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Could anyone tell me what the names of the Greek letters in the screenshot are? Is the first one alpha? They are used in calculating ICRF rotations. Wikipedia uses a different font for their list of characters, so it's hard to tell.

enter image description here

posfan12
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    Orientation models use three Euler angles to describe body orientation. The first two angles are the right ascension and declination of the north pole of a body as a function of time. The third angle is the prime meridian location (represented by "W"), which is expressed as a rotation about the north pole, and is also a function of time. – Mick Sep 21 '18 at 08:23
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    …and yes, those letters are an alpha ($\alpha$) and a delta ($\delta$). – pela Sep 21 '18 at 08:24
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    Do you want the names of the Greek letters or the quantity it stands for? –  Sep 21 '18 at 09:18
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    This is a reminder to everyone involved to be polite when correcting each other. – called2voyage Sep 21 '18 at 12:37
  • Do you have Symbol installed on your computer ? Can you Google lowercase Greek alphabet, and click on the images tab ? – Lucian Sep 21 '18 at 18:12
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    I think it's reasonably obvious that the poster is asking for the names of the Greek symbols on lines 1 and 2. So @pela's comment should be made into answer, probably with Mick's background info on what the equations are for – astrosnapper Sep 21 '18 at 20:20
  • @astrosnapper I don't regard this as a reasonable question. It might have been closed as "unclear" but it could just as easily be closed under the "homework-type-question" policy. – StephenG - Help Ukraine Sep 21 '18 at 23:59
  • @pela answered my question. – posfan12 Sep 22 '18 at 02:39
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    @astrosnapper Since the OP has verified that pela answered the question, I have reopened (since "unclear" is no longer a valid close reason), but the question is now off-topic here unless the OP is really also looking for the information Mick provided--in which case the question needs to be revised. – called2voyage Sep 24 '18 at 13:54
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    I'm voting to close this question as off-topic - it really does just look like a request for the greek alphabet. – Rory Alsop Sep 24 '18 at 14:26
  • I don't disagree but I'm inclined to give the OP the benefit of the doubt. They may be just getting started and before you can ask further questions about the astronomical concepts involved, they need to be on the same page as potential answer providers with regard to symbols and terminology used. So this question could well have been answered outside of AstroSE but the question was fairly clear, on topic and on a suitable subject matter for AstroSE. – astrosnapper Sep 24 '18 at 17:19

1 Answers1

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The first one is alpha (α); the second one is delta (δ). You can study the shapes of the letters here:

https://en.wikipedia.org/wiki/Greek_alphabet

Here's what they mean (information from a comment to your question):

Orientation models use three Euler angles to describe body orientation. The first two angles are the right ascension and declination of the north pole of a body as a function of time. The third angle is the prime meridian location (represented by "W"), which is expressed as a rotation about the north pole, and is also a function of time.

Alphecca
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    Thanks. The Wikipedia article is the first place I looked. But they use a sans serif font in that article instead of the serif font used in the screenshot I posted as well as here on SE. Delta looks very different, for instance. – posfan12 Sep 25 '18 at 01:26
  • @posfan12 Sure thing. – Alphecca Sep 25 '18 at 01:45