Observation Observing a Sun Eclipse

CAUTION! OBSERVING A SOLAR ECLIPSE IS A MUCH DANGEROUS AS THE USUAL OBSERVATION OF THE SUN! OBSERVING A SOLAR ECLIPSE WHATEVER THE FORM OF IT (total, annular, partial, etc.) WITHOUT APPROPRIATE TECHNIQUES MAY HARM YOURSELF, CAUSING BLINDNESS AND/OR IRREVERSIBLE INJURIES! 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

Observing a solar eclipse, whatever the type, is as dangerous as observing the Sun. Observing the Sun or a solar eclipse without any appropriate protection is dangerous because your eye is exposed to the strong intensity of sunlight and to the ultraviolet and infrared radiation of it which both are -silently- harmful to the retina. Appropriate techniques for the observation of the Sun thus has to protect the observer against such three components of sunlight! In any case, avoid last minute experimentations in terms of the techniques chosen for the observation of a eclipse and make some trials before!

->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!

->Warning! No matter what recommended technique you use, do not stare continuously at the Sun. Take breaks and give your eyes a rest!

->Warning! If your eclipse glasses or viewers are compliant with the ISO 12312-2 safety standard, you may look at the uneclipsed or partially eclipsed Sun through them for as long as you wish. Furthermore, if the filters aren't scratched, punctured, or torn, you may reuse them indefinitely

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). Always inspect your solar filter before use; if scratched or damaged, discard it! For a complete review 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 12 or higher) may be used safely, hand held, to look naked-eye to the Sun. STRICTLY DO NOT use them otherwise. You may also use any appropriate solar filters used with instruments which may otherwise be used too for naked-eye observing. All the other types of filters, especially those home-made, like CD-roms, film negative, medical radiographies MOSTLY ARE NOT safe as most consider them unsafe. Don't use them without further information. Some details may be found at Sky & Telescope, for example. As far as dedicated solar eclipse glasses manufactured and spread at the occasion of a solar eclipse are concerned, it looks like you may also use them for the observation of the Sun as, for example, you may use them to observe a Venus transit. If you normally wear eyeglasses, keep them on. Put your eclipse glasses on over them, or hold your handheld viewer in front of them. AT LAST, let's call your attention against looking at a low-hanging and/or reddened Sun. Even if it is tempting, don't! Even low on the horizon, and/or reddened, the Sun is as dangerous as a plain Sun!

As far as the question of using a welding glass in conjunction with a instrument or binoculars, most sources warn not to do as the magnifying power of those will amplify the sunlight beyond the filtering power of the glass! One brand of a solar aluminized metal sheet however to use with a instrument states that the protection afforded is equivalent to that of a shade-12 welding glass, which implies a welding glass may be used in such conditions. That brand however is further warning that a welding glass, according to current scientific knowledge, might not protect against a type of eye damage called 'phototoxic reactions,' albeit their filter is protecting against 'photocoagulation,' or thermal damage to retina (check more)

• 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) as the projection surface should be by three feet behind the opening. 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. A variation is the 'pinhole mirror', which gets a small image however, is by which you cover a pocket mirror with a piece of paper that has a quarter-inch hole punched in it and place the mirror at sunlight on the window in a darkened room so it reflects a disk of light onto a far wall inside. The farther away the wall the better, as a large hole has a bright image and a small one a sharp but dim one. Derivations of the pinhole method are also 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). Eclipse charts from other source may slightly differ from that description

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 eclipse (partial or total) occurs. 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. Left of the map, both pink lines, with a form of elongated leaf, are showing where the eclipse ends by sunrise (leftmost line) and where it begins by sunrise (rightmost one), respectively as the line between both is where the eclipse's maximum is reached by sunrise. Conversely, right of the map, both pink lines are showing where the eclipse begins by sunset (rightmost line) and where it ends by sunset (leftmost one), as the line between both is where the eclipse's maximum is reached by sunset

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. More accurately, the point of greatest eclipse is where the axis of the Moon’s shadow passes closest to the center of the Earth and since that is a strictly geometric concept, astronomers use this point to compare different eclipses with each other. On the other hand, the point of greatest duration is where totality lasts the longest along the very center of the path of totality. Typically, the duration of totality at greatest duration and greatest eclipse differs by just a few tenths of a second as their geographic location may differ by 6 to 60 miles

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 partial eclipse for the location of the Greatest Eclipse like indicated on the map; 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 of the total or annular eclipse for the location of the Greatest Eclipse like indicated on the map. Such values are those for the location of the Greatest Eclipse like indicated of the eclipse's map. As far as the other locations where the eclipse is seen either in its total, annular or partial form -one speaks of 'local circumstances' to the eclipse- one has to use varied sources (Web sites, etc.) to get the values in local time of the main eclipse's moments. 'Curves of maximum eclipse' on the eclipse's map, allow to a first approximation in terms of when the greatest of the eclipse occurs for a given time. With our example, the eclipse's greatest in northern Chile is seen by 21h 30 UT

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"