The Emu in the Sky

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The photograph above shows the aboriginal "emu-in-the-sky" constellation in the sky. It won its creator, Barnaby Norris, third prize in the prestigious 2007 "Eureka" awards.

To see the "constellation", look at the dark dust-clouds, not the stars!

Below it is the emu engraving at the Elvina engraving site, in Kuring-Gai Chase National Park, near Sydney The constellation is positioned above the engraving as it appears in real life in Autumn.

Many Aboriginal groups have stories about the “Coalsack” – the famous
dark cloud next to the Southern Cross. Some see it as the head of a lawman, or a
possum in a tree, but many groups tell stories of a great emu whose head is the
Coalsack, and whose neck, body, and legs are formed from dust lanes stretching
across the Milky Way. It’s easy to make out the emu in a dark autumn sky, and once
you’ve seen it, the Milky Way will never look the same again This “Emu in the Sky”
has became an icon of the Australian SKA Pathfinder (ASKAP) project.

The Aboriginal Astronomy project aims to study stories like this in a systematic way,
and to explore the importance of astronomy in Aboriginal cultures. The project has
two parts. One is to examine the culture of Aboriginal people, such as the Yolngu
people in Australia’s Top End, whose culture is thriving, and who can tell us about
the role that astronomy plays in their culture. For example, a few weeks ago we were
privileged to be invited to visit the remote Yolngu community of Dhalunbuy. There,
an elder told us a story of the evening star, whose appearance signals the time to
collect Raika nuts, and showed us an “evening star rope” made of stringy vine and
possum fur decorated with the nuts. It was a memorial made at the time of death of his
grandmother, and is still used in modern funeral ceremonies to establish contact with
ancestors. Little of this is known to western science or ethnology.

The other part of the project is to study the artefacts of those Aboriginal cultures
whose culture was badly damaged by the arrival of Europeans 200 years ago. For
example, we are studying a 50-metre stone circle in Victoria which appears to be
aligned on the equinox and solstice sunsets, and we are trying to understand a possible
lunar calendar in South Australia. Closer to home are thousands of rock engravings
around Sydney, most notably in Ku-ring-gai Chase National Park, just 20 km north of
Sydney. Amazingly, many Sydneysiders are unaware of this beautiful sacred art on
their doorstep, showing animals, people, creator spirits, and strange symbols whose
meaning is unknown. It has been suggested that some engravings may be
astronomical, and may even represent constellations.

However, while many sites have been recorded, few have been reliably surveyed, and
most records consist of no more than a hand-drawn sketch, inevitably reflecting the
preconceptions of the recorder. For example, a crescent may be drawn by an
archaeologist as a boomerang, and by an astronomer as a crescent moon. Instead, a
serious study needs an unbiased photographic record. Such a record also has value for
future generations who may not be able to see the real thing, as the engravings are
rapidly being destroyed by acid rain.

However, photographing them is tricky. The grooves are shallow and frequently
obscured by natural undulations in the rock. Received wisdom is to photograph them
at sunrise or sunset, when the low angle of the Sun outlines the grooves with shadows.
But we can’t always wait for sunset, and even then the resulting photo is likely to be
marred by shadows of nearby trees.

Instead, Barnaby Norris and I decided to replace the Sun by a 1000 Joule studio flash
(emitting something like 1MW of light), together with batteries and an inverter for use
at remote sites. Three telescopic pool poles were used to construct a tripod five metres
high, from which we suspend a remotely-operated digital SLR camera vertically
above the engraving. Further image processing, sometimes including spatial filtering,
then clearly shows up the engravings.

One of the most beautiful sites in Ku-ring-gai Chase National Park, close to the
Elvina Track, features a finely engraved emu. A few years ago, Hugh Cairns of
Sydney University pointed out that this engraving looks more like the Emu in the Sky
than a real emu. Furthermore, the Aboriginal artists oriented the engraving to line up
with the Emu in the Sky just when real-life emus are laying their eggs. To illustrate
this, we decided to take a photo of the engraving with the Emu in the Sky correctly
positioned above it. Our low-angle flash technique took care of the engraving, but
what about the sky?

Since the night sky at the Elvina Track site is now ruined by the streetlights of
Sydney, we decided to photograph it from Siding Spring Mountain. A further
challenge is that the emu stretches half-way across the sky, so doesn’t fit in the field
of view of a normal lens. A fish-eye lens on an equatorial mount would do the trick,
but would distort the image, preventing a realistic comparison with the engraving. So
instead we made a mosaic of smaller images that could be stitched together in
software. Furthermore, by taking a series of short exposure images, we wouldn’t need
an equatorial drive, as we could correct for sky rotation in software.
Having taken the photos, Barnaby spent two months stitching the hundreds of images
together, working out how to correct for the distortions and sky rotation while keeping
the shape true to the projection seen by the human eye from the Elvina Track site. The
result was magnificent (see above) and in August won Barnaby
a $2000 prize in the New Scientist Eureka science prizes.

All material on this page © Ray Norris 2007 except where otherwise indicated.
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