Totality

Dark Sun over Libya, 29 March 2006

Julian, Honorary Tuareg


Introduction

An eclipse to put all others in the shade! Expectations were high and so was the outcome - where better to see a total eclipse than from the Sahara desert (satellite photo: overview / detail), where the chance of being clouded out was a mere 10%. The astronomical circumstances would allow this eclipse to last a full 4 minutes 4 seconds from our location. An almost unfair advantage, and a real privilege to see it from a country only recently reopened to Western visitors, and still largely unspoilt by the effects of tourism.

This was by far the longest totality I have seen, and is more than double my entire accumulated minutes of totality up to that point - 2 eclipses with a grand total of 2 minutes! The long duration arises from a combination of a close Moon (5% larger than the Sun), which means a large shadow, and a near-noon and near-equatorial situation, meaning that the Earth's own rotation counteracts a third of the Moon's 2000mph (3200kph) speed, thereby extending the duration of the eclipse.

For a full account of our 3 week trip, and a good quantity of photos, please see my journal. This was originally written up on My Trip Journal, which I can thoroughly recommend as a way of making friends and family at home envious of your travels in as real a time as local internet access allows.

The entry for 29th March is a full account of eclipse day, but on this page I mention more on the features of the eclipse itself and include many additional and larger pictures. For a better appreciation of events I recommend that you visit the journal first then come back to this page (there are links to come back here), but however you do it, read them both and enjoy!


Build up to Totality

I caught the moment of First Contact, when the first small bite appears out of the Sun, visually in the telescope. However, connecting it all up and helping others get their camera ready meant I was not ready to start photography through it just yet, so the Moon was about a third of the way across before I secured this shot...

First bite out of the Sun

The Moon is about 2/3 of the way across the Sun now. Notice the 3 sunspots on the left side of the Sun - these were the only the blemishes on the unwise unmarked sun, typical of when solar activity is low, as it was at this time.

Sun two-thirds covered

The same thing projected on the ground by Michael, using one half of a pair of binoculars, and photographed by Sabine...

Projection of the Sun by binoculars

The crescent Sun gets narrower and the advancing limb of the Moon reaches and covers the sunspots...

Sunspots disappear
In the one minute between these frames the Moon advances roughly 23 miles (37km) relative to our position on the Earth. In terms of the sunspots this represents about 8000 miles (13000km) across the face of the Sun, because the Sun is some 400 times further away than the Moon.

The narrowing crescent made a fine sight in the telescope and with eclipse viewers. With a crescent as narrow as this, you would have to be really unfortunate not to be able to catch totality too!

Narrowing crescent

Almost totality now, with just a minute to go. Excitement mounts...!

Thin sliver of Sun

With the advancing Moon the crescent became not only narrower but also shorter. By now, and even at the T - 5 minute stage if you look carefully, it is clear that the Moon is larger than the Sun - the excess is in fact 5.2%.

Contrast this with the annular eclipse of 6 months ago, where the Moon was at the far point in its orbit and failed to cover the Sun completely. The shortfall was 4.2%, so on this occasion the crescent, instead of being snuffed out by the Moon, actually extends around it in an embrace. At the moment of annularity the arms meet up at the back of the Moon and form the "Ring of Fire" characteristic of annular eclipses.

Meanwhile, for anybody not looking through a telescope, strange things were happening to our surroundings...

The temperature was falling - this had become evident some half an hour into the eclipse, and some measurements from Judith's mobile phone revealed the drop quite well...

 

Normally the minimum temperature lags totality by a few minutes so the apparent increase at 10:30 is probably an aberration, given that the phone was sitting in a handbag! Not very scientific, but I think the trend is obvious enough!

Time (UT & Relative to 2nd Contact)

Temperature (degrees C (and F))
10:00 (T - 26 mins) 34 (91)
10:15 (T - 11 mins) 28 (82)
10:16 (T - 10 mins) 27 (80)
10:25 (T - 1 mins) 23 (73)
10:30 (End of totality) 25 (77)
Near 4th Contact 35 (93)

The light began to change much earlier than I had noticed in previous eclipses - normally the human eye accommodates the falling light level very well, in contrast with our perception of temperature, which is very sensitive. While the ground appeared unchanged, apart from our sharpening shadows caused by the narrowing Sun, the sky began to darken about half an hour before totality, and by 10:00UT (12 noon local) Venus was clearly visible.

 

Venus at 10:22UT, 5 minutes before the onset of totality.

Sanyo A5, 8mm; 1/45s @ f/3.3, ISO125

Venus

The following 4 shots looking south west, in the direction of the oncoming shadow, show the change wonderfully...

09:34 (T - 50 minutes) is essentially normality. (1/1000s @ f/5.6, ISO100; credit Matthias)

10:24 (T - 3 minutes) shows a significant sky darkening but to the eye the desert still looked reasonably normal. (1/60s @ f/2.8; credit Guenther)

10:25 (T - 2 minutes) has the light draining from the sky, which takes on a wierd grey colour. The Moon's shadow is now only 50 miles (80km) away and approaching rapidly so we are looking into a huge volume of unlit sky, a cylinder roughly 100 miles (180km) in diameter. (1/60s @ f/3.5, ISO100; credit Matthias)

10:30 (Totality, T + 3 minutes) is looking from within the shadow out to the sunlit sky beyond, which appears like a sunset stretching all the way around the horizon. (1/8s @ f/2.8; credit Sabine)

Scene 50 minutes before totality Scene 3 minutes before totality
Scene 2 minutes before totality Scene during totality
The aperture and shutter speeds above give a true indication of the relative light level, though unfortunately the cameras providing 2 of the shots failed to record the effective film speed (ISO number). The shot at 10:25 has 32 times more exposure than the one at 09:34 - the ground is not hugely dfferent, either in the picture or at the time, which reveals just how good the eye is at handling different light levels without us noticing.

Totality

The last points of light winked out on the left hand side of the Sun, but the high Sun in a clear sky meant that it was difficult, and dangerous, to see Bailey's Beads with the naked eye without a filter. Then totality..., filters and viewers off, night descends with alarming speed, and the outer corona springs into view around the jet black silhouette of the Moon...

Corona - medium exposure - click for details
Click on the picture to see another one with the details - this one is too beautiful to spoil with writing!

The pearly white outer atmosphere of the Sun streams away along the magnetic field lines radiating away from the Sun's north and south magnetic poles - who needs a bar magnet experiment at school when you can see it on a grand scale in the sky!

The corona is relatively evenly spaced around the Sun, in fact having an almost rectangular shape when viewed with the naked eye. This is characteristic of a "solar minimum" eclipse, where the Sun reaches a low point in its activity in its 11 year cycle. Now is just such a time.

I have said on previous eclipses, and will probably do so again, that a single photograph doesn't come close to revealing the true beauty of totality as seen by the eye, especially through binoculars or a telescope (my first opportunity for this). With its greater ability to handle both bright and faint simultaneously, the eye picks up both the inner corona and the outer wispy streamers in exquisite detail, whereas on a photograph some part or other is either over or under exposed.

Increasing the exposure reveals the full extent of the corona, but of course makes the inner corona grossly over-exposed. This picture even shows a suggestion of Earthshine, the light of the Full Earth shining back onto the night side of the Moon. This is easy enough to see when the Moon is a thin cresent within a few days of New, as in this picture by Brent taken two and a quarter days after the eclipse, but I have never noticed it in an eclipse before - perhaps the black sun is not so black after all!

Corona - long exposure

To reveal the inner corona a much shorter exposure is needed. This shot is towards the end of totality, with the Moon very much off centre and the brightening at lower right heralding the imminent reappearance of the Sun's brilliant photosphere. Still rather over-exposed is a pink fiery prominence, rising like a flame above the chromosphere, which itself revealed as a thin pink band on the right...

Corona - short exposure

Third Contact. The Sun's blinding photosphere bursts back onto the scene in a beautiful Diamond Ring...

Diamond Ring - click for details
Click on the picture to see another one with the details - again too beautiful to spoil with writing!

Although this picture isn't quite the shortest exposure the camera can do, I was operating with a very 'fast' optical system at this magnification, so had to rely on others to show the chromosphere correctly exposed. Roger and Annie, who piggy-backed their camera onto one of my two telescopes, capture the elusive Bailey's Beads perfectly as the Sun breaks through two valleys on the trailing edge of the Moon. They last only a matter of moments, before joining up and before you know it, totality is over...

Prominences Bailey's Beads

The wide shadow of this eclipse, about 113 miles (180km) across at this point, meant that little light was able to reach us from the sunlit region around the edge, so it did get seriously dark during totality, as this photos reveals...

Roll the mouse over to see the same scene before and during totality
Click picture to open Totality in a new window

Return to Normality

The sky brightened rapidly after Third Contact. In reality, being near local noon and with the Sun at 62 degrees altitude, the Moon's shadow fell almost vertically on the Earth so the brightening was probably a mirror image of the darkening before totality. However, with our eyes now accustomed to the dark, the return to sunlight seemed that much more intense.

Turning around I was instantly aware of a subtle rippling effect on the ground, much like the way sunlight behaves on the bottom of a swimming pool. These were "Shadow Bands", an elusive phenonemon seen within 30 seconds or so of totality, both before and after - some of us did indeed see them before totality but I caught them only now.

Photography of them was unfortunately unsuccessful. Perhaps their movement, a slow walking pace towards the east, blurs them out in the pictures at 1/45s shutter speed, or they are lost in the gravelly desert floor. No amount of tweaking the settings of the images shows any sign of them. Perhaps the secret is to video them, because it is their movement that maked them so obvious.

Not the Shadow Bands!

The emerging Sun started off as a narrow crescent, but of course was now on the other side of the Sun. This shot shows it at about the time the shadow bands were fading away, meaning that an exceptionally thin crescent is needed to produce them...

Thin sliver of Sun reappears

The crescent Sun grows at the same rate as it shrank before totality...

Crowing crescent

Normality restored and a group photo to prove it...

Click the picture for a larger version


Conclusion

A spectacular eclipse, thoroughly successful and a privilege to see it from this strange land. While not everything in the eclipse camp went to plan, it was nevertheless a perfect result, in conditions that could hardly be bettered.

If you wish to read more of our adventures and see a good collection of pictures, albeit rather small, please see my journal. Besides the eclipse we saw more Greek, Roman and Berber ruins than you could possibly wish for, travelled through hundreds of miles of desert scenery, and went off-road in spectacular rock and dune filled deserts in Tuareg country, in the far south west of Libya.

Here is a selection of sites of other members of our party and also some further information and pictures of the eclipse....

Journal of 3 weeks in Libya (or straight to Eclipse Day - 29 Mar 2006)  Julian Taylor
Eclipse pictures Frederic Pertuisot
Southern Comets Homepage - travelled from Australia to see the event Michael Mattiazzo
Poisaya - a short hop from France to see the event Yannick Blin & Isabelle Rapin
Link to Fred Espenak / NASA Total Eclipse 2006 (Circumstances of eclipse / Pictures)  
British Astronomical Association Total Solar Eclipse 2006 gallery  
Space Weather Solar Eclipse Gallery  

3 Oct 2005 Solar Eclipse Home 1 Aug 2009


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