How to take photos of outer space

Above image: The Fighting Dragons of Ara, reprocessed from banked captures. Joe Nidd

MOTAT: So, Joe, explain what astrophotography is?

Joe: Astrophotography is taking a photograph of an object in space, which could be anything from the Moon and planets to deep space objects in both our own Milky Way and galaxies far beyond.

How did you get into astrophotography?

I had an interest in space for a long time, so I bought a telescope. Which was probably a mistake because that led me down an expensive and time-consuming trail to where I am today!

I really enjoyed looking at planets, the Moon and stars and wanted to be able to share what I was seeing with friends and family.

So about six years ago I was gobsmacked to discover that I could capture what I was seeing using pretty basic equipment. The only other images I had seen of deep space were from NASA Hubble Imaging and the like.

And so, I wondered what I could achieve if I invested in some better equipment. It escalated from there and now I have a remote-operated observatory in Naseby, where the night sky is among the darkest category of skies in the world on the Bortle scale, with almost no light pollution.

Tell us a bit about your set-up.

Well, my observatory is self-built and it’s about 2.5m x 2.5m. There’s a concrete pier in the form of a 400mm diameter pipe filled with concrete and steel – because you need the telescope to be very stable. A lot of my images are taken with an effective focal length of two or more meters and each exposure can be five minutes or longer, so it needs to stay completely still. You can’t risk a gentle breath of wind ruining a 5-minute exposure which is a reality at these focal lengths.

On top of the concrete pier is an equatorial mount aimed directly at the Southern Celestial Pole. If you drew a line through the Earth from north to south through the South Pole, I aim the telescope at the point in space where that line would intersect, so when Earth rotates, everything appears to be rotating around that point. If the mount then tracks at exactly the speed required to counter the Earth’s rotation, it can lock onto an individual star for hours at a time, and that means I can take very long exposures and tell the computer, hey, I want to go back and look at that exact spot night after night to build up enough data to reveal these extremely faint objects.

I rigged up an off-the-shelf gate opener to the roof of the observatory (which is mounted on garage door runners) so I can remotely open and close it from home. I’m connected to a computer in the observatory and then that's connected to all the equipment. I can watch the images being captured in real-time and make sure everything's on track including monitoring the temperature and humidity. It can drop to -10 degrees in the winter at 600m above sea level in the Maniototo so I even need to run warmers on the lenses! All of this is automated so I can set up, go to bed, and then process all the data once I have everything I need to compile the final image.

Why are dark skies important?

The goal of astrophotography is to capture extremely faint objects that are sometimes tens of millions of light years away and way beyond the capabilities of the naked eye. Sometime my targets are far beyond the extents of our galaxy. The darker the sky, the more likely it is that you will be able to image the extremely faint light against any background light pollution.

That kind of time and distance is hard to fathom.

Yes, so, if we use Thor's Helmet as an example, which is in the Milky Way – in the context of the universe, that's right next door – the emitted light started its journey over 12,000 years ago. That photon has travelled at the speed of light (approximately 300,000 km per second), more or less in a straight line, for those 12,000 years. And then, by some chance, that individual photon managed to enter my telescope and hit the sensor. And there are so few of those photons that reach us, you need to keep your sensor pointing at something for maybe 20 or 30 hours to capture enough light to get a clear image on some of the fainter objects.

So those beautiful astrophotography captures are way more than a simple point and click?

Absolutely! You can put many hours into getting something that's got any kind of clarity at all, not to mention the time spent processing hundreds of images. In the case of Thor’s Helmet, each exposure is around five minutes long. And in each of those exposures you can barely make out the nebulosity (gas clouds illuminated by stars) – it's a very faint signal among a lot of noise.

We use software to “stack” the collection of images. An algorithm works out the commonalities between these images to make sure each of the points of light were genuinely photons coming from the object being captured and not just noise from atmospheric distortion, electronic equipment noise or other sources of subtle noise that can give a false signal in any one sub-exposure.

Once upon a time astrophotography was really only accessible to a few observatories, universities and NASA but now consumers can buy technology to capture extraordinary images from their backyard!

How do you find star clusters or nebulae to photograph that are beyond the Milky Way, our galaxy?

We typically use software to aim the telescope at very specific points in the sky. These objects are usually indexed in a way that the coordinates are know so the telescope mount can be instructed to move to them. Once the telescope is close, we take images to “plate solve” – comparing the image against a database of stars to ensure that we have the object exactly where we want it in the frame. Given how small these objects appear, it is essential to get the pointing perfect as an imperceivably small movement can be the difference between having the object in the frame and not.

Many of the most well-known nebulae we photograph are within our Milky Way galaxy. When we see the band of the Milky Way across the sky, we're looking across the plane of our spiral galaxy. There are so many stars within a tiny area you are focused on, you almost can't see the blackness of space behind it, let alone the faint objects in the distance. So, if we're doing really deep space imaging beyond our galaxy, we sometimes turn our telescopes away from the Milky Way, where you're looking out into areas without the stars of the Milky Way drowning out the incredibly faint objects at distances sometimes beyond 10 million light years from earth. In these images you can see the pink jewels of nebulae very similar to the nebulae we see in the Milky Way.

The beautiful colours we see in these nebulae, both in the Milky Way and in distant galaxies, is the gas in interstellar clouds being excited by the radiation emitted from nearby stars or being illuminated by the starlight from nearby bright stars.

Are the colours in your images what is actually out there?

In some astrophotography, we use very restrictive filters in astrophotography to block out light pollution and moonlight, so we don’t always photograph everything on the broad light spectrum between infrared and ultraviolet. Also, for around half of every month, it’s difficult to photograph faint objects at all because the moon is too bright for much of the night.

When shooting emission nebulae, we shoot in an extremely narrow band, typically only capturing the three major gasses nebulae emit: sulphur, hydrogen, and oxygen. We go down to a six-nanometre (or less) bandwidth, which is a tiny slice of the visual spectrum. That means there is almost no other light coming in from any source, allowing us to just pick up the light emissions from the gas in the nebula we are photographing.

We then assign a colour to each of the bands of wavelength we capture. These images are referred to as “false colour”, meaning these particular images fall somewhere between art and science. You've got the raw data in your monochrome narrowband images, and then how you choose to combine and portray those can be both beautiful and very informative for science communication, highlighting the specific gasses and how they are structured in each nebula.

Many astrophotographers end up moving away from the super-bright colours often seen in NASA’s classic images combined using the “Hubble palette”. There is a real skill getting something as close to the natural colours as possible, often various shades of red with many other subtle colours depending on the object. Thor's Helmet was shot in false colour, but the way I've compiled it is to get it as close as possible to what you would see if shot in natural colour, while still taking advantage of the detail available through narrowband imaging. The image of the Carina Nebula below is compiled using a modified version of the Hubble palette creating definition between the different gasses which would otherwise appear as different shades of red.

Do you need a deep pockets and good knowledge of outer space to be able to do astrophotography?

No on both counts, actually.

I’ll admit that I have spent a reasonable amount as I have been lured into chasing those small increments of improvement in the images I capture, but anyone can achieve very good results for a modest investment using a second-hand DSLR camera, telescope and mount.

And I would say my knowledge of space was pretty elementary before I got into astrophotography. My astrophotography has actually been the gateway to knowledge as I often begin a new project capturing an object which then leads me to research the structure and attributes of that object. The most difficult thing to comprehend is the distance and size of the objects I am capturing. I’m yet to feel that I have truly appreciated what a light year really represents relative to the basic daily human understanding of distances, or how 10 million stars can even begin to be quantified in the mind, but it is deeply humbling to try.

Joe Nidd’s astrophotography has appeared in exhibitions and books and can be seen on his Instagram account @joe_nidd_astrophotography He also exhibits at the Stardust Gallery in Naseby.

In 2024 he won the Winterstellar Astrophotography Competition Deep Space Award with Fighting Dragons of Ara, which features in MOTAT’s latest Science Alive Te Manawa Magic Box display, Illumination. He also received Bronze in the Deep Space category of the 2024 Sky-Watcher Australia Awards and was highly commended by the Royal Astronomical Society of New Zealand in both 2022 and 2023.