Observers at Ceduna, Lyndhurst, and various South Australian towns slightly south of Andamooka, Glendambo and Roxby Downs, and slightly north of Leigh Creek and Woomera, will witness a Total Solar Eclipse as the Moon passes between the Earth and the Sun, entirely "blocking out" the Sun for around 30 seconds.
The shadow seen on the Earth where the sun is completely covered up in a Total Eclipse, is called the umbra. A total eclipse is only observable within the narrow strip of land or sea over which the umbra passes.
The shadow seen on the Earth where the sun is partially covered up, is called the penumbra. A partial eclipse is observable from within much wider area of land or sea. Occasionally, when the Moon skims between the Sun and the Earth, but not directly between them, a partial solar eclipse is observed.
Although the Sun and the Moon appear almost the same apparent size from the Earth, their apparent sizes depend on their distances from the Earth. As the Sun and Moon's distance from the Earth constantly varies due to the elliptical orbit of the Earth around the Sun, and the Moon around the Earth, the distance of the Sun and Moon changes just enough so that the Sun and Moon's apparent sizes appear to change over the course of time.
As such, when the Moon is furthest in its orbit from the Earth, and the Sun is at its closest point to the Earth, an annular eclipse occurs, as the apparent size of the Moon is smaller than that of the Sun. When this type of solar eclipse occurs, the Moon's does not completely cover up the Sun, and a ring of the Sun is visible right around the Moon.
Totality occurs less than an hour before sunset, which will provide an excellent opportunity to photograph the landscape of the Australian Outback in conjunction with the eclipsed Sun.
The total duration of totality of the eclipse is around 30 seconds, depending on your location. Observers at Ceduna will have 32 seconds to witness this amazing event, while those at Lyndhurst, in the northern Flinders Ranges will have around 26 seconds of totality. Around the town of Woomera, observers will have around 29 seconds of totality. The remainder of the eclipse path is mostly in the remote Outback Australian desert.
The first sign of the eclipse from the Earth will be when the Moon's disc first "touches" the Sun. This is known as "First Contact". Depending on your location, First Contact will be anywhere between 6.38pm - 6.45pm for South Australia, 3.56pm - 4.04pm for Western Australia, 5.38pm - 6.03pm for the Northern Territory, or 7.06pm - 7.14pm for NSW, Victoria and Tasmania. All times are "Local Time". At First Contact, the Moon begins to take a "bite" out of the Sun, as the eclipse progresses, this "bite" gets larger.
As totality approaches, and the Sun is nearly covered, narrow bands of shadow and light known as shadow bands, may be seen racing across the ground. These are multiple images of the remaining "slice" of the Sun, caused by irregular refraction in the Earth's atmosphere. If you are observing the eclipse under trees, you may see dozens of images of the crescent Sun being projected on the ground due to the "pinhole camera" effect of the space between the leaves.
As the Moon proceeds to completely cover the Sun, the Moon's shadow may be seen rushing in very quickly from the west. The remaining slice of the crescent Sun gradually shrinks to a sliver, and then breaks up into dozens of distinct points of light, known as Bailey's Beads. These are caused by the Sun shining through mountains and valleys around the edge of the Moon. When only one Bailey's Bead is left, the amazing "Diamond Ring Effect" may be observed. "Second Contact" then occurs, signalling the first instant of totality.
During totality, the sky will darken, with strange shadow effects caused by scattered light from the edge of the eclipse, however the horizon will still appear fairly bright. The surrounding outback landscape will takes on an eerie appearance, with the eclipsed Sun "floating" a few degrees above the western horizon surrounded by the faint halo of the Sun's corona, too dim to be seen at any time other than during a total eclipse. The Sun's lower atmosphere, the chromosphere, may be seen as a reddish glow around the edge of the Moon. You might also spot various solar prominences or arcs of glowing red gas looping around the Sun. When the sky is nearly dark, Mercury and Antares should be seen nearby.
Around 30 seconds after Totality begins, the whole process will go into reverse. This is "Third Contact", the moment at which the Moon begins to uncover the Sun once again, a final opportunity to spot the "Diamond Ring Effect", "Bailey's Beads", and shadow bands on the ground.
Following Third Contact, the Moon gradually uncovers the Sun, and semi-normal daylight returns, leaving a gradually diminishing "bite" on the Sun's surface, as the Sun will slowly set with a small "bite" still missing. "Fourth Contact", the point at which the Moon's silhouette finally leaves the Sun, will be visible only from Western Australia.
If you do not have one of these filters, you can project an image of the Sun through a small pinhole onto a flat surface, and watch the image. If you're not sure what to do, then observe with someone who does know how to safely observe an eclipse, or contact your Local Astronomy Club.
When the moon begins to cover the sun, it can be very tempting to take a peek directly at the sun. However, the sun is just as dangerous then as it would be looking directly at the full sun. If you look directly at the sun during the partial eclipse, serious permanent damage can occur to your retina (part of the eye), causing permanent blindness.
It is only safe to look at a solar eclipse when the moon completely covers the disk of the sun and the corona is visible. There are safe ways of observing an eclipse, such as using a pinhole camera or projecting a telescope image onto a sheet of paper.
The totally eclipsed sun may be safely viewed without protection, but be extremely cautious when totality ends - even a minute flash of direct sunlight can cause permanent irreversible damage to your eyes!