A Total Solar Eclipse

​What is a Total Solar Eclipse?

 

An eclipse of the Sun occurs when the orbit of the moon passes in front of the Sun as seen from the Earth. The shadow of the moon follows a narrow path on the surface of the Earth, bringing daytime darkness for a brief period and allowing observers to see a range of unusual natural phenomena. The most spectacular sight is a total solar eclipse, when the moon completely covers the Sun, with crimson prominences licking around the jet-black disk and streamers of the solar corona reaching far out into space.

Eclipse diagram
Total Solar Eclipse, Diamond Ring and Prominences

The orbit of the Moon

 

As the Moon goes around the Earth it follows an orbit which is elliptical, appearing very slightly smaller when further out and larger at the closer point. Whilst it is not possible to detect this difference in size without accurate instruments, when the moon is at its closest point it is large enough to completely obscure the disk of the Sun and the closer it is the longer the duration of the eclipse.

Phases of a Total Solar Eclipse

There are five stages in a total solar eclipse:

  1. Partial eclipse begins (1st contact): The Moon becomes visible over the Sun's disk. It looks like the Moon has taken a bite out of the Sun.

  2. Total eclipse begins (2nd contact): The Moon covers the entire disk of the Sun. Observers in the Moon's umbral path may be able to see the diamond ring effect and Baily's beads just before totality.

  3. Totality and maximum eclipse: The Moon completely covers the disk of the Sun. Only the Sun's corona is visible. This is the most dramatic stage of a total solar eclipse. At this time, the sky goes dark, temperatures can fall, and birds and animals often go quiet. The midpoint of time of totality is known as the maximum point of the eclipse.

  4. Total eclipse ends (3rd contact): The Moon starts moving away, and the Sun reappears. Those fortunate enough to be in the Moon's umbral can see Baily's beads and the diamond ring effect just after totality ends.

  5. Partial eclipse ends (4th contact): The eclipse ends as the Moon leaves the Sun's disk.

What is an Annular Solar Eclipse?

When the Moon is at a more distant point of its orbit the Sun is not completely covered and a very small, bright circle or annulus remains visible around the moon. This is known as an annular eclipse and although it lacks the unique drama of a total eclipse, it is an unusual and interesting event particularly when it is possible to observe the effect of the declining light levels on wildlife.

The path of the shadow

A total eclipse of the Sun is only visible from a very small strip on the Earth's surface, occurring once every eighteen months or so. Unless you are exceptionally lucky, as the shadow can pass over any part of the Earth, you are almost certainly going to need to travel away from home to see this event. For most people travelling to see an eclipse, this is a large part of the attraction as nature has set the destination and the journey is usually a discovery of unknown places and new people.

Where can I see an Eclipse of the Sun?

You will find information about future solar eclipses on many sites on the internet, including this one. Look for a track of the eclipse shadow path and you can see which countries and towns will be under the shadow. You will want to pick a location with facilities such as transportation and hotels and also a place which offers good weather prospects as a cloudy sky could prevent observation of the complete eclipse. The closer you can get to the centre of the eclipse path, the longer the duration of the total eclipse.

The Eclipse observation site

On the day of the eclipse you will want to get to your observation site in good time before “first contact”. That is when the edge of the moon first touches the edge of the Sun. At this stage you will need a special viewer to look at the Sun as a curved 'bite' is taken from one side.

Phases of a total solar eclipse
USA 2012 Annular - Nick James

Credit: Nick James

Observation site, San Juan, Argentina 2019

​Waiting for the Moon

Tension starts to build as the moon progressively covers the Sun. The light level goes down, but at the same time your eyes adapt to the gradual changes so the change remains almost unnoticed until the eclipse is well advanced. The landscape is drained of colour and shadows sharpen as the Sun is reduced to a bright crescent and eventually a single point.

​Stars and Planets

Look at the shadows under a tree and you will see the leaves create a thousand small arcs of light. The temperature only drops a degree or two, but there is a sense of chill in the air as the radiant heat from the Sun is cut off. 

A blue sky has turned to a pale morning grey and bright planets have reappeared. The last couple of minutes before totality race through at top speed as the moon's shadow hurtles towards you. The sun is reduced to a single searing point of brightness and as this final point is extinguished, bright beads remain momentarily along the edge as the sunlight shines through the valleys on the moon.

Observation site, Fortin Noguiera, Argentina, 2020

Credit: Nick James

​The Eclipse event

Suddenly the brightness is gone, leaving a jet-black disk of the moon clothed in the flowing robes of the solar corona and surrounded by the delicate red rim of the chromosphere. Crimson licks of prominences reach out from the rim and as your eyes become accustomed to the dark, the fine structure of the corona becomes visible.

There is an unearthly red glow around the horizon and a sense of a large dark shadow looming above. The time of totality ticks by, then a few flickers of bright beads on the edge of the dark disk herald the end of the performance. The burst of light which shocks your dark adjusted vision is the final climax. Always expected but always a surprise: sunlight returns, colour and warmth are restored, everything is back to normal. Until next time...

TSE2019 Posta Kamak Argentina 2019

Credit: Nick James

Planning to see an Eclipse

 

Success in observing an eclipse requires a mix of detailed research and, as far as the weather goes, an element of luck! 

 

You need to know the date of the eclipse, the track the shadow will follow and the time the sun will be eclipsed at each point along the track. You will need climate data for the track for that time of year to pick the most promising location for a clear sky.

The eclipse duration will be of shorter if your observation point is towards either end of the track and reduces if you are away from the centre of the track. It is better to sacrifice some duration in favour of better prospects of a clear sky. You will also need to find a way to get to the chosen location, flights, hotels and such like and then you usually need local transport on the day. The increased interest in viewing an eclipse makes it essential to fix all these matters up a long time in advance.

TSE202020 Fortin Noguiera, Argentina 2020

Credit: Andreas Moeller

When is the next Total Solar Eclipse?

 

Our current eclipse projects can be viewed here

Eclipse Tracks

 

All eclipse tracks on this site are reproduced from the site constructed and maintained by Xavier Jubier, we acknowledge are grateful to him for his permission to use them. Without doubt he has produced the best web site for detailed information about the tracks of the Moons shadow across the earth’s surface  http://xjubier.free.fr/en/site_pages/SolarEclipsesGoogleEarth.html

 

The site is maintained by Xavier Jubier as a free service and provides a vast amount of technical detail about the time and place of eclipses.  Using Google Earth maps as the basis for the geographical locations, the program gives details of exactly what eclipse will be observed at any point on the planet.  If you enjoy maps as much as we do, you will find this site a real treat!

Viewing an eclipse through eclipse viewers

Credit: Nick James