Onehouse Observatory

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Aurorae

21st January 2005: Onehouse, Suffolk, UK (latitude 52 degrees)

On 20th January, Active Region 10720 was responsible for a class X7.1 solar x-ray flare. This produced the strongest high-energy space radiation storm since 1989. A strong Coronal Mass Ejection was associated with this solar flare, and at least part of the ejection was believed to be directed towards Earth. This prompted a Middle Latitude Auroral Activity Warning.

The first indication of auroral activity at this location was observed at 21.30 UT, once earlier cloud had cleared. A diffuse, shallow arc was seen above the northern horizon. It was about 10 degrees wide and had a more distinct lower boundary, below which stars could be seen clearly. The lower edge of the arc was at an elevation of about 15 degrees. The visibility of the arc was similar to that of the Milky Way from a dark site, and its colour was a slightly greenish grey.

For about an hour the diffuse arc was the only indication of auroral activity, and during that time it appeared to remain stable. However, at 22.30 UT the display increased dramatically, as detailed in the sequence of images below. All of the images were taken with a Nikon Coolpix 4500. They are 8 second exposures at ISO 400 and f/2.6.

 

22.33 UT: A broad curtain of red light, shading to purple at its base, was visible from WNW to NNW. It had a convex upper boundary extending to an elevation of about 40-45 degrees. Below the curtain was the green glow of the auroral arc. A display of this intensity is rare in the UK, particularly at such a southerly latitude.

 

22.34 UT: At the northern edge of the curtain, broad, near-vertical rays of pinkish white light extended upwards from the auroral arc. There was a rippling effect as the intensity of the light varied in different areas of the curtain. The bright star at lower right is Deneb.

 

22.35 UT: The rays became more numerous and appeared to shift towards the W, permeating the curtain. Soon afterwards, the aurora faded rapidly from view. In this image, the stars of Cepheus, Lacerta, Andromeda and Cassiopeia become more obvious. Note that the visibility of the display was hampered by strong moonlight.

 

22.40 UT: By now the display seemed to be over, as nothing could be seen by eye. However, greatly reduced activity was captured in this final image, showing approximately the same area of sky from a slightly different location. Observations continued until 00.50 UT, but no further activity was noted.

 

This brief period of intense auroral activity was recorded by SAMNET's York (UK) magnetometer, as shown on this graph. The black line reveals fluctuations in the Earth's magnetic field, as compared to a typical quiet day, shown in blue. The difference between the current field and a quiet day is shown on the bar chart, where green = quiet, orange = active and red = stormy. The graph is reproduced with the permission of AuroraWatch from its website at http://www.dcs.lancs.ac.uk/iono/aurorawatch/