Effect of axial tilt on a planet

[Janx]

here's one easy way to figure some stuff out:
get a tennis ball
draw an equator line on it
stick a pin in the top to measure the north pole
Stick a pin to represent the location you're curious about on the ball
set the ball in a yogurt cup and the proper tilt angle you want

shine a light on the ball, to represent the sun

As you rotate the ball (around the pole axis) you should be able to see how long your location marker pin is in the sunlight. You can't rotate the cup, that doesn't really model the planetary rotation correctly.

Longer days=summer/warmer climate.

I would expect, that if you put the location pin near the north pole, and tilt the pole NEAR the sun, the location pin would be in sunlight far longer than if the pole were vertical or away from the sun.

 

[Tarril Wolfeye]

Probably not; the mass of rings is minimal compared to a good moon -- our moon is roughly 25% of the mass of the Earth. Rings can vary from the ephemeral structures around Jupiter to something more like the magnificent structures of Saturn, but in any case, they'd likely be a fraction of 1% of the mass of the host planet.

Rings are cool, though. Imagine the mythology of a world that has a ever-present, unmoving series of big silver bands that go across the entire sky, visible day or night.

That world is called Eberron and the ring is called Syberis.

 

[Warehouse23]

Just to clear up the "Venus has a longer day issue" (sorry, I'm a planetary geologist, so this kind of question strikes near to my heart): Venus rotates more slowly than the Earth. Therefore, 1 "day" (the time it takes to complete a rotation around the planet's axis) is "long." In polar regions on Earth, the Earth's obliquity keeps the poles pointed towards the sun for long stretches of the year (almost 6 months), producing "long days" (where day is defined as the time between when the sun is above the horizon and when it returns above the horizon after setting).

 

[lgburton]

I hope this is not too much of a thread hijack, but...

What would a world be like with a perfectly circular orbit and no axial tilt?

with the following assumptions in mind:
planet approximatly one astronomical unit from the sun
planet's surface covered by same ammount of water as the earth's


the big question here is how are the landmasses of this world arranged? if the landmasses were more polar, or all in a single hemisphere, then the planet would be very temperate - warm and comfortable, though a fair ammount of hurricanes would spawn.

if, however, more than 70% ish (forgive the lack of a presciese number here, it's been a long time since the geology class i learned about this stuff in) of the equator's area were covered in landmass, the land would reflect the light back into space, along with all of the heat that comes with it. the oceans would get colder (signifigantly - 10 degrees or more), and the whole thing would trigger a Day After Tomorow-like ice-age - except that the ice would cover even more of the planet's surface, reflecting even more sun back into space... etc etc.

and yes, this did happen on earth, a few billion years ago. the only way the earth got out of it was the fact that the ice age killed off most of the alge in the water, and over a few million years, volcanism put out enough CO2 to start a good greenhouse effect going on.


and that is a quick answer to that particular question! sorry bout the thread hijack.

 

[BiggusGeekus]

I'm a planetary geologist

Dude, you totally need to post more often.

 

[lgburton]

You *don't* want to take out the moon. The moon is what keeps the earth's tilt/rotation stable; it essentially transforms the Earth/Moon system into a gyroscope. Without the moon, the axial tilt varies wildly (like Mars') and the formation/continuation of life is very hard if not impossible.

this statement is incorrect.

1) earth's axial tilt has had, over the last several billion years, as signifigant an axial tilt as mars does now. life happened anyway!

2) mars' axial tilt does not vary "wildly." it is, at the moment, within acceptable (earth-like) boundries. the reason that seasons on mars are so different is a combination of 2 things
-2a) the northern half of mars is signifigantly lower in altitude than the southern half
-2b) mars' orbit is signifigantly more eliptical than earth's, producing a much longer northern hemisphere summer (at the same time a much longer southern hemisphere winter).

3) the reason that mars does not currently have life is still under debate in many different fields - but theories generally include the lack of liquid water, the high salinity of the soil, the fact that it's a signifigantly smaller planet, and the fact that it's twice as far from the sun as earth!

 

[Warehouse23]

Thanks, Biggus! Any time folks have questions about geology, astronomy, etc., or want informed speculation, they should feel free to ask. It might make the OT forums a little more erudite, but I think that's okay.

If folks want to see how wildly obliquity can change, even over the course of a few millions of years, I recommend checking out Laskar's papers (1993 and onwards), most of which appear in Nature. They're neat integrations of the whole solar system to calculate the orbital and rotational variations in planetary behavior.

 

[Desdichado]

D'oh! I should post the entire set-up and have you shoot holes in it!

 

[Dannyalcatraz]

Originally Posted by Dannyalcatraz

Seasons are caused by the eccentricity of the planet's orbit.

Someone
If that were true, both hemispheres of a planet would have the same season at the same time, and we know that this isn´t true.

Sorry...that should have read primarily.

If you compare the seasons between the Northern and Southern hemispheres, you'll find that their summers and winters aren't as harsh South of the equator, and that's a function of eccentricity of orbit.

Quote:

Originally Posted by Dannyalcatraz
According to my old college astronomy book:

Length of day is determined primarily by planetary rotation. Venus' day is actually longer than its year.


Janx
Then why are the days and nights longer in Alaska than in Texas? It's partly based on their location from their equator to the pole and the TILT of the earth. The tilt would affect the length of time that location is exposed to the sun.

Note the modifier "primarily."

Let's define "day" as the period of sunlight falling on a particular region- the time from sunrise to sunset. On most of the planet, the planet's rotation defines that period absolutely. However, Earth's axial tilt causes the planet to rotate at an angle relative to the plane of its orbit. Thus, the polar regions to rotate in a circle that either stays in the light or in darkness for months at a time.

Of course, I'm not a planetary geologist like Warehouse23. I'm sure he can do a better job of explaining this than I can with 1 semester of astronomy under my belt.

 

[drothgery]

Sorry...that should have read primarily.

If you compare the seasons between the Northern and Southern hemispheres, you'll find that their summers and winters aren't as harsh South of the equator, and that's a function of eccentricity of orbit.

Err... no formal education on this topic here, but isn't that largely a function of there being far more water relative to land in the southern hemisphere?