At this level, the sun's gravity can't hold on to the rapidly moving particles, and they stream away from the star. The sun's activity shifts over the course of its year cycle, with sun spot numbers, radiation levels, and ejected material changing over time. These alterations affect the properties of the solar wind, including its magnetic field, velocity, temperature and density. The wind also differs based on where on the sun it comes from and how quickly that portion is rotating.
The velocity of the solar wind is higher over coronal holes, reaching speeds of up to miles kilometers per second. The temperature and density over coronal holes are low, and the magnetic field is weak, so the field lines are open to space. These holes occur at the poles and low latitudes, reaching their largest when activity on the sun is at its minimum. Temperatures in the fast wind can reach up to 1 million F , C.
At the coronal streamer belt around the equator, the solar wind travels more slowly, at around miles km per second. Temperatures in the slow wind reach up to 2. The sun and its atmosphere are made up of plasma, a mix of positively and negatively charged particles at extremely high temperatures. Their faster counterparts put those numbers to shame, flying by at to miles to kilometers per second. The quickest winds come whizzing out of coronal holes , temporary patches of cool, low-density plasma that appear in the corona.
These serve as great outlets for solar wind particles because open magnetic field lines run through the holes. Basically, the open lines are highways that shoot charged particles out of the corona and into the heavens beyond. Don't confuse them with closed magnetic field lines , looping channels along which plasma bursts out of the sun's surface and then plunges right back down into it.
Less is known about how the slow winds form. However, their point of origin at any given time seems to be affected by the sunspot population. When these things are scarce, astronomers observe slow winds coming out of the sun's equatorial region and fast ones streaking out of the poles.
But when sunspots become more common, the two kinds of solar wind appear in closer proximity to each other all across the glowing spheroid. No matter how fast a gust of solar wind is moving as it bids the corona "farewell," it will eventually slow down. Solar winds exit the sun in all directions. By doing so, they maintain a capsule of space that houses the sun, the moon and every other body in our solar system.
It's what scientists call the heliosphere. The seemingly vacant spaces between the stars in our galaxy are actually full of interstellar medium ISM , a cocktail that includes hydrogen, helium and amazingly small dust particles. Essentially, the heliosphere is a giant cavity surrounded by this stuff.
Rather like a super-sized onion, the heliosphere is a layered construct. The termination shock is a buffer zone far beyond Pluto and the Kuiper Belt where solar wind rapidly declines in speed. Past that point lies the heliosphere's outer boundary, a place in which the interstellar medium and solar winds become evenly matched in terms of strength. Closer to home, the particles in solar winds are responsible for the aurora borealis "northern lights" and aurora australis "southern lights".
Above the Sun's active sunspot regions dark areas caused by magnetic disturbances on the surface, or photospheric layer, loops of magnetic field lines trap some plasma and hold it back. Projecting outward, the solar wind forms an immense "bubble" around the Sun, called the heliosphere.
This bubble extends far beyond the orbit of most planets in our solar system. Artist's drawing of the heliosphere. As the solar wind projects further and further outward from the Sun, it spreads itself thin. It can then no longer resist the inward push of the instellar space medium the part of our galaxy that lies between the stars.
The solar wind is a flow of particles that comes off the sun at about one million miles per hour and travels throughout the entire solar system. While the solar wind protects Earth from other harmful particles coming from space, storms can also threaten our satellite and communications networks. The surface of the sun is blisteringly hot at 6, degrees Fahrenheit—but its atmosphere, called the corona, is more than a thousand times hotter.
As the sun spins, burns and burps, it creates complex swirls and eddies of particles. These particles, mostly protons and electrons, are traveling about a million miles per hour as they pass Earth.
The wind would also pose a threat to astronauts traveling through space, so NASA wants to get a better understanding of its properties. In , Eugene Parker was an assistant professor at the University of Chicago when he began looking into an open question in astrophysics: Are particles coming off of the sun? But scientists had noticed an odd phenomenon: The tails of comets, no matter which direction they traveled, always pointed away from the sun—almost as though something was blowing them away.
Parker began to do the math. He wrote a paper and submitted it to the Astrophysical Journal ; the response from scientific reviewers was swift and scathing. It is extraordinarily difficult to accelerate anything to supersonic speeds in the laboratory, and there is no means of propulsion. The breakthrough discovery reshaped our picture of space and the solar system. Scientists came to understand that the solar wind not only flows past Earth, but throughout the solar system and beyond.
It also both protects and threatens us. So understanding the precise structure and dynamics and evolution of the solar wind is crucial for civilization as a whole.
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