# What does it mean that the Sun`s rotation axis is: RA 286.13° , Dekl: 63.87°?

first post here.

I found 1 related Question, which has not solved my Problem.

SHORT QUESTIONs VERSION:

Suns axis is 7,25° tilted from the ecliptic. But in which direction?

LONG QUESTION:

Nasa defines the Suns Rotation axis as described in the title: https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html

Why is it described with (Ra, Declination)? Is this a (Earth) Aequatorial System placed in the middle of the Sun?

If true, then this should work (What is the angle between the equator of the sun, and the plane of the Earth's orbit). As the best anwer says, the angle between ecliptical pole and sun Rotation axis should be 7.25°. I get 4°, what is going on here? Have I messed up the angle calculation?

Thanks a lot, this is making my Brain burn : D

## 1 Answer

You can think of the position given in your title as the coordinates of the star that is directly over the Sun's north pole. (Similar to how Polaris is almost directly over the Earth's north pole.) Likewise, the ecliptic plane has a north pole which can be located by right ascension and declination.

7.25° to 7.26° appears to be the correct calculation, based on the following:

• North pole of sun: 286.13° RA, 63.87° declination
• North pole of ecliptic: 270° RA, 66.5738° declination (per Wikipedia)

$$cos(angle)=sin(dec1)sin(dec2)+cos(dec1)cos(dec2)cos(RA1-RA2)$$ $$cos(angle)=sin(63.87)sin(66.5738)+cos(63.87)cos(66.5738)cos(286.13-270)$$ $$angle=7.26$$

• Ohh I used: North pole of ecliptic 282° RA, 66.57° declination for calculating, dont ask me why. So they use the Aequatorial System centered in the Sun, I didnt know that works, but it makes sense since Equinox is the only "invariable" direction in the ecliptic plane. Thanks a lot John, you helped me a lot. Oct 15, 2018 at 22:54