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Guide to the solar eclipse

Solar eclipse captured by Hinode craft

Solar eclipse of 2012, which darkened parts of the US and south-east Asia. (Courtesy: JAXA/Hinode)

By James Dacey

On Friday, our old friend the Moon will swing by to remind us that she’s not just there to reflect the Sun’s light; she can sometimes block it out too. A total solar eclipse will be visible to those lucky few people living in the Faroe Islands or the Norwegian archipelago of Svalbard. Many others across Europe, North Africa and Russia will be treated to the (almost as good) spectacle of a partial solar eclipse.

In Bristol, UK, where Physics World is produced, the peak of the eclipse will occur around 9.30 a.m., when 87% of sunlight will be blocked by the passing of the Moon. The UK Hydrographic Office has provided full details of the path of the eclipse and the local times for start, peak and end of the eclipse in your location.

Apologies for the patronizing tone, but for those of you who will get the chance to experience Friday’s eclipse please remember DO NOT stare directly at the Sun, even during maximum eclipse or if it is cloudy. “Eclipse blindness” and retinal burns are not things made up by the media to scare people, and if you don’t believe me, ask the College of Optometrists. One of the safe ways to view the event is to purchase a pair of eclipse glasses, which significantly cut the amount of visible light and near-infrared radiation reaching the eyes. NASA recommends going for a pair that transmits less than 0.003% of visible light and less than 0.5% UV.

Home made pinhole camera

Eclipse camera. (Courtesy: Eugene Kim)

Another safe option is to create a home-made pinhole camera to project a live view of the eclipse onto a screen. The simplest way to do this is to pierce a tiny hole in a piece of paper or card, hold this up in the air with your back to the Sun, then project the image onto another piece of card placed at least a metre away from the first one. Better still, swap the first card with a colander and you can watch multiple eclipses for the price of one! I got that last recommendation from this downloadable guide by the Royal Astronomical Society (RAS), which is one of the best resources I have come across for tips on safe viewing of the eclipse.

If you want to have a guided experience of the eclipse, it is worth doing a quick Web browse for local astronomy groups in your area that may well be hosting an eclipse viewing event. Those of you in London, for instance, will be able to join the RAS and the Baker Street Irregular Astronomers in Regent’s Park, where you can peer through a range of telescopes to see solar features such as sunspots and prominences. Here in Bristol, a couple of us will be joining the Bristol Astronomical Society for a viewing event at Castle Park in the city centre. If the weather is kind to us, we’ll be doing some filming and posting some footage on this website after the event. In the UK you can check your local weather forecast via the MET Office.

If you do not live in the path of the eclipse, then you can follow the event online, such as via Slooh, a website that streams live views from a network of telescopes around the world.

Eclipses also bring an opportunity for ground-breaking science. Famously, it was the British astronomer Arthur Eddington’s 1919 eclipse expedition to the island Príncipe off the west coast of Africa that provided early proof of Einstein’s theory of general relativity. Back in 2008 the BBC produced a great dramatization of those events, Einstein and Eddington, with the scientists played by David Tennant and Andy Serkis, respectively, which we reviewed at the time. You should be able to find a DVD from major online retailers.

This time round, researchers are again setting their sights on new discoveries. A team from Europe and the US will be positioned in Svalbard on Friday to study the Sun’s atmosphere, the corona. One of the great outstanding mysteries of astrophysics is why the temperature of the plasmas in the Sun’s corona is so much higher than the core of the star. These coronal plasmas are only visible on Earth during a total solar eclipse.  The team on Svalbard, nicknamed the “Solar Wind Sherpas”, will be imaging the eclipsed Sun using specially adapted cameras to make estimates of the temperature in the corona.

There has also been quite a lot made in the media of the effects that the eclipse might have on power grids across Europe because of the growth of the solar power industry. A lot of this is pure scaremongering but there are some genuinely interesting scientific inquiries into the impact of the eclipse. One of these is to look at the effects of a sudden reduction in solar radiation on the Earth’s atmosphere and local weather conditions. For instance, during the last major solar eclipse in the UK in 1999, researchers at the Reading University Atmospheric Observatory (where the maximum eclipse was almost 100%) found some evidence to suggest that the wind had changed direction at the onset and end of the eclipse.

This time round, the University of Reading is launching weather balloons at various sites across the path at the peak of the eclipse, including Iceland and the Faroe Islands. Reading meteorologists have also teamed up with BBC Learning to run a citizen-science project during Friday’s eclipse. The National Eclipse Weather Experiment (NEWEx) is asking the UK public to provide estimates of their local weather conditions during the course of the eclipse, including temperature and wind speed using the Beaufort scale.

Another fascinating suggestion is that the cosmic-ray activity may change during solar and lunar eclipses. Science teachers around the UK in possession of CERN@school detectors are being encouraged to get students to measure background radiation levels during Friday’s event. The mass of data may help shed light on that claim and may also yield other unexpected outcomes.

So go out, enjoy the eclipse and don’t stare directly at the Sun.

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  1. Julio Herrera

    Another interesting thing to watch is the behaviour of birds during an eclipse. They’ll go quiet, and this gives contributes to the special atmosphere during the event.

  2. M. Asghar

    The higher temperature of the plasmas in the Sun’s corona than that of its core is understood to be caused by the exciation of Afven waves in the corona’s plasma.


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