Questions tagged [definition]

Questions targeting the exact (possibly mathematical) description of a phenomena or term.

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What is the difference between spectroscopy, spectrography and spectrometry?

Spectroscopy is the study of spectra, spectrography is the writing of the spectra, and spectrometry is the measure of spectra. So from an etymological perspective, there is no real difference between ...
usernumber's user avatar
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Are there two mean Suns?

Are there two mean Suns? In the book I'm reading, the authors appear to refer to a mean Sun on the ecliptic moving in a circular orbit with constant angular velocity and with the same orbital period ...
Peter's user avatar
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Deriving the Tully-Fisher relation from the virial theorem

So I know this is a loose proof and a lot of assumptions are made, but I do not understand how these assumptions lead to the quantities we obtain so I will be asking questions at each step: start with ...
realanswers's user avatar
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What are Euclidean-normalized differential source counts?

I would like to know what the Euclidean-normalized and differential source counts mean in "Euclidean-normalized differential source counts". It would be great to hear a) a clear definition ...
kelpfish's user avatar
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When and why was zero right ascension defined to be at the vernal equinox?

When (and why) was zero right ascension defined to be at the vernal equinox? Who established or defined this standard?
pr1268's user avatar
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How close must a full moon be to become a supermoon?

According to this answer there is a scale of super moons depending on how close the full moon(henceforth anti-sol) is to perigee. So how close to anti-sol does the moon's perigee need to be to be ...
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