The Magnetic Sun
Sun magnetic field lines (screen capture, NASA)
Sun magnetic field lines (screen capture, NASA)
Did you know that the Sun, like Earth, has magnetic field? This field affects our planet and our solar system! Let’s learn more about how it works.
What is a magnetic field?
Some materials can produce a magnetic field. We call objects made from these materials magnets. Permanent magnets create and maintain their own magnetic fields. A fridge magnet is an example of a permanent magnet. Other objects only have the properties of a magnet temporarily. They get these by being magnetized.
Magnetism is a force exerted by magnets when they attract or repel each other. This force is caused by the movement of charged particles. Because of this movement, every atom acts like a tiny magnet. In most materials, equal numbers of electrons spin in opposite directions. This cancels out their magnetism. But in strongly magnetic materials, like iron, nickel, cobalt and steel, the electrons all spin in the same direction.
Did you know?
Strongly magnetic materials can become magnetized by entering the magnetic field of a magnet.
Magnets have two ends, called poles. One is called the north pole and the other the south pole. Opposite poles (north and south) attract each other. Same poles (north and north, or south and south) repel each other. This helps explain why magnets can pull together or push apart.
We cannot see magnetic fields with our eyes, but we can visualize them using iron filings and a bar magnet, as in the video below.
Magnetic Field Around Stack of Magnets With Iron Filings (1:03) from C. Stephen Murray
The pattern that the filings make are magnetic field lines. Magnetic field lines are close together where the magnetic force is strong. They are further apart where the magnetic force is weak. The density of the field lines indicates the strength of the field.
Image - Text Version
Shown are five colour illustrations of magnetic fields around different types of magnets. The title “Magnetic Fields” is in the top left corner. Below, a subtitle reads “S=South pole” in blue letters and “N=North pole” in red letters. Each magnet is half blue and half red. Starting on the top left, the first diagram is labelled “Bar Magnet.” It is a long, rectangular bar. The left half is blue and labelled “S.” The right half is red and labelled “N.” Grey lines with arrows along them fan out around the magnet. These are labelled “Field lines.” The lines spread out from the north pole and curve around to the south pole. The lines are closer together near the ends of the magnets, and further apart near the centre. The next diagram is labelled “Horseshoe Magnet.” It is shaped like a capital letter U. The top left end of the U is the south pole, and the top right end is the north. Again, field lines spread out from the north pole, curve out and back to the south. They are closer together at the ends of the poles, creating a dense area of lines between and just above the ends of the U. They are further apart outside and below the U. The third diagram is labelled “Electric Current.” It has a cylindrical battery along the bottom. The left half is blue and labelled with a minus sign. The right half is red and labelled with a plus sign. A gold coloured wire connects the negative and positive ends with a coiled section in between. Here, the magnetic field lines go through the coiled wire, connecting to form circles around it. The fourth diagram is labelled “Unlike Poles Attract.” This shows two bar magnets, side by side. The left end of each are the south poles, and the right are north poles. Magnetic field lines start from the north poles, stretch and spread out, then connect back to the south poles. They also spread out between the north pole of the left magnet and the south pole of the right magnet, creating a bubble shape. The fifth diagram is labelled “Unlike Poles Repel.” This also shows two bar magnets, side by side. The outside ends of each are the south poles, and the inside are north poles. Magnetic field lines start from the north poles, stretch and spread out, then connect back to the south poles. None of the field lines go between the two magnets.
The Sun’s Magnetic Field
The Sun’s core is exposed to massive amounts of pressure from the outer layers of the Sun. This pressure strips electrons from hydrogen atoms. This mixture of positively charged atomic nuclei and negatively charged electrons is what scientists call plasma. The movement of these electrons in the Sun’s plasma creates a complex and dynamic magnetic field. This extends throughout the Solar System.
Did you know?
Plasma is a state of matter.
Scientists have tried to understand the Sun’s magnetic field using computer models. The animation on the right was created using the Potential Field Source Surface (PFSS) model. The white lines represent closed field lines. These start and end at the Sun. Green represents positive open field lines and purple represents negative open field lines. Open field lines do not connect back to the Sun. They connect with other magnetic fields in space.
Image - Text Version
Shown is a colour animation of white, purple and green lines moving rapidly around a grey sphere. The Sun is represented as a grey sphere. Occasionally, small black splotches with white edges move around the surface. Above, the closest lines are rows of white loops. They start on the Sun, curve up into space, and back down. The resulting shapes look like fat slugs moving around the surface. Around and in between the white shapes are much longer green and purple lines. These fan out into space without curving or looping. They are moving and shifting all the time, but the green lines move around the top half of the sphere, and the purple around the bottom.
Evolution of the solar magnetic field from 1997 to 2013. (NASA)
Magnetic field lines can cross and suddenly snap. This can send nearby particles off into space at great speeds. This is called magnetic reconnection. It’s a lot like when a rubber band is stretched out and released.
Magnetic reconnection plays an important role in events like solar flares and coronal mass ejections. In the image on the right, there is a magnetic reconnection between the two bright areas on the left.
Image - Text Version
Shown is a colour illustration of loops of yellow light bursting up from the surface of the Sun. The Sun’s curves down the left edge of the image. Its surface is mottled red and orange. Yellow glows from underneath. In a few spots, bright yellow breaks through the surface. Above these, bursts of wispy yellow light can be seen against the blackness of space.
The Sun’s Corona
Most electromagnetic field activity takes place on the Sun’s corona. The corona is the outermost layer of the sun. The activity we can see includes sunspots, solar flares, solar wind and coronal mass ejections. These events are sometimes referred to as solar storms. They influence space weather, which impacts Earth's magnetic field.
Did you know?
The corona is much hotter than the Sun's surface. The corona is about 1 million °C and the surface is about 5 500 °C!
Sunspots
A very noticeable feature of the Sun are sunspots. Sunspots look like dark blotches on the surface of the Sun. The “spots” are planet-sized areas where the magnetic field is very strong. They look darker because they are cooler than their surroundings. But they are still quite hot! The surface of the Sun is about 5 500 degrees Celsius. A sunspot is about 3 200 degrees Celsius.
Sunspots have two main parts.
- The umbra is the darkest part of a sunspot. This is where the magnetic field is very strong. It points straight up from the Sun's surface.
- The penumbra is the less dark area surrounding the umbra. It has stretched structures called penumbral filaments. These look like they are reaching out from the umbra.
Image - Text Version
Shown is a black and white photograph of two black splotches with grey edges on a light grey surface. The camera looks down at a mottled grey and white surface. There is a large black splotch in the top centre, and a smaller one below and to the left. Each one has a dark grey fringe around its edge. These look like shiny threads stretching into the black. A few tiny black spots are scattered over the rest of the surface.
The Solar Cycle
The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is the cycle of activity the sun goes through about every 11 years. This activity is measured in the number of sunspots.
During a solar cycle, the Sun's behaviour follows a known pattern. It starts with low activity, then goes to high activity, and back to low activity again. Like sunspots, the number of solar flares also follows the solar cycle.
The magnetic field of the Sun flips once during each solar cycle. This means that the north pole becomes the south pole and the south pole becomes the north pole. The flip happens when the solar cycle is near the solar maximum. This is the time when there is the greatest amount of solar activity.
After two solar cycles, the Sun's magnetic field returns to its original state. At this point, it has completed a Hale cycle. By keeping track of the number of sunspots, scientists know where the Sun is in the cycle.
As of 2023, the Sun is in Solar Cycle 25. This means it is the 25th cycle since the first recording of sunspot activity in 1755.
Image - Text Version
Shown is a black and white graph showing past sunspots and predictions for the future. The x axis is labelled “Universal Time.” It runs from 2020 on the left to 2032 on the right. The y axis is labelled “Sunspot Number.” It runs from 0 at the bottom to 200 at the top. A legend along the bottom edge provides information about three different lines on the graph. The first is a blue diamond with a line through it, labelled “Monthly Values.” The second is a purple line labelled “Smoothed Monthly Values.” The third is a red line labelled “Predicted Values.” From 2020 to 2023, there is a streak of blue diamonds connected by zig zagging blue lines. These go from just over 0 in 2020 to about 170 in 2023. A purple line runs through the centre of these, ending just before 2023. A red line runs just under the diamonds, from 0 in 2020 to about 90 in 2023. The line curves up to 120 by 2025, then back down close to 0 by 2032. Below, a timeline shows a line curving sharply up and down between 1755 and 2023.
With solar activity on the rise, don’t be surprised if you start hearing more about our amazing magnetic Sun!
Learn More
The Sun is Waking Up Right On Schedule (2022)
This article from Sky & Telescope explores the solar cycle. According to scientists the sun’s activity is happening as they predicted it would!
Understanding the Magnetic Sun (2016)
This YouTube video (1:56 min.) from NASA Goddard uses a computer model to show how the Sun’s magnetic field works.
References
Khan Academy. (N.d.). What are magnetic fields?
Hill, D. (2023). Sun Releases Strong Solar Flare. NASA.
Wikipedia (n.d.). Solar Cycle.