APOD: The Sun in X-rays from NuSTAR (2021 Nov 23)

[APOD Robot]

The Sun in X-rays from NuSTAR

Explanation: Why are the regions above sunspots so hot? Sunspots themselves are a bit cooler than the surrounding solar surface because the magnetic fields that create them reduce convective heating. It is therefore unusual that regions overhead -- even much higher up in the Sun's corona -- can be hundreds of times hotter. To help find the cause, NASA directed the Earth-orbiting Nuclear Spectroscopic Telescope Array (NuSTAR) satellite to point its very sensitive X-ray telescope at the Sun. Featured here is the Sun in ultraviolet light, shown in a red hue as taken by the orbiting Solar Dynamics Observatory (SDO). Superimposed in false-colored green and blue is emission above sunspots detected by NuSTAR in different bands of high-energy X-rays, highlighting regions of extremely high temperature. Clues about the Sun's atmospheric heating mechanisms come from NuSTAR images like this and shed light on solar nanoflares and microflares as brief bursts of energy that may drive the unusual heating.

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[VictorBorun]

I wonder what is that thing in red (presenting UF) that looms over horizon

[orin stepanek]

Hot; hot; hot! Don't want to visit there! Glad I don't live there; but I
love the nice days it creates here on Earth!

Super kitty; up; up; and away!

[raschumacher]

Do magnetic fields sort particles by energy? The cold ones stay on the surface and the hot ones rise?

[neufer]

Do magnetic fields sort particles by energy? The cold ones stay on the surface and the hot ones rise?

A convective atmosphere such as our own troposphere or mesosphere allows warm particles at the base to rise against gravity thereby losing energy into the cold particles above.

A non-convective atmosphere such as our stratosphere is usually heated from above (e.g., solar UV heating ozone) such that warm particles are on top of the colder particles.

The sun's corona is somehow heated locally (probably by some combination of magnetic reconnection and "small scale" turbulence).
................................................................................................................
Dr. Raymond Stantz: The whole building is a huge, superconductive antenna that was designed and built expressly for the purpose of pulling in and concentrating spiritual turbulence.

[Fred the Cat]

As we probe the sun one question may solve others.

[VictorBorun]

Do magnetic fields sort particles by energy? The cold ones stay on the surface and the hot ones rise?

A convective atmosphere such as our own troposphere or mesosphere allows warm particles at the base to rise against gravity thereby losing energy into the cold particles above.

A non-convective atmosphere such as our stratosphere is usually heated from above (e.g., solar UV heating ozone) such that warm particles are on top of the colder particles.

The sun's corona is somehow heated locally (probably by some combination of magnetic reconnection and "small scale" turbulence).
................................................................................................................
Dr. Raymond Stantz: The whole building is a huge, superconductive antenna that was designed and built expressly for the purpose of pulling in and concentrating spiritual turbulence.

I think the most popular confusion with hot coronas and ionospheres is an idea that the space is cold, stars are hot and a thing in a solar system is hot if it's near the star.
In fact it's correct only for thick media that can radiate thermal photons.
A thin media like hot coronas and ionospheres has so few collisions between molecules, atoms, ions or electrons, that you can think of it as having a Greenhouse blanket. It's get hot by some flash in the star and then struggles to cool off

[neufer]

Alfvén(?) with tightly wound braids & MHD wave stocking

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Hinode image (Jan. 12, 2007) reveals the filamentary nature of the corona.

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Magnetic MHD Alfvén S-waves, flow from the base of black hole jets.

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<<Many coronal heating theories have been proposed, but two theories have remained as the most likely candidates: wave heating and magnetic reconnection (or nanoflares).

In 2012, high resolution soft X-ray imaging with the High Resolution Coronal Imager aboard a sounding rocket revealed tightly wound braids in the corona. It is hypothesized that the reconnection and unravelling of braids can act as primary sources of heating of the active solar corona to temperatures of up to 4 million kelvin. The main heat source in the quiescent corona (about 1.5 million kelvin) is assumed to originate from magnetic MHD waves. In plasma physics, an Alfvén wave, named after Hannes Alfvén, is a type of magnetohydrodynamic wave in which ions oscillate in response to a restoring force provided by an effective tension on the magnetic field lines.

The convection zone of the sun, the region beneath the photosphere in which energy is transported primarily by convection, is sensitive to the motion of the core due to the rotation of the sun. Together with varying pressure gradients beneath the surface, electromagnetic fluctuations produced in the convection zone induce random motion on the photospheric surface and produce Alfvén waves. The waves then leave the surface, travel through the chromosphere and transition zone, and interact with the ionized plasma. The wave itself carries energy and some of the electrically charged plasma.

Recently, Alfvénic motions have been found in the lower solar atmosphere and also in the quiet Sun, in coronal holes and in active regions using observations with AIA on board the Solar Dynamics Observatory. These Alfvénic oscillations have significant power, and seem to be connected to the chromospheric Alfvénic oscillations previously reported with the Hinode spacecraft. After the seminal work of Jess et al. (2009), in 2017 Srivastava et al. detected the existence of high-frequency torsional Alfvén waves in the Sun's chromospheric fine-structured flux tubes. They discovered that these high-frequency waves carry substantial energy capable of heating the Sun's corona and also in originating the supersonic solar wind. In 2018, using spectral imaging observations, non-LTE (local thermodynamic equilibrium) inversions and magnetic field extrapolations of sunspot atmospheres, Grant et al. found evidence for elliptically-polarized Alfvén waves forming fast-mode shocks in the outer regions of the chromospheric umbral atmosphere. They provided quantification of the degree of physical heat provided by the dissipation of such Alfvén wave modes above active region spots. NASA's Parker Solar Probe is intended to approach the Sun to a distance of approximately 9.5 solar radii to investigate coronal heating and the origin of the solar wind.>>

[neufer]

I think the most popular confusion with hot coronas and ionospheres is an idea that the space is cold, stars are hot and a thing in a solar system is hot if it's near the star.
In fact it's correct only for thick media that can radiate thermal photons.
A thin media like hot coronas and ionospheres has so few collisions between molecules, atoms, ions or electrons, that you can think of it as having a Greenhouse blanket. It's get hot by some flash in the star and then struggles to cool off

Greenhouse blankets are characteristic of thick opaque atmospheres like Venus's not thin transparent atmospheres like the corona.

In fact, the corona loses energy like a sieve by fast escaping particles with long mean free paths as well as by wide Doppler emission lines & cyclotron radiation.

If the corona wasn't so rapidly losing energy there would be much less interest in figuring out how it is being constantly heated.

[VictorBorun]

I think the most popular confusion with hot coronas and ionospheres is an idea that the space is cold, stars are hot and a thing in a solar system is hot if it's near the star.
In fact it's correct only for thick media that can radiate thermal photons.
A thin media like hot coronas and ionospheres has so few collisions between molecules, atoms, ions or electrons, that you can think of it as having a Greenhouse blanket. It's get hot by some flash in the star and then struggles to cool off

Greenhouse blankets are characteristic of thick opaque atmospheres like Venus's not thin transparent atmospheres like the corona.

In fact, the corona loses energy like a sieve by fast escaping particles with long mean free paths as well as by wide Doppler emission lines & cyclotron radiation.

If the corona wasn't so rapidly losing energy there would be much less interest in figuring out how it is being constantly heated.

ok, no blanket, just a sieve. Still it's miles tighter than thick radiating things like Moon surface that is in a kind of thermal equlibrium with space radiation, if we take a weighted mean of the 0.5° diameter disk of Sun (6000 K) and the rest of the sky (3 K).
We first hear how cold it is on Moon even in the day; therefore we are surprised when next we hear how hot Earth's ionosphere is.

[BillBixby]

ok, no blanket, just a sieve. Still it's miles tighter than thick radiating things like Moon surface that is in a kind of thermal equlibrium with space radiation, if we take a weighted mean of the 0.5° diameter disk of Sun (6000 K) and the rest of the sky (3 K).
We first hear how cold it is on Moon even in the day; therefore we are surprised when next we hear how hot Earth's ionosphere is.

In the ionosphere, radiation from the sun is so powerful that it ionizes, or breaks electrons free from different atoms present in the atmosphere. Due to fluxes in solar radiation, temperatures in the ionosphere vary from 200 Kelvin (or -99 degrees Fahrenheit) to 500K (or 440 degrees Fahrenheit).Oct 15, 2021

https://study.com/academy/lesson/ionosp ... ahrenheit).

[Chris Peterson]

ok, no blanket, just a sieve. Still it's miles tighter than thick radiating things like Moon surface that is in a kind of thermal equlibrium with space radiation, if we take a weighted mean of the 0.5° diameter disk of Sun (6000 K) and the rest of the sky (3 K).
We first hear how cold it is on Moon even in the day; therefore we are surprised when next we hear how hot Earth's ionosphere is.

The Moon is not "cold" during the day. Temperature is a measure of the kinetic energy of particles in a material. The surface of the Moon cycles between "hot" and "cold" (in human terms) as it absorbs and radiates photons. The "air temperature" on the Moon is determined by the kinetic energy of free atoms of gas. Likewise for the upper atmosphere, where (if you are not in sunlight) you will freeze to death by radiative loss even though the surrounding air temperature may be hundreds or thousands of degrees, but there simply aren't enough atoms to efficiently transfer enough of that energy to you conductively.

[VictorBorun]

ok, no blanket, just a sieve. Still it's miles tighter than thick radiating things like Moon surface that is in a kind of thermal equlibrium with space radiation, if we take a weighted mean of the 0.5° diameter disk of Sun (6000 K) and the rest of the sky (3 K).
We first hear how cold it is on Moon even in the day; therefore we are surprised when next we hear how hot Earth's ionosphere is.

The Moon is not "cold" during the day. Temperature is a measure of the kinetic energy of particles in a material. The surface of the Moon cycles between "hot" and "cold" (in human terms) as it absorbs and radiates photons. The "air temperature" on the Moon is determined by the kinetic energy of free atoms of gas. Likewise for the upper atmosphere, where (if you are not in sunlight) you will freeze to death by radiative loss even though the surrounding air temperature may be hundreds or thousands of degrees, but there simply aren't enough atoms to efficiently transfer enough of that energy to you conductively.

So it is misleading to talk about the temperature of Moon's atmosphere; more to the point is the temperature of Moon's surface. A walker in a black spacesuit with 21°C inside will be losing heat because the environment is mostly cold; therefore a white spacesuit will be wiser.

I wonder if a low orbit satellite or cruise shuttle can heat itself with the energy of headwind, for an orbit or two.
But here the temperature of the media in the reference to the low orbit satellite will correspond to 8 km/s velocity, and the thermal movement of ions in ionosphere will be irrelevant.

[neufer]

ok, no blanket, just a sieve. Still it's miles tighter than thick radiating things like Moon surface that is in a kind of thermal equlibrium with space radiation, if we take a weighted mean of the 0.5° diameter disk of Sun (6000 K) and the rest of the sky (3 K).

We first hear how cold it is on Moon even in the day; therefore we are surprised when next we hear how hot Earth's ionosphere is.

The Moon is not "cold" during the day. Temperature is a measure of the kinetic energy of particles in a material. The surface of the Moon cycles between "hot" and "cold" (in human terms) as it absorbs and radiates photons. The "air temperature" on the Moon is determined by the kinetic energy of free atoms of gas. Likewise for the upper atmosphere, where (if you are not in sunlight) you will freeze to death by radiative loss even though the surrounding air temperature may be hundreds or thousands of degrees, but there simply aren't enough atoms to efficiently transfer enough of that energy to you conductively.

The 5,772 K Sun will be in thermal equilibrium with a totally absorbent "black" surface of temperature 393.6 K [= 5,772 K / sqrt(215)] out at 1 AU (= 215 solar radii). The Moon does has an almost black (i.e., average albedo ~0.136) surface but even such -120º C surface temperatures do not penetrate into the soil very far: https://alma-telescope.jp/en/news/mt-lu ... _telescope

[Chris Peterson]

ok, no blanket, just a sieve. Still it's miles tighter than thick radiating things like Moon surface that is in a kind of thermal equlibrium with space radiation, if we take a weighted mean of the 0.5° diameter disk of Sun (6000 K) and the rest of the sky (3 K).

We first hear how cold it is on Moon even in the day; therefore we are surprised when next we hear how hot Earth's ionosphere is.

The Moon is not "cold" during the day. Temperature is a measure of the kinetic energy of particles in a material. The surface of the Moon cycles between "hot" and "cold" (in human terms) as it absorbs and radiates photons. The "air temperature" on the Moon is determined by the kinetic energy of free atoms of gas. Likewise for the upper atmosphere, where (if you are not in sunlight) you will freeze to death by radiative loss even though the surrounding air temperature may be hundreds or thousands of degrees, but there simply aren't enough atoms to efficiently transfer enough of that energy to you conductively.

The 5,772 K Sun will be in thermal equilibrium with a totally absorbent "black" surface of temperature 393.6 K [= 5,772 K / sqrt(215)] out at 1 AU (= 215 solar radii). The Moon does has an almost black (i.e., average albedo ~0.136) surface but even such -120º C surface temperatures do not penetrate into the soil very far: https://alma-telescope.jp/en/news/mt-lu ... _telescope

Likewise for the Earth (and other solid bodies). Thermal mass is yet another complicating factor.