Astrophotography is taking pictures of things in space: galaxies, glowing clouds of gas, star clusters, planets and the Moon. It is photography pointed at the night sky, with a few extra tricks to catch light that is far too faint for your eyes, or your phone, to pick up.
Why can't I just use my phone?
A phone can photograph the Moon, and under a very dark sky it might catch the Milky Way. But most of what you see in this gallery is invisible to your eyes, even looking through a big telescope. Galaxies and nebulae are incredibly faint. To the eye they look like dim grey smudges, if you can see them at all.
The big idea: collect light for a long time
Your eyes work in real time. They can't save up light. A camera sensor can. If you leave the shutter open, it keeps collecting light, and things too dim to see become visible. In astrophotography a single exposure can last minutes, and one finished picture is built from many of them, adding up to hours.
What it takes
- A telescope or camera lens to gather the light from a tiny patch of sky.
- A camera made for the job. Astronomy cameras are often cooled, which keeps the sensor quiet and the picture clean.
- A tracking mount. The Earth is spinning, so the sky slowly slides past. A motorized mount follows it so the stars stay sharp instead of smearing into streaks.
- A dark sky. City lights wash out faint objects, so the best pictures come from dark, clear places.
- Software and patience. The camera's raw result is only the starting point.
How one picture gets made
- Pick a target. A galaxy, a nebula, a cluster.
- Take lots of long exposures. Each one lasts from about a minute to several minutes, and there can be hundreds of them.
- Stack them. Software lines the pictures up and averages them. Random grain and noise cancel out, while the real, faint detail stays and gets stronger.
- Process the result. A stacked image looks almost black at first. Processing brings out the hidden detail and balances colour, contrast and sharpness. The goal is to reveal what is really there, not to invent anything.
Where the colours come from
Many astronomy cameras take black-and-white pictures through coloured filters (red, green and blue), and the three are combined into a natural-looking colour image.
Other pictures use narrowband filters, which only let through the glow of one particular gas: hydrogen, oxygen or sulfur. Each gas is then given a colour, often teal, gold and blue. These images are still real pictures of where those gases are. The colours are chosen to make the structure easy to see. This is the style often called the "Hubble palette", and you'll see it on much of this site.
Remote telescopes
Clear, dark nights are rare, so many astrophotographers, me included, also use remote observatories. These are telescopes in places like Spain, Chile, Australia and the USA that you can book over the internet. The telescope collects the raw data and I process it into the final image. Each image page lists the telescope, camera and filters used, and credits the source of the data.
How long does a picture take?
A long time. The Andromeda Galaxy on this site is built from 85 hours of exposure, collected over more than two years. The Shark Nebula is 40 hours gathered across one week. More time means more detail and less grain.
Words you'll see on this site
- Nebula
- A giant cloud of gas and dust in space. Some glow, some reflect starlight, some are dark silhouettes.
- Galaxy
- A huge island of billions of stars, like our own Milky Way.
- Light-year
- The distance light travels in one year, about 6 trillion miles. If something is 2.5 million light-years away, the light in the picture left it 2.5 million years ago.
- Exposure / integration time
- How long the camera collected light. "Total: 40h" means 40 hours of exposure added together.
- Narrowband
- Filters that pass only the light from specific gases. You'll see them written as Ha (hydrogen), OIII (oxygen) and SII (sulfur).
- Mosaic
- Several overlapping pictures stitched together to make one bigger view of the sky.