Sunspot AR 11598 releases a huge flair.

On Monday  22 October 2012 NASA's Solar Dynamics Observatory detected a major flare erupting from Sunspot AR 11598, peaking at 3.22 am GMT on Tuesday 23 October. The event has been classified as an X1.8 type flare, which implies an energy discharge of between 0.001 and 0.01 Whatts per square meter, enough to cause disruption to radio signals of the flare was directed towards the Earth. This is the third significant flare since the sunspot came into view on 20 October, and it has been followed by about a dozen smaller events, suggesting it has a high probability of sending a large flare in our direction.

The location of AR 11598 on the Sun's surface. Solar Monitor.

Solar flares are major energy discharges from the Sun's surface; these are immediately disruptive to life on Earth themselves, but are almost invariably accompanied by coronal mass ejections, streams of charged particles (ions and electrons) which can be disruptive to radio signals and power supplies when they reach the Earth (although modern power networks tend to be better insulated against their effects than was the case in the past), as well as triggering Aurora Borrealis and Aurora Australis events.

Auroras are triggered by the interaction of charged particles in coronal mass ejections with the Earth's magnetic field. They tend to be concentrated at the poles, where the magnetic field crosses, rather than running parallel to, the atmosphere, and produce light by exciting atoms in the upper atmosphere, provoking them to produce light.

See also Sunspot AR 1520 releases a powerful Solar Flare, The Earth reaches its aphelion, Solar flare may hit Earth on 4 July 2012, NASA's Solar Dynamic Observatory observes the transit of Venus, and Comet C/2011 W3 (Lovejoy) survives a close encounter with the sun.

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Sunspot AR 1520 releases a powerful Solar Flare.

On Thursday 12 July 2012 at 4.52 pm GMT, NASA's Solar Dynamics Observatory witnessed a sunspot labeled AR 1520 (Active Region 1520), currently facing towards the Earth, produce one of the largest Solar Flares so far this year. This has been classed as an X1.4-class flare, potentially large enough to cause disruption to communications networks and electricity supplies on Earth, though in this case highly unlikely to do so. The flare caused the release of a coronal mass ejection (stream of plasma) that is traveling towards us at 1400 km per second, and will reach the Earth on Saturday 14 July, at about 5.00 am, GMT. This is likely to produce some spectacular auroras in the polar regions, but not to cause any serious harm.

An X1.4 class flare erupted from the center of the sun, peaking on 12 July 2012 at 4.52 GMT. It erupted from Active Region 1520 which rotated into view on July 6. NASA/Solar Dynamics Observatory/Atmospheric Imaging Assembly.

Sunspots are magnetic storms on the face of the Sun. These inhibit convection currents in the Sun's photosphere, causing localized cooling; the surface of the Sun can drop from its usual 5778 K to as low as 3000 K in a Sunspot, causing them to darken compared to the rest of the Sun (though they are in fact still pretty bright). Since Sunspots are magnetic they have magnetic poles, with positive and negative charges. These can be connected by coronal loops, streams of magnetic flux carrying plasma above the surface of the Sun. This can lead to a short circuit in which a large amount of magnetic energy is released suddenly, producing a brightening we perceive as a Solar Flare.

Image of coronal loops over the eastern limb of the Sun, taken on 29 June 1999 around 2.00 am, GMT. NASA/Transition Region and Coronal Explorer.

This in turn can lead to the release of a coronal mass ejection, a stream of charged particles, mainly electrons and protons but with some ionized atoms of heavier elements such as helium or oxygen. This travels out from the Sun, typically taking about two days to reach the Earth's orbit.

A coronal mass ejection breaking away from the Sun. Universe Today/JAXA/Hinode.

When these streams of charged particles reach the Earth they can cause magnetic storms. These are usually harmless, with the energy being released in spectacular displays of light near the Earth's poles known as the Aurora Borealis (north) and Aurora Australis (south), but occasionally large events cause problems for electrical systems on Earth, such as the March 1989 event that knocked out electrical distribution networks in Quebec (such distribution networks are now generally better safeguarded against these events).

An Aurora Borealis display over Sommarøya in Norway in January 2011. Thilo Bubek/National Geographic.

Aurora displays come in a variety of colours, caused by electrons from the coronal mass ejection striking different atoms in the Earth's atmosphere. This is because the energy of the atoms increases each time it is struck by an electron, but atoms can only absorb so much energy before they must release some, and each atom always releases energy as light (photons) at a specific wavelengths. In the Earth's atmosphere this is effected by altitude, thus Oxygen releases either green or red light and Nitrogen releases either blue or violet light. Typically auroras shimmer as different reactions occur, photographs do not really do them justice.

Gasses release light at specific wavelengths in response to other stimuli besides coronal mass ejections. Thus the blue colour of the daytime sky is the colour of Nitrogen in the lower atmosphere reacting to the (steady) energy input from sunlight, whereas the red colour of sunrises and sunsets is the colour of oxygen higher in the atmosphere reacting to the same; we see this at dawn and dusk because the sun is no longer in line of sight with the lower atmosphere. Neon lights are red because Neon gas releases red light in response to electrical charge, and Sodium lights orange for the same reason. Molecules made up of more than one sort of atom, such as Carbon Dioxide (CO₂), Water (H₂O) or Methane (CH₄) release light in the infra-red part of the spectrum, which can lead to warming of the atmosphere (the Greenhouse Effect), hence the current concerns about the release of such gasses into the atmosphere by industrial processes, and the effect this might have on our climate.

The colours of a sunset are caused by our being able to see the upper atmosphere, once the Sun is out of line of sight with the lower atmosphere. Joe Bauwens.

See also The Earth reaches its aphelion, Solar flare may hit Earth on 4 July 2012, NASA's Solar Dynamic Observatory observes the transit of Venus, Comet C/2011 W3 (Lovejoy) survives a close encounter with the sun and Two solar flares coming our way.

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Solar flare may hit Earth on 4 July 2012.

On Monday 2 July 2012 NASA's Solar Dynamics Observatory witnessed a large Solar Flare issuing from the AR1515 Sunspot, in the direction of Earth. It is thought likely that this will reach us on 4 July 2012. The flare is currently classed as a Class M Flare, likely to cause Aurora Borealis and Aurora Australis displays (Northern and Southern Lights), but unlikely to cause significant disruption to communication or electricity distribution networks.

Solar Dynamics Observatory footage of the AR1515 Solar Flare. NASA.

Sunspots are the result of intense magnetic storms on the surface of the Sun, which inhibit the convection currents in the photosphere, causing a localized cooling. This can lead to mass ejections of charged particles (i.e. Solar Flares) from the Sun's corona. These streams of charged particles interact with the magnetic fields of any planets in their path, releasing energy as photons (light) and producing spectacular displays near the magnetic poles (auroras). Particularly large Solar Flares can cause damage to electronic systems on satellites, and occasionally even on the ground. 

See also NASA's Solar Dynamic Observatory observes the transit of Venus, Comet C/2011 W3 (Lovejoy) survives a close encounter with the Sun, Two solar flares coming our way, Solar storm baths Earth in protons and Comet seen falling into the Sun. 

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NASA's Solar Dynamic Observatory observes the transit of Venus.

A planet is said to transit the Sun when it passes in front of the Sun from our point of view. From Earth it is possible to witness two planets transiting the Sun, Mercury and Venus, since these planets orbit closer to the Sun than the Earth; from Mars it is also possible to see Earth transiting the Sun, etc. Venus, seen from Earth, transits the Sun four times every 243 years, on a cycle of 125.5 years, eight years, 105.5 years, eight years, 125.5 years, and so on. The most recent of these transits occurred on 5-6 June 2012), provoking excitement among both amateur and professional astronomers. This will not happen again till December 2117.

NASA's Solar Dynamic Observatory constantly observes the Sun from a geosynchronous orbit 36 000 above the Pacific Ocean. This placed it in an excellent position to observe the transit of Venus, untroubled by the clouds which bedeviled many Earth-bound observers.

Composite image of Venus transiting the Sun at a wavelength of 171 Å. NASA/Solar Dynamic Observatory.

As well as providing us with dramatic images, this also allows the Solar Dynamic Observatory to perform useful science. The Observatory observes the Sun at a number of different wavelengths. All gasses are opaque at some wavelengths and transparent at others. Therefore by calculating how much light is absorbed by the atmosphere of Venus at different wavelengths, scientists hope to be able to learn more about the composition of that atmosphere.

Film of the 2012 transit of Venus at a wavelength of 171 Å. NASA/Solar Dynamic Observatory.

This space-based view of the transit also tells us something about possible future observations. The next observable transit of Venus will not occur until December 2117, but this is not necessarily the next time we will see this event. Venus (and any other body in the Solar System) is always transiting the Sun from some point of view. It is possible that in the next century humans will come to explore the Solar System far more extensively than we have done to date. While it is unlikely that we will ever send a mission specifically to observe a transit of Venus, it is quite possible that the next humans to observe such a transit will not be on Earth, but rather in space visiting, or on route to, some other body in out Solar System.

See also NASA releases digitally remastered view of Copernicus Crater, New Cassini Images of Titan, Tethys and Methone, Images of Vesta, Martian Dust Devils and NASA releases new Cassini images of Saturn's moons Enceladus, Janus and Dione.

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