If you were lucky enough to see the solar eclipse this morning, you will have experienced a moment of darkness as the Moon temporarily blocked the Sun’s light from reaching the Earth.
You will have been briefly standing in the Moon’s shadow as it travelled over the surface of the Earth. The shadow moved over the Atlantic Ocean towards the UK, before passing to the north of Scotland and on towards Svalbard, over a period of approximately 4 hours.
During the hours of daylight this shadow was visible from space, and EUMETSAT’s geostationary imaging satellite, Meteosat-10, was perfectly placed to observe it.
Sitting at 0 degrees longitude (the same as Greenwich, London), approximately 35,000km above the Earth, the satellite captures the Sun’s light that is reflected back into space from the Earth’s atmosphere and surface.
It does this using the visible channels of its imaging instrument, SEVIRI. During an eclipse the Moon blocks the path of the Sun’s light rays, leading to an absence of reflected light from the affected part of the Earth. Hence, the SEVIRI imagery observes an anonymously dark patch: the Moon’s shadow.
How noticeable this dark patch is in the SEVIRI imagery is determined by the atmospheric conditions. Regions of cloud exhibit high albedo (the degree to which light is reflected), and consequently they reflect a great deal of light. The Moon’s shadow will therefore be most noticeable when it passes over cloudy areas.
Land surfaces have a lower albedo, but the reduction in reflected light will still be noticeable to SEVIRI. The ocean surface has the lowest albedo, reflecting only 6% of the Sun’s light. Accordingly, in oceanic regions with clear skies the Moon’s shadow may not be very clear in the satellite imagery.
A SEVIRI image captured during the solar eclipse that occurred on 3rd November 2013 can be seen in the picture on the left, above. At 13:15 GMT the Moon’s shadow was centred over the ocean to the south of West Africa.
The reduction in the brightness of clouds in the region is the most obvious impact of this. The centre of the shadow indicates the region of total eclipse. Moving away from this area the shadow fades, indicating regions that experienced only a partial eclipse.
While cloud cover in some parts of the UK meant that many saw only glimpses of the eclipse, or nothing at all, those same clouds provided a good opportunity to capture some images of the shadow from space.
You can see a loop of imagery from this morning’s eclipse below.