# Do the planets in our system orbit in the same plane in which we are orbiting the galactic core?

And how about other systems that we know about? For example, very few exoplanets are transiting, so those that are, is it coincidence or what?

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• Dr Bob
Lv 6

The planets in our solar system all orbit in roughly the same plane. The plane of the earth's orbit (the ecliptic) is inclined by 60.2 degrees to the plane of the galaxy. You can see this in a dark sky if you notice that the Milky Way is highly inclined to the constellations of the ecliptic.

Should we expect other planetary systems to be in a plane similar to that of the galaxy? Probably not. Remember that the galaxy formed about 13 billion years ago, whereas many stars (such as the sun) formed more recently; so their formation was affected more by local conditions than by the original rotation of the galaxy. (For instance, a supernova goes off and gives some spin to nearby systems in the process of forming a star and planets.)

Regarding the external planets, I think the number of eclipsing planets is a matter of coincidence. A planet is small and its orbit is large; we have to be lined up just right to see an external planet pass in front of its star.

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The inclination given by Hermoderus of 63 degrees is incorrect. I can't blame him, because I've seen this incorrect value many times, even in a professional astronomy paper! 63 degrees is the inclination of the galactic plane to the *equator*, not the ecliptic. I gave a long explanation of how you get 60.2 degrees at

One of the things I mentioned there is that the coordinates of the galactic north pole (in the equatorial system) are

alpha = 12 h 51 m

delta = 27 degrees 8 minutes

= approximately 27.1 degrees

The inclination of the galactic plane to the equator is therefore

90-27.1 = 62.9 degrees

but the inclination to the ecliptic is 60.2 degrees. It's a small difference, but people often confuse the two.