Shooting stars: exhibition showcases photos of sky at night

Visitors to the National Botanic Gardens in Dublin are in for a rare treat next month during the first major exhibition of photography by Irish astronomers.

The art of capturing the stars on film and, more recently, with digital cameras has become very sophisticated, but as you can see from the examples here Irish astronomical photographers are no slouches. The photographs by enthusiastic astronomers were taken from various locations around Ireland and from locations abroad favoured by clear skies and reduced light pollution.

As the earth is always moving and long-time exposures are the norm, computer-programmed tracking devices are sometimes used for long exposures to keep the lens on target.

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Part of the Orion image by Tom O’Donoghue and Olly Penrice. It was captured over a four-year period, with the image processing taking a further six months to process

Multiple exposures

Sometimes multiple exposures are made, and software is used to delete the obscured images and retain the clear ones, which are overlaid to build the final image.

For bright objects such as planets short video photography is used. Over a two-minute video clip as many as 3,000 images may be captured, but just 300 images clear of atmospheric turbulence, dust and light pollution are retained to create the finished result. For deep sky objects such as galaxies, colour cameras or mono cameras can be used. DSLR cameras give good results using the internal colour filters.

But mono cameras are more sensitive and filters may be used to capture the colour values. Unlike in a modern digital camera where red, green and blue filters are used simultaneously and instantly to capture a photograph, these filters may be used one at a time to build up the colour of the scene over a longer or multiple shutter exposure.

This allows more light to enter the camera, resulting in a much clearer final result. The use of specialist filters such as hydrogen alpha (H-a), sulphur (SII) and oxygen (OIII) ones allows the astronomers to capture aspects of space invisible to the naked eye.

The images on show will feature several Irish winners of the International Astronomy Photographer of the Year competition organised by the Greenwich Observatory in London.

Mosaic image

Among the works on show will be what is believed to be the largest and most detailed mosaic image of a constellation ever taken by amateurs. The image of Orion by Tom O’Donoghue, with

Olly Penrice

, took four years of data collection and a further six months of processing to complete.

While some of the most impressive images in the exhibition were taken on very sophisticated cameras, it is possible to take good photographs of the night sky with modern consumer equipment.

"Observing and taking photos of what appears in the sky at night is a fascinating hobby which is becoming more popular in Ireland," says John Dolan of the Irish Astronomical Society.

“Telescopes can now be obtained at reasonable cost and recent advances in digital photography have made taking photographs of the night sky more accessible. Many of the photographs in this exhibition have been taken using standard consumer DSLR cameras. The low light capability in these cameras has greatly improved in recent years.”

While the exhibition is for the public, aspiring astronomical photographers will also find inspiration and the advice they need to take their first steps.

Guides and advice

The exhibition will also display the equipment used for viewing and imaging the night sky. Guides and advice will be available along with information on your local astronomy club.

Broadcaster and space commentator Leo Enright will open Images of Starlight on February 2nd. Entry is free and it runs until February 21st.