How can we find the distance to a star that is too distant to have a measurable parallax?
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Most stars are too distant to have measurable parallaxes. These distances can be estimated from the star's spectral type, luminosity class, and apparent magnitude in a process called spectroscopic parallax, which relies on the location of the star in the H-R diagram. If you record the spectrum of a star, you can determine its spectral class, and that tells you its horizontal location in the H-R diagram. You can also determine its luminosity class by looking at the widths of its spectral lines, and that allows you to estimate the star's vertical location in the diagram. Once you plot the point that represents the star in the H-R diagram, you can read off its absolute magnitude, and find the distance by comparing the star's apparent and absolute magnitudes.
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Why did the terrestrial planets lose the majority of the gas in their primary atmospheres?
a. They were too hot and their escape velocities too low to hold onto them. b. The solar wind was too strong and blew these gases off the planets. c. Their high surface temperatures made the gas chemically react with the rock. d. The initial gases were so heavy when the planet differentiated that they sank to the core.
In modern physics, what is heat?
a. A change in energy marked by a change in temperature. b. A change in temperature caused by a change in energy. c. The flow of energy between objects due to a difference in their temperature. d. The opposite of cold. e. A change in work.
A puddle of water (n = 1.33) is covered with a very thin layer of oil (n = 1.20). How thick is the oil in the region that strongly reflects light with a wavelength of 531 nm?
a. 111 nm b. 221 nm c. 443 nm d. 295 nm e. 239 nm
A part for a land-based gas-turbine made of Haynes 25 must carry a tensile stress of 140 MPa (20 ksi). For a design lifetime of 10 years, what is the allowable temperature for this part, based only upon high-temperature creep rupture?
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