Meteors

Empty space in our solar system is not actually empty as there are many millions of tiny particles hanging around between the planets. As the earth races on its orbit round the sun, some of these particles are swept into the atmosphere and even something the size of a grain of sand will become a bright meteor in our sky. On any clear night away from the city lights you are likely to see perhaps two or three meteors every hour, but occasionally there can be far more. These “meteor showers” can usually be tied back to the passage through the solar system of a comet or asteroid, sometimes centuries in the past. The tail of a comet is astronomical scale pollution but the resulting meteors can contribute some very useful data for scientists to analyse and of course they can produce a spectacular natural firework show.

2010/11 Quadrantid Meteor Shower

Geminid Meteor Shower

Currently the most active of the regular annual showers, with rates outstripping those of even the Perseids for a 24-hour interval centred on their 13/14 December maximum, the Geminids are a real treat for observers prepared to brave the winter cold (or to travel to warmer locations...)! Unusual in being associated with an asteroid - (3200) Phaethon - rather than a comet, the shower has grown in intensity since the 1980s as a result of the meteor stream orbit being dragged gradually outwards across that of the Earth. A consequence is that we currently encounter the most densely-populated parts of the meteor stream. This happy situation is temporary - in a few more decades, Geminid displays can be expected to diminish in intensity. Here we have an excellent opportunity to follow, year on year, the evolution of a meteor stream.

Geminid meteors enter the atmosphere at a relatively slow 35 km/sec, and thanks to their robust (presumably rocky/asteroidal as opposed to dusty/cometary) nature tend to last longer than most in luminous flight. Unlike swift Perseid or Orionid meteors, which last only a couple of tenths of a second, Geminids may be visible for a second or longer, sometimes appearing to fragment into a train of ‘blobs’. Their low speed and abundance of bright events makes the Geminids a prime photographic target.

The Aurora Borealis

The Aurora Borealis is caused by solar wind particles reacting with the earth’s upper atmosphere.   Our sun has periods of greater or lesser activity (solar maximum and solar minimum), the aurora is much stronger during a maximum period.    Following a longer than usual minimum period, activity on the sun is again climbing towards maximum activity.   Because of the way in which the magnetic field of the earth reacts with the solar wind particles, the aurora displays are mostly seen in a “doughnut” shaped area known as the “auroral oval” around the North or South Poles.

Solar Eclipses

An eclipse of the Sun occurs when the orbit of the moon crosses in front of the Sun as seen from the Earth. The shadow of the moon follows a narrow path on the surface of the Earth, bringing daytime darkness for a brief period and allowing observers to see a range of unusual natural phenomena. The most spectacular sight is a total solar eclipse, when the moon completely covers the Sun, with flames of crimson prominences licking around the jet black disk and streamers of the solar corona reaching far out into space.

As the moon goes around the Earth it follows an orbit which is elliptical, appearing very slightly smaller when further out and larger at the closer point. Whilst it is not possible to detect this difference in size without accurate instruments, when the moon is at its closest point it is large enough to completely obscure the disk of the Sun and the closer it is the longer the duration of the eclipse. At a more distant point the Sun is not completely covered and a very small, bright circle or annulus remains visible. This is known as an annular eclipse and although it lacks the unique drama of a total, it remains an unusual and interesting event particularly when it is possible to observe the effect of the declining light levels on wildlife.

2010 Solar Eclipses

2010 brings two solar eclipses, each with its own special attractions. The annular in January will have the novelty of being the longest annular eclipse of the 21st century. For this event we will observe from the southern edge of the passing shadow, with the mountains and valleys of the moon breaking into the bright line of the annulus to form Baily's Beads (see below). Our chosen site in the Masai Mara National Park in Kenya offers very good prospects for a clear sky and great opportunities for observation of both the event and the effect on animals and birds in the area.

Observing the total eclipse in July offers particular challenges, with the track crossing a large part of the South Pacific Ocean, avoiding all but a very few islands. The best prospects for a clear sky along the track of the eclipse are in French Polynesia and this will be our choice for this event. Most of the islands within the path of the eclipse shadow can only be reached by long sea journeys. The tiny atoll of Anaa is one of the very few islands on the track which have the benefit of an airstrip, but as there are no hotels we plan only a brief stay on the island before retreating to the manicured comforts of Tahiti’s or Moorea's hotels.

The Total Eclipse Experience

On the day of the eclipse you will want to get to your observation site in good time before “first contact”, when the edge of the moon first touches the edge of the Sun. At this stage you will need a special viewer to look at the Sun as a curved 'bite' is taken from one side. Now the tension starts to build as the moon progressively covers the Sun. The light level goes down, but at the same time your eyes adapt to the gradual changes so the change remains almost unnoticed until the eclipse is well advanced.

The landscape is drained of colour and shadows sharpen as the Sun is reduced to a bright crescent and eventually a single point. Look at the shadows under a tree and you will see the leaves create a thousand small arcs of light. The temperature only drops a degree or two, but there is a sense of chill in the air as the radiant heat from the Sun is cut off. A blue sky has turned to a pale morning grey and bright planets have reappeared. The last couple of minutes before totality race through at top speed as the moon's shadow hurtles towards you. The sun is reduced to a single searing point of brightness and as this final point is extinguished, bright beads remain momentarily along the edge as the sunlight shines through the valleys on the moon. Suddenly the brightness is gone, leaving a jet black disk of the moon clothed in the flowing robes of the solar corona and surrounded by the delicate red rim of the chromosphere. Crimson licks of prominences reach out from the rim and as your eyes become accustomed to the dark, the fine structure of the corona becomes visible.

There is an unearthly red glow around the horizon and a sense of a large dark shadow looming above. The time of totality ticks by, then a few flickers of bright beads on the edge of the dark disk herald the end of the performance. The burst of light which shocks your dark adjusted vision is the final climax. Always expected but always a surprise: sunlight returns, colour and warmth are restored and everything is back to normal. Until next time...