Solar Eclipse 2009 July
22
The longest total solar
eclipse of the 21st Century occurred on 2009
July 22. The path of
totality started at sunrise in
India, passed through Tibet and Bhutan before heading across heavily populated
areas of China before heading off over the Pacific south of Japan to leave
finally the Earth at sunset in the central Pacific. The exceptionally long maximum
duration of 6min 39secs was due to a number
of factors:
- the eclipse occurred
when the Moon was near perihelion (largest
apparent diameter as seen from Earth) and the Earth was near aphelion (smallest
apparent solar diameter),
- maximum eclipse occurred near the equator so
the observer was physically closer to the Moon by an Earth radius, and
- the Earth's rotation
maximised the motion of the observer within the Moon's shadow thereby partially offsetting the
speed of the Moon's shadow across the Earth's surface.
The first two factors
contributed to the Moon's apparent diameter being around 8% larger than the
Sun's.
Local weather conditions
were always going to be critical.
As it turned out conditions where I was (together with a thousand or more like minded
people) were unfavourable at the Qiantang River
Tidal Bore observation area near Hangzhou, China. Partial phases leading to totality were generally obscured by
thick cloud
and intermittent rain showers and lightning activity to the north increased the
tension enormously.
The air temperature fell
noticeably in the lead up to totality. We were then treated to an awesome
fade in light before being plunged into deep darkness as totality ensued above
the thick cloud blanket. We cheered and clapped our hands to greet the Moon's
umbra (and in the hope of scaring the clouds away) whilst across the river the Chinese celebrated in typical fashion
with a fireworks display. Five minutes and forty seconds later the light rose again
and I was surprised to see a hint of exit diamond ring visible through a very brief
thinning of the clouds. It was all over, but extremely memorable.
The partial phases to 4th contact were more
easily observed through high cloud.
An hour and a half after 4th contact we were
treated to the world famous Qiantang River tidal bore, as a meter high wave raced up stream to return water on the incoming high tide.
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