UNDERSTANDING OUR SUN

Our solar system is composed of the Sun and all things which orbit around it: the Earth, the other eight planets, asteroids, and comets.

However, since it is by far the closest star to the Earth, it looks bigger and brighter in our sky than any other star. With a diameter of about 1.4 million kilometer s (860,000 miles), it would take 110 Earths strung together to be as long as the diameter of the Sun.The Sun is mostly made up of hydrogen (about 92.1% of the number of atoms, 75% of the mass). Helium can also be found in the Sun (7.8% of the number of atoms and 25% of the mass). The other 0.1% is made up of heavier elements, mainly carbon, nitrogen, oxygen, neon, magnesium, silicon, and iron. The Sun is neither a solid nor a gas but is actually plasma. This plasma is tenuous and gaseous near the surface but gets denser down towards the Sun’s fusion core.
Stars like the Sunshine for nine to ten billion years. The Sun is about 4.5 billion years old, judging by the age of moon rocks. Based on this information, current astrophysical theory predicts that the Sun will become a red giant in about five billion (5,000,000,000) years.

Sun Facts

  • The sun is the largest object in the solar system
  • The sun contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest).
  • The sun is the closest star to Earth
  • The sun is an average star, its size, age, and temperature fall in about the middle of the ranges of these properties for all stars.
  • Some in our galaxy are nearly as old as the universe, about 15 billion years, our sun is a 2nd-generation star, only 4.6 billion years old.
  • Some of the sun’s material came from former stars.
  • We’ve always known the sun, unlike many other objects in our solar system, the sun has been known to humans since the dawn of time. There is no discovery date or discoverer.
  • Since its creation, the sun has used up about half of the hydrogen in its core
  • The solar “surface,” known as the photosphere, is just the visible 500-km-thick layer from which most of the Sun’s radiation and light finally escape, and it is the place where sunspots are found.
  • Above the sun’s photosphere lies the chromosphere (“sphere of color”) that may be seen briefly during total solar eclipses as a reddish rim, caused by hot hydrogen atoms, around the Sun.
  • The corona (“crown”) is above the chromosphere, extending outward from the Sun in the form of the “solar wind” to the edge of the solar system.
  •  One unsolved mystery of the sun involves the corona (“crown”), why is extremely hot – millions of degrees kelvin.
  • It is physically impossible to transfer thermal energy from the cooler surface of the Sun to the much hotter corona, the source of coronal heating has been a scientific mystery for more than 60 years.
  • The Greeks named the sun Helios, the Romans used the name Sol, which is still in use today.
  • Ulysses was the first spacecraft to study our Sun’s poles.
  • The sun’s strong gravitational pull holds Earth and the other planets in place.
  • The sun is made up of distinctive areas In addition to the energy-producing solar core, the interior has two distinct regions: a radiative zone and a convective zone.
SOLAR STRUCTURE

Core

This is the inner most part of the Sun. Here gravity has squeezed the Sun so much that hydrogen compresses together to form helium and release energy through nuclear fusion. All the energy that comes away from the Sun and all the reaches the Earth started in the core. The core is around 150 times as dense as water and has a blazing temperature of around 15 million degrees Celsius or 28 million degrees Fahrenheit.

Radiative Zone

This is the layer of the Sun above the super dense core. The density slowly decreases moving away from the core. Light produced by nuclear fusion in the core travels out in the shell called the radiative zone. This layer is not as dense as the core but it is still so dense that light from the core bounces around taking about 100,000 years to move through the radiative zone.

Convection Zone

This is the layer of the Sun above the radiative zone. When the density of the radiative zone becomes low enough energy from the core in the form of light is converted into heat. Much like the bubbles in a pot of boiling, the heat from the edge of the radiative zone rises until it cools enough that it sinks back down. This pattern of heated material rising then cooling happens in big bubbles called convection cells.

Solar Atmosphere

Photosphere

The material that reaches the top of the convection zone cools by giving of light. This region of the Sun is the first part of the Sun that is visible to us and we call it the photosphere. This is where the light we see from the Sun originates. If we could look at the Sun directly (never stare at the Sun without the proper equipment) we would see the photosphere. Even though the layer is not solid we call this part of the Sun the surface and it is also where the solar atmosphere starts. Its temperature is around 5,800 Celsius or 10,000 degrees Fahrenheit.

Chromosphere

Above the photosphere is a layer of the atmosphere about 2,000 km thick called the chromosphere. The temperature increases as you move higher to about 20,000 degrees Celsius at the top of the chromosphere. The chromosphere is no longer white light like the photosphere but is mostly red in the visible light. It can be seen as red flashes during a total solar eclipse.

Corona

The highest part of the solar atmosphere is called the corona. The corona starts around 10,000 km above the solar photosphere. Unlike the atmosphere of the Earth the atmosphere of the Sun continues to get hotter as you move away from the solar surface. The answer to why exactly this happens is one of the biggest questions of astronomy and solar physics of the 20th and 21st centuries. At 20,000-25,000 km away from the solar surface, the corona has an average temperature of 1,000,000 to 2,000,000 million degrees Celsius. But the density is very low, about 1 billion times less dense than water.

Sunspots



Sunspots appear as dark patches in the solar photosphere. These are areas where strong magnetic field has emerged from below the solar surface. The strong magnetic field suppresses the release of heat into the photosphere making sunspots cooler than their surroundings. Because they are much cooler than the surrounding photosphere sunspots appear darker even though they are still many 1000s of degrees Celsius.
An active region on the sun — an area of intense and complex magnetic fields — has rotated into view on the sun and seems to be growing rather quickly in this video captured by NASA’s Solar Dynamics Observatory between July 5-11, 2017. Such sunspots are a common occurrence on the sun, but are less frequent as we head toward solar minimum, which is the period of low solar activity during its regular approximately 11-year cycle. This sunspot is the first to appear after the sun was spotless for two days, and it is the only sunspot group at this moment. Like freckles on the face of the sun, they appear to be small features, but size is relative: The dark core of this sunspot is actually larger than Earth.
Credit: NASA’s Goddard Space Flight Center/SDO/Joy Ng, producer 
Music credit: ‘The Answer’ by Laurent Levesque [SACEM] from Killer Tracks
NASA Scientist C. Alex Young discusses recent sunspot activity during Live Shot. 
Credit: NASA’s Goddard Space Flight Center

Filaments



Sometimes magnetic field in the solar atmosphere holds up solar plasma from the chromosphere into the solar corona. The filaments are held up in a kind-of magnetic hammock. The relatively cool filament material appears dark when observed against the bright solar disk. Filaments can stretch far across the Sun measuring 100s of thousands of kilometers. The equivalent of 10 or more Earths lined up in a row.
On August 31, 2012 a long filament of solar material that had been hovering in the sun’s atmosphere, the corona, erupted out into space at 4:36 p.m. EDT. The coronal mass ejection, or CME, traveled away from the sun at over 900 miles per second. This movie shows the ejection from a variety of viewpoints as captured by NASA’s Solar Dynamics Observatory (SDO), NASA’s Solar Terrestrial Relations Observatory (STEREO), and the joint ESA/NASA Solar Heliospheric Observatory (SOHO).
Credits: NASA’s Goddard Space Flight Center/SDO/STEREO & joint ESA/NASA Solar Heliospheric Observatory (SOHO)

Prominences



Prominences are really just the same thing as filaments only viewed from a different perspective. Filament are seen on the solar disk however filament are very high up in the solar atmosphere, way above the surface. So when a filament is on the edge of the Sun the filament sticks out with space instead of the solar surface behind it. This makes the filament very bright compared to the dark (cold) background of space. We call a filament viewed this way a prominence. They can be simple looped shaped object or very irregular with a complicated structure.
Over a six-hour period on April 21, 2015, NASA’s Solar Dyanmics Observatory (SDO) observed a wing-like prominence eruption. SDO views the sun in various wavelengths of the extreme ultraviolet, including 171 (shown in gold) and 304 (shown in orange) angstroms.
Credits: NASA’s Goddard Space Flight Center/SDO

Coronal Holes



Coronal Holes are areas on the Sun that appear dark when observed in Extreme Ultraviolet and x-ray light. They are regions where the magnetic field on the solar surface opens up into space making it easier for coronal material to escape. Because these areas have less corona, they have less material to emit light and so appear dark compared to the rest of the corona. Coronal holes are believed to be the origin of the high-speed solar wind. They occur mostly near the north and south poles but they can occur at other places on the solar disk.
NASA questions whether an area of the sun’s open magnetic field will effect Earth’s electronic communications.

The Sun is not just a big bright ball. It has a complicated and changing magnetic field, which forms things like sunspots and active regions.

The magnetic field sometimes changes explosively, spitting out clouds of plasma and energetic particles into space and sometimes even towards Earth.




sun grid
The solar magnetic field changes on an 11 year cycle. Every solar cycle, the number of sunspots, flares, and solar storms increases to a peak, which is known as the solar maximum. Then, after a few years of high activity, the Sun will ramp down to a few years of low activity, known as the solar minimum. This pattern is called the “sunspot cycle”, the “solar cycle”, or the “activity cycle”.
The regions overlying sunspots are called active regions. Here the sun’s magnetic field becomes concentrated and twisted because of the motions of the solar atmosphere at and below the solar surface. As these regions become more complex they can eventually become unstable causing the release of the magnetic energy. This is analogous to twisting a rubber band tighter and tighter until it snaps releasing energy in the form of heat and motion. The same thing happens in the solar atmosphere with the active region magnetic fields. This release of energy heats up and accelerates solar material.

Solar Wind



The outer corona is heated up to such high energies that it eventually expands away from the Sun as a stream of electrons, protons and other atomic particles. The stream travels away from the Sun at speeds of around 200-400 km/s but can reach speeds of 900 km/s. The solar wind fills the entire solar system so all the planets sit inside the outer solar atmosphere. We live inside the atmosphere of a star. Sometimes concentrated high-speed solar wind streams come from the Sun and impacts the Earth. These can produce magnetic disturbances in the Earths upper atmosphere called a geomagnetic storm and produce the Southern and Northern Lights (The Aurora).

Solar Flares



Solar flares are a sudden, explosive release of magnetic energy in the form of electromagnetic radiation (most of the light spectrum, from radio waves to gamma-rays) and very fast atomic particles. Solar flares occur in regions of concentrated magnetic field such as sunspots.
Flares happen when the powerful magnetic fields in and around the sun reconnect. They’re usually associated with active regions, often seen as sun spots, where the magnetic fields are strongest.
Flares are classified according to their strength. The smallest ones are B-class, followed by C, M and X, the largest. Similar to the Richter scale for earthquakes, each letter represents a ten-fold increase in energy output. So an X is 10 times an M and 100 times a C. Within each letter class, there is a finer scale from 1 to 9. C-class flares are too weak to noticeably affect Earth. M-class flares can cause brief radio blackouts at the poles and minor radiation storms that might endanger astronauts.
Although X is the last letter, there are flares more than 10 times the power of an X1, so X-class flares can go higher than 9. The most powerful flare on record was in 2003, during the last solar maximum. It was so powerful that it overloaded the sensors measuring it. They cut-out at X28. A powerful X-class flare like that can create long lasting radiation storms, which can harm satellites and even give airline passengers, flying near the poles, small radiation doses. X flares also have the potential to create global transmission problems and world-wide blackouts. 
CREDIT: NASA Goddard Space Flight Center / SDO

Coronal Mass Ejections (CMEs)



Sometimes when magnetic energy is released the corona becomes so disturbed that large pieces of it are released into space. Billions of tons of solar material and magnetic field are hurled from the Sun into interplanetary space at speeds up to several million mph. As they move away from the Sun they expand becoming as wide across as the distance from the Earth to the Sun. CMEs can occur when filaments/prominences become unstable and fly away from the Sun. We call this a filament/prominence eruption.
On July 23, 2012, a massive cloud of solar material erupted off the sun’s right side, zooming out into space. It soon passed one of NASA’s Solar Terrestrial Relations Observatory, or STEREO, spacecraft, which clocked the CME as traveling between 1,800 and 2,200 miles per second as it left the sun. This was the fastest CME ever observed by STEREO.
Two other observatories – NASA’s Solar Dynamics Observatory and the joint European Space Agency/NASA Solar and Heliospheric Observatory — witnessed the eruption as well. The July 2012 CME didn’t move toward Earth, but watching an unusually strong CME like this gives scientists an opportunity to observe how these events originate and travel through space.
STEREO’s unique viewpoint from the sides of the sun combined with the other two observatories watching from closer to Earth helped scientists create models of the entire July 2012 event. They learned that an earlier, smaller CME helped clear the path for the larger event, thus contributing to its unusual speed.
Such data helps advance our understanding of what causes CMEs and improves modeling of similar CMEs that could be Earth-directed.
CREDIT: NASA Goddard Space Flight Center / SDO
This video features two model runs. One looks at a moderate coronal mass ejection (CME) from 2006. The second run examines the consequences of a large coronal mass ejection, such as The Carrington-Class CME of 1859. These model runs allow us to estimate consequences of a large event hitting Earth, so we can better protect power grids and satellites.
In an effort to understand and predict the impact of space weather events on Earth, the Community-Coordinated Modeling Center (CCMC) at NASA Goddard Space Flight Center, routinely runs computer models of the many historical events. These model runs are then compared to actual data to determine ways to improve the model, and therefore forecasts of future space weather events.
Sometimes we need an actual event to have data for comparison. Extreme space weather events are one example where researchers must test models with a rather limited set of data.
The vertical lines on the left represent magnetic field lines from the sun.
CREDIT: NASA Goddard Space Flight Center / SDO

The Difference Between a CME & a Solar Fare

Coronal mass ejections (CMEs) and flares are both solar events, but they are not the same. This video shows the differences between the two by highlighting specific features of each. 
CREDIT: NASA Goddard Space Flight Center

Solar Energetic Particles (SEPs)



When a large solar flare or CME occurs they can accelerate a large number of atomic particles, electrons, protons and various elements to very high energies. When SEPs impact the cameras on a spacecraft the recorded images look like a television screen with a lot of static or snow.

The Sun’s Magnetic Field

C. Alex Young is interviewed about the current solar cycle and what a magnetic flip means for the earth and NASA’s study of magnetic fields. Credit: NASA/GSFC/PFSS

Magnetism Facts

  • All magnetic fields are produced by moving or spinning charged particles…somewhere
  • Lines of magnetic force do not actually exist.
  • Magnetic poles always come in pairs.
  • The strongest magnetic field in nature is from the magnetar star SGR 1806-20, which has been estimated as 800 trillion Gauss.
  • A typical galaxy like the Milky Way has a magnetic field strength of about 0.000003 Gauss.
  • A refrigerator magnet has a strength of 100 Gauss.
  • A sunspot can have a magnetic field with a strength up to 10,000 Gauss, but they live very short lives!
  • Most magnetic storms on Earth happen during the Equinoxes in March and September
  • The sun’s magnetic poles flip their location on the sun every 22 years, called the Hale Magnetic Cycle.
  • Earth’s magnetic poles reverse their geographic locations every 300,000 years. The last event happened 780,000 years ago.
  • Magnetic pole ‘reversals’ have no effect on the rotational poles of a star or planet.
  • The geographic location of Earth’s North Magnetic Pole is currently moving nearly due-North at a speed of 100 meters per day.
  • Earth’s magnetic field is declining in strength by 5% every century.
  • Depending on your rate and direction of motion, a pure magnetic field can be turned into an electric field and vice versa.
  • Magnetic fields and electric fields are aspects of a more basic field in nature called the electromagnetic field.
  • A toy magnet produces more force on a paperclip than the entire mass of Earth through its gravity.
This visualization shows the position of the sun’s magnetic fields from January 1997 to December 2013. The field lines swarm with activity: The magenta lines show where the sun’s overall field is negative and the green lines show where it is positive. A region with more electrons is negative, the region with less is labeled positive. Additional gray lines represent areas of local magnetic variation. 
The entire sun’s magnetic polarity flips approximately every 11 years — though sometimes it takes quite a bit longer — and defines what’s known as the solar cycle. The visualization shows how in 1997, the sun shows the positive polarity on the top, and the negative polarity on the bottom. Over the next 12 years, each set of lines is seen to creep toward the opposite pole eventually showing a complete flip. By the end of the movie, each set of lines are working their way back to show a positive polarity on the top to complete the full 22 year magnetic solar cycle. 
At the height of each magnetic flip, the sun goes through periods of more solar activity, during which there are more sunspots, and more eruptive events such as solar flares and coronal mass ejections, or CMEs. The point in time with the most sunspots is called solar maximum. 

The Sun as seen by the Solar Dynamics Observatory (SDO)

Updated multiple times daily. Click for larger images.
AIA 171AIA 193AIA 211AIA 304
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The Sun as seen by the Solar and Heliospheric Observatory (SOHO)

Updated multiple times daily. Click for larger images.
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