Confused about summer

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orienteer

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Excuse me, but I grew up on Earth.

I have been curious to know what summer means on other objects in our solar system.

Mercury is tidally locked to the sun, so Summer should be an area, not a season.

Venus, Earth, Mars, Jupiter and Saturn all have small tilts and round orbits, so I believe they should have similar seasons. The Giants would be more of a weather pattern, but you know what I mean.

Uranus and Neptune have large tilts to their axises, but I am not sure if they point forward, which would have drastic seasonal changes, or towards the sun, which would end up more like Mercury.

Pluto has an elliptical orbit, so summer ends up being based on perihelion, and any tilt to the axis would create some sort of oscillations within the pattern.

Now, what happens if the object is not sun centered? Our moon is tidally locked to Earth. I do not think it's axis is tilted, so there should not be a summer. Is that true of all moons?

When you are beyond Saturn, how much does the sun even affect the seasons?

Thanks in advance.
 
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MeteorWayne

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orienteer":3g9wl62j said:
Excuse me, but I grew up on Earth.

I have been curious to know what summer means on other objects in our solar system.

Mercury is tidally locked to the sun, so Summer should be an area, not a season.
Not correct. A Mercury year lasts about half a Mercury day. Since the inclination is near zero, it doesn't have seasons for the same reasons as earth, but because of it's higly eccentric orbit, it is much closer to the sun at perihelion, and 50% further away 44 days later. This probably causes some seasons.

Venus, Earth, Mars, Jupiter and Saturn all have small tilts and round orbits, so I believe they should have similar seasons. The Giants would be more of a weather pattern, but you know what I mean.
Well, except for Jupiter that's correct. Replace it with Neptune. Jupiter has almost no tilt, so has almost no seasons.

Uranus and Neptune have large tilts to their axises, but I am not sure if they point forward, which would have drastic seasonal changes, or towards the sun, which would end up more like Mercury.
Again. Neptune is incorrect; it has a tilt close to earth's. Uranus points in the same direction on it's side , so it spend half it's orbit with a pole pointing at the sun, and half pointing away. So it's seasons (4 seasons) last about 21 years each.

Pluto has an elliptical orbit, so summer ends up being based on perihelion, and any tilt to the axis would create some sort of oscillations within the pattern.
Pluto is also tilted on it's side so each of it's 4 seasons last ~ 60 years, with the eccentricty superimposed on that.

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Saiph

Guest
Just a bit of a clarification on Mercury's rotation. You are correct that it's tidally locked with the sun, but that doesn't mean it's a 1 orbit to 1 rotation lock (1:1 ratio) like the moon is with earth. It's actually a 2:3 ratio, it rotates 3x for every 2 orbits.

It's mild tilt means it does have seasons, but they don't matter much (especially with no atmosphere), and it's high orbital eccentricity means it's more affected by how it's orbital radius changes over it's year...unlike earth and most other planets.
 
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MeteorWayne

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From what I've found, Mercury's axial tilt is < 0.3 degrees. That's more than mild...that's nonexistant :)
 
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neilsox

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Before you argue with MW, the 9 degree tilt of Mercury is comparing the plane of Mercury's orbit to the plane of Earth's orbit. So the seasons are almost entirely dependent on the elliptical orbit. Mars seasons are much like Earth, except some areas of Mars are colder than others, because Mars has a more eliptical orbit than Earth.
Earth's moon has an annual distance change due to the eliptical orbit of Earth, so seasons are barely discernable on the Moon. Neil
 
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MeteorWayne

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Yes these are latest numbers I can find and verify (from Wiki, but I looked at references)

Orbital inclination is

7.005° to Ecliptic
3.38° to Sun’s equator
6.34° to Invariable plane

Obliquity (axial tilt relative to it's orbit, which for earth is ~ 23 1/2 degrees, and causes our seasons) is 2.11 =/- 0.1 arc minutes, or 0.035 degree. ( Margot, J.L. et al, Science, Volume 316, Issue 5825, pp. 710- (2007).)
 
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orienteer

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Saiph said
"Just a bit of a clarification on Mercury's rotation. You are correct that it's tidally locked with the sun, but that doesn't mean it's a 1 orbit to 1 rotation lock (1:1 ratio) like the moon is with earth. It's actually a 2:3 ratio, it rotates 3x for every 2 orbits."

So if a Mercuric year is 88 Earth days, a Mercuric day is 58.6 Earth days. Therefore a season would occur between noon nd sundown. I am not sure why this qualifies as tidally locked. I thought tidally locked meant that the more massive side of the planet was gravitationally bound to the Star.

Now for Uranus.

Meteor Wayne said;
Uranus points in the same direction on it's side , so it spends half it's orbit with a pole pointing at the sun, and half pointing away. So it's seasons (4 seasons) last about 21 years each.

The summer solstice would be when the pole is pointing mostly toward the sun, and the fall equinox would have the pole pointing forward with regard to the orbit. The winter solstice would be when the pole is away from the sun and the spring equinox would be pointing backward. Therefore, solstice would be an all day or all night affair, while equinox would have more earth like days. Would the temperature vary like earth, or would the solstices be much more stagnant due to the lack of night (or day)? Does the wind current point to the dark pole due to the warm air having a higher pressure?
 
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CalliArcale

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orienteer":36k5812d said:
So if a Mercuric year is 88 Earth days, a Mercuric day is 58.6 Earth days. Therefore a season would occur between noon nd sundown. I am not sure why this qualifies as tidally locked. I thought tidally locked meant that the more massive side of the planet was gravitationally bound to the Star.
Tidally locked, as I understand it, just means that the tidal interaction between the two has more or less stabilized, and they have reached equilibrium (which will mean some kind of resonance between orbital and rotational periods). Because Mercury is very close to the Sun but has a very elliptical orbit, it actually cannot achieve a 1:1 resonance. But it can achieve a 3:2 resonance, and that's indeed what it has settled into.

The Moon is said to rotate synchronously, which means it has a 1:1 resonance between its orbital and rotational periods. Pluto and Charon are more interesting -- they are *mutually* synchronous, so there is a 1:1:1 resonance between Pluto's rotational period, Charon's orbital period, and Charon's rotational period. Cool, eh?
 
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