|Eclipses of the Sun occur as a natural consequence of the
periodic and harmonic motions of the planets around the Sun. These motions
result periodically in situations where the Moon, Mercury or Venus will
lay directly along the line of sight to our Sun, the Sun being eclipsed
by the respective planetary body. Although Mercury and Venus are far greater
in size than our Moon, their angular extent in the sky are far reduced
due to their correspondingly greater distance from the Earth. The eclipses
due to these planetary bodies being of interest only to the most ardent
of solar observers. The angular size of the Sun and the Moon are comparable
however, at around half a degree. Thus during the periods when the Moon
is in front of the Sun the strong emission from the photosphere is completely
blocked out. When this occurs it is called this a total eclipse. Conversely
when the the Moon only blocks part of the Sun, it is a partial eclipse.
During a total eclipse, the outer atmosphere of the Sun, its `Corona` becomes
visible to the naked eye.
The sun observed during a total solar eclipse by Professor E. Hiei. This excellent observation of the suns corona during totality reveals the components and configuration of the suns corona close to solar minimum. Note the bright blobs distributed around the moons limb, these represent valleys through which the sun's bright chromospheric emission is seen (Bailys Beads).
The discovery of the corona and its very nature was enabled by the many eclipse observations, the most important of which were the European total solar eclipses as they has the highest concentration of observers. The last solar eclipse where totality was observed from the UK occured in 1999. This gave observers the opportunity to observe the totality for just over two minutes in the south-western edge of Cornwall.
The next total solar eclipse will occur on 26 March 2006 and can be seen along a narrow corridor which runs through Europe, Africa and south Asia. Visit Mr. Eclipse for more infromation on dates of up coming solar eclipses. The animation shows the path of the umbral and penumbral shadow cast on the Earth by the moon during a total solar eclipse in 2001. Although, we now have dedicated spacecraft to study the problems presented by the Sun's Corona it is still useful to perform experiements on the corona using the longer wavelength (UV) bright emission lines which represent forbidden (very hot) atomic transistions. These emissions are unattenuated by our atmosphere but are usually hard to distinguish above the usually dominant photospheric light. One such experiment was conducted by scientists of the CLRC.
Fred Espaneks Eclipse Homepage
A free Eclipse leaflet is available from the RAS by phoning 01717344582
UK's 1999 Eclipse Home Page