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

<p><a href="https://en.wikipedia.org/wiki/Greek_alphabet" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Greek_alphabet</a></p>

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

<blockquote>
  <p>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.</p>
</blockquote>

CC BY-SA 4.0
2018-09-25T01:26:16.327Z
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
CC BY-SA 4.0
2018-09-25T01:45:16.753Z
@posfan12  Sure thing.
Alphecca
CC BY-SA 4.0
2018-09-24T22:37:10.397Z
2018-09-24T22:37:10.397Z
Alphecca
<p>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.</p>

<p><a href="https://i.sstatic.net/Rxd4T.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Rxd4T.png" alt="enter image description here"></a></p>

CC BY-SA 4.0
2018-09-21T08:23:06.263Z
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
CC BY-SA 4.0
2018-09-21T08:24:41.377Z
…and yes, those letters are an alpha ($\alpha$) and a delta ($\delta$).
pela
CC BY-SA 4.0
2018-09-21T12:37:55.680Z
This is a reminder to everyone involved to be polite when correcting each other.
called2voyage
CC BY-SA 4.0
2018-09-21T18:12:07.103Z
Do you have [Symbol](http://en.wikipedia.org/wiki/Symbol_(typeface)) installed on your computer ? Can you Google *lowercase Greek alphabet*, and click on the images tab ?
Lucian
CC BY-SA 4.0
2018-09-21T20:20:06.167Z
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
CC BY-SA 4.0
2018-09-21T23:59:40.527Z
@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
CC BY-SA 4.0
2018-09-22T02:39:19.970Z
@pela answered my question.
posfan12
CC BY-SA 4.0
2018-09-24T13:54:47.130Z
@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
CC BY-SA 4.0
2018-09-24T14:26:15.763Z
I'm voting to close this question as off-topic - it really does just look like a request for the greek alphabet.
Rory Alsop
CC BY-SA 4.0
2018-09-24T17:19:01.240Z
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
<rotation>
Identify Greek letters used in formulas
posfan12
# Identify Greek letters used in formulas

(Asked by: username_0 on 2018-09-21)

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](https://i.sstatic.net/Rxd4T.png)](https://i.sstatic.net/Rxd4T.png)

**Tags:** rotation

> **Comments:**
> **username_1**: 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.  
> **username_2**: …and yes, those letters are an alpha ($\alpha$) and a delta ($\delta$).  
> **username_3**: This is a reminder to everyone involved to be polite when correcting each other.  
> **username_4**: Do you have [Symbol](http://en.wikipedia.org/wiki/Symbol_(typeface)) installed on your computer ? Can you Google *lowercase Greek alphabet*, and click on the images tab ?  
> **username_5**: I think it's reasonably obvious that the poster is asking for the **names** of the Greek symbols on lines 1 and 2. So @username_2's comment should be made into answer, probably with username_1's background info on what the equations are for  
> **username_6**: @username_5 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.  
> **username_0**: @username_2 answered my question.  
> **username_3**: @username_5 Since the OP has verified that username_2 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 username_1 provided--in which case the question needs to be revised.  
> **username_7**: I'm voting to close this question as off-topic - it really does just look like a request for the greek alphabet.  
> **username_5**: 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.  

---

## 1 answers

### Answer by username_8 on 2018-09-24. Score: 2 | Accepted answer

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.

> **Comments:**
> **username_0**: 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.  
> **username_8**: @username_0  Sure thing.  

---

