Magnetic-field

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The upper atmosphere of the Sun is dominated by plasma filled magnetic loops (coronal loops) whose temperature and pressure vary over a wide range. The appearance of coronal loops follows the emergence of magnetic flux, which is generated by dynamo processes inside the Sun. Emerging flux regions (EFRs) appear when magnetic flux bundles emerge from the solar interior through the photosphere and into the upper atmosphere (chromosphere and the corona). The characteristic feature of EFR is the -shaped loops (created by the magnetic buoyancy/Parker instability), they appear as developing bipolar sunspots in magnetograms, and as arch filament systems in . EFRs interact with pre-existing magnetic fields in the corona and produce small flares (plasma heating) and collimated plasma jets. The GIFs above show multiple energetic jets in three different wavelengths. The light has been colorized in red, green and blue, corresponding to three coronal temperature regimes ranging from ~0.8Mk to 2MK. 

Image Credit: SDO/U. Aberystwyth

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Earth is not the only planet in our solar system with auroras. As the solar wind–a stream of rarefied plasma from our sun–blows through the solar system, it interacts with the magnetic fields of other planets as well as our own. Saturn’s magnetic field second only to Jupiter’s in strength. This strong magnetosphere deflects many of the solar wind’s energetic particles, but, as on Earth, some of the particles get drawn in along Saturn’s magnetic field lines. These lines converge at the poles, where the high-energy particles interact with the gases in the upper reaches of Saturn’s atmosphere. As a result, Saturn, like Earth, has impressive and colorful light displays around its poles. (Image credit: ESA/Hubble, M. Kornmesser & L. Calçada, source video; via spaceplasma)

This is a manifestation of the Meissner Effect. When a superconductor reaches a critical temperature (usually very cold, 1 - 70 K) it expels all magnetic field lines. So if you place it on top of a magnet, it will float. It will float on a cushion of magnetic field. Additionally it will experience almost no friction so if you make a circular track of magnets it will levitate around it for quite a long time. And look awesome doing it. That vapour trail isn’t propulsive. It’s just how cold that superconductor is, it’s condensing the air around it.

This might be the most awesome combination of science and design I’ve seen: a clock created by Zelf Koelman that displays time with liquid. It’s called Ferrolic after the ferrofluid which can display recognizable shapes in response to magnets embedded inside the clock’s aluminum frame.

A ferrofluid (put together of ferromagnetic and fluid) is a liquid that becomes strongly magnetized in the presence of a magnetic field. It  was invented in 1963 by NASA’s Steve Papell as a liquid rocket fuel.

Ferrolic is controlled by an intelligent internal system that is accessible trough a web-browser. The inventor wrote in this way users can assign “the creatures” to display time, text, shapes and transitions. The clocks are more of a prototype so far, the first ones were available at a price of about $8,000 each.

see the video and more information here

Coronal rain

On July 19, 2012, an eruption occurred on the sun that produced a moderately powerful solar flare and a dazzling magnetic display known as coronal rain. Hot plasma in the corona cooled and condensed along strong magnetic fields in the region. Magnetic fields, are invisible, but the charged plasma is forced to move along the lines, showing up brightly in the extreme ultraviolet wavelength of 304 Angstroms, and outlining the fields as it slowly falls back to the solar surface.

Credit: NASA,SDO

During a solar flare, magnetic field lines on the sun are often visible due to the flow of plasma–charged particles–along the lines. According to theory, these magnetic lines should remain intact, but they are sometimes observed breaking and reconnecting with other lines. An interdisciplinary team of researchers suggests that turbulence may be the missing link. In their magnetohydrodynamic simulation, they found that the presence of chaotic turbulent motions made the magnetic line motion entirely unpredictable, whereas laminar flows behaved according to conventional flux-freezing theory. (Photo credit: NASA SDO; Research credit: G. Eyink et al.; via SpaceRef; submitted by jshoer)

It may look like a giant ball oozing with earthworms, but it’s actually a simulation of Jupiter’s massive and complex magnetosphere — a magnetic field that extends more than four million miles from its surface.

The Earth generates a magnetic field by the convection of molten nickel-iron alloys in its outer core. Jupiter’s outer core is also thought to be responsible for its enormous magnetic field, though it is liquid hydrogen crushed by intense pressure into a metallic form that generates the magnetism rather than iron compounds. In addition, the gas giant’s surface is buffeted by powerful winds and huge storms, like the famous Great Red Spot. Scientists believe that these surface winds interact with the metallic liquid hydrogen below to stimulate some of the secondary properties of the magnetic field. 

Magnetic fields of planets compared:

(Sources 1, 2, 3

For teaching: astrophysics

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Solar magnetohydrodynamics

The sun is a magnetohydrodynamics (MHD) system that is not well understood. It is thought that the energy necessary to heat the corona is provided by turbulent motion in the convection zone below the photosphere, and two main mechanisms have been proposed to explain coronal heating:

The first is wave heating, in which sound, gravitational or magnetohydrodynamic waves are produced by turbulence in the convection zone. These waves travel upward and dissipate in the corona, depositing their energy in the ambient gas in the form of heat. The other is magnetic heating, in which magnetic energy is continuously built up by photospheric motion and released through magnetic reconnection in the form of large solar flares and myriad similar but smaller events—nanoflares. Currently, it is unclear whether waves are an efficient heating mechanism.

The field of MHD was initiated by Hannes Alfvén, for which he received the Nobel Prize in Physics in 1970. He described the class of MHD waves now known as Alfvén waves. Observations show that all waves except Alfvén waves have been found to dissipate or refract before reaching the corona. Current research focus has therefore shifted towards flare heating mechanisms.

The magnetic filament above erupted on April 19, 2010. The black “hair-like object” is a speck of dust on the CCD camera.

Credit: SDO/AIA

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Earth’s ever-changing magnetic field

This animation shows changes in Earth’s magnetic field from January to June 2014 as measured by ESA’s Swarm trio of satellites.
The magnetic field protects us from cosmic radiation and charged particles that bombard Earth, but it is in a permanent state of flux. Magnetic north wanders, and every few hundred thousand years the polarity flips so that a compass would point south instead of north. Moreover, the strength of the magnetic field constantly changes – and it is currently showing signs of significant weakening.
The field is particularly weak over the South Atlantic Ocean – known as the South Atlantic Anomaly. This weak field has indirectly caused many temporary satellite ‘hiccups’ (called Single Event Upsets) as the satellites are exposed to strong radiation over this area.

Source: ESA/Dot2Dot

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Sometimes fluids are slow-moving enough that it takes timelapse techniques to reveal the flow. Fog is one example, and, as seen above, magnetic silly putty is another. The putty is an unusual fluid in a couple of ways. First, having been impregnated with ferromagnetic nanoparticles, it is sensitive to magnetic fields, making it a sort of ferrofluid. And secondly, being silly putty, it’s a non-Newtonian fluid, meaning that it has a nonlinear response to deformation - a fact that will be familiar to anyone who has tried to knead putty versus striking it. With a strong enough magnet, the putty makes for an impressively tenacious creeping flow. (Video credit: I. Parks; via io9; submitted by Chad W.)

Coronal loop

The corona is the outer part of the solar atmosphere. Its name derives from the fact that, since it is extremely tenuous with respect to the lower atmosphere, it is visible in the optical band only during the solar eclipses as a faint crown (corona in Latin) around the black moon disk. When inspected through spectroscopy the corona reveals unexpected emission lines, which were first identified as due to a new element (coronium) but which were later ascertained to be due to high excitation states of iron. It became then clear that the corona is made of very high temperature gas, hotter than 1 MK(megakelvin). Almost all the gas is fully ionized there and thus interacts effectively with the ambient magnetic field. It is for this reason that the corona appears so inhomogeneous when observed in the X-ray band, in which plasma at million degrees emits most of its radiation. In particular, the plasma is confined inside magnetic flux tubes which are anchored on both sides to the underlying photosphere. When the confined plasma is heated more than the surroundings, its pressure and density increase. Since the tenuous plasma is optically thin, the intensity of its radiation is proportional to the square of the density, and the tube becomes much brighter than the surrounding ones and looks like a bright closed arch: a coronal loop.

Credit: Fabio Reale

Sun will flip its magnetic field soon

The sun is gearing up for a major solar flip, NASA says. In an event that occurs once every 11 years, the magnetic field of the sun will change its polarity in a matter of months, according new observations by NASA-supported observatories.

The flipping of the sun’s magnetic field marks the peak of the star’s 11-year solar cycle and the halfway point in the sun’s “solar maximum” — the peak of its solar weather cycle.

“It looks like we’re no more than three to four months away from a complete field reversal,” Todd Hoeksema, the director of Stanford University’s Wilcox Solar Observatory, said in a statement. “This change will have ripple effects throughout the solar system.”

As the field shifts, the “current sheet” — a surface that radiates billions of kilometers outward from the sun’s equator — becomes very wavy, NASA officials said. Earth orbits the sun, dipping in and out of the waves of the current sheet. The transition from a wave to a dip can create stormy space weather around Earth, NASA officials said.

“The sun’s polar magnetic fields weaken, go to zero, and then emerge again with the opposite polarity,” Stanford solar physicist Phil Scherrer said in a statement. “This is a regular part of the solar cycle.”

Image credit: NASA

Oil filled cube with a suspension of iron powder makes a mesmerizing demonstration of the magnetic field lines.

This is how they started:

Magnetic fields are widely used throughout modern technology, particularly in electrical engineering and electromechanics. The Earth produces its own magnetic field, important in navigation, and it shields the Earth’s atmosphere from solar wind. Rotating magnetic fields are used in both electric motors and generators.

video credit: UniServeScienceVIDEO