. | emits light |
| A telescope's resolution is measured in units of _______. | degrees, arc-minutes, or arc-seconds |
| A telescope's resolution depends on: | The size of the telescope and the wavelength of light being observed |
| Scientists use the ___________ temperature scale, which sets the point where all thermal motion stops equal to a temperature of 0. | Kelvin |
| The temperature of an object is a direct measure of the amount of ________________ within it. | microscopic motion |
| The coolest stars appear ________ in color. | red |
| The __________ of a visible light wave is constant, regardless of the color. | speed |
| A(n) _____________ telescope uses lenses to focus light. | refracting |
| Why must an X-ray telescope be placed in outer space? | Earth's atmosphere is opaque to X-rays. |
| Consider an observatory setup that includes a telescope, a camera, and different colored filters. By comparing the brightness of a star as observed through two different color filters, you can measure the __________ of the star. | temperature |
| What type of spectrum does the Sun produce? | Absorption spectrum |
| Consider an object that emits a continuous, black-body spectrum that peaks at a wavelength of 600 nm. If the object's temperature were to suddenly double, at what wavelength would the peak of its new black-body spectrum be? | 300 nm |
| hydrogen can emit or absorb green light that has a wavelength of 486.1 nm. If you were to observe a hydrogen emission source and measure the wavelength of the green light to be at 488.5 nm, what can you tell about the light source? | It is moving away from you. |
| Compared with a spectrum from a ground-based observation, the spectrum of a star observed from above Earth's atmosphere would show ... | slightly fewer absorption lines. |
| Consider a cool gas placed in front of a hot light bulb. The observed spectrum of the light bulb will contain dark lines where some light has been absorbed by the gas. Those dark lines reveal the | chemical composition of the cool gas |
| What are the three different kinds of spectra used to analyze matter? | continuous, emission (bright line), and absorption (dark line) spectra |
| What properties of stars can we measure? | Temperature Orbital motion Pulsations Rotation |
| Refracting telescopes use... | Lenses |
| Reflecting telescopes use... | Mirrors |
| What is the speed and distance of a planet when it is farthest from the sun's orbit | The slowest speed |
| What are the three factors of the scientific method in astronomy? | Observe, theory, and predict |
| The Sun is approximately ______ times larger than Earth in diameter. | 100 |
| In accordance with the scientific method, a scientific theory must be . | testable |
| The stars in a constellation are physically close to one another. (T/F) | False |
| A lunar eclipse can occur only during the full phase of the moon. (T/F) | True |
| A long, thin cloud that stretches from directly overhead to the western horizon would have an angular size of ___________ degrees. | 90 |
| What model was the incorrect idea that Earth is at the center of the universe. We now know that our solar system is centered on the Sun, which is just of one of billions of stars in our galaxy, and Earth is just one of the planets that orbits the Sun. | geocentric |
| During retrograde motion, planets actually stop and move backward in space. (T/F) | False |
| is credited as being the first person to use a telescope to observe objects in outer space, such as stars, planets, and the moon. | Galileo |
| The speed of a planet orbiting the Sun is independent of the planet's position in its orbit. (T/F) | False |
| Kepler's ___ law of planetary motion states that: P^2 = a^3 where: P = the orbital period (time to orbit the Sun) in Years, a = the semimajor axis (size of the orbit, or average distance from the Sun) in Astronomical Units (AU). | third |
| While ocean waves are made out of water, and sound waves consist of vibrating air molecules, light ("electromagnetic radiation") is energy carried in a wave that is made of ____, which is why light travels at the fastest possible speed in the universe. | vibrating electric and magnetic fields |
| According to the radiation laws ("Wien's Law" & "Stefan's Law"), both the wavelength of the peak emission and the total energy emitted by a star depend on the star's . | temperature |
| If the temperature of the Sun were to suddenly double, the Sun's total emitted energy (brightness) would increase by a factor of . | 16 |
| How does the speed of visible light compare with the speed of an X-ray? | Visible light and X-rays travel at the same speed, as all wavelengths of light do. |
| In Chapter 3 you learned about blackbody radiation: when a dense object emits a continuous spectrum of light, the properties of which depend on the temperature of the object. Which of Kirchhoff's Laws describes blackbody radiation? | A luminous solid, liquid, or a sufficiently dense gas, emits light of all wavelengths and so produces a continuous spectrum of radiation. |
| Emission lines, produced by a low-density hot gas, reveal the of the gas. | chemical composition |
| When light is emitted by electrons in a hot gas, the light comes out in quantized "packets". These "packets" of light are called . | photons |
| An atom can be identified as a single element (as in the periodic table of elements). What property of an atom determines which element is represents? | The number of protons in the atom's nucleus. |
| Electron transitions within molecules usually produce emission or absorption of light in the region(s) of the electromagnetic spectrum. | visible & ultraviolet |
| Changes in molecular vibration usually produce emission or absorption of light in the region(s) of the electromagnetic spectrum. | infrared |
| Changes in molecular rotation usually produce emission or absorption of light in the region(s) of the electromagnetic spectrum. | radio |
| Which of the following properties of a star can the spectroscopic study of starlight reveal? | Doppler shift, thermal broadening, and otational broadening |
| The of a telescope refers to the telescope's ability to collect light. Larger telescopes can be used to study fainter and more distant objects. | light-gathering power |
| The of a telescope refers to the telescope's ability to form distinct, separate images of objects lying close together in the field of view. | angular resolution |
| The angular resolution of an image produced by a telescope depends on both the size of the telescope AND the wavelength (color) of the light being observed. (T/F) | True |
| What is astronomical spectroscopy | separating a star's light by wavelength in order to use emission and/or absorption lines to study various stellar properties |
| Astronomical photometry is another observational technique that uses telescopes. Photometry is a method of | measuring the overall brightness of a star or galaxy |
| The Hubble Space Telescope's main advantage over all other telescopes is that ... | The Hubble Telescope is in space, so it does not have to contend with observing through Earth's atmosphere. |
| What telescope is used to study long-wavelength, low-energy, radio waves emitted by various types of objects and molecular clouds within our galaxy and beyond? | Radio telescopes |
| Compared with optical telescopes, radio telescopes are . | generally much larger than most optical telescopes |
| what telescopes are used to study short-wavelength, high-energy, X-rays emitted by high-energy events such as star mergers and supernova explosions. | X-ray telescopes |
| Compared with optical telescopes, X-ray telescopes are . | not capable of observing through Earth's atmosphere, so they must be placed in outer space. |
| There currently exist telescopes capable of detecting gamma-rays from highly energetic sources in outer space. (T/F) | True |
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