Deep Sky
Deep sky astrophotography is about photographing objects – galaxies, nebulae, star clusters, and other objects – outside the solar system. To collect enough light for these faraway objects, an image often involves multiple hours, or even tens of hours, of exposure time spanned across days, weeks or months. Careful post-processing is then needed to bring out the colours and contrast from the very faint images.
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Helix Nebula
The Helix Nebula is a planetary nebula. It sits about 700 lightyears from Earth in the constellation of Aquarius, and spans about 3 lightyears across. As viewed from Earth, it is about half a full moon across.
Planetary nebulae, despite the name, have nothing to do with planets. They are formed at the end of life of a low to medium mass star, when all its fuel for nuclear fusion has been exhausted. The material in the outer layer of the star is ejected into space, while the core collapses into a white dwarf. The white dwarf continues to emit intense radiation, ionizing the ejected material and causing it to glow – hydrogen glows in red, while oxygen glows in blue-green.
Captured with my Skywatcher Quattro 8” telescope and QHY268M camera, with a total exposure time of 4 hours. Processed in HOO palette with RGB stars.
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In the Vastness of Space (NGC 2403)
How big is the universe? Every star in this image is within the Milky Way, our home galaxy. Through this star field we can see NGC2403, a spiral galaxy about 50,000 lightyears in diameter, half the size of Milky Way. The photons from NGC2403 travelled for 10 million years, before falling on the camera sensor to create this image. Yet, Milky Way and NGC2403 are just two of the estimated 2 trillion galaxies in the universe.
This image was captured in RGB and H-alpha with a total exposure time of 8.5 hours, using a SkyWatcher Quattro 8-inch f/4 Newtonian telescope on an equatorial mount.
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Starlight Textures (the Pleiades)
The Pleiades, or Seven Sisters, is probably the best-known star clusters. At only 400 lightyears away, its six brightest stars are easily visible to the naked eye as a tight, dipper-shaped cluster.
The Pleiades are traveling through an area in space rich in interstellar dust. In astrophotography, the Pleiades are surrounded by blue nebulosity with intricate texture. The blue colour is due to dust preferentially reflecting the blue light from the stars, the same physics that make the sky blue on Earth.
This image was captured in RGB with a total exposure time of 7.5 hours, using a Canon 300mm f/4 L telephoto lens on a star tracker.
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Rosette Nebula
Like a red rose in the night sky, the Rosette Nebula is a favourite of astrophotographers. The Rosette Nebula is 130 light-years across and 5000 light-years from Earth. It is an H-II region where the hydrogen gas is undergoing active star formation. The hot young stars formed emit intense radiation that ionizes the hydrogen, creating the characteristic red glow of the nebula. The strong stellar winds from these stars also blow a hole in the gas cloud, and will eventually disperse the gas leaving an open cluster of stars at the centre.
This image was captured with 3 hours of exposure with an astro-modified DSLR and narrowband astrophotography filter.
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Andromeda Galaxy
At a distance of 2.5 million lightyears, the Andromeda Galaxy is one of the closest neighbours of the Milky Way. It is also one of the furthest light sources visible to the unaided eye as a fuzzy grayish patch of light. Astrophotography allows Andromeda to be rendered in colour and great details, showing the dust lanes and blue outer regions of young, hot stars. Andromeda is estimated to contain one trillion stars. Two satellite galaxies, M32 (above Andromeda) and M110 (below) is also seen in this image. Andromeda and Milky Way are expected to collide and merge in about 4 to 5 billion years to form a giant single galaxy.
This image was captured with 1.5 hours of exposure under the dark skies of Northern Ontario.
