What is a solar flare?
A solar flare is a large explosion of magnetic energy in the Sun’s atmosphere which causes an intense burst of increased brightness. They cannot be detected by the naked eye from the surface of the earth but can be observed through telescopes, space x-rays and thermal imaging equipment.
The amount of energy released by a flare can be equivalent to millions of 100-megaton hydrogen bombs exploding at the same time – ten million times greater than that released by a volcanic eruption.
Often lasting just a few minutes, solar flares heat material to many millions of degrees and produce a burst of radiation across the electromagnetic spectrum, including from radio waves to x-rays and gamma rays.
When, why and where do they occur?
A flare occurs when magnetic energy that has built up in the solar atmosphere is suddenly released - mostly in the active regions around sunspots. Their frequency varies from several a day, when the sun is particularly active, to less than one a week during quiet periods.
Large flares are less frequent than smaller ones. Solar activity varies within an 11-year cycle at the peak of which there are typically more sunspots and therefore more solar flares.
What affect can they have on earth?
X-rays and UV radiation emitted by solar flares can cause long-lasting radiation storms the Earth’s ionosphere – the uppermost part of the planet’s atmosphere – and trigger radio black-outs around the world.
Each flare produces streams of highly energetic particles in the solar wind and the Earth's magnetosphere that can present radiation hazards to spacecraft and astronauts. A solar flare on January 20, 2005 released the highest concentration of protons ever directly measured and took just 15 minutes to reach Earth, indicating a velocity of approximately one-third light speed.
Scientists have warned that a really big solar eruption could destroy satellites and wreck power and communications grids around the globe.
Nasa recently said that Britain could face widespread power blackouts and be left without critical communication signals for long periods of time if the earth is hit by a once-in-a-generation “space storm”.
How do we know they are coming?
The methods currently used to predict flares are problematic and it is not presently possible to tell when an active region of the Sun will produce a flare.
But certain properties of sunspots and active regions of the Sun correlate with flaring. Magnetically complex regions called delta spots produce most of the largest flares, so a simple scheme of sunspot classification is commonly used as a starting point for predicting flares. Predictions are usually stated in terms of the probability of a flare within 24 or 48 hours. The US National Oceanic and Atmospheric Administration issues forecasts of this kind.
A number of space missions have been deployed to observe flares, including Hinode - a new spacecraft launched by the Japan Aerospace Exploration Agency in 2006 to observe the phenomena in closer detail.
When were they discovered?
The first flare ever to be observed was also the most powerful on record. It occurred in 1859 and was reportd independently by the British astronomers Richard Carrington and Roger Hodgeson. The scientists observed the flare as the localised brightening of small areas within a group of sunspots. The event left a trace in Greenland ice in the form of nitrates and beryllium-10, which allow its strength to be measured today.
Often lasting just a few minutes, solar flares heat material to many millions of degrees and produce a burst of radiation across the electromagnetic spectrum, including from radio waves to x-rays and gamma rays.
When, why and where do they occur?
A flare occurs when magnetic energy that has built up in the solar atmosphere is suddenly released - mostly in the active regions around sunspots. Their frequency varies from several a day, when the sun is particularly active, to less than one a week during quiet periods.
Large flares are less frequent than smaller ones. Solar activity varies within an 11-year cycle at the peak of which there are typically more sunspots and therefore more solar flares.
What affect can they have on earth?
X-rays and UV radiation emitted by solar flares can cause long-lasting radiation storms the Earth’s ionosphere – the uppermost part of the planet’s atmosphere – and trigger radio black-outs around the world.
Each flare produces streams of highly energetic particles in the solar wind and the Earth's magnetosphere that can present radiation hazards to spacecraft and astronauts. A solar flare on January 20, 2005 released the highest concentration of protons ever directly measured and took just 15 minutes to reach Earth, indicating a velocity of approximately one-third light speed.
Scientists have warned that a really big solar eruption could destroy satellites and wreck power and communications grids around the globe.
Nasa recently said that Britain could face widespread power blackouts and be left without critical communication signals for long periods of time if the earth is hit by a once-in-a-generation “space storm”.
How do we know they are coming?
The methods currently used to predict flares are problematic and it is not presently possible to tell when an active region of the Sun will produce a flare.
But certain properties of sunspots and active regions of the Sun correlate with flaring. Magnetically complex regions called delta spots produce most of the largest flares, so a simple scheme of sunspot classification is commonly used as a starting point for predicting flares. Predictions are usually stated in terms of the probability of a flare within 24 or 48 hours. The US National Oceanic and Atmospheric Administration issues forecasts of this kind.
A number of space missions have been deployed to observe flares, including Hinode - a new spacecraft launched by the Japan Aerospace Exploration Agency in 2006 to observe the phenomena in closer detail.
When were they discovered?
The first flare ever to be observed was also the most powerful on record. It occurred in 1859 and was reportd independently by the British astronomers Richard Carrington and Roger Hodgeson. The scientists observed the flare as the localised brightening of small areas within a group of sunspots. The event left a trace in Greenland ice in the form of nitrates and beryllium-10, which allow its strength to be measured today.
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