Astrophotography from the city: yay or nay?
Let me get this straight: there is nothing, n-o-t-h-i-n-g, as a truly dark sky for astrophotography.
On the other hand, good astrophotography from the city is certainly possible, although challenging (not necessarily a bad thing), particularly if you are on a budget.
Being able to photograph the night sky from your place, whether it is a tiny apartment near the city center or an area with a large backyard in the suburbs, means you can enjoy more often your passion for the stars.
Plus, with the current pandemic of COVID-19, many of us are either in lockdown or under curfew night, leaving us star lovers miserably pacing our apartment in the city while good winter nights are getting wasted.
To stop the wasting of good nights, we have put together this beginner guide to Urban Astrophotography, and I hope you will be inspired and decide to give it a try.
Why Should I Do Urban Astrophotography? Won’t I Be Wasting My Time?
Let’s put it this way: best is good’s worst enemy.
If you always wait for the best conditions, with the best equipment, you will not do astrophotography very often, do you?
I am writing from Belgium, one of the most light-polluted among the European countries (not to say in the whole world).
But even if you don’t live in Belgium and can have easier access to dark skies than me, don’t be so fast dismissing the possibility to image from your place.
Sure, seeing conditions are bad in the city: light pollution, air pollution, thermal gradient, and turbulent air are constant.
Fog, on the other hand, is often an exclusive of places out of town.
Have you ever left your place in the city under a clean sky to arrive at your location in the countryside and find it completely wet and foggy?
Have you ever called it off because weather forecasts for your imaging location give a high probability of finding fog?
Knowing how to photograph from the city would have turned a wasted night into an ok (or even fine) astrophotography night, all from the comfort of your home or nearby city park.
Finally, astrophotography is a never-ending learning process: being able to image from your place means you can comfortably run tests and practice your skills without wasting those (rare?) good nights at your dark location.
Best Targets For Urban Astrophotography
The best targets for astrophotography under the heavily light-polluted city sky are the brightest ones: the Moon, the Sun, the planets, some star clusters, and a few galaxies and nebulae.
For the Moon, the Sun, and the planets, light pollution is not a big deal as they are very bright targets.
You may even shoot through the window from within your apartment. But if you do so, make sure you check the tips I gave in the section towards the end of the article.
Photographing the Moon
The Moon is the most obvious target, as it is the one that is most visible in the night sky, even from the city.
The Moon looks quite small in the sky, so you need some long telephoto lenses to get some details other than the large maria.
As per the imaging equipment, you do not need much to be happy: being on a budget, I started with using long legacy telephoto lenses (200 and 300mm lens with 2X teleconverter).
For anything from 300mm up to 800mm on a full-frame camera, you can even shoot handheld, particularly if most of the Moon is illuminated.
But for image stacking and precise manual focusing and better image quality, I strongly advise you to use a tripod.
Particularly from the city, aim to use the fastest possible shutter speed so as to freeze the seeing (lunar wobbling due to atmospheric turbulences) for the sharpest images.
For lunar surface closeup, you really need a telescope and a tracking mount. An alt/az tracking mount is the easiest option for lunar and planetary astrophotography from the city, as it does not require polar alignment.
Photographing the Sun
Beginners often overlook the Sun, but it is the most powerful and dynamic object in our sky: it deserves to be photographed from time to time.
We just published an article with facts about our Sun, to boost your curiosity.
The other nice thing about solar photography is that whatever gear you use for the Moon, you can use it with the Sun. And this is because both the Moon and the Sun have the same apparent size in the sky.
White light sun photography is the simplest and most affordable type of solar photography: all you need is a full aperture solar filter fitter in front of your telescope or lens.
These filters can be made in glass (expensive) or with a special film mounted on a cell (affordable) that can fit a range of telescope diameters.
Never use a filter after the telescope: as sunlight is concentrated on a very tiny area of the filter, this can degrade and crack. You may get permanently blinded or burn a hole into your camera sensor.
With the Sun, you do not play games: never use DIY solutions, never leave your instrument unattended while it is pointed at the Sun and never allow children to use a telescope or binocular to observe the Sun without being supervised by an adult.
Ok, so: what can you observe and photograph with a white light solar filter? Surface features such as the sunspots and solar faculae, and surface granulation.
The Sun activity goes up and down in cycles of 11 years.
At the time of this article, the Sun just entered into a new cycle (solar cycle 25), and solar activity is finally building up with new sunspots appearing almost every week.
Eventually, if you get really passionate about the sun, you can then step up the game and get a specific solar telescope.
With that, you can photograph the Sun in a very… very… narrow Ha band. With those, you can image details on the solar filters like flares and CME (Corona massive ejects)
Keep looking at the NASA SOHO website to see what is going on with the Sun right now.
Photographing the Planets
The planets are in our cosmic garden, particularly when compared to deep-sky targets. But they are so much smaller than most deep-sky objects that you need a telescope to be able to get some details.
Jupiter and Saturn are the easiest planets to photograph: with a small telescope, you can make out Jupiter’s bands and Saturn’s rings.
Venus is our closest neighbor but has no details to show, being enveloped in thick clouds, so you can photograph its phases. Mars is small: you need a relatively large telescope to get some decent details.
You got it: for the planets you need a telescope, at least a small maksutov like mine and a planetary camera. Although, you could use your DSLR in video mode if you don’t have the budget for both the camera and the telescope.
Photographing Star Systems And Star Clusters
Splitting multiple star systems is a nice activity to carry out from the city.
Polaris, Albireo, Mizar, and many other stars are, indeed, multiple star systems.
All you need is a telescope with a focal length of about 1000mm and a Barlow lens. Tracking may help but is not strictly necessary.
Fun fact: being able to split Mizar and Alcor in Ursa Major by eyes was a good way to check how sharp one’s vision was.
Star Clusters such as M13 in Hercules are quite bright: the light pollution of the city will only spoil a bit of star colors.
Totally worthy to go after the brightest cluster from your balcony, if you ask me.
Photographing Deep Sky Objects
Deep sky astrophotography is the most challenging type of astrophotography from the city. The problem is light pollution here, as deep-sky objects are usually faint.
And light pollution makes it difficult (and costly) to take the needed longer exposures.
Still, filters are available that can help reduce the sky brightness and make the DSO come through.
In any case, try choosing bright targets such as M42 and Flame Nebula in Orion or the Pleiades. Andromeda is probably the only galaxy you can photograph decently from the city.
The next step will be using a modified DSLR or deep-sky astro camera and use dual-band filters such as the Optolong L-Enhance on emission nebula. This filter allows only the Ha and Oiii signals to pass, thus filtering out all the light pollution.
A broader filter like the Optolong L-PRO is ideal for photographing reflection nebulae, like the Pleiades and Galaxies from light-polluted areas.
These filters are also available as clip-in filters for Sony, Canon, and Nikon camera systems mostly, and in 1.25” and 2” size.
Ideally, for deep-sky astrophotography, you should be able to see Polaris so as to polar align your equatorial mount or tracker. A guiding system is not needed, as you will take relatively short exposures due to the light pollution.
How To Do Astrophotography In The City And Deal With The Many Challenges – A Quick Guide
Technically, the basics of doing astrophotography in the city are the same as doing astrophotography everywhere else:
- The mount is the most important single piece of astrophotography equipment.
- For deep-sky astrophotography, you need to use an equatorial mount.
- For long doing exposures, you need to have a good polar alignment.
- Find your target.
- You should photograph for image stacking for the best results.
- You should aim to photograph your target for the longest possible time (integration time).
- Calibration frames (darks, bias, flat and dark flat frames) are needed for the best possible results.
What is different when you photograph from the city rather than in the field are the challenges and limitations you will have to face when going over the basics listed above.
The more obvious problem we think of when considering doing astrophotography from the city is bad seeing from light pollution, air pollution, and thermal gradients making the air over the city very turbulent.
But this is not much of a deal-breaker as having a safe place to set up your equipment or having a large enough patch of visible sky.
More troublesome are the following aspects:
- Can you set up your equipment in a safe place?
- Can you see Polaris from where you can set up your gear, so to properly align your equatorial mount to the celestial pole?
- Can you see enough sky to track your deep-sky target for ½ or one hour at least?
- Can you see enough sky to perform two or three-star alignment if you use a mount with a GoTo system?
If you cannot set up your equipment in a safe place, you are done: what remains for you is imaging the Moon, the Sun, and the planet through your apartment window, if you can see them.
Other than that, there are ways to deal with all the rest.
How To Deal With Polar Alignment
I am lucky enough that I can see Polaris from the front garden of my building and from my balcony on the backside of the building.
One thing I like about doing the polar alignment in the city is that you cannot be fooled: you look in the polar scope and the only star you see is Polaris.
If you are not used to it, at a darker location you will find the view inside the polar scope to be quite crowded, making it difficult to locate Polaris among the other stars.
If you cannot see Polaris (or sigma-Octans), there are ways to work around it:
- You can use the D.A.R.V methods to null star drifting or…
- You can perform an electronically assisted polar alignment using a computer and a guiding or imaging camera.
If you have your own private garden, you can create references for your tripod to make polar alignment fast or build a fixed pier.
How To Deal With The Amount Of Visible Sky
I live in an 8-story building that is shaped like a U, surrounding the front garden. I can see about 50º of the sky from my window but cannot polar align, so I usually photograph in alt/az mode from within my apartment.
I can polar align from the front garden, but I can only image things that are visible in the West and South part of the sky and close to the zenith.
If you, like me, have a limited amount of visible sky, to reach the desired total integration time you need to image through different nights and combine the multiple sessions.
In theory, this is not a problem, but consider your target could be visible from your place only for a short period each year.
A software like Stellarium is a must to see what targets you will be able to see from your place.
How To Find Your Target
To find your target, a GoTo system is helpful, even more so in the city as you can see very few stars.
Depending on your location, though, you may struggle to perform the needed star alignment to let the mount know how it is oriented, as you may see only a few stars all clustered in the same part of the sky. You should dig into your mount menu to find out all the possible star alignment available.
If you don’t have a goto, a red dot star finder combined with manual star-hopping is still a quick way to find your target.
But since we are at home and it is not much of a trouble to use our laptop, you may well use plate solving to help you locate your target.
How To Deal With Light Pollution
Astrophotography filters are the key to deal with light pollution, butmind that if you do not live in a remote area, you will have to invest in these kinds of filters anyway. So don’t think filters are useful only in the city.
Dual-, tri-bands and UHC filters are used to make emission nebula pop, and in doing so, they filter out all the remaining light frequencies, including light pollution from streets and cities.
If you are in a Bortle 4 sky or higher, you will also need a filter like the Optolong L-Pro or the Astronomik CLS or a didymium filter like the Hoya Red Intensifier to cut down residual light pollution toward the horizon.
The final option is going narrowband with monochrome, cooled astro cameras: a costly but extremely efficient solution that will let you get the most from the night sky, even from heavily light-polluted areas.
Tips For Urban Astrophotography
Here some tips for urban astrophotography.
Dealing With Air Turbulences
Cities are “heat reservoirs”: in the wintertime, we warm our houses and some of the heat escapes from roofs and facades. Plus, we have working chimneys.
In the summer, roads, sidewalks, and roofs all absorb solar heat that they release back into the atmosphere during the cooler night.
All this creates a very poor seeing. Here some tips you may find useful.
- Reduce your optical resolution: high magnification will exacerbate the effects of poor seeing: better to use lower magnifications so that the negative effect of the turbulent air (image wobbling) will remain confined to fewer pixels, and the overall image will look sharper.
- Wait until your target is well above the rooftops and far from chimneys.
- If you can, go to a city park or other grass areas: they absorb much less heat during the day than your driveway or the sidewalk in front of your house.
- If you cannot go outside because you have no place or your target would not be visible from the street, you can shoot from within your apartment, but, particularly in winter, keep your window close.
If you do shoot through the window, make sure to:
- Clean your window.
- Stay as square as possible with it to avoid multiple reflections from the different glass surfaces.
- Have the room you are in as dark as possible to avoid having the inside of your home reflected on the windows.
Sure, you have to shoot through “poor quality” glass, but you will avoid mixing the hot air from your apartment with the cold air outside;
Also, plan ahead and close the heater below the window to reduce turbulence inside the room.
Dealing With Vibrations
Balconies, sidewalks, hardwood floors, and such can transmit vibrations.
- Step lightly when you walk on a balcony and avoid having your washing machine doing the centrifuge on, or near it.
- Step lightly if you set up on the hardwood floor in your house: they are not the most stable floors you could set up on
- Avoid setting up on pavements next to passing traffic: trucks, in particular, can create lots of vibrations
- Anti-vibration pads are available on the market for your tripod feet and can help to damp some ground vibrations, but they are rather expensive.
Urban Astrophotography: What Will You Need?
Let’s recap what you need to have fun with astrophotography from the city:
- Some way to polar align if you want to do deep-sky astrophotography.
- A decent amount of visible sky.
- Long telephoto lenses and a telescope for the Moon, the Sun, and the Planets.
- Filters, for dealing with light pollution and to photograph the Sun.
- A sturdy tripod and/or a tracking mount (either alt/az or equatorial, but the alt/az are easier to work within the city).
Because light pollution will not let you go very long with the exposure time, you may not need a guiding system, particularly if you use standard photographic equipment and not long telescopes.
Nowadays, astrophotography from the city is a reality, thanks to new technology in terms of guiding, plate solving, goto, and electronically assisted polar alignment, but also thanks to the improvement in manufacturing affordable filters to suppress light pollution and in photographic gear in general.
While nothing can beat a truly dark sky, with a few tips and tricks, a bit of practice, and a bit of equipment, you can take good quality images even from your place in the city.