This page contains questions and answers from our readers relating to solar physics. Please DO NOT HESITATE to send us any solar related questions that you may have, especially if there is something within these pages that you did not understand or simply would like to know more about. Somebody else just might be wondering the same thing and this page is anxiously sitting here waiting to provide that information!
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amateur radio astronomy
astronauts and flares
cause of solar flares
climate and solar activity
Compton Gamma Ray Observatory
coronal mass ejection
current images of the Sun
damage to satellites
duration of a flare
electrical power failures
forecast of solar activity
frequency of flares
GOES weather satellites
intensity of flares - graphs
the ionosphere and flares
Is the Sun burning?
migraines and flares
particles emitted from flares
radio communication and flares
space shuttle and flares
speed of ejected material
stars and flares
sunspot numbers (counts)
today's flare activity
weather and flares
Here is a series of questions from a reader in Toronto, Canada:
Are all solar flares of the same intensity?
Solar flares are not all the same intensity. In fact, there are many more low-intensity flares than high-intensity flares. The number of flares increases with decreasing intensity right on down to the limit of the sensitivity of the instruments that have been used to detect them.
How often do solar flares occur at solar minimum and at solar maximum, on a day-to-day basis?
This depends upon the flare intensity. The statistics of flares that were detected from 1980 through 1989 with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission show that flares occurred at an average rate of about one per day at solar minimum. At solar maximum the average rate was as high as 20 per day (averaged over a 6 month interval). So the rate at solar maximum is roughly a factor of ten greater than at solar minimum. It is important to realize, however, that the flare rate is very irregular. There can be long periods of time at solar minimum when no detectable flares occur. Then a large active region can form and produce many flares in just a few days. If you are interested in more detail, plots of these things can be found in a paper by Crosby, Aschwanden, and Dennis published in volume 143 of the journal Solar Physics (page 275, 1993).
Tables and graphs of an index that measures daily solar flare activity can be found at
What is the duration of a solar flare - minutes? hours? days?
The duration of a solar flare in the energetic hard x-rays is seconds to minutes (this is called the impulsive phase of the flare). The evolution of the less energetic soft x-rays from a flare is more gradual. This emission can last from minutes to hours.
What is the velocity of plasma from a solar flare as it heads toward Earth?
An important point needs to be made before answering this question. Geomagnetic storms are observed to be primarily if not entirely associated with large ejections of mass from the Sun called coronal mass ejections. Coronal mass ejections (CMEs) were originally thought to be driven by solar flares. It is now known that many CMEs occur without any observable flare associated with them. Likewise, many flares occur for which no associated CME is observed. Therefore, phenomena associated with geomagnetic storms such as power grid failures, many satellite failures, and the aurora are most closely associated with CMEs rather than flares. On the other hand, interruptions in radio communications and expansion of the Earth's atmosphere, resulting in increased drag on satellites in low Earth orbit, are associated with radiation from flares. The electromagnetic radiation from flares travels at the speed of light and reaches the Earth in eight minutes. CMEs, on the other hand, travel at speeds from 100 to 1000 kilometers per second and take several days to reach the Earth. The relative importance of studying CMEs versus flares for the purpose of predicting many phenomena at the Earth is presently a subject of much controversy.
One solar flare crippled the communications satellite Anik E1 permanently and temporarily interfered with other satellites - why weren't all affected equally?
The best way to protect sensitive components from energetic particles and, in some cases, radiation is to shield them. (Also, special "hardened" electronic components are used in space.) Shielding adds weight to the satellite and, therefore, increases its cost. The sensitive components on Anik E1 were presumably not shielded well enough to withstand the large storm that occurred. The effects of the storm are not the same at all locations. It may be that Anik was damaged while other satellites were not because it just happened to be in a location where the effects of the storm were particularly intense. The Anik satellites are in high, geosynchronous orbits that expose them to the Earth's radiation belts. But other satellites are in similar orbits.
My answer to this question is just an "educated guess". If anyone out there knows more about this incident, please write!
A question from Ventura, California:
Where can I find some information pertaining to the effect of solar flares on power transmission lines and the amount of power that could be expected to develop on the lines based on past flares?
Two articles on this topic by John G. Kappenman are Geomagnetic Storms & Impacts on Power Systems: Lessons Learned from Solar Cycle 22 and Outlook for Solar Cycle 23 and Geomagnetic Storms Can Threaten Electric Power Grid.
Also see Power Failure in Canada During 1989 from the IPS Radio & Space Services and A Primer on the Space Environment from the NOAA Space Environment Center.
From an unknown location:
Do you know of any Web site that supplies daily information about solar flares, and which graphs the information on a daily basis over time?
Also, from Dr. Raul Ibarra in Guadalajara, Mexico:
I came across some medical literature that mentions that when SOLAR FLARES are "more intense" - MIGRAINES AGGRAVATE or EXACERBATE. The same has been reported to the number of patients in Intensive Care Units and in Emergency Rooms. So, there is a DIRECT CORRELATION. For my clinical practice I've developed a Chart called "Monthly Chronogram", where the patient reports during one month the date and the hour of the "aggravations" of her/his disease. Is there a chart that shows the intensity of solar flares in graphical images for each month of 1996?
The NOAA Space Environment Laboratory has this kind of data. I suggest looking at their plots of the soft x-ray emission from the Sun. The most recent plot can be found at
Plots for the entire year can be found at
These plots show measurements of the soft x-ray flux from the Sun over a time interval of three days (Universal Time). The data were obtained by a detector on each of two GOES weather satellites. Each detector observes in two soft x-ray energy bands. Therefore each plot shows four curves. The letters on the right side of the plot (A, B, C, M, & X) represent a classification scheme for the intensity of flares. A flare is a C flare if its peak flux falls between the horizontal lines labeled C and M. The peak flux of an M flare falls between the lines labeled M and X. The flare is also given a number between 1 and 10, depending upon where the peak falls between the lines. A really intense X flare can have a number greater than 10.
To see what large flares look like, look at the plot 20050119_xray.gif containing January 19, 2005. This period contains an X4 flare on Jan. 17, an X1 flare on Jan. 19, and four M flares. Compare this with the very quiet period shown in 20070724_xray.gif and you should get a good feel for the data.
You can also look at plots of flares observed by the Compton Gamma Ray Observatory (CGRO) at
Find the section titled "GIF versions of the BATSE Solar Flare Light Curve plots" and click on the year. Click on 1996 or 1997 to see some recent flare plots. You can find the largest flares observed by CGRO by finding the largest numbers in the "Peak Rate" column. The time axis on these plots is also UT. These plots are posted a few days to a week after the flare occurs.
If you compare the NOAA plots with the CGRO plots, you will see that the flares in the NOAA plots last longer than those in the CGRO plots. This is because the NOAA plots are of soft x-rays, while the CGRO plots show higher energy, hard x-rays. The hard x-rays are primarily from energetic electrons that do not last long, while the soft x-rays are primarily from ten-million degree gas that takes a while to cool.
Showing a convincing correlation between solar activity and human phenomena has been notoriously difficult. Even if a correlation appears to be statistically significant, showing that the phenomenon is in fact directly related to solar activity is difficult, and a physical (or biological) explanation for the relationship is required before the correlation will be generally accepted in the scientific community.
Questions from Doug Kjos of the Plaza Public School in Plaza, North Dakota:
What's the lifespan profile of sunspots?
The lifespan of a sunspot can be anywhere from less than an hour for a small spot to as long as several months.
I've seen reference to a formal naming system for sunspots. Where can this be found?
There is no naming or numbering system for sunspots. There is a system for numbering active regions, however. An active region can contain one or more spots. The National Oceanic and Atmospheric Administration (NOAA) numbers active regions consecutively as they are observed on the Sun. According to David Speich at NOAA, an active region must be observed by two observatories before it is given a number (a region may be numbered before its presence is confirmed by another observatory if a flare is observed to occur in it, however). The present numbering system started in 1973 and has been consecutive since then. Active region numbers are presently in the 8000s. An example of an active region "name" is "AR5128" (AR for Active Region) or "NOAA Region 5128". Since we only see active regions when they are on the side of the Sun facing the Earth, and the Sun rotates approximately once every 27 days (the equator rotates faster than the poles), the same active region may be seen more than once (if it lasts long enough). In this case the region will be given a new number. Hence, a long-lived active region may get several numbers.
A question from Kaye Horton in Lavina, Montana:
Do solar flares have an effect on the weather?
There is no known relationship between individual solar flares and weather.
There is, however, evidence for a relationship between the solar activity cycle and global
climate. The best known case is the correlation of a long period of solar inactivity
called the Maunder Minimum (1645-1715) with the lowest temperatures recorded during the
"Little Ice Age" that occurred from 1500 to 1850. Almost no spots were observed
on the Sun during this period. There is evidence for the correlation of other periods of
low solar activity with cooler temperatures on Earth as well.
The temperature above the north pole in the stratosphere (about 10 km above the surface of the earth) appears to be correlated with the 11 year sunspot cycle. The stratospheric temperature above the pole is relatively warm or cool when the Sun is active, depending upon which way stratospheric winds are blowing above the equator. There are also other climatic effects that appear to be associated with the sunspot cycle.
The physical mechanism responsible for these apparent correlations is not known. Until such a mechanism is found, the existence of a direct relationship between the solar cycle and climate will not be generally accepted.
If you are interested in learning more about this, check out the article "The Sun-Climate Question: Is there a Real Connection?" by George C. Reid.
Two questions from Pennsylvania:
How are solar flares caused exactly? Can any elements such as metals or chemicals cause solar flares to erupt on the Sun's surface? If so, what kind of elements or chemicals?
Solar flares are thought to result from the build up and explosive release of
magnetic energy in the solar
atmosphere. The outer layer of the Sun is convective, meaning that the gas rolls up and down like in a pot of
boiling water. This ionized gas (plasma) drags the Sun's magnetic field with it, twisting it
and strengthening it. In some regions the magnetic field becomes particularly strong and
breaks out into the solar atmosphere as discrete, loop-like structures. In active regions
where flares occur, these structures either interact or become internally unstable, giving
a flare. The signs of a flare are gas rapidly heated to high temperatures, electrons and ions accelerated to high energies, and bulk mass motions. The energy in
the magnetic field is thought to be converted into these things through a process called magnetic
reconnection, in which oppositely directed magnetic field lines "break" and
connect to each other and part of their energy is transferred to the gas in the solar
atmosphere. This is the basic picture. Some aspects of it may not be entirely correct and
many of the details are not yet understood.
No particular metal or chemical is believed to cause a solar flare. Rather, the flare results from the local interaction of the solar magnetic field with the gas in the outer layer of the Sun and the solar atmosphere.
Can flares erupt on any star's surface, or just the Sun's?
Flares do erupt on the surface of other stars. Most stars are in fact too far away for flares having the brightness of those that occur on the Sun to be observed. However, there are certain stars, called flare stars, that produce flares that are much more energetic than solar flares. There are also certain pairs of stars (close binary stars) that apparently flare as a result of their interaction. We can learn a lot about our Sun and the general processes that drive flares by comparing the similarities and differences in these different stars and star systems.
A question from Peter Curran in Rotselaar, Belgium:
I am trying to find an historical record of sunspot activity. Do you have such a record or could you direct me to another possible source?
Sunspot numbers are available from the NOAA National Geophysical Data Center at the following FTP site:
Here you will find files containing yearly mean sunspot numbers from 1700 to the present, monthly mean sunspot numbers from 1749 to the present, and daily counts from 1980 to the present.
Note that these sunspot numbers are not simply counts of the number of spots on the Sun. They are a weighted sum of the number of sunspot groups and the number of individual spots counted on the Sun each day. NOAA has a web page describing this at
You can also find useful information about sunspot numbers at the Australian IPS "Interesting Facts and Educational Material" page.
Sunspot numbers and information can be found on CompuServe as well (GO SUNSPOT).
Several frequently asked questions:
Is there a Web site where current solar activity can be acquired?
Where can I find current images of the Sun?
Where can I find a Web site that forecasts solar activity?
Daily information about solar flare activity and a forecast of solar activity can be found at the NOAA "Today's Space Weather" Web page. The 3-day plot of x-ray flux is particularly useful for quickly seeing if a flare has occurred. Click here for a description of this plot.
Current images of the Sun that can be found at
Recent images of solar active regions can be found at
NOAA space weather advisories can be found at
The Australian Ionospheric Prediction Service (IPS) also has a daily summary of solar activity and forecast at
From an unknown location:
Do flares have a measured effect on the ionosphere?
Solar flares do have an effect on the ionosphere. The evolution of the x-ray emission from a flare is mimicked in the ionosphere as a Sudden Ionospheric Disturbance (SID). This particularly affects radio communications at frequencies below around 30 MHz that depend upon the reflection of the signal off the ionosphere for long distance communications. A good place to learn more about this is the Australian Ionospheric Prediction Service's (IPS) "Interesting Facts and Educational Material" Web page.
From a student in Sao Paulo, Brazil:
I am doing a research project on detecting solar flares with a long wave radio. If you could please help me out in any way, or suggest a different way of detecting flares that is not too expensive, I will be grateful.
I can suggest several possibilities. Here are two books that include information about solar radio receivers that an amateur could build:
Beck, R., Hilbrecht, H., Reinsch, K., and Volker, P., Solar Astronomy Handbook. Willmann-Bell, Inc. (Richmond, VA) ISBN 0-943396-47-6 (1995).
Taylor, Peter O., Observing the Sun. Cambridge University Press, ISBN 0-521- 40110-0 (1991).
Also, you should check out the Society of Amateur Radio Astronomers Web site. This site contains a page of additional references. The experienced amateur radio astronomers who belong to this Society can provide motivation and invaluable practical information for such a project.
Another question from an unknown location:
I would greatly appreciate it if you would tell me which specific types of ions or particles are emitted from a solar flare.
There is an active field of space research dedicated to studying the composition of ions from the Sun in general, and specifically from solar flares. The simple answer to your question is that the types of particles detected in space from solar flares reflect the composition of the solar corona. The corona is mostly hydrogen, so a lot of energetic protons and electrons are observed. Since the protons are heavier and more energetic than the electrons, they are of particular concern because of the damage they can do to astronauts and to electronic equipment. The next most abundant element is helium, which is observed along with its isotope helium-3. Heavier ions such as carbon, oxygen, silicon, iron, and many others are present at a much lower level. The relative abundance and charge state of these ions provide important clues to the processes that energize them.
If you have access to journals and are prepared to deal with a technical paper, I suggest that you look at a paper titled "Composition of Energetic Particles from Solar Flares" by Garrard and Stone in the journal Advances in Space Research (Volume 14, No. 10, pp. 589-598, 1994). This will give you an introduction to this area of research and provide references to other papers on the subject.
From Hezzick Doyle at Western Kentucky University:
What special precautions are taken aboard the space shuttle to prevent damage to their electronic components and how are the astronauts protected?
The primary protection is the Shuttle orbit. The altitude of the Shuttle is
typically 300-500 km (200-300 miles)
above sea level. This is well within the Earth's magnetic field (the "magnetosphere") and below the Earth's radiation belts (the van Allen belts). This magnetic
field protects us from most of the charged particles from space, including from the Sun.
Since these charged particles can travel along the Earth's magnetic field to lower
altitudes at the poles, however, the Shuttle orbit also avoids the regions around the
north and south poles. (Enhanced fluxes of charged particles around the poles are
responsible for the beautiful auroral displays visible at high latitudes). Manned missions
to the Moon or Mars are much more dangerous, since these require leaving the protection of
the Earth's magnetic field.
Some high-energy charged particles ("cosmic rays") do penetrate down to the Shuttle orbit and to the surface of the Earth. Collisions with the Earth's atmosphere stops most of these particles. The flux of these particles is higher at the Shuttle, however, since its orbit is above much of the atmosphere. Therefore, the risk of damage is higher at the Shuttle orbit than at the surface of the Earth. The Shuttle shroud does provide protection, but not from the highest energy particles. The Shuttle astronauts have in fact seen flashes resulting from the interaction of high-energy protons with their eyes. Nevertheless, the increased health risk is not unacceptably high.
For answers to more questions about the Space Shuttle and astronauts, check out NASA Human Space Flight Frequently Asked Questions.
How does the sun burn? Is there oxygen in space? Isn't that needed for fire?
burning in a fire is a chemical reaction, requiring oxygen. If such a chemical reaction
were responsible for the heat of the Sun, the Sun would have lasted for less than 100
million years. We know, however, that the Sun must be several billion years old.
Therefore, a greater source of energy is required.
We now know that the Sun is powered by nuclear fusion reactions taking place at the center of the glowing ball of gas that we observe from the Earth. Unlike the Earth's atmosphere, most of the gas in the universe is hydrogen. The Sun's energy primarily comes from the fusion of hydrogen into helium. The glow we see from the Sun's surface is from gas that is kept hot by heat from these fusion reactions at the Sun's center. The temperature of the gas at the surface of the Sun is about 6000 degrees. The temperature at the center of the Sun is 16 million degrees!
So, although the Sun is very hot, there is no fire in or on the Sun in the sense of a chemical wood fire or candle flame here on Earth that requires oxygen to burn.
The amount of oxygen in space is tiny compared to the amount of hydrogen (more than 1000 hydrogen atoms for each atom of oxygen). Nevertheless, oxygen is still the third-most abundant element and was necessary for the water and, ultimately, life on Earth. The precise amount of oxygen in the Sun is currently being debated and revised, and this has important consequences for the precise modeling of the Sun's interior.
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