
#1
Dec412, 12:59 PM

P: 53

Why does Earth have an axial tilt?
I thought it may be due to the suns mass and the gravitational effect on space. But Mercury and Venus doesn't have a tilt so I concluded that cant be a plausible explanation. 



#2
Dec412, 01:53 PM

PF Gold
P: 1,566

One of the theories I've read on this is that at one time the planet was struck by a smaller planet which later became our moon, which is also acting as a stabilizer currently




#4
Dec412, 02:37 PM

Mentor
P: 22,008

why does Earth have an axial tilt 



#5
Dec412, 04:26 PM

PF Gold
P: 3,021

Perhaps the OP question might have been better phrased as
1. If it is true that the accretion and formation of first the sun and then the planets occurs via a rotating disk over time, i.e. the spinning disk forming a spinning sun/planets, then 2. Why don't all the rotational axis of the planets align better with that of the sun? 3. Do post formation impacts explain all the misalignments? *I don't know to what degree 1. is true. 



#6
Dec412, 05:18 PM

Mentor
P: 14,481

The answer given by Mordred is the current best guess as to why the Earth has an axial tilt that is not zero but also is apparently quite stable. 



#7
Dec412, 06:32 PM

Mentor
P: 22,008

....But not exactly. [I could always change the precision criteria, though... ] 



#8
Dec512, 07:20 AM

P: 461

And given that there are 360 degrees in a circle, the odds were 360:1 against the tilt rounding to zero.
Do all cultures divide a circle into 360 degrees? 



#9
Dec512, 07:32 AM

Mentor
P: 22,008





#10
Dec512, 09:02 AM

Mentor
P: 14,481

Explaining Uranus and Venus is a bit difficult with these theories because they don't fit. They don't fit at all. The standard explanation is that something big hit them. It turns out that this hand wave solution may not be needed the case with Venus; what hit Venus might well have been just been chaos theory, triggered by perturbations from Jupiter and the Earth. (Per this chaosbased explanation of Venus's axial tilt, the Earth escaped the chaos thanks to the stabilizing influence of the Moon.) Explaining the very weird orbits of the hoard of exoplanets discovered in the last ten years is even harder. The simple, naive theory suggests that planets should naturally be in circular orbits. A number of those exoplanets are in anything but circular orbits. The last ten years of discoveries coupled with improved simulations of our own solar system make this simple theory appear to be a bit too naive. In any case, the current hypothesis regarding the formation of the Moon is also regarded as explaining why the Earth has it's own somewhat anomalous axial tilt. 



#11
Dec512, 10:24 AM

P: 615





#12
Dec512, 11:48 AM

P: 642





#13
Dec512, 04:37 PM

P: 53

Interesting replies guys, thanks for helping me clear that up and understand that a bit better.
Another thought popped into my mind when reading them Did planetary formation begin prior to the ignition of the sun or afterwards? 



#14
Dec1712, 12:43 PM

P: 365

One possible explanation is the theory that the Earth was struck by a planetoid which later became the Moon. The Earth never settle back into its original no Axial Tilt because the Moon and Earth form a Barycenter. A Barycenter is when two bodies have a mutual center of mass compared to the sun distance. This creates a "wabble" in the orbit explaining why the Earth has kept its Axial Tilt




#15
Dec1712, 03:09 PM

PF Gold
P: 11,057





#16
Dec1812, 08:06 AM

P: 10

//offtopic
Let the angle be λ and half* a circle be β (0≥λ≥β and β≠0) The mesuring unit for λ and β must be the same  doesn't matter radian, degrees or other  see almost all used If we chose some λ, the chance C that λ is some constant a (0≤a≤β) is 1/(all possible choices for λ) If we assume that λ∈ℝ, then all possible choises for λ are ∞ (all the real numbers between 0 and β) ⇔ C=1/∞ ⇔ C→0 for any a for any β for any mesuring unit. So for a=0° C→0. The same is for a=(the actual tilt of the Earth's axis). * if you do a full rotation, there will be two points at wich the axis will lie on one line  just in opposite direction (so if the initial rotation is clockwise and we rotate the axis by half a circle the rotation will be counter clockwise). That's why β is half a circle. 



#17
Dec1912, 05:29 AM

P: 514

This protoplanet would still clear the space around it, because the material there either orbits a bit faster or a bit slower, giving it a chance to run into the protoplanet. Checking on Exoplanet Orbit Database  Exoplanet Data Explorer, the champion eccentricity is for HD 80606 b: 0.9340. This is for a planet at least 4 times Jupiter's mass orbiting a star not very much different from the Sun. A planet with an orbit with an eccentricity close to what a comet's orbit typically has. Its semimajor axis is 0.45 AU, making it much like the numerous "warm Jupiters" and "hot Jupiters" that have been found, planets that are too close to have formed with their likely compositions. 



#18
Dec1912, 06:15 AM

Sci Advisor
HW Helper
P: 2,275

There's 360 degrees in a circle  and how many days in a year? Each night, the stars shift approximately 1 degree (slightly less). 360 is pretty close to 365.25, but 365.25 would be a horrible number to build a numbering system around. But, to answer the original question, only civilizations that came into contact with Babylon, or came into contact with someone who had come into contact with Babylon, use 360 degrees in a circle. That winds up being a pretty big percentage of civilization, but not everyone. 


Register to reply 
Related Discussions  
History of the Earth's Axial Tilt  General Astronomy  2  
History of the Earth's Axial Tilt  Earth  1  
Difference between axial tilt and inclination  General Astronomy  7  
Where does the sun rise, w/ axial tilt?  General Physics  9 