Meghan Hodges
Light pollution is the artificial glow that prevents us from getting a clear view of a starry night sky. It is caused by the reflected light of streetlamps and other forms of artificial illumination. This poses a challenge for astronomers and astrophotographers, who have long advocated for darker skies and reduced light pollution. While large apertures can improve the view of bright and faint objects, they are not a substitute for dark skies. Light pollution affects the visibility of galaxies and nebulae, even with large apertures. The choice of aperture depends on observing conditions and the type of objects being observed. In light-polluted areas, small, bright objects like the Moon, planets, star clusters, and binary stars are more suitable targets for small to medium apertures. For deep-sky observing, larger apertures are recommended, but dark skies are still essential. Ultimately, the best solution for light pollution is to travel to a dark-sky site, but this may not always be feasible.
| Characteristics | Values |
|---|---|
| Effect of light pollution on aperture | Light pollution from towns and cities makes viewing the night sky a tricky business. |
| Aperture and sky brightness | Stars and star clusters are the objects where aperture and sky brightness are most nearly interchangeable. |
| Effect of aperture on faint objects | Increasing aperture improves the views of all bright and faint objects, by increasing resolution, affording higher magnification, and gathering more light. |
| Effect of aperture on contrast | Increasing aperture will not improve the contrast of extended (non-point) objects. |
| Effect of aperture on magnification | A larger aperture affords the ability to get a larger exit pupil at higher magnification. |
| Effect of aperture on filters | A larger aperture affords the ability to use more narrow-band filters. |
| Effect of aperture on portability | Increasing aperture reduces portability, eventually making it more difficult to get to dark sky sites. |
| Effect of aperture on deep-sky observing | Large apertures are not a substitute for dark skies, and small apertures and bright skies both hurt deep-sky objects. |
| Effect of aperture on integrated brightness | The gain in faintness seen when doubling the aperture is 1.5 magnitudes, regardless of sky brightness. |
| Effect of aperture on surface brightness | For extended sources, all apertures have the same limit to contrast discrimination. |
| Effect of aperture on object size | A larger aperture makes an object larger, which is a significant factor in detection, but applies equally for all sky conditions. |
| Effect of aperture on light pollution | Large apertures are useless or even counter-productive under heavy light pollution. |
| Effect of aperture on deep space observing | Buy the biggest aperture telescope you can afford if you are a deep space observer. |
| Effect of aperture on planetary observing | A small to medium-size telescope may match your lunar/planetary observing requirements better than a big scope. |
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What You'll Learn
A large aperture is not a solution to light pollution
Light pollution is the artificial glow that prevents us from getting a clear view of a starry night sky. It is caused by the reflected light from streetlamps and other forms of artificial illumination. While a large aperture can improve the view of bright and faint objects by increasing resolution, affording higher magnification, and gathering more light, it is not a solution to light pollution.
Firstly, a large aperture does not improve the contrast of non-point objects. For extended sources, all apertures have the same limit to contrast discrimination. This means that a larger aperture will not improve the visibility of objects with low surface brightness, such as nebulae, as the object and the sky will exhibit the same surface brightness and brightness ratio, resulting in the same contrast.
Secondly, light pollution can obliterate the faint halos of bright planetary nebulae, which are the objects where aperture matters most and sky brightness least. Galaxies, in particular, are challenging to observe from light-polluted sites, and dark skies are of paramount importance for their observation.
Thirdly, while a large aperture can collect more starlight than a small aperture, it may not always be practical for those observing from light-polluted cities or suburban areas. Large apertures can be cumbersome to transport and store, and they may not be necessary for observing small, bright objects that can be seen through light pollution, such as the Moon, planets, star clusters, and binary stars.
Lastly, large apertures can suffer more under light pollution due to the increased impact of local sources of light pollution on night vision. This can result in a darker background and reduced portability, making it more difficult to access dark sky sites.
In conclusion, while a large aperture can provide benefits in terms of improved resolution and light-gathering capabilities, it is not a solution to light pollution. The most effective way to deal with light pollution is to travel to a dark-sky site, and a large aperture is not a substitute for a truly dark sky.
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A dark sky is the only solution
Light pollution is the artificial glow that prevents us from getting a clear view of a starry night sky. It is caused by the reflected light of streetlamps and other forms of artificial illumination. The glare of light pollution can be a nuisance for amateur astronomers, and it has also been recognised by environmentalists, ecologists, and healthcare professionals as disrupting the natural day-night cycle.
While increasing aperture improves the views of bright and faint objects by increasing resolution, affording higher magnification, and gathering more light, it does not improve the contrast of extended (non-point) objects. Therefore, in the battle against light pollution, increasing aperture alone is not a solution. A dark sky is the only solution to get the best views of galaxies and nebulae.
For example, the galaxy M33 is one of the brightest Messier objects as measured by integrated brightness, but the light is spread out over a large area. In this case, a larger aperture would not improve the view. Instead, a dark sky is necessary to reduce the sky glow that can wash out the night sky and blot out the stars.
Similarly, bright planetary nebulae like M76 and M57 are best observed with a large aperture and minimal sky brightness. However, even with a large aperture, light pollution can obliterate the faint halos of these nebulae. Therefore, a dark sky is essential to optimise the use of a large aperture and get the best views of these objects.
In conclusion, while aperture plays a role in the visibility of celestial objects, a dark sky is the only solution to truly combat light pollution and get the best viewing experience. Travelling to a dark-sky site, usually in rural areas away from artificial lighting, is the most effective way to deal with light pollution and optimise the use of your telescope.
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Light pollution does not affect different apertures differently
Light pollution refers to the artificial glow that prevents us from getting a clear view of a starry night sky. It is caused by the reflected light from streetlamps and other forms of artificial illumination. Light pollution can have a detrimental effect on stargazing and astronomy, making it challenging to observe celestial objects.
When it comes to the impact of light pollution on different apertures, it is commonly believed that larger apertures are useless or even counterproductive under heavy light pollution. However, this claim is not entirely true. Light pollution does not affect different apertures differently. Regardless of the sky's brightness, all apertures have the same limit to contrast discrimination.
For point sources like stars, the gain in faintness observed when doubling the aperture is consistent, regardless of the level of light pollution. In other words, the same magnitude delta is observed whether the sky is country dark or city bright. Therefore, increasing the aperture will improve the views of bright and faint objects by providing higher resolution, higher magnification, and gathering more light.
However, it is important to note that increasing the aperture will not improve the contrast of extended (non-point) objects. For example, galaxies and nebulae can be challenging to observe under light-polluted skies, even with a large aperture scope. The key factor in improving the observation of such objects is accessing dark skies, rather than relying solely on larger apertures.
In summary, while light pollution can impact the effectiveness of different apertures, it does not affect them differently. The choice of aperture should be based on the same criteria as for a dark observing site, and larger apertures can indeed provide benefits in terms of resolution and light-gathering capabilities. However, it is essential to recognize that dark skies are crucial for optimal observations, especially for extended sources such as galaxies and nebulae.
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Large apertures are useless under heavy light pollution
Light pollution from towns and cities makes viewing the night sky a tricky business. The artificial glow from streetlights and other forms of illumination prevents us from getting a clear view of the stars. This is a common issue for amateur astronomers, who often have to deal with light pollution from neighbours' windows or security lights.
Some observers and vendors, especially those dealing with small telescopes, claim that large apertures are useless or even counter-productive under heavy light pollution. However, this is not necessarily true. While large apertures do not improve the contrast of non-point objects, they do improve the views of all bright and faint objects by increasing resolution, affording higher magnification, and gathering more light. This means that a large aperture instrument will collect more starlight than a small aperture, regardless of ambient light conditions.
That being said, large apertures are not a substitute for dark skies. For galaxies, dark skies are of paramount importance. If the skyglow is bright enough to swamp the Milky Way, it will also swamp the outer disks of most galaxies as seen through a telescope, reducing the viewer to observing the nearly featureless cores. Similarly, bright planetary nebulae often have faint halos that can be obliterated by light pollution.
Therefore, if you always have to observe from a light-polluted area, it is recommended that you do not buy more aperture than your light pollution conditions will allow you to use. Instead, focus on observing small, bright objects that can be seen through the light pollution, such as the Moon, planets, star clusters, and binary stars. Save observations of faint objects outside the solar system for times when you can access a dark sky site.
To summarise, while large apertures are not useless under heavy light pollution, they are also not a solution to the problem. The most effective way to deal with light pollution is to travel to a dark-sky site, where you will have access to clearer views of the night sky.
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Light pollution from towns and cities makes stargazing difficult
The impact of light pollution on stargazing can be mitigated to some extent. While access to truly dark skies is ideal, it is not always possible. Stargazers can still enjoy astronomy even in light-polluted cities by observing small, bright objects that can be seen through the artificial glow. These include the Moon, planets, star clusters, and binary stars. Additionally, high-resolution planetary imaging can be successfully conducted under light-polluted skies, as demonstrated by astrophotographers working from urban and suburban locations.
The choice of telescope for stargazing in light-polluted areas is important. A common misconception is that large apertures are useless or counterproductive under heavy light pollution. However, this claim is largely unfounded, as a large aperture instrument will collect more starlight than a small aperture, regardless of ambient light conditions. Nevertheless, it is crucial to consider the practical aspects of owning a large telescope, such as storage and transportation.
When observing from light-polluted sites, it is recommended to focus on objects within the solar system, as they are typically brighter and easier to spot. Planets like Jupiter, Saturn, Mars, and Venus can be captivating targets for small to medium-aperture instruments. Additionally, brighter double and multiple-star systems, such as Albireo and Epsilon Lyrae, can be interesting targets during summer and autumn months.
While light pollution poses challenges for stargazing, it is possible to mitigate its effects through a combination of telescope selection, observing objects within the solar system, and seeking out locations with darker skies when possible.
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Frequently asked questions
No, aperture is not worthless in light-polluted skies. A larger aperture will allow you to see fainter objects and gather more light, improving the view. However, it will not improve the contrast, and light pollution can still obscure the view.
Light pollution can reduce the number of visible stars and wash out the night sky, making astronomy and stargazing challenging. Light pollution can also negatively impact the viewing experience, even with a larger aperture.
A larger aperture can help collect more starlight and improve the view, even in light-polluted skies. However, it is essential to consider the trade-offs, such as reduced portability and the need for higher magnification.
If you are observing from a light-polluted location, it is recommended to focus on small, bright objects such as the Moon, planets, star clusters, and binary stars. For deeper sky observations, it is best to prioritise access to dark sky sites over aperture size.
