Strategies I Employ to Reduce Artificial Light Impact on My Telescope Views
Peep here, I reside in a Bortle 8 domain. That translates to off-white on DarksiteFinder.com's light pollution map. Checking out the Andromeda Galaxy from here using my 8" telescope, it appears as a tiny, slightly grayish fuzzy smudge in the sky. But slide over to a darker red zone, roughly Bortle 6, and that smudge enlarges into a much larger oval-shaped object with a vibrant core, resembling what I imagine a galaxy should look like.
Stepping up to a Bortle 4 location, which is approximately a yellow zone, I can't spot the Andromeda Galaxy with my naked eye effortlessly, but in my telescope, it starts showing hints of dust lanes and the spiraling structure we anticipate. The two little companion galaxies, M32 and M110, also become apparent using my telescope.
The transformation isn't down to the telescope; it's all about the light pollution in the sky. At the darker locations, the galaxy offers more contrast against the lower background glow in the sky.
In this piece, let's discuss the rising issue of light pollution, strategies to tackle it, and how it affects the visibility of different cosmic targets. We'll briefly touch upon the enrichment insights to provide more context.
When we talk about light pollution, we're referring to two main types: ground and sky.
- Ground light pollution, or glare, stems from your surroundings, i.e., your house lights, neighbor's lights, and nearby street lights.
- Sky light pollution, or sky glow, arises due to the collective emission of light from our local area radiating outward for dozens or hundreds of kilometers. In urban environments, we often refer to this as the "sky glow dome" which originates from highway lights, building lights, and other light sources.
The Ground Side: Curtailing Glare
Ground light pollution, typically called glare by scientists and DarkSky, arises from our home lights, neighbors' lights, and the nearby street light. It can also come from nearby parking lots, hospitals, or other commercial sites that keep lights on round-the-clock.
If you live in a rural area with scattered houses and no nearby commercial buildings or street lights, then this might not be an issue for you unless someone in your family leaves a specific light on, shining out the window. In cities and suburbs, you'll need to tackle ground light pollution while observing the night sky.
But you can perhaps lessen the impact of ground light pollution with a bit of effort.
Curing Ground Light Pollution: Dark Adaptation
The impact of ground light pollution is on your eyes. Your iris regulates the quantity of light reaching your retina, where your light-sensitive cells reside. To see as much as possible when gazing at the night sky through binoculars or telescope eyepiece, we want our eyes to fully dark adapt, letting in the maximum amount of light.
To experience dark adaptation, stand in a brightly lit room at night. Keep the shades or blinds closed to minimize outside light. Now, turn off the lights.
At first, you may not be able to see anything as your eyes adjust to the bright room (similar to how you are now). In a few moments, your eyes will start dark adapting, picking up trace amounts of light filtering through the window, and past the shades. The iris will contract, and your pupil will expand to let in more light. The full process can take 20 minutes or longer until your eyes fully dark adapt.
By testing this outside, step from your well-lit home to the darkest spot you can find immediately outside your door. Look up at the sky. Initially, you may see very few stars, but more and more will appear as you wait. This will take approximately 20 minutes until your eyes dark adapt to your local ground light pollution level, allowing you to see more stars than when you first stepped out the door (assuming the outdoor area is darker than your home).
This also applies to the eyepiece. Try the same experiment, stepping from the house, but this time keep your eye on your binoculars or the eyepiece of your telescope and just observe. Over time, you'll see more and more stars in the eyepiece as your eyes dark adapt.
Achieving the Best Dark Adaptation for Your Peepers
- Choose an observation site with the fewest lights in your line of sight. Try to find a spot where passing car headlights cannot be seen. Unfortunately, a quick flash of passing car headlights can undo 20 minutes of dark adaptation, so you'll need to wait again.
- Block out light sources when possible. Place a tree or a fence between you and the light. Consider putting up some sort of screen. Place a building between you and the street light.
- Steer clear of light sources that regularly stay on. If you're living indoors and forget something in the lit room and run in to fetch it, your dark adaptation will be completely broken, and you'll need to wait another 20 minutes or so for your eyes to get dark adapted again.
- Wear a hood to block surrounding light and place it over your head while looking through the eyepiece. This will help your eyes dark adapt more efficiently.
- Some people put an eyepatch over their observing eye to allow it to achieve maximum dark adaptation. When they come to the eyepiece, they keep the eye closed, flip up the eyepatch, and only open the eye when they're at the eyepiece. Again, a hood can help maintain the dark adaptation of the eye.
- Avoid looking at bright mobile screens. If you have to, turn on a red filter, which might help preserve dark adaptation.
Dealing with sky light pollution might be demanding. The only viable solution is to drive to a darker location.
In the past, light pollution filters were a partial solution, but they've lost a considerable part of their value as they can no longer effectively filter newer light sources like white LEDs. To learn more about light pollution filters, you might wanna check out this enrichment insight on Light Pollution Filters History.
For dealing with sky light pollution, you might need a car, as it's the easiest solution – driving to a darker location!
Catching a Darker Sky
There are various tools available to help identify areas with less sky glow.
- Lightpollutionmap.info is the most comprehensive and up-to-date of these. You can pinpoint any location you want and get an estimated Sky Quality Meter and Bortle Scale reading. These readings can give you a general idea of where you should head.
- Darksky.org has a list of International Dark Sky Parks as well as Urban Night Sky Places.
- Your local astronomy club probably recommends some dark sky sites or even owns land on them.
Remember, no map can fully reflect real ground conditions. A park might be in a darker zone, but if they have the ball field all lit up, it's not indicated on the dark site finder map. That's a ground light pollution/glare issue.
Now, let's dive into understanding how light pollution interacts with different cosmic targets.
Let's briefly touch upon the enrichment insights to provide more context.
Things get tricky when a magnitude number is assigned to a deep-sky object like a galaxy or a nebula. While the total amount of light from a magnitude 8 nebula might be equal to that of a magnitude 8 star, the star is a point source, while the light from the nebula is spread out over a larger area. This can cause issues in comparison when evaluating targets. To account for differences in surface brightness levels, we'll rely on the Bortle Scale in this section.
Classifying Objects by Light Pollution Tolerance
Here, we categorize targets based on their resistance to light pollution. Objects that are less affected by light pollution include point sources, such as stars or planets, and deep-sky objects that can be resolved through binoculars or a telescope.
- Sun
- Moon
- Planets
- Open star clusters
- Double stars
Fainter stars, as well as faint Solar System objects (e.g., dim dwarf planets and icy moons), can be washed out by light pollution despite being point sources. Here, surface brightness plays a more significant role in determining visibility.
- Galaxies
- Nebulae
- Globular star clusters
- Comets
Strategies for Dark Sky Observing Sessions
- Learn about the light pollution level in your observing area and plan targets accordingly. If you reside in a highly light polluted location (Bortle 6-9), you might want to focus primarily on stars, planets, open clusters, and double stars. For a brief understanding of the Bortle Scale, you can read this enrichment insight.
- Go for observations during early hours of the morning or at midnight, as many urban locales turn off lights after 10 p.m. or midnight.
- Use high-quality telescope equipment. Poor optics can scatter light and make sources of glare or sky glow appear harsher than they should at the eyepiece.
- Ensure your telescope provides a sea of black when looking down its tube and the reflection from the secondary mirror. If light leaks in, make adjustments to improve the situation.
- Minimizing smoke, dust, and humidity in the atmosphere maximizes the visibility of distant objects. So, when planning an observing session, be mindful of the weather conditions.
- Moon phase also impacts how much light pollution you face. Full or bright phases of the Moon reflect sun's light, making observing challenging. Plan around the Moon's phases when deciding when to observe.
- In the world of astronomy, we encounter two primary types of light pollution: ground light pollution, or glare, and sky light pollution, or sky glow.
- Ground light pollution, commonly referred to as glare, originates from sources such as house lights, neighbor's lights, street lights, and other local light sources like hospitals or commercial sites.
- Sky light pollution, or sky glow, arises due to the collective emission of light from our local area radiating outwards for dozens or hundreds of kilometers, often referred to as the "sky glow dome" particularly in urban environments.
- When it comes to ground light pollution, our rural neighbors might not feel its impact, but urban and suburban observers have to work around it to enjoy the night sky.
- To combat ground light pollution's impact, it's essential to achieve dark adaptation, allowing our eyes to fully adjust to the dark, maximizing the amount of light they can take in while gazing at the night sky through binoculars or telescope eyepieces.
- Dark adaptation involves stepping from a brightly lit room into a dark spot outside, letting your eyes adjust for approximately 20 minutes or more to dark adapt to your local ground light pollution level.
- To facilitate better dark adaptation, find a spot with the fewest lights in your line of sight, block out light sources when possible, and steer clear of light sources that stay on regularly.
- Leaving car headlights on while observing and looking at bright mobile screens can undo 20 minutes of dark adaptation, so it's advisable to turn on a red filter for your screen and park the car in a dark location before observing.
- Dealing with sky light pollution can be challenging, as the only viable solution is to drive to a darker location, making use of various tools like Lightpollutionmap.info, Darksky.org, and local astronomy club recommendations to find the best observing spots.
