2004: Sun and Earth

2018-06-08T13:34:39Z

Fergatron: /* Explanation */

{{comic
| number = 2004
| date = June 8, 2018
| title = Sun and Earth
| image = sun_and_earth.png
| titletext = But we don't need to worry about the boiling masses sandwiching the thin layer in which we live, since we're so fragile and short-lived that it's unlikely to kill us before something else does! Wait, why doesn't that sound reassuring?
}}

==Explanation==
{{incomplete|Created by a hurried VOLCANO - Lots of things missing: (1) links (2) description of how the Sun is a massive convective system (3) description of how the Earth is a massive convective system (4) probably reword everything}}

This is one of a number of comics which describe everyday events in unusual terms, making them sound really weird. In this case, both the Sun and the Earth are "massive convective systems" blasting "huge plumes of heat", which contrasts sharply with the daily idea of the Sun being a ball in the sky and the Earth the thing under our feet.

Massive convecting systems are built upon the back of one simple thing: an energy gradient. The energy gradient (between the center of the system, in the cases we are discussing, and the surface) drives the convection-- so long as the increase in rate of energy lost by this means is greater than the internal friction of the system there will be convection. So in the case of the sun, the energy lost by transporting hot plasma to the surface of the sun must be greater than the total resistance that all those billions (and billions and billions etc.) of tonnes of matter have, to movement (friction, momentum etc).

The energy to drive these convecting processes is ultimately derived from gravitational collapse. In simple terms, as massy bodies (even just gas particles in a cloud in the early solar system) approach one another they gain energy, because gravitational attraction increases with proximity. It is the collected energy from the approach of a multitude of small particles that keeps the core of the earth molten.

The magnitude of these systems gives you an idea of the size of the fluctuations you can expect. The sun is very massive, meaning the fluctuations in it's convective or heat-dissipating behavior are very large. This is an instance of the {{w|Fluctuation-dissipation_theorem|Fluctuation-Dissipation theorem}}. These fluctuations take the form of a solar flare, as explained below. For a more thorough (but non-technical) explanation of the role of gravity and entropy in such systems, see [https://arxiv.org/abs/0907.0659].

In fact, the {{w|Sun}} does produce great amounts of light and heat and blasts it towards us, which is why we can live on Earth. Since Ludwig Boltzmann pointed out the fact in 1875, people have been working on establishing exactly how such far from equilibrium systems as life might depend upon, or be formed by [https://www.quantamagazine.org/first-support-for-a-physics-theory-of-life-20170726/ 1], such massive entropy gradients as between the sun and earth (or rather the sun and empty space).

Main sequence stars like the sun transport energy by {{w|Radiation_zone|radiation}} and by {{w|Convection_zone|convective currents}} of {{w|Plasma (physics)|plasma}}, bringing the heat generated in the core of the sun to its surface. These quickly moving charged particles create a massive magnetic field, which occasionally gets concentrated into a {{w|solar prominence}} which can snap, causing a large amount of charged particles to get shot into space as a {{w|solar flare}}. If the Earth happens to be in the direction of the solar flare, we can notice all sorts of interesting and often damaging effects. Thankfully, there are lots of other directions available for the sun to shoot the solar flare, so they don't come by the Earth that often.

The {{w|Earth#Internal_structure|Earth's interior}} is very hot. {{w|Mantle convection}} causes {{w|plate tectonics}} which is the main cause of {{w|Volcano|volcanic activity}} (next to {{w|Mantle_plume|mantle plumes}}), which essentially also consists of huge blasts of heat.

This could sound like a very bad scenario, however the title text reminds us that the real scenario we live in is far worse, as we are not likely to die from a Sun blast or volcano eruption.

This comic was likely inspired by the recent eruptions of the {{w|Kīlauea}} and {{w|Volcán de Fuego}}. In contrast, solar activity is currently low, because the {{w|Sunspot#Solar_cycle|sunspot solar cycle}} is in the low end of the 11-year cycle.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[At the bottom of the image a curved shape depicting a small part of the Earth's surface and labeled as "Earth" is shown. At the top a similar sized shape but opposite curve is labeled as "Sun". The surface of the Sun is seething while on Earth's surface a few plants, two birds, and Cueball together with Megan are visible.]

:[Two arrows pointing to the Earth and the Sun with a caption:]
:Massive convective systems which occasionally blast huge plumes of heat at us without warning through mechanisms we can't directly observe and don't really understand.

:Cueball: What a nice day

{{comic discussion}}

2004: Sun and Earth

2018-06-08T12:49:09Z

Fergatron: /* Explanation */

explain xkcd - User contributions [en]

2004: Sun and Earth

2004: Sun and Earth