The war on the war on xmas has already started

[bilby]

Watching the Winter Solstice happen is pretty cool. I get a great view and appreciation for the event because the south side of my house, which has a glassed-in porch, overlooks a river so the horizon is unbroken. Seeing the sun arc lower and lower into the southern sky lets me appreciate what our ancestors knew and celebrated.

That Jesus thing is a crock of phony baloney.

But the Solstice is when the Earth is the closest it gets to the sun for this revolution. That is independent of the sun rising.

Nope. The Solstice is when the Sun is at its furthest South (in December) or North (in June) of the equator. Solstices are due to the Earth's axial tilt, and are independent of the distance to the Sun. The next Solstice will be at 10:44UTC on December 21st 2016, and will be a southernmost track solstice, (ie Winter in the Northern hemisphere and Summer in the Southern Hemisphere). As the earth is approximately spherical, and hence lines of latitude are very close to perfectly circular, the day of the solstice is also the longest or shortest day of the year at any point on the surface, other than on the Equator where day length doesn't vary significantly. (Source)

When the Earth is closest to the sun, that's known as Perihelion; In 2017 Perihelion is at 14:18UTC on January 4th, and Aphelion (the point when the Earth is farthest from the sun) is at 20:11UTC on July 3rd. (Source).

Earth’s mean distance from the Sun at perihelion is 0.9832899 AU (147,098,074 km); in 2017, perihelion will be 0.9833094 AU, which is 2919 km farther away than the mean, and Earth’s mean distance from the Sun at aphelion is 1.0167103 AU (152,097,701 km), and in 2017 aphelion will be 1.0166756 AU, which is 5190 km closer than the mean.

The change in distance to the sun on the Earth's due to axial tilt alone varies from 0km at the Equator to about 5000km at the poles; the variation due to the elliptical nature of the Earth's orbit is about 5,000,000km (4,990,020 km between January and July 2017), so the change in distance to the sun due to axial tilt is only at MOST 0.1% of the total change in distance - and in the Northern Hemisphere, you can be up to five million km closer to the sun in winter than you are in summer.

The reason that it is warmer in summer has very little to do with the distance to the sun - the total distance only varies by about 0.3% - the important thing is the angle with which the sun's rays arrive at your latitude. The total energy incident on your location when the sun is directly overhead is twice what it would be if the sun were 30 degrees above the horizon, ceteris paribus; This large effect completely swamps the 0.3% difference in distance between aphelion and perihelion, which only makes for about 7% difference in the incident solar energy density arriving at any point on the Earth's surface (7% is a lot more than 0.3%, of course, because the effect is amplified by the inverse square law - the energy density is proportional to the inverse square of the distance).



Of course, if the distance from the Earth to the Sun were the cause of the seasons, it would be Summer in both the Northern and Southern hemispheres at the same time - so that it isn't, is a good piece of evidence that the angle of incidence of insolation is more important than the distance, just as these calculations predict.


TL;DR - Axial Tilt. It's the reason for the season.

 

[Atheos]

As the earth is approximately spherical, and hence lines of latitude are very close to perfectly circular, the day of the solstice is also the longest or shortest day of the year at any point on the surface, other than on the Equator where day length doesn't vary significantly. (Source)

Since we're waxing scholarly it is worth pointing out that at the poles (North and South) the sun rises and sets only once each year. When it rises it would appear to simply spiral around an observer for 3 months as it gradually gets higher in the sky, then continue spiraling downwards toward the horizon until it sinks out of sight for 6 months.

(Vid)

 

[Jimmy Higgins]

But the Solstice is when the Earth is the closest it gets to the sun for this revolution. That is independent of the sun rising.

Nope. The Solstice is when the Sun is at its furthest South (in December) or North (in June) of the equator. Solstices are due to the Earth's axial tilt, and are independent of the distance to the Sun. The next Solstice will be at 10:44UTC on December 21st 2016, and will be a southernmost track solstice, (ie Winter in the Northern hemisphere and Summer in the Southern Hemisphere). As the earth is approximately spherical, and hence lines of latitude are very close to perfectly circular, the day of the solstice is also the longest or shortest day of the year at any point on the surface, other than on the Equator where day length doesn't vary significantly. (Source)

When the Earth is closest to the sun, that's known as Perihelion; In 2017 Perihelion is at 14:18UTC on January 4th, and Aphelion (the point when the Earth is farthest from the sun) is at 20:11UTC on July 3rd. (Source).

Earth’s mean distance from the Sun at perihelion is 0.9832899 AU (147,098,074 km); in 2017, perihelion will be 0.9833094 AU, which is 2919 km farther away than the mean, and Earth’s mean distance from the Sun at aphelion is 1.0167103 AU (152,097,701 km), and in 2017 aphelion will be 1.0166756 AU, which is 5190 km closer than the mean.

The change in distance to the sun on the Earth's due to axial tilt alone varies from 0km at the Equator to about 5000km at the poles; the variation due to the elliptical nature of the Earth's orbit is about 5,000,000km (4,990,020 km between January and July 2017), so the change in distance to the sun due to axial tilt is only at MOST 0.1% of the total change in distance - and in the Northern Hemisphere, you can be up to five million km closer to the sun in winter than you are in summer.

The reason that it is warmer in summer has very little to do with the distance to the sun - the total distance only varies by about 0.3% - the important thing is the angle with which the sun's rays arrive at your latitude. The total energy incident on your location when the sun is directly overhead is twice what it would be if the sun were 30 degrees above the horizon, ceteris paribus; This large effect completely swamps the 0.3% difference in distance between aphelion and perihelion, which only makes for about 7% difference in the incident solar energy density arriving at any point on the Earth's surface (7% is a lot more than 0.3%, of course, because the effect is amplified by the inverse square law - the energy density is proportional to the inverse square of the distance).

View attachment 8920

Of course, if the distance from the Earth to the Sun were the cause of the seasons, it would be Summer in both the Northern and Southern hemispheres at the same time - so that it isn't, is a good piece of evidence that the angle of incidence of insolation is more important than the distance, just as these calculations predict.


TL;DR - Axial Tilt. It's the reason for the season.

Well fuck me then.

I knew the angle of the earth's tilt was the cause of the season, however, I always thought the Solstices marked the perihelion and aphelion of the orbit, which apparently are only close right now by happenstance and in a while, the perihelion will occur on the equinox! *sigh*

 

[Angry Floof]

Ya big nerds!

 

[Jimmy Higgins]

Ya big nerds!

Don't look at me, I had no idea what I was talking about.

 

[funinspace]

Ya big nerds!

Don't look at me, I had no idea what I was talking about.

It's ok, take a cookie; we'll keep on pretending to act as if we think you are in the know

 

[C_Mucius_Scaevola]

Jesus and Mo nails it. As usual.