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    Astronomy problem

    ok the question is, Calculate the photons you expect to receive per Angstrom at the focus of a Cassegrain telescope of aperture 30cm for a star of V magnitude 9.0, observed at a zenith distance of 60 degrees. Assume extinction coefficient of 0.15 magnitudes per airmass, reflectivity at each...
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    Parametrizing a paraboloid

    how do I parametrize the paraboloid z = x^2 + y^2 ? thx
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    H- and HII ions

    what is the reason why the number of H- ions in a gas must always be less than the number of HII ions?
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    A rock, the earth, an ellipse and the joys of angular momentum

    To answer your first part, we have angular momentum L = mvr energy E = 1/2(mv^2) - GMm/r rearrange energy equation until you have v = something... substitute that into L = mvr for v multiply m into the squareroot and that's your answer.
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    Stellar atmosphere

    how can i calculate the fractional abundance of HI, HII, H- and e- for hydrogen in the photosphere (T=5770K) and density 10^17?
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    Elliptical orbits

    hey all, I'm just wondering, what conditions are necessary so that we could have 2 elliptical orbits such that the perihelion distance of one is the same as the aphelion of the other?
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    How does velocity affects the shape of orbit

    suppose a mass m reduces its orbital velocity by 2 at some point in its circular orbit, but leaving its direction of travel unchanged at that moment, how does the orbit change? I know the new orbit is elliptical but i have no idea how to get to that conclusion.