Observations

This Friday’s annular (ring-like) eclipse of the Sun is the longest for the next 1000 years!

Annular Eclipse 2010 Jan 15. Image courtesy of Fred Espenak, NASA's GSFC
Image courtesy of Fred Espenak, NASA’s GSFC

On January 3rd 2010 at 11am AEDT, the Earth reached its closest approach to the Sun known as perihelion. This makes the Sun look its largest for the year. Incidentally, according to the laws of planetary motion devised by the German astronomer Johannes Kepler in the early 1600s the relative closeness means that we were also travelling at our fastest in out yearly free trip around the Sun. Is this why Canberra’s Summernats car shows are held during January each year?

On January 17th at 12:41pm AEDT the Moon will reach its most distant point of its “moon-thly” orbit around the Earth known as apogee. This makes the Moon look close to its minimum size.

The result of these extremes of a big Sun and small Moon is that an eclipse close to these dates will produce a long lasting annular or ring eclipse. This Friday January 15th such an eclipse will occur but sadly it will not be visible from Australia.

The eclipse begins in Western Africa at 05:14 UT (4:14pm AEDT). The eclipse path is 331 km wide at its start as the antumbra (the circular silhouette of the Moon) quickly travels east-southeast at 10km per second.

Sun, Earth and Moon geometry means the eclipse shadow changes speed and the rapid start decreases to just 1.5km/s and increases again at the end of the eclipse. The maximum duration of just over 11 minutes at 6:59 UT to 7:10 UT will be observed from the Indian Ocean off the coast of Kenya. At over 11 minutes it will be the longest annular eclipse of the 3rd Millennium and the duration will not be exceeded until the year 3043.

The path will then pass between India and Sri Lanka, across the Bay of Bengal to Burma and lastly China’s Shandong province at 08:59UT.

However, it is vital to note that despite 91% of the Sun’s disk being covered by the Moon, it is still exceedingly dangerous to look at with the unaided eye. Permanent damage may result by attempting to look at it so please ensure that if you live under the path of the antumbra or to the sides where a partial solar eclipse will be visible than you and everyone else do not observe the Sun directly. Use appropriate filters or make a pinhole camera and project a small image of the Sun or, better still, visit your local public observatory.

For more information and the complete source of the information presented here visit the NASA web site produced by Fred Espenak, NASA’s GSFC here.

2 responses to “This Friday’s annular (ring-like) eclipse of the Sun is the longest for the next 1000 years!

  • How dim is the light on earth of an annular Antumbra compared to the light of the Umbra of a total eclipse?

    • Robert, from within the antumbra you would still observe (although you shouldn’t look at it) a ring of the Sun’s disc. The light from it would seem as bright as daylight because your eyes would accommodate for the small decrease in illumination. Under a total eclipse’s umbra it feels like early to mid twilight (not quite dark enough to think about switching on a light) but again your eyes accommodate to the change in illumination. The effect is surely measurable although I am not aware of anyone having done this. Does anyone know if this sort of measurement has been done?

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