Observing a Sun Eclipse
Observing a Sun eclipse requires safe observational techniques. Observing a solar eclipse is as much dangerous as the usual, daily observation of the Sun. This may cause permanent eye damages, up to blindness! WHATEVER the percentage of the Sun occulted by the Moon, STRICTLY NEVER look directly at the occulted Sun naked-eye nor through the viewfinder of a camera nor of a similar instrument, STRICTLY NEVER look to the occulted Sun through any astronomical instrument (binoculars, reflector, refractor). The only moment when you may directly look the eclipse without any protection is at totality: from the moment when the solar disk totally disappears behind the Moon's disk -when the Diamond Ring fades- to the moment when it is near to reappear -when the western edge of the Moon begins to brighten, announcing the re-appearance of the Sun. It is obvious that, IN THE CASE of an annular eclipse, (when even at the totality the disk of the Moon let pass around a rim of Sun's light) you have to keep the protection tools all along the duration of the eclipse. Obviously the same for a partial eclipse.
Safe Observation Techniques
The main safe methods for astronomically observing an eclipse are:
- specially dedicated solar filters: if you observe through an instrument, you will have to use specially designed astronomical filters which are to be used on the front end of the instrument. STRICTLY NEVER use filters which screw at the bottom of the ocular as the light augmented by the optical system of the telescope will very quickly heat and break this kind of filter (which is obviously very dangerous). As for naked-eye observation, you may take-off the filter at the moment of totality -but not in case of an annular (see above).
- the projection method: the principle of the projection method is to use an astronomical instrument to project the image of the Sun on a screen (these systems are either found on the market or home-made). Be aware that some instruments are not to be used for this due to the risks for the instrument and be aware that an eclipse observation spanning over a great amount of time, there may be risks for the instruments, even if suited for the projection method.
- as far as binoculars are concerned, astronomical filters exist too for them, and, taking your responsibilities about possible damages to your instrument, you may use binoculars with the projection technique. Dedicated filters exist too for cameras.
- to look to the eclipse naked-eye you may use one of the followings: welder glasses: welding glass, welder goggles or the glass for it (both, rating 14 or higher) may be used safely to look naked-eye to the Sun. STRICTLY DO NOT use them otherwise. Appropriate solar filters used with instruments may otherwise be used too for naked-eye observing. All the other types of filters, especially those home-made, like CD-ROMs, film negative, may or may not be safe. Do not use them without further information.
As a conclusion, any other method is unsafe and greatly eye-damaging. Be aware too that even safe solar eclipse observing methods may remain limited. At last be always aware of the fact that the Sun is dangerous to your eyes (you may unadvertly have the reflex of looking to the Sun). Brief about Sun dangers people attending your observation and who would not be used to astronomy. Do not let your instrument(s) unattended (specially when children are about). Be sure that the solar filter you are using is solidly affixed to the instrument, binoculars, so e.g. not to be taken off by a gust of wind or any other mean. Etc. Note that observing the Sun is to be exposed to the Sun; so think of the appropriate protections (hat, solar cream, etc)