Green flashes are elusive phenomena during sunset and
sunrise caused by the atmospheric refraction near the horizon. The shorter the wavelength, the
larger the refraction, thus at sunset the refractive delay of the
sunset is longer for shorter wavelengths: The green/blue sun sets later than the
yellow sun. To observe these phenomena, a clear atmosphere is essential. The
even rarer blue and violet flashes can be observed in particular from high
altitudes, where the air is even clearer and less atmospheric reddening is
affecting the observation. The pictures presented here have all been shot from
the MAGIC telescope site or the summit of the Roque de los Muchachos an altitude of 2200 m a.s.l., and the sun sets in an “ocean of
clouds” rather than on the horizon, i.e. also at high altitudes. Note that
the violet flash observed on 14.01.2004 09:06 shows the rising sun over the island of Tenerife.
The height of the valley through which the flash shines is approx. 2000 m a.s.l.
All pictures have been
taken during 2003-4 from the Roque de los Muchachos
Observatory (2200 m a.s.l.), Canary Island of La Palma, at sunset or
sunrise. Times are WET (=UTC) or WEST (=UTC+1). Equipment: Canon EOS 10D,
320mm/800mm effective focal length lens. No digital enhancements to
the pictures shown here. Find more recent pictures taken with advanced optics in the September 2007 gallery.
For explanations on the phenomenon of the green flash, see the introduction to Green Flashes by Andrew Young.
