Astronomical Imaging

Tuesday 16th April 2013

Unfortunately, our scheduled speaker, Dr Johanna Jarvis had to cancel her appearance at our lecture night due to ill health. Luckily, one of our own members, David Morris, was able to step in and give us the benefit of his experience as a seasoned observer of the night sky. His talk was entitled "Astronomical Imaging" with an emphasis on the actual practice of observing using a variety of astronomical tools.

David began his talk by pointing out that the star patterns in the night sky have been recorded in cave paintings, a comet is represented in the Bayeux Tapestry and the ancient monument of Stonehenge represents an ancient astronomical observatory. Before the advent of photography observers recorded what they saw through the eyepiece of a telescope using pencil and paper.

He showed pictures from a book published in 1885 called "The Moon: Considered as a Planet, a World, and a Satellite" by the astronomers Nasmyth and Carpenter. In it were photographs of what appeared to be the lunar surface. However, David explained that these were actually photographs of plaster models of the lunar surface made from Nasmyth and Carpenter's own sketches. There was only one true astronomical photo of the moon taken by another astronomer, Warren De La Rue.

David explained that, nowadays, amateur astronomers can make use of a number of devices to capture the night sky. A digital camera (preferably on a sturdy tripod) can be used to take photographs of the Milky Way and the constellations, as well as the Moon and planets or passing satellites. If the shutter can be held open for long enough then the stars appear to leave long concentric arcs centred on our planet's axis of rotation near the star known as Polaris.

Some astrophotographers put webcams to use and take a video of the brighter Solar System objects such as the Moon or planets. They then choose a number of the best frames that make up the video and add them together using special computer software to make a final single image.

Those with telescopes and cameras can use the magnification afforded by optical system to image dimmer more distant objects such as planetary nebulae. These are nothing to do with planets but are the remains of the outer atmosphere of a star as it comes to the end of its life when the nuclear reactions in its core die down. These nebulae come in many different shapes and colours and are a popular target for astrophotographers.

After the talk we were able to set up a number of telescopes and binoculars in the car park outside the meeting room. Using the Society's Sky-Watcher Dobsonian 10" telescope we managed to observe the comet PANSTARRS (C/2011 L4) which was just below the constellation of Cassiopeia. The smaller telescopes and binoculars were also used to see a brilliant Jupiter and its four brightest "Galilean" moons; Io, Europa, Ganymede and Callisto. The evening was rounded off by the fleeting appearance of an Iridium satellite "flare" high overhead and the swift passage of a bright point of light which was in fact the International Space Station.