Observing a Sun Eclipse

CAUTION! 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. see safe observation techniques

Safe Observation Techniques

Observation: Using a Solar Eclipse Map

Safe Observation Techniques

Warning! You will note that some manufacturers advice against the use of such or such telescopes with such or such techniques. check your telescope manual, and/or manufacturer for further instructions!

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). For a complete overview about using solar astronomical filters with instruments, see the tutorial "Observing the Sun"
• 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. For a complete overview of the projection method and of the instruments not suited for the method, see the tutorial "Observing the Sun"
• as far as binoculars are concerned, astronomical filters exist too for them, and, taking your responsabilities about possible damages to your instrument, you may use binoculars with the projection technique (for more details see the tutorial "Observing the Sun"). 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. A good start to look for some is to look at the site of Sky & Telescope
• anecdotally, let's say some words of the pinhole projection: based on an optical principle, the pinhole projection takes advantage of the fact that Sun passing through a narrow hole will yield, at distance, an image of the Sun's disk. There are a lot of possibilities for such a "pinhole camera" (two cardboards -one with the pinhole, a box, etc). The main thing is just to use it your back to the Sun. An improvement to the method is to shade -box, screening- the part on which the Sun is projected. Derivations of this method are that you may yield such a projected image by the simple mean of crossing your hands one above the other, fingers stretched and adjusting to get the pinhole image, or that Nature naturally provides some natural pinholes projectors (e.g. sunlight passing through the leaves of a tree will produce these images at distance, or on a wall, etc)

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. see more at the tutorial "Observing the Sun". At last be always aware of the fact that the Sun is dangerous to your eyes (you may inadvertly 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) inattended (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)

Observation: Using a Solar Eclipse Map

a total solar eclipse is a remarkable, and rare sight. picture site 'Amateur Astronomy', from Celestia

Technical data useful for the observation may be drawn from the usual eclipses maps. These maps display, on an Earth's view, a view of the path of totality or annularity (there where the eclipse is plain, where the Moon's umbra hits the Earth) and a view of the "path of partiality" (zones of the Earth where the eclipse is only seen as partial, where only the Moon's penumbra is concerned). see an example map (map courtesy courtesy Fred Espenak, NASA/Goddard Space Flight Center, site Fred Espenak's Eclipse Home Page)

The penumbra affected zones are often grid-lined drawn; north and south of the grid mark the north and south limits of the path of penumbra (in case of an eclipse being only partial for any place on the Earth, this grid has only one limit). East and west of the grid for the partial penumbral eclipse -a part outside of the grid, a part inside it- are the zones (in form of loops) where the eclipse ends at sunset or begins at sunrise (when the penumbral zone has a north and a south limit, the loops are separated: otherwise they are linked). Each loop is delineated between the outside of the grid part and the inside one by a line which marks where the maximum of the eclipse (partial or total) takes place. Vertical lines (i.e. running from northern to southern limit of the grid-penumbral zone) link the places where the eclipse is at its maximum at the same time (they are said "curves of maximum eclipse") as horizontal lines (i.e. running from western to eastern limits of the grid-penumbra zone) link the places where eclipse magnitude is the same at its magnitude -northern and southern "horizontal" limits of the grid being the places of magnitude 0 and lines scaling from there by increments of 20% towards the central path (these lines are said "curves of constant eclipse magnitude"). The intensity of the eclipse is varying each side the path of totality or annularity, function of the latitude or of the distance to the path. That is that the further the central path of the eclipse, the less of Sun is occulted by the Moon and reciprocally, the nearer the path, the more of Sun is seen occulted

Running center of the zone, now, is the path of totality or annularity, there where the eclipse is total, the totality being the one of a total or of an annular eclipse. In case of a partial eclipse for any place on Earth, there is not such path, as the Moon's umbra just misses the Earth and the eclipse is just partial for every place concerned. The point marked "Greatest eclipse" is technically the point where the umbra passes at the nearest of Earth's center (it may be considered as the equivalent to the greatest magnitude and to the greatest duration (total eclipse) of the eclipse; for partial eclipses, the point is on the day/night terminator

Timing of the eclipse is given too. P1 to P4 technically are moments of first-last external-internal tangency of the penumbra with Earth's limb as U1 to U4 are the same moments for umbra. Practically P1 to P4 mark the moments of the eclipse for the places where it is partial; P2 and P3 only exist if the whole cone of the penumbra is contained by the Earth's disk. And U1 to U4 mark the moments for the places (path of totality or annularity) where the eclipse is total (total or annular)

At last other data may be found -among them: S.D. is the semi-diameter for Sun and Moon (in "Sun -or Moon- at Greatest Eclipse"); "eclipse magnitude" is technically the fraction of the Sun's diameter obscured by the Moon at greatest eclipse; gamma is the minimal distance in Earth radii of the umbra axis from the Earth's center at greatest eclipse. "Local circumstances" give data for the place of greatest eclipse (coordinates, altitude and azimuth of the Sun, width of the central path, duration of the eclipse)

For details about how a Sun eclipse works, see the tutoriel "Sun Eclipses"