Helena Joyce
Light pollution is a common issue for astronomers, both amateur and professional, and it can significantly impact the quality of observations. The effects of light pollution vary depending on the telescope used and the type of celestial object being observed. Light pollution can cause fainter objects, such as galaxies, nebulae, and dwarf planets, to be drowned out or washed out by the excess light. However, brighter objects, such as planets and the moon, are less affected by light pollution and can still be observed with smaller telescopes or even binoculars. Several factors, such as telescope type, light pollution filters, observing position, and local light shielding, can help mitigate the effects of light pollution and improve observation quality.
Telescope for light pollution
| Characteristics | Values |
|---|---|
| Telescope type | Refractor, Dob, SCT, Maksutov (MAK), or RASA |
| Telescope features | Light pollution filter, dew shields, eyepieces, camera filters |
| Aperture | Bigger aperture helps when using light pollution filters |
| Magnification | High magnification with long focal lengths |
| Location | Bortle scale measures light pollution levels from 1 (no light interference) to 9 (inner-city viewing) |
| Viewing position | Avoid observing from inside with doors/windows open; don't view over rooftops or vents |
| Viewing direction | Point telescope towards darkest area of the sky with least skyglow |
| Lighting | Use shielded lighting that points downward; turn off lights when observing |
| Eyes | Allow eyes to adapt to darkness for 30 minutes |
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What You'll Learn
Light pollution filters
Multi-narrowband filters work by blocking out most obtrusive artificial light and are best paired with astronomy-dedicated cameras or modified DSLRs. However, they may have a limited response on stock DSLRs.
While light pollution filters can be beneficial, they may not be necessary for observing bright planets, as these celestial bodies are often still visible even under heavy light pollution. Additionally, with the transition to LED lighting, which emits light across the entire spectrum, some users have found that light pollution filters have become less effective in blocking light pollution.
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Telescope type
The type of telescope you should get depends on several factors, including your budget, the light pollution in your area, and how portable you need the telescope to be.
If you're looking for a telescope that offers the best value for money, a dobsonian telescope (or "dob") is a good option. They provide excellent optical quality for their price, but they are large and bulky, making them difficult to transport. If portability is important to you, a Schmidt-Cassegrain telescope (SCT) might be a better choice. SCTs are more compact and easier to transport than dobs, but they are generally more expensive.
If you live in an area with high light pollution, you may want to consider a telescope with a light pollution filter. These filters work by blocking the wavelengths of light commonly emitted by street lamps, improving the visibility of celestial objects. However, they can also make your views appear dimmer, especially when observing nebulae. There are several types of light pollution filters available, including broadband, narrowband, and line filters, each blocking out specific wavelengths of light.
Another telescope type to consider is a Maksutov-Cassegrain (Mak) telescope. Maksutov telescopes have long focal lengths and are capable of high magnification, making them suitable for observing planets, the Moon, and stars. They are less optimal for viewing dimmer deep-sky objects (DSOs).
Refractor telescopes are another option. They are versatile and capable of producing excellent results across various applications. However, they are limited by their aperture and price, and you will likely need to purchase a larger refractor telescope to observe deep-sky objects (DSOs) in light-polluted skies.
Smart telescopes, such as the Unistellar eQuinox 2, are also worth considering if you live in an urban area with light pollution. These telescopes often feature smart light pollution reduction capabilities, allowing you to explore the night sky without leaving your light-polluted environment. They tend to be expensive, but they offer simplicity and ease of use, with built-in cameras and smartphone apps for celestial navigation.
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Location
The location of your telescope observations will have a significant impact on the clarity of your view. Light pollution, which is common in cities, can obscure your view of the night sky.
To mitigate the effects of light pollution, it is recommended to find an observing location with the fewest lights in your line of sight. Passing car headlights, open doors or windows, and streetlights can all contribute to light pollution. If possible, try to position yourself so that passing car headlights are not in your direct line of sight, as this can undo the adaptation of your eyes to the dark. It is also suggested to avoid observing targets that are directly over rooftops or above hot air vents, as the warm air can create air currents and cause the view to shimmer.
If you are unable to find a location with minimal light pollution, there are other strategies you can employ. Light pollution filters for telescopes are available, which work by filtering out the wavelengths of light commonly emitted by street lamps. While these filters can dim the view, they can also help to reduce the impact of light pollution. Additionally, you can try to pinpoint the darkest area of the sky with the least amount of skyglow and aim your telescope in that direction.
The time of day can also impact the amount of light pollution you experience. Observing in the early morning or midnight can reduce light pollution, as many urban areas dim their streetlights after 10 p.m. or midnight, and there is generally less human activity contributing to light pollution during these times.
It is worth noting that some telescopes are better suited for use in light-polluted areas. For example, the Celestron SCT telescope is known for performing well in extremely light-polluted skies. Additionally, telescopes with features like Smart Light Pollution Reduction, such as the Unistellar eQuinox 2, can automatically reduce the effects of light pollution.
In conclusion, while light pollution can be a challenge for telescope observations, careful selection of location and time of day, as well as the use of appropriate telescopes and filters, can help to mitigate its impact and improve your viewing experience.
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Magnification
To counteract this, telescopes with high magnification capabilities can help bring these faint objects into view. Celestron's Maksutov (MAK) and refractor telescopes, for example, offer high magnification due to their long focal lengths. A 32-centimeter (12.5-inch) scope can detect stars up to magnitude 17.5, while a 50-centimeter (20-inch) instrument with moderate magnification can reach 19th magnitude.
Additionally, a Rowe-Ackermann Schmidt Astrograph (RASA) equipped with a light pollution filter is excellent for imaging deep-sky objects from light-polluted cities. Accessories like dew shields, eyepieces, and camera filters can also help mitigate light pollution to some extent.
It is worth noting that light pollution filters may dim the views, so a bigger aperture might be beneficial. Aperture refers to the size of the telescope's lens or mirror and plays a crucial role in light-gathering capabilities. In light-polluted areas, a larger aperture can help collect more light, improving the visibility of faint objects.
When dealing with light pollution, it is also important to consider the targets you want to observe. Planets, the Moon, bright double stars, and brighter deep-sky objects are less affected by light pollution and can be observed with smaller telescopes or even binoculars. Fainter stars, dwarf planets, and icy moons may be washed out by light pollution, requiring larger apertures or darker locations.
Lastly, the location of observation plays a significant role in managing light pollution. Astronomers often use the Bortle scale to classify light pollution levels, with Bortle 1 being the darkest and most ideal for astronomy. By travelling to darker locations away from cities, you can significantly reduce light pollution and improve your observations.
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Targets
The planets are one of the few stargazing and astronomy target groups that are pretty much completely unaffected by light pollution. You can get great views of the planets of the Solar System with a small telescope even from brightly-lit cities. High-resolution planetary imaging can be conducted with great success under light-polluted skies. Jupiter with its cloud bands and Saturn with its rings are superb targets for even small-aperture instruments.
Among the stars that are able to poke through the light pollution in built-up areas, you’ll find some interesting targets for a small to medium aperture telescope. These include some of the brighter double and multiple-star systems, where two or more stars either appear close together or are, in fact, whirling together as a gravitationally-bound group through space. In the summer and autumn months, notable examples such as Albireo (Beta (β) Cygni) in Cygnus, and Epsilon (ε) Lyrae in Lyra, are comfortably within reach of a 150–200mm aperture telescope from sites with fairly bright night skies.
From suburban locations, with a 200–250mm aperture telescope, you can even get nice eyepiece views of the faint discs of Uranus and Neptune.
A Mak-Newt is a fine scope for planetary, lunar, and stars, it's less optimal for DSOs though. A refractor is a general all-purpose good at everything scope. It excels at everything but is always limited by aperture/price. So, you'd likely get a small refractor, which means wide-field, which means DSOs, which there are few of in a light-polluted sky.
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Frequently asked questions
Light pollution is unwanted light that projects up into the night sky, making the atmosphere much brighter than the natural night sky. It can come in two forms: the glare from harsh lighting near your observation site and skyglow.
Light pollution can drown out the light from faint objects like galaxies and nebulae, making them harder to see. It can also increase the brightness of the sky background, making it difficult to observe faint stars.
There is no single "best" telescope for light-polluted areas. However, certain telescopes are better for viewing objects that are less affected by light pollution, such as planets, the moon, bright double stars, and brighter DSOs. A Mak-Newt telescope is a good option for viewing planets, the moon, and stars, while a refractor telescope is a versatile option that can be used for various types of observation but may be limited by aperture and price. If you're looking for a more portable option, consider a smaller telescope or a good pair of binoculars, which can provide clear views of star clusters, bright planetary nebulae, and summer and winter showpieces like the Orion Nebula and the Lagoon Nebula.
Here are some tips to minimise light pollution:
- Use a light pollution filter: These filters are designed to suppress the glow from artificial light sources, making it easier to observe celestial objects. However, they may dim the view and make some objects appear fainter than they actually are.
- Consider your observing position: Avoid observing from inside a building with open doors or windows, as the warm air escaping can create air currents and cause the view to shimmer. Also, try to avoid targets that are directly over rooftops or above heat sources.
- Allow your eyes to adapt to the darkness: Give your eyes at least 30 minutes to adjust to the dark before starting your observation session.
- Shield your lighting: To reduce skyglow, ensure that your outdoor lighting is shielded and pointed downwards.
