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Kim Handle
(Brooklyn - United States)Kim worked for the Professional Development Department in Education at the New York Hall of Science in Corona, Queens for the past three years and has recently accepted a fellowship at Brooklyn College. Kim's undergraduate work was in environmental ...
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- Contributed By: Athabasca University
Objectives
It has been established that a planet is a spherical, nonluminous body that orbits a star. Planets are typically either rocky or gaseous (see Unit 2, Lesson 1), and can range in size anywhere from one-sixth the size of the Earth, to over ten times larger in diameter than the Earth. Jupiter is one such “gas giant,” and others are currently being discovered orbiting distant stars.
Stars, by contrast, are luminous, gaseous bodies, and are often much larger than planets. It is because of their luminosity and extremely large mass that we can see them from distances of over 38,550,000,000,000,000 kilometres! But instead of appearing as the giants they are, they appear as tiny pinpricks of light in the night sky.
Regardless of their size, all stars are created in the same manner. Stars are formed in nebulae (plural for nebula) - huge clouds of gas and dust. Over time, the gas - mostly hydrogen - attracts other particles of gas and dust together by gravity creating a very dense cloud in a process called accretion. The cloud eventually gets so massive that it collapses on itself, forming a protostar in the centre. The pressure is so great in the core of the cloud, that the temperature of the centre of the collapsed cloud is about 10,000,000 K, more than enough to ignite the hydrogen gas and keep it burning.
The core of this “baby star” ignites from the high temperature and produces energy through fusion, the process of combining two atoms together, turning hydrogen into helium in a protostar. This is the same process that occurs in a hydrogen bomb – weapons that are usually over a thousand times more powerful than the atomic bomb dropped on Hiroshima. The centre of stars essentially has explosions such as these occurring continuously.
The size of the original nebula determines the size of the star that is formed. Often, nebulae are so large that several stars are formed at the same time, creating binary systems of two stars, and star clusters of many stars. Not all of the matter in the nebula collapses into the protostar. Instead, dust and debris accrete to form planetessimals and eventually planets. It is from this point forward that the life of a star changes depending on how massive it is.
Did you know?
The standard unit of temperature used in astronomy is the Kelvin (K), named after Lord William Thomson Kelvin (1824-1907), a Scottish physicist and mathematician. 0 K is the same as -273 degrees Celsius, meaning water freezes at 273 K and boils at 373 K. 0 K is also referred to as “absolute zero” and is defined as the temperature at which there is a complete absence of heat energy, and hence, no particle movement. The temperature of outer space is just below 3 K!
Canadian Contributions
Dr. A.R. Taylor, of the University of Calgary, specializes in the research of star-formation areas in the Milky Way Galaxy. Educated at the University of Western Ontario and the University of British Columbia, Dr. Taylor currently oversees the Radio Astronomy Laboratory at the University of Calgary, a project that involves over 40 scientists worldwide, working toward understanding the nature of star formation areas and the effects of their surroundings on nebulae.
Throughout most of a star’s life, fusion continues to provide the star with energy, which it releases into space primarily as light. Stars live a very uneventful life as long as there is hydrogen to keep them burning.
Stars which are smaller than our Sun burn their hydrogen fuel relatively slowly, (much like a small car is more fuel efficient). They can live from 10 billion to 100 billion years. Most stars fall within this range. The Sun will live for 10 billion years in total, and is currently 5 billion years old.
Medium stars are hotter, burn their fuel more quickly, and live between 30 million and 5 billion years. The heaviest stars are so hot and burn their hydrogen so quickly that they live for less than 2 million years.
Did you know?
Astronomers classify stars by their temperature, and use letters to categorize them. From hottest to coolest, the classification goes O, B, A, F, G, K, M, so that an O star is hotter than a F star, which is hotter than a K star. The widely-used acronym used to remember the sequence is “Oh, Be A Fine Girl/Guy, Kiss Me!”
When a star exhausts the supply of hydrogen in its core, there is no longer any source of heat to support the core against gravity. The core of the star collapses under gravity's pull until it reaches a high enough density and temperature to start a new kind of fusion – fusing helium into carbon.
This is when small stars, like our Sun, stop burning. Once the helium is used up, the outside of the star expands to 10-100 times its original size (swallowing up the majority of the inner planets) and eventually it leaves behind a hot core of carbon imbedded in a new nebula of its own expelled gas. Radiation from this hot core will ionize the nebula producing a striking planetary nebula. The carbon core will eventually cool and become a white dwarf, the dense dim remnant of a once bright star.
Larger, hotter stars will continue burning after all the helium is gone – because, higher temperatures allow fusion to continue as carbon fuses into oxygen, neon, silicon, sulphur and other elements up to and including iron. Iron is the most stable form of nuclear matter and the largest atomic element that can be created in this process.
The iron core of the star cannot collapse, so when the star tries to collapse further, the remaining matter "bounces" off the core. This produces an even larger explosion known as a supernova. For up to one month, a single star undergoing a supernova can burn brighter than a galaxy of a billion stars.
Supernova explosions do two things that are important in the creation of matter:
- compare stars and planets
- distinguish between the life cycles of stars of different sizes
- establish how the Sun compares to other stars
It has been established that a planet is a spherical, nonluminous body that orbits a star. Planets are typically either rocky or gaseous (see Unit 2, Lesson 1), and can range in size anywhere from one-sixth the size of the Earth, to over ten times larger in diameter than the Earth. Jupiter is one such “gas giant,” and others are currently being discovered orbiting distant stars.
Stars, by contrast, are luminous, gaseous bodies, and are often much larger than planets. It is because of their luminosity and extremely large mass that we can see them from distances of over 38,550,000,000,000,000 kilometres! But instead of appearing as the giants they are, they appear as tiny pinpricks of light in the night sky.
Regardless of their size, all stars are created in the same manner. Stars are formed in nebulae (plural for nebula) - huge clouds of gas and dust. Over time, the gas - mostly hydrogen - attracts other particles of gas and dust together by gravity creating a very dense cloud in a process called accretion. The cloud eventually gets so massive that it collapses on itself, forming a protostar in the centre. The pressure is so great in the core of the cloud, that the temperature of the centre of the collapsed cloud is about 10,000,000 K, more than enough to ignite the hydrogen gas and keep it burning.
Gas pillars, star forming regions
The core of this “baby star” ignites from the high temperature and produces energy through fusion, the process of combining two atoms together, turning hydrogen into helium in a protostar. This is the same process that occurs in a hydrogen bomb – weapons that are usually over a thousand times more powerful than the atomic bomb dropped on Hiroshima. The centre of stars essentially has explosions such as these occurring continuously.
The size of the original nebula determines the size of the star that is formed. Often, nebulae are so large that several stars are formed at the same time, creating binary systems of two stars, and star clusters of many stars. Not all of the matter in the nebula collapses into the protostar. Instead, dust and debris accrete to form planetessimals and eventually planets. It is from this point forward that the life of a star changes depending on how massive it is.
Caption: 1. As the particles in a nebula of gas and dust attract each other,
the nebula condenses to a smaller size. 2. As it gets smaller, it becomes
denser and eventually collapses. 3. The centre of the nebula becomes so hot
that the gas is ignited, and 4. it becomes a protostar.
the nebula condenses to a smaller size. 2. As it gets smaller, it becomes
denser and eventually collapses. 3. The centre of the nebula becomes so hot
that the gas is ignited, and 4. it becomes a protostar.
Did you know?
The standard unit of temperature used in astronomy is the Kelvin (K), named after Lord William Thomson Kelvin (1824-1907), a Scottish physicist and mathematician. 0 K is the same as -273 degrees Celsius, meaning water freezes at 273 K and boils at 373 K. 0 K is also referred to as “absolute zero” and is defined as the temperature at which there is a complete absence of heat energy, and hence, no particle movement. The temperature of outer space is just below 3 K!
Canadian Contributions
Dr. A.R. Taylor, of the University of Calgary, specializes in the research of star-formation areas in the Milky Way Galaxy. Educated at the University of Western Ontario and the University of British Columbia, Dr. Taylor currently oversees the Radio Astronomy Laboratory at the University of Calgary, a project that involves over 40 scientists worldwide, working toward understanding the nature of star formation areas and the effects of their surroundings on nebulae.
Throughout most of a star’s life, fusion continues to provide the star with energy, which it releases into space primarily as light. Stars live a very uneventful life as long as there is hydrogen to keep them burning.
Stars which are smaller than our Sun burn their hydrogen fuel relatively slowly, (much like a small car is more fuel efficient). They can live from 10 billion to 100 billion years. Most stars fall within this range. The Sun will live for 10 billion years in total, and is currently 5 billion years old.
Medium stars are hotter, burn their fuel more quickly, and live between 30 million and 5 billion years. The heaviest stars are so hot and burn their hydrogen so quickly that they live for less than 2 million years.
The top left corner of Orion features the star Betelgeuse (pronounced beetle-juice), which
is a red giant – a very large, cool star. Its red colour indicates its low temperature.
The opposite corner (bottom right) features the star Rigel, a blue-white, very hot star.
is a red giant – a very large, cool star. Its red colour indicates its low temperature.
The opposite corner (bottom right) features the star Rigel, a blue-white, very hot star.
Did you know?
Astronomers classify stars by their temperature, and use letters to categorize them. From hottest to coolest, the classification goes O, B, A, F, G, K, M, so that an O star is hotter than a F star, which is hotter than a K star. The widely-used acronym used to remember the sequence is “Oh, Be A Fine Girl/Guy, Kiss Me!”
When a star exhausts the supply of hydrogen in its core, there is no longer any source of heat to support the core against gravity. The core of the star collapses under gravity's pull until it reaches a high enough density and temperature to start a new kind of fusion – fusing helium into carbon.
This is when small stars, like our Sun, stop burning. Once the helium is used up, the outside of the star expands to 10-100 times its original size (swallowing up the majority of the inner planets) and eventually it leaves behind a hot core of carbon imbedded in a new nebula of its own expelled gas. Radiation from this hot core will ionize the nebula producing a striking planetary nebula. The carbon core will eventually cool and become a white dwarf, the dense dim remnant of a once bright star.
The Cat’s Eye Nebula (above) and the Eskimo Head Nebula (below),
two examples of planetary nebulae.
two examples of planetary nebulae.
Larger, hotter stars will continue burning after all the helium is gone – because, higher temperatures allow fusion to continue as carbon fuses into oxygen, neon, silicon, sulphur and other elements up to and including iron. Iron is the most stable form of nuclear matter and the largest atomic element that can be created in this process.
The iron core of the star cannot collapse, so when the star tries to collapse further, the remaining matter "bounces" off the core. This produces an even larger explosion known as a supernova. For up to one month, a single star undergoing a supernova can burn brighter than a galaxy of a billion stars.
The Crab Nebula is all that is left after a supernova observed by
Chinese astronomers in the year 1054!
Chinese astronomers in the year 1054!
Supernova explosions do two things that are important in the creation of matter:
- They release all of the elements created in the star through fusion out into space
- The extreme heat from the explosion allows the formation of all the elements heavier than iron, such as copper, silver, gold, and lead, and releases them into space
Objectives
As mentioned in Unit 6, Lesson 1, the Sun produces radiation when hydrogen fuses into helium, due to the high pressure and temperature in the core of the star. Nuclear fusion occurs when light atoms combine to form heavier atoms, releasing great amounts of energy in the process.
Did you know?
Radiation's getting a bad reputation comes from radioactive decay like what happens with uranium, a radioactive material. With radioactivity, the nucleus of the material is actually unstable in its present state and it naturally splits, giving off smaller particles such as neutrons, protons, or slightly larger clusters of both. These escaping particles are also called radiation, specifically alpha rays and beta rays. As well, this process sometimes releases gamma rays, which is a true form of radiation: light.
Specifically, four hydrogen atoms combine to make one helium atom. However, the mass of a helium nucleus is less than the mass of the four hydrogen atoms which fused to create it. The extra mass is converted into energy through the famous relationship E=mc2, where m is the mass to be converted, and c is the speed of light. This process occurs in all stars, including the Sun, which is composed of about 90% hydrogen.
The difference between one helium atom and four hydrogen atoms is a mere 0.000 000 000 004 Joules of energy (it takes about 36 000 Joules to run a toaster for 30 seconds!). Though it may not seem like much, converting just one gram of hydrogen into helium creates 350 000 000 000 000 000 000 000 000 000 000 000 Joules – over a billion billion times the energy created in a hydrogen bomb!
The main body of the Sun can then be divided into three sections, defined by changes in the behaviour of the heat energy. As aforementioned, fusion occurs in the core of the Sun. From there, the heat energy pushes outward from the core in an effort to “float” to the surface. In a sense, this is what stabilizes the star and prevents it from collapsing inward due to intense gravitational pressures. The temperature of the core of the Sun is about 15 000 000°C.
In the radiative zone, the energy from the nuclear reactions in the core continues to radiate outward, traveling – more or less – in a straight line, until it reaches the convective zone. By the time the energy has reached this top 200 000km of the star, it has cooled considerably. This difference in temperature causes convective motion: warm gas rises even closer toward the surface due to a lower density, cools as it reaches the outer edge of the Sun and becomes more dense, and then begins to fall back toward the core. As it falls, the gas regains heat energy and begins to rise toward the surface again, continuing the cycle. At the top of its motion, some heat is also released into space, and eventually reaches us here on Earth.
Try This!
Inflate a balloon to a medium size, and knot it. Place it in a freezer for a few hours. What happens? As the air inside the balloon cools, it cannot support the elasticity of the balloon, which loses its shape. Warming up the balloon again will cause it to “re-inflate” as the hot air pushes out from the centre of the balloon – just like the heat energy pushes out from the centre of a star.
Did You Know ? Surprisingly, it takes more than a million years for the energy to get from the core of the Sun to the corona (leaving the Sun) because of the high density of the Sun!
We can see evidence of convective motion in the granules observed on the photosphere (surface) of the Sun. Bright areas are the hot gas rising while the dark areas surrounding the bright spots are the cool gas falling back toward the centre. Each granule is between 1000km and 5000km in diameter, and only lasts a few minutes before moving or changing shape, due to the constant motion of the gas. The average temperature of the photosphere is about 5700°C – still very hot, but certainly not as hot as the core.
- explain how the Sun produces radiation
- distinguish between different regions in the cross-section of a star
- describe the granules on the surface of the Sun
Particles from the corona travel away
from the Sun and stretch far out
into space
from the Sun and stretch far out
into space
As mentioned in Unit 6, Lesson 1, the Sun produces radiation when hydrogen fuses into helium, due to the high pressure and temperature in the core of the star. Nuclear fusion occurs when light atoms combine to form heavier atoms, releasing great amounts of energy in the process.
When small, light atoms combine to form heavier atoms,
a great deal of energy is released.
a great deal of energy is released.
Did you know?
Radiation's getting a bad reputation comes from radioactive decay like what happens with uranium, a radioactive material. With radioactivity, the nucleus of the material is actually unstable in its present state and it naturally splits, giving off smaller particles such as neutrons, protons, or slightly larger clusters of both. These escaping particles are also called radiation, specifically alpha rays and beta rays. As well, this process sometimes releases gamma rays, which is a true form of radiation: light.
Specifically, four hydrogen atoms combine to make one helium atom. However, the mass of a helium nucleus is less than the mass of the four hydrogen atoms which fused to create it. The extra mass is converted into energy through the famous relationship E=mc2, where m is the mass to be converted, and c is the speed of light. This process occurs in all stars, including the Sun, which is composed of about 90% hydrogen.
The difference between one helium atom and four hydrogen atoms is a mere 0.000 000 000 004 Joules of energy (it takes about 36 000 Joules to run a toaster for 30 seconds!). Though it may not seem like much, converting just one gram of hydrogen into helium creates 350 000 000 000 000 000 000 000 000 000 000 000 Joules – over a billion billion times the energy created in a hydrogen bomb!
The main body of the Sun can then be divided into three sections, defined by changes in the behaviour of the heat energy. As aforementioned, fusion occurs in the core of the Sun. From there, the heat energy pushes outward from the core in an effort to “float” to the surface. In a sense, this is what stabilizes the star and prevents it from collapsing inward due to intense gravitational pressures. The temperature of the core of the Sun is about 15 000 000°C.
In the radiative zone, the energy from the nuclear reactions in the core continues to radiate outward, traveling – more or less – in a straight line, until it reaches the convective zone. By the time the energy has reached this top 200 000km of the star, it has cooled considerably. This difference in temperature causes convective motion: warm gas rises even closer toward the surface due to a lower density, cools as it reaches the outer edge of the Sun and becomes more dense, and then begins to fall back toward the core. As it falls, the gas regains heat energy and begins to rise toward the surface again, continuing the cycle. At the top of its motion, some heat is also released into space, and eventually reaches us here on Earth.
The interior layers of the Sun.
Try This!
Inflate a balloon to a medium size, and knot it. Place it in a freezer for a few hours. What happens? As the air inside the balloon cools, it cannot support the elasticity of the balloon, which loses its shape. Warming up the balloon again will cause it to “re-inflate” as the hot air pushes out from the centre of the balloon – just like the heat energy pushes out from the centre of a star.
Did You Know ? Surprisingly, it takes more than a million years for the energy to get from the core of the Sun to the corona (leaving the Sun) because of the high density of the Sun!
We can see evidence of convective motion in the granules observed on the photosphere (surface) of the Sun. Bright areas are the hot gas rising while the dark areas surrounding the bright spots are the cool gas falling back toward the centre. Each granule is between 1000km and 5000km in diameter, and only lasts a few minutes before moving or changing shape, due to the constant motion of the gas. The average temperature of the photosphere is about 5700°C – still very hot, but certainly not as hot as the core.
Up close, granules look like little bubbles on the surface of the Sun – and that’s exactly what
they are! Bright spots are hot, rising gas, while darker lines indicate cool, falling gas.
they are! Bright spots are hot, rising gas, while darker lines indicate cool, falling gas.
Objectives
Most commonly, highly charged particles from weak coronal mass ejections interact with the Earth’s atmosphere to create one of the most beautiful and enchanting sights in Canadian skies: the Northern Lights (aurora borealis). There is more information on this topic in Unit 5, Lesson 2. These natural light shows are very pretty, and relatively harmless.
More intense coronal mass ejections of radiation aimed directly at the Earth can do greater amounts of damage. In the past, large amounts of radiation impacting the Earth have caused disruptions in both satellite communication signals and power grids, causing large-scale power outages. In 1997, radiation from a solar flare hit a telecommunication satellite, rendering it temporarily inoperable. Thousands of people relying on pager service, such as doctors and emergency personnel, were rendered helpless.
Canadian Connection Canada has experienced its fair share of coronal mass ejection-related disasters. In 1972, a high-voltage transformer at the British Columbia Hydroelectric Authority exploded. A change in the Earth’s magnetic field, due to solar plasma interacting with the magnetosphere, caused a spike in electrical current, leading to the explosion. In 1989, nearly the entire province of Quebec lost power when solar plasma interacted with the Earth. Millions of people were left in the dark.
Satellites aren’t the only objects in space susceptible to damage from solar radiation. Astronauts must be very careful not to expose themselves to radiation from a flare. When they are not protected by the Earth’s atmosphere, even wearing highly protective space suits will not shield them from severe radiation poisoning during times of high solar activity. Space missions are planned around times of coronal mass ejections, and during a spacewalk, the space shuttle always positions itself between the astronaut and the Sun, just in case an unpredicted coronal mass ejection occurs.
However, it is not always the coronal mass ejections that do damage to the Earth. Instead, it is what is sometimes found at the root of the flare: sunspots. Like the Earth, the Sun also has a magnetic field surrounding it. Since the Sun is mostly gas and plasma, however, an interesting phenomenon occurs as it rotates. Different locations on the surface of the Sun rotate at different rates, causing the surface material – and the magnetic field lines – to twist around on themselves. If a magnetic field line gets twisted enough, it can bulge out from the surface of the Sun, carrying with it charged particles from the surface.
While prominences look as though they are fixed to the surface of the Sun, they also release great quantities of radiation and ionized particles into space, much like coronal mass ejections.
At the base of these magnetic field line loops – and hence at the base of the prominences – the surface of the Sun is also altered. The hot gas which gets sucked up into the prominence leaves behind a darker, cooler area. Imagine a stovetop element: when cool, the element is black. However, when heated the element glows a bright orange-red. Similarly, the hot surface of the Sun emits orange-yellow light while the cooler areas appear black. This makes them very easy to spot by ground-based observers.
Did you know? On average, sunspots are about 1500°C cooler than their surroundings! Though they might look quite small through a telescope, sunspots are usually about the same size as the entire planet Earth!
Some years, there are large numbers of sunspots on the surface of the Sun, while during others years, only a few are observed. After many decades of watching and counting sunspots, astronomers have determined that the quantity of spots follows an 11-year cycle, also called the sunspot cycle. Over the 11-year period, the number of sunspots on the surface of the Sun declines to a minimum and then increases again. The last solar maximum – the point in the cycle where there are the most sunspots – occurred in the year 2000, meaning the next peak in sunspot activity will be in approximately the year 2011.
Because these maxima and minima can be predicted, we can therefore also predict the occurrence of a greater number of prominences and a greater risk to the Earth because of them. It is also interesting to note that by knowing the relative number of sunspots on the surface of the Sun, we can predict long-term weather patterns!
The “Little Ice Age” was a period of time between the late 1500s and the mid 1800s when glaciers advanced, winters in the northern hemisphere were unusually cold and the summer growing seasons were shortened. These conditions were well-documented in art and writings from the times, and are still, to this day, perceived as being unusual. One of the leading theories for why the climate changed so dramatically has to do with the number of sunspots observed during that same time period. Solar activity was extremely low, with some years having no sunspots at all. Fewer sunspots indicates fewer releases of solar radiation and hence less solar energy reaching the Earth.
Over a few years, this does not make a large impact on our climate. However over several decades, the lower amount of overall radiation reaching the Earth can have an impact on long-term weather patterns. During the next solar maximum (~2011), it is expected that there will be a greater number of sunspots than average. Will this make our climate even warmer?
- explain the effects of solar coronal mass ejections on the Earth
- compare the Earth’s climate during peaks and lows of the sunspot cycle
Most commonly, highly charged particles from weak coronal mass ejections interact with the Earth’s atmosphere to create one of the most beautiful and enchanting sights in Canadian skies: the Northern Lights (aurora borealis). There is more information on this topic in Unit 5, Lesson 2. These natural light shows are very pretty, and relatively harmless.
Plasma errupts from the Sun
More intense coronal mass ejections of radiation aimed directly at the Earth can do greater amounts of damage. In the past, large amounts of radiation impacting the Earth have caused disruptions in both satellite communication signals and power grids, causing large-scale power outages. In 1997, radiation from a solar flare hit a telecommunication satellite, rendering it temporarily inoperable. Thousands of people relying on pager service, such as doctors and emergency personnel, were rendered helpless.
Canadian Connection Canada has experienced its fair share of coronal mass ejection-related disasters. In 1972, a high-voltage transformer at the British Columbia Hydroelectric Authority exploded. A change in the Earth’s magnetic field, due to solar plasma interacting with the magnetosphere, caused a spike in electrical current, leading to the explosion. In 1989, nearly the entire province of Quebec lost power when solar plasma interacted with the Earth. Millions of people were left in the dark.
Satellites aren’t the only objects in space susceptible to damage from solar radiation. Astronauts must be very careful not to expose themselves to radiation from a flare. When they are not protected by the Earth’s atmosphere, even wearing highly protective space suits will not shield them from severe radiation poisoning during times of high solar activity. Space missions are planned around times of coronal mass ejections, and during a spacewalk, the space shuttle always positions itself between the astronaut and the Sun, just in case an unpredicted coronal mass ejection occurs.
However, it is not always the coronal mass ejections that do damage to the Earth. Instead, it is what is sometimes found at the root of the flare: sunspots. Like the Earth, the Sun also has a magnetic field surrounding it. Since the Sun is mostly gas and plasma, however, an interesting phenomenon occurs as it rotates. Different locations on the surface of the Sun rotate at different rates, causing the surface material – and the magnetic field lines – to twist around on themselves. If a magnetic field line gets twisted enough, it can bulge out from the surface of the Sun, carrying with it charged particles from the surface.
As charged particles from the surface of the Sun travel along twisted magnetic field
lines, they create a prominence – a giant loop of ionized gas protruding from the
surface. Due to the shape of the magnetic field lines, prominences nearly always
exhibit a loop-shape.
lines, they create a prominence – a giant loop of ionized gas protruding from the
surface. Due to the shape of the magnetic field lines, prominences nearly always
exhibit a loop-shape.
While prominences look as though they are fixed to the surface of the Sun, they also release great quantities of radiation and ionized particles into space, much like coronal mass ejections.
At the base of these magnetic field line loops – and hence at the base of the prominences – the surface of the Sun is also altered. The hot gas which gets sucked up into the prominence leaves behind a darker, cooler area. Imagine a stovetop element: when cool, the element is black. However, when heated the element glows a bright orange-red. Similarly, the hot surface of the Sun emits orange-yellow light while the cooler areas appear black. This makes them very easy to spot by ground-based observers.
A close-up view of a sunspot illustrates how cooler areas of the surface of the Sun
appear darker than their hotter surroundings. Magnetic field lines are invisible
– we cannot see them emanating from the sunspot.
appear darker than their hotter surroundings. Magnetic field lines are invisible
– we cannot see them emanating from the sunspot.
Did you know? On average, sunspots are about 1500°C cooler than their surroundings! Though they might look quite small through a telescope, sunspots are usually about the same size as the entire planet Earth!
Some years, there are large numbers of sunspots on the surface of the Sun, while during others years, only a few are observed. After many decades of watching and counting sunspots, astronomers have determined that the quantity of spots follows an 11-year cycle, also called the sunspot cycle. Over the 11-year period, the number of sunspots on the surface of the Sun declines to a minimum and then increases again. The last solar maximum – the point in the cycle where there are the most sunspots – occurred in the year 2000, meaning the next peak in sunspot activity will be in approximately the year 2011.
Because these maxima and minima can be predicted, we can therefore also predict the occurrence of a greater number of prominences and a greater risk to the Earth because of them. It is also interesting to note that by knowing the relative number of sunspots on the surface of the Sun, we can predict long-term weather patterns!
The “Little Ice Age” was a period of time between the late 1500s and the mid 1800s when glaciers advanced, winters in the northern hemisphere were unusually cold and the summer growing seasons were shortened. These conditions were well-documented in art and writings from the times, and are still, to this day, perceived as being unusual. One of the leading theories for why the climate changed so dramatically has to do with the number of sunspots observed during that same time period. Solar activity was extremely low, with some years having no sunspots at all. Fewer sunspots indicates fewer releases of solar radiation and hence less solar energy reaching the Earth.
Over a few years, this does not make a large impact on our climate. However over several decades, the lower amount of overall radiation reaching the Earth can have an impact on long-term weather patterns. During the next solar maximum (~2011), it is expected that there will be a greater number of sunspots than average. Will this make our climate even warmer?
