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Forum » SpaceEngine » Science and Astronomy Discussions » Negative Axial Tilt
Negative Axial Tilt
TalynDate: Monday, 02.07.2012, 15:26 | Message # 1
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Can anyone explain me the axial tilt of an object, since I am not an astrophysicist?

As far as I understand, every planet revolves around a star in a plane called the ecliptic. If a planet rotates with the poles pointing straight up/down and the equator lined up with this ecliptic , then the axial tilt is 0.

Since the earth has an axial tilt of 23.5º, the north pole is tilted towards the sun 23.5º in the summer and the south pole is covered in eternal night for a short period.

Now if a planet has an axial tilt of 90º, that means that one of the poles is pointing straight at the sun in the summer, leaving the other pole in eternal night for half a year. I would expect extreme weather paterns on such a world.

Above 90º, the planet assumes a "retrograde" rotation, with the sun rising in the west and setting in the east.

What I don't understand is the negative value we find in some planets on SE.

Am I missing something here?
Can anyone enlighten me?





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HarbingerDawnDate: Monday, 02.07.2012, 18:48 | Message # 2
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The negative value is - I'm pretty sure - simply a case of SE being a computer program. A value of -17° would give the same magnitude of tilt as a value of +17°, just in the opposite direction. So a planet with Axial Tilt +17° and Equator Ascending Node 80° would have the same characteristics as a planet with Axial Tilt -17° and Equator Ascending Node 260°. So to figure out the true axial tilt, simply take the absolute value of what is listed in the program (e.g. |-17| = 17 ).

If you find any numbers greater than 180° you can always add/subtract 360 to get an equivalent value (e.g. 200° = -160°, -330° = 30°, etc.).





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TalynDate: Monday, 02.07.2012, 19:57 | Message # 3
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Ok I think I understand it now smile

So any planet with an ABSOLUTE value between 23.5º and 336.5º is basically the same as another planet with an ABSOLUTE value between 156.5 and 203.5, and with that configuration the seasons would range from non existent to something similar to what we experience on earth, except that in the later case, the sun would set in the east and rise in the west.





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HarbingerDawnDate: Monday, 02.07.2012, 19:59 | Message # 4
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Correct smile




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smjjamesDate: Sunday, 07.10.2012, 02:59 | Message # 5
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I need some help understanding the large axial tilts here in SE. I was going to make a new thread, but this one is much better I think I may have passed alot of good looking earthlike planets just because I misunderstood that the axial tilt was retrograde and misinterpreting the lots of high axial tilts.

While they don't actually show as negative numbers, I read the explaination given above and the axial tilt of this one should come out to -94 degrees, which is basically a retrograde uranus I believe.


This would come out to 42 degrees retrograde, right?


However, I'm still confused how it would be when the axial tilt is more than 360 or something like 470 in the case of this post. This particular gas giant would be 14 degrees with normal rotation, right? If it goes past 360, why doesn't SE just start back from 0?

Attachments: 3448944.jpg(249Kb) · 3506141.jpg(173Kb) · 8540438.jpg(208Kb)





 
HarbingerDawnDate: Sunday, 07.10.2012, 03:18 | Message # 6
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Quote (smjjames)
this one should come out to -94 degrees, which is basically a retrograde uranus I believe.
This particular gas giant would be 14 degrees with normal rotation, right?

Yes.

Quote (smjjames)
This would come out to 42 degrees retrograde, right?

No. 90<|x|<270 is retrograde. That would be 42° prograde.





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Edited by HarbingerDawn - Sunday, 07.10.2012, 03:19
 
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