# Thread: A planet's axial tilt, inclination and climate

1. What's the difference between a "planet's axial tilt" and it's "inclination" and how do these affect it's climate/weather/seasons????

Im just curious!

2.

3. Axial tilt (or obliquity) is the tilt of the axis of a planet's rotation referenced to it's orbital plane around the sun (or more correctly around the barycenter of the solar system, but that's getting unnecessarily complex). For earth, it's currently 23.44 degees.

Inclination is the angle between a planet's orbital plane and that of the earth. By definition, earth's inclination is zero. The highest is about 7 degrees (among the planets) for Mercury. Asteroids and comets can have any inclination at all up to 180 degrees (a pure retrograde motion, orbiting the sun in exactly the opposite direction from the earth). Several comets come very close, including 55P/Tempel-Tuttle, the parent object of the Leonid meteor shower (~ 162 degrees). This causes the very high entry velocities for the Leonid meteors (~71 km/s) since we are hitting them nearly head on.

More correctly, since Jupiter is most of the mass of the solar system, we should be using that as the reference, which would give the earth an inclination of about 1.3 degrees.

As far as seasons, inclination has almost no effect except for Mercury, seasons are driven by obliquity, eccentricity of the orbit, and a number of other orbital parameters, depending on the albedo and material of the planet in question.

I hope this isn't a homework question!

I know, too much information Sometimes, I can't help myself...

Wayne

4. Originally Posted by lokariototal
What's the difference between a "planet's axial tilt" and it's "inclination" and how do these affect it's climate/weather/seasons????

Im just curious!
Look up Milankovitch cycles.

5. What is interesting is the potential long term instability of axial tilt.

On Mars variations in the size of the polar caps could have generate a 1-2 degree change over the planets life. This is small comapared with inherent instability that allows the axial tilt to vary from less than 20 degrees to over 40 degrees. It is chance that its present obliquity is very close to that of the Earth. The Earth's axial tilt also varies, but over a much smaller range, probably stabilised by the moon.

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