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Solar Flares and Aurorae

Astronomers at Cardiff University Observatory monitored the extreme activity on the Sun during late 2003.

The sunspot groups in the images below are among the largest sunspot groups that have ever been observed. The group to the left of centre in the image taken on 27 October was responsible for triggering a gigantic coronal mass ejection (CME) towards the earth. This particular CME struck the Earth on the evening of Wednesday 29 October 2003, causing spectacular displays of the Aurora Borealis or Northern Lights. This was visible over most of Britain and could be seen as far south as Cardiff.

Image of sun showing several sunspot groups

On 27 October 2003 Cardiff students Rhian Chapman and Matt Lambert took this image of several sunspot groups. Several active sunspot regions can be seen.

Sunspot groups on surface of sun

On 3 November 2003 Rhiann Chapman and Matt Lambert took this image of the same sunspot groups just as they were about to disappear around the limb of the Sun.

Sunspot groups in H-alpha emission. A solar prominence can be seen above one of the sunspots.

On 3 November 2003 Cardiff students Sam Caws and Philip France took this image of the same sunspot group in H-alpha emission. A solar prominence can be seen above one of the sunspots.


The sunspot group to the right of centre erupted later the same week, causing a further auroral display on Friday 31 October 2003. This was also visible over most of Britain, and could also be seen at the latitude of Cardiff. This level of sunspot activity is unusual because the Sun is currently 3 years past the maximum of its 11-year sunspot cycle. It is very unusual to see such activity at this stage in the Solar cycle.

Cartoon of a solar flare erupting and hitting the Earth.

Any coronal mass ejection that hits the earth causes auroral displays and can cause power failures as well as problems with communications and satellites. This picture shows a cartoon of a solar flare erupting and hitting the Earth.


The following images of the aurora were taken on 29 October 2003 by Nick Hart of the Cardiff Astronomical Society. The characteristic veil of colours can be seen, typical of an auroral display. Typical colours of such a display can be orange or purple or green, in an apparent curtain of colour.

Aurora of 29 October 2003. The characteristic veil of colours can be seen.
Aurora of 29 October 2003. The characteristic veil of colours can be seen.
Aurora of 29 October 2003. The characteristic veil of colours can be seen.

On 4 November 2003, Cardiff student Stuart Flatt took this radio scan of the Sun at a wavelength of 3cm. The 1-metre radio dish was used in transit mode to observe the Sun as it tracked through the beam of the dish. The x-axis records elapsed time since the start of data recording. The y-axis records radio intensity measured in arbitrary units. The thick line is the data recorded. The trace differs from the expected beam profile (estimated by the dashed line) as the intensity flares up for a short period of time before dying away again.


Radio flares such as these are moderately uncommon, but when they occur the radio intensity of the flare can exceed the radio intensity of the Sun at a particular wavelength, making these truly spectacular events. This particular event was the precursor to a spectacular event recorded by SOHO, the solar observation satellite, as the following two images show:

Large solar flare recorded by SOHO, the solar observation satellite
Large solar flare recorded by SOHO, the solar observation satellite

This flare on 4 November 2003 is believed to be the largest ever recorded, surpassing the previous record flares of 2 April 2001 and 16 August 1989.

WARNING: DO NOT LOOK AT THE SUN DIRECTLY OR THROUGH A TELESCOPE WITHOUT SOLAR FILTERS.

IT IS NOT SAFE TO LOOK AT THE SUN EVEN THROUGH SUNGLASSES. SERIOUS EYE DAMAGE CAN RESULT.