<p>We can describe the direction of the axis of the Earth with two angles.</p>
<p>The first is the angle between the axis and the norm of the orbit (ε).</p>
<p>The second is the angle P formed
by the major axis of the orbit and the projection of the axis of the Earth onto the plane of the orbit.</p>
<p>At present, ε measures about 23.45◦, P is about 12.25◦ (P is also
the angle which is covered by the Earth between the beginning of winter (21st December)
and the arrival of the earth at perihelion (2nd January).)</p>
<p>Does the angle P have a specific name in astronomy?</p>
<p>Thanks</p>

CC BY-SA 4.0
2024-12-31T11:42:28.070Z
So you mean axial tilt or obliqity of the ecliptic? The tilt of earth axis against its orbital plane? Please add a graph to show what angle you mean.
planetmaker
CC BY-SA 4.0
2024-12-31T13:04:09.217Z
No it’s not the axial tilt nor the obliqity. For the figure see Fig. 4. at page 9 of http://info.ifpan.edu.pl/firststep/aw-works/fsII/mul/mueller.pdf
Vincent ISOZ
CC BY-SA 4.0
2024-12-31T16:01:26.353Z
The argument of periapses of the Earth’s orbit in celestial coordinates is the angle from perihelion to the ascending node of equatorial plane. The projection of the Earth’s axis would be 90 degrees less.
eshaya
CC BY-SA 4.0
2024-12-31T17:05:57.080Z
If there was a name for it, the author likely would have used it.  The equation of time was figured out before orbits were, so it wouldn't be surprising that physical properties of it have no classical name.
Greg Miller
<orbital-mechanics><analemma>
Vocabulary: name of an angle
Vincent ISOZ
# Vocabulary: name of an angle

(Asked by: username_0 on 2024-12-31)

We can describe the direction of the axis of the Earth with two angles.

The first is the angle between the axis and the norm of the orbit (ε).

The second is the angle P formed
by the major axis of the orbit and the projection of the axis of the Earth onto the plane of the orbit.

At present, ε measures about 23.45◦, P is about 12.25◦ (P is also
the angle which is covered by the Earth between the beginning of winter (21st December)
and the arrival of the earth at perihelion (2nd January).)

Does the angle P have a specific name in astronomy?

Thanks

**Tags:** orbital-mechanics, analemma

> **Comments:**
> **username_1**: So you mean axial tilt or obliqity of the ecliptic? The tilt of earth axis against its orbital plane? Please add a graph to show what angle you mean.  
> **username_0**: No it’s not the axial tilt nor the obliqity. For the figure see Fig. 4. at page 9 of http://info.ifpan.edu.pl/firststep/aw-works/fsII/mul/mueller.pdf  
> **username_2**: The argument of periapses of the Earth’s orbit in celestial coordinates is the angle from perihelion to the ascending node of equatorial plane. The projection of the Earth’s axis would be 90 degrees less.  
> **username_3**: If there was a name for it, the author likely would have used it.  The equation of time was figured out before orbits were, so it wouldn't be surprising that physical properties of it have no classical name.  

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