The amazing thread on aphelion and periphelion!!

[Squid]

A common misconception is that Earth's varying distance from the Sun causes the four seasons. In fact, the 23.5-degree tilt of our planet's spin axis is more important. The tilt of the north pole toward the Sun in June causes summer north of the equator, while summer south of the equator comes six months later when the south pole is facing the Sun. The ellipticity of Earth's orbit does cause a small change in solar heating from July (aphelion) to January (perihelion), but it's not the dominant factor in shaping seasonal weather patterns.

 

"Sunlight falling on Earth is about 7% less intense in July than it is at our closest approach to the Sun in January," says Roy Spencer of the Global Hydrology and Climate Center. You might expect northern summer to be cooler because it occurs when Earth is farther from the Sun. Not so, explains Spencer. "The oceans and land on Earth are not evenly distributed around the globe. The northern hemisphere has more land; the southern hemisphere has more water. This tends to moderate the impact of differences in sunlight between perihelion and aphelion."

 

Editor's Note: Do you have trouble remembering the difference between perihelion and aphelion? An old astronomer's trick is to recall that the words "away" and "aphelion" both begin with the letter "A".

 

At aphelion the land-crowded northern half of our planet is tilted toward the Sun. For a given amount of sunlight, land warms up more than water (in other words, land has a lower heat capacity). Sunlight is therefore more effective at raising the temperature of the northern hemisphere. This results in the surprising fact that northern summer is a little warmer than southern summer even though Earth is farther from the Sun in July.

 

On planets like Mars with orbits much more eccentric than ours, the varying distance to the Sun can have a big influence on seasonal conditions. For example, northern summer on Mars lasts 24 days longer than winter because the planet is close to aphelion when the north pole is tilted toward the Sun. Planets move more slowly at aphelion than they do at perihelion (see Kepler's 2nd Law of planetary motion) and, so, seasons occurring near aphelion last longer. During the long martian summer, so much CO2 frost at the north pole sublimes into gaseous form that the global pressure of Mars' atmosphere increases by up to 30%.

 

Imagine leaving for a lunchtime picnic on the 4th of July only to arrive at the park and discover the humid summer air to be one-third denser than normal! This won't happen on Earth because our orbit is more nearly circular than the Red Planet's.

 

Earth has one of the most circular orbits in the solar system. Only Neptune and Venus follow more perfectly circular paths around the Sun. The other six planets trace paths that are significantly elliptical. Pluto, the planet with the greatest orbital eccentricity, follows a path so lopsided that it sometimes travels closer to the Sun than Neptune. Just last year Pluto ended a 20-year stint as the eighth planet when it crossed Neptune's orbit in February on its way back to the outer solar system.

After Pluto, the second and third most elliptical orbits belong to Mercury and Mars, respectively. As this diagram illustrates, their paths around the Sun (solid lines) depart significantly from that of a circle (dotted lines). Future astronauts visiting Mars or Mercury would notice that the apparent size of the Sun varies a great deal throughout the year. On Mars, for example, the aphelion Sun is 0.30 degrees across. At perihelion it would grow to 0.36 degrees in diameter, an increase of 20%.

[eric8]

A common misconception is that Earth's varying distance from the Sun causes the four seasons. In fact, the 23.5-degree tilt of our planet's spin axis is more important. The tilt of the north pole toward the Sun in June causes summer north of the equator, while summer south of the equator comes six months later when the south pole is facing the Sun. The ellipticity of Earth's orbit does cause a small change in solar heating from July (aphelion) to January (perihelion), but it's not the dominant factor in shaping seasonal weather patterns.

 

"Sunlight falling on Earth is about 7% less intense in July than it is at our closest approach to the Sun in January," says Roy Spencer of the Global Hydrology and Climate Center. You might expect northern summer to be cooler because it occurs when Earth is farther from the Sun. Not so, explains Spencer. "The oceans and land on Earth are not evenly distributed around the globe. The northern hemisphere has more land; the southern hemisphere has more water. This tends to moderate the impact of differences in sunlight between perihelion and aphelion."

 

Editor's Note: Do you have trouble remembering the difference between perihelion and aphelion? An old astronomer's trick is to recall that the words "away" and "aphelion" both begin with the letter "A".

 

At aphelion the land-crowded northern half of our planet is tilted toward the Sun. For a given amount of sunlight, land warms up more than water (in other words, land has a lower heat capacity). Sunlight is therefore more effective at raising the temperature of the northern hemisphere. This results in the surprising fact that northern summer is a little warmer than southern summer even though Earth is farther from the Sun in July.

 

On planets like Mars with orbits much more eccentric than ours, the varying distance to the Sun can have a big influence on seasonal conditions. For example, northern summer on Mars lasts 24 days longer than winter because the planet is close to aphelion when the north pole is tilted toward the Sun. Planets move more slowly at aphelion than they do at perihelion (see Kepler's 2nd Law of planetary motion) and, so, seasons occurring near aphelion last longer. During the long martian summer, so much CO2 frost at the north pole sublimes into gaseous form that the global pressure of Mars' atmosphere increases by up to 30%.

 

Imagine leaving for a lunchtime picnic on the 4th of July only to arrive at the park and discover the humid summer air to be one-third denser than normal! This won't happen on Earth because our orbit is more nearly circular than the Red Planet's.

 

Earth has one of the most circular orbits in the solar system. Only Neptune and Venus follow more perfectly circular paths around the Sun. The other six planets trace paths that are significantly elliptical. Pluto, the planet with the greatest orbital eccentricity, follows a path so lopsided that it sometimes travels closer to the Sun than Neptune. Just last year Pluto ended a 20-year stint as the eighth planet when it crossed Neptune's orbit in February on its way back to the outer solar system.

After Pluto, the second and third most elliptical orbits belong to Mercury and Mars, respectively. As this diagram illustrates, their paths around the Sun (solid lines) depart significantly from that of a circle (dotted lines). Future astronauts visiting Mars or Mercury would notice that the apparent size of the Sun varies a great deal throughout the year. On Mars, for example, the aphelion Sun is 0.30 degrees across. At perihelion it would grow to 0.36 degrees in diameter, an increase of 20%.

 

Catching the boss spraying, Do that on your own time

 

and we need the count page down here asap

[olyclimber]

I see...so I should eat for in the fall to prepare for the winter?

[slothrop]

Eric, don't you have a few cover sheets to finish up before you can even start to think about the count page? Yeeeeaaaah....

[eric8]

once I finish up my tps reports

[snoboy]

Obviously it has to do with the tilt, and not the distance from the sun, otherwise we would have seasons at the same time as they do in the S hemisphere, and we don't.

[Dru]

What about syzygy