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The edge of the Sun doesn’t have to be absolutely sharp in order to look that way to us. It just has to go from being transparent to being completely opaque in a distance that is smaller than your eye can resolve. Remember from Astronomical Instruments that the ability to resolve detail depends on the size of the telescope’s aperture. The pupil of your eye is very small relative to the size of a telescope and therefore is very limited in the amount of detail you can see. In fact, your eye cannot see details that are smaller than 1/30 of the diameter of the Sun (about 1 arcminute). Nearly all the light from the Sun emerges from a layer that is only about 400 km thick. What fraction is this of the diameter of the Sun? How does this compare with the ability of the human eye to resolve detail? Suppose we could see light emerging directly from a layer that was 300,000 km thick. Would the Sun appear to have a sharp edge?
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Chapter 15 Solutions
Astronomy
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- Answer these questions for celestial bodies at each of the following temperatures and then draw a conclusion about the relationship between temperature and wavelength of maximum intensity. What is the wavelength of maximum intensity? In which part of the electromagnetic spectrum (gamma-ray, X-ray, UV, visible light, IR, microwave, or radio) does this peak wavelength lie? Give an example of an object that might have this temperature. a. 50 K b. 500 K c. 5000 K d. 50,000 Karrow_forwardWhy is it difficult to observe at infrared wavelengths? What do astronomers do to address this difficulty?arrow_forwardA powerful telescope can observe an object down to about the 30th magnitude in the B-band. To what distance can this kind of telescope observe a star like the Sun? What kind of energy flux is observed at this telescope in terms of the solar constant?arrow_forward
- One of the instruments on board the Unreal X-ray Observatory (UXO) has a detector with 3600 pixels x 1800 pixels and a field of view of 30 ar- cmin x 15 arcmin. If each pixel is 24 µm x 24 μm in size, calculate the plate scale, in arcsec mm-¹, and hence determine the focal length of the UXO telescope.arrow_forwardThe angular separation in degrees of two objects is (physical separation × 360°) / (2 π × distance). If an individual was observing our solar system from Castor at a distance of 10.2 light years. What angular resolution, in arcsecond, is needed to resolve the Sun-Jupiter system (5.46 AU) as distinct points of light?arrow_forwardWhat are the arguments for building the TMT telescope?arrow_forward
- The Mars Reconnaissance Orbiter (MRO) flies at an average altitude of 280km above the Martian Surface. If its cameras have an angular resolution of 0.2 arc seconds, what is the size of the smallest objects that the MRO can detect on the Martian surface? Use the equation: S =x × d / 206265 arcseconds / radian , where S is the true size of the object, d is the distance from the detector to the object, and x is the angular size of the object. Your answer will be in km (you can ignore the radians unit (it should appear, but the equation made a simplifying assumption that dropped it out.arrow_forwardThe Giant Magellan Telescope is a new telescope being built in Chile with a mirror 25 meters in diameter. Part 1: If you neglect the impact of Earth's atmosphere, what is the angular resolution limit (diffraction limit or resolving power) of this telescope in green light (500 nm)? Give your answer in arcseconds. Part 2: The current Magellan telescope has a mirror 6 meters in diameter. How much more light per second will the Giant Magellan capture compared to the current Magellan?arrow_forwardThe Gaia spacecraft's telescope has an accuracy of 0.00005 arcsec. The human eye, meanwhile can only resolve about 1 arcminute. How many times better is the resolution of the Gaia spacecraft compared to the human eye?arrow_forward
- You record the spectrum of a distant star using a telescope on the ground on Earth. Upon analysing the spectrum, you discover absorption lines spaced at intervals typical of oxygen atoms. Which of the following are possible interpretations of this evidence? Select all that apply. The width of the spectral lines gives the diameter of the star The star is likely orbited by habitable planets with breathable atmospheres. The height of the spectral lines above the star's general blackbody spectral curve tells us how much oxygen is in the star The atmosphere of Earth contains oxygen The red or blueshift of the set of lines can tell us the speed of the star's motion toward or away from usarrow_forwardTwo stars (a and b) in a binary system have apparent V-band magnitudes of 8.0 and 8.4 mag, and B-V colour indices of 0.3 and -0.5 mag, respectively. (a) Which star is brightest in the V-band? (b) Which star is brightest in the B-band? (c) Which star would appeal bluer to the naked eye? (d) What is the ratio of monochromatic fluxes of the stars in the B-band? (e) What is the total apparent magnitude of the system in the V-band (assuming it is unresolved)?arrow_forwardTwo identical stars are moving in a circular orbit around one another with an orbital separation of 2 AU. The system lies 200 light-years from Earth. If we happen to view the orbit head-on, how large a telescope would we need to resolve the stars, assuming diffraction-limited optics at a wavelength of 2 μm?arrow_forward
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