Melanie Davies writes about the 2015 solar eclipse – the last one visible from Europe for more than a decade
On the morning of Friday 20th March 2015, we’ll be in for an astronomical treat… an eclipse of the Sun. A total solar eclipse happens roughly once a year somewhere in the world, but we only get to see one in the UK about once every 50 years. So unless it’s completely cloudy, it’ll be well worth preparing yourself for this rare spectacle. It’s rare because even though we think of the Earth-Moon-Sun trio dancing around each other in nice neat orbits, the Moon, in fact, orbits on a slight tilt with relation to the Sun, which means they rarely line up.
From counties along the south coast of England, only a partial eclipse will be visible, when only part of the Sun’s disc will be obscured; 85% to be precise. So if you want to experience totality (when the Sun is completely covered), you’ll have to take a trip to the north; to the Faroe Islands or Svalbard. In the south east, the eclipse will start (first contact) at about 8.24am; the peak of the partial eclipse will occur at about 9.30am; and it’ll all be over (last contact) by around 10.40am. The exact start and finish times depend on you location. For those lucky enough to experience totality, when day turns eerily to night, it’ll last all of 2 minutes and 46 seconds if you’re in just the right place (in the Norwegian Sea).
Have you ever wondered what causes a solar eclipse? It happens when the Moon comes between the Sun and the Earth, temporarily blocking its light and heat. As the Sun, planet, and Moon are in constant motion, an eclipse is very short-lived. When it happens, the Moon’s shadow follows a narrow path over the Earth’s surface.
Seen from the International Space Station, the eclipse looks like a fuzzy black dot moving across land or sea, often both. We occasionally see eclipses happening elsewhere too, like the shadows of the Galilean moons crossing the face of Jupiter, and even eclipsing binary stars, when we see the light of one star dipping as its companion star crosses in front of it.
There’s a small group of enthusiasts who never miss an eclipse and will travel anywhere in the world just to get a glimpse of one. Eclipse chasers go to extraordinary lengths, even chartering planes or boats if the eclipse’s path tracks only across the sea. David Makepeace is an eclipse aficionado, and self-proclaimed ‘busiest eclipse chaser in Canada. “Since 1991, I have chased eclipses of all kinds to every corner of the globe – from India to Brazil, Antarctica to Libya, Mexico to China. I have resisted the accumulation of possessions, put off marriage and a family, and valued adventure travel above my career – all to facilitate the lifestyle. I’m constantly planning exotic adventures to stand in the shadow of the Moon and I have a big desire to share the experience!” David explains with a passion. “If you haven’t seen one of these things yet you don’t know what you are missing!”
There are three types of eclipse: partial and total mentioned earlier, and the lesser-known annular. Ever heard the expression ‘a ring of fire’? An annular eclipse creates this amazing visual phenomenon. To explain what’s happening, we’ll have to learn a bit more science! The Moon doesn’t travel in a perfect circle as it orbits the Earth; instead it takes an elliptical route – sometimes closer to Earth (perihelion passage) and sometimes further away (aphelion). When the new Moon (between us and the Sun) is at aphelion, it looks smaller, and when this optically smaller Moon covers the Sun, we see the very outer edge still blazing, hence the ring of fire.
This year, the annual BBC Stargazing Live extravaganza has been timed to coincide with the 2015 eclipse, so there’ll be lots of organised observing events; search for an event near you to get the best chance of seeing the eclipse in high resolution. Astronomical societies, universities and observatories across the county will have solar scopes and specially adapted telescopes at the ready. But if you don’t fancy that, buy yourself a pair of eclipse glasses or make a simple pinhole projector, which is by far the safest way to see it. Never be tempted to look directly at the Sun as it could cause serious eye damage. Your eyes don’t have nerves, so you can’t feel the damage being done to your retinas.
To make a pinhole projector, all you need is two pieces of white card (about A4 size will do), or even a couple of paper plates, plus a very sharp pencil. Make a 2mm hole in the centre of one of them with your sharp pencil. Now, with your back to the Sun, line up the two sheets of card – the pierced one nearest the Sun – so that an image of the eclipse appears in the centre of the plain card. Then be amazed as you watch the Moon take a bite out of the Sun!
To find out more about eclipses, visit solareclipse2015.org.uk. And if you want to learn more about space science, in an easy to digest format, go to creative-space.org.uk, and search for the cosmic conundrums page.