Fri, 20 Feb 2015
How to observe the partial eclipse on March 20
On the morning of Friday 20 March 2015, the whole of the UK will be treated to a partial eclipse of the Sun. These are quite rare, and this one will be a major event. That morning, the Moon will pass right in front of the Sun, blotting out up to 95% of its disc. The Sun will look like a crescent instead of a disc, and there’ll be various other things to look for.
Download a PDF leaflet, especially prepared for this event jointly by the SPA and RAS. This is suitable for printing out at A4 size and you are welcome to distribute it freely in PDF or printed form.
Look at our guide to photographing the eclipse through a telephoto lens.
If you want to view the eclipse safely but don't have proper eclipse glasses, follow our simple guide on using a small mirror to project an image of the Sun – especially suitable for classroom use.
If you want to project the Sun's image through a telescope or binoculars, follow our important safety tips to protect both eyesight and your telescope.
Watch our Chief Stargazer Dr Lucie Green, of BBC's Stargazing Live, explain what the eclipse is all about and how to view it. You are welcome to embed this video on your own site.
When should I look?
The eclipse begins at about 8.30 am on the morning of Friday, 20 March, with mid eclipse at about 9.30 am. It's all over by about 10.40. These times vary depending on where you are in the UK. You can get timings for your own location at this external website.
What will I see?
During the eclipse, the Sun will appear to have a bit taken out of it as the Moon passes in front of it. At mid eclipse there will only be a thin crescent of Sun visible.
How can I view it?
The Sun is so bright that looking at it directly will blind you. Even a mid eclipse, the remaining bright crescent is too bright to view, You need to cut its brightness down by about 100,000 times. Ordinary sunglasses are useless, and you should never use household materials such as bin liners, food wrappers or the like (see below). So either use an authorised eclipse viewer, or project the Sun’s image as described in the PDF leaflet on this website. A welder's No 14 glass is also OK.
Where can I get an eclipse viewer from?
The SPA doesn't have any viewers left, other than those being supplied to its members. The eclipse leaflet lists suppliers, but apply in good time as stocks may be limited.
I’ve often had to look into a low sun when driving – what’s the problem?
Under those circumstances your eye will not fix on the Sun itself but will dart around and a reflex action prevents you from gazing at the actual Sun. But when trying to see the eclipse you may try to force yourself to overcome this reflex, which is dangerous.
Can I view it through thin cloud?
Quite often we do see the Sun’s disc through cloud with no problems. The problem is that when viewing an eclipse we tend to stare at it for longer than we would usually do so, which could cause a buildup of heat. This must be your own decision – if the Sun is so much dimmed by cloud that it’s hardly brighter than the cloud itself, it may be OK for you to look at it briefly, but eyesight sensitivity varies from person to person and this is not based on medical advice. Look away the instant that the cloud thins.
What about looking at a reflection in water?
This cuts the brightness down to only about a few per cent of the original brightness – not nearly enough for safety.
Why can't I look through a negative like I did when I was young?
Years ago, most photos were taken on black and white film, and the black areas of the negatives were made of silver particles. A couple of layers of these could cut down all wavelengths of light quite well. But colour negatives use dyes rather than silver, and these don't absorb all wavelengths of light equally. The worst thing is that even though they cut down the visible light, so the Sun looks dim, they may allow through other wavelengths, such as infrared (heat) which will quietly fry your eyeball without your realising it until it's too late. The same applies to many other dense materials, such as bin liners, smoked glass, food packaging and CDs. So don't take the risk!
How dark will it get?
At mid eclipse the landscape will be dimmer than if the Sun were not eclipsed, though if you didn’t know there was an eclipse in progress you might think that there was cloud dimming the sunlight. It could look quite eerie.
Will I see stars at mid eclipse?
No, not from the UK, though you might see Venus some distance to the east of the Sun.
Will I see the Sun’s corona and prominences?
No, not from any part of the UK mainland. You would have to be on or very near to the line of the total eclipse to see these phenomena.
What if it’s cloudy?
Again, at mid eclipse it will get dimmer, but no more so than if there is particularly dense cloud.
If I miss this one, when will the next one be?
There’s a small partial eclipse on 21 August 2017. We will see just a small bite out of the Sun around sunset. But this is a total eclipse in the US, so if you fancy seeing one this is your best bet. It will be easier to get accommodation near the eclipse line in the US than for other eclipses in other parts of the world. After that, the next partial eclipse visible from the UK is in June 2021.
I've read that there could be power blackouts because of the eclipse. Why?
These stories are total nonsense. It's true that solar power farms will experience a reduction in the power generated, but the dimming due to the eclipse even in Scotland is no greater than you'd get on a cloudy day. And the greatest dimming lasts only a few minutes. So the effect on power supplies will be negligible.
SPA members will receive a FREE hand-held eclipse viewer with their March issue of Popular Astronomy.
Added by: Robin Scagell