Light pollution – are we losing the night sky or is there still hope?

I guess it was inevitable that I would eventually write a post about light pollution – the modern day scourge which reduces the visibility of celestial objects and forces astronomers to travel hundreds or sometimes thousands of miles in order to avoid it. There’s even a saying that an astronomers most useful piece of equipment is a car! Probably the most damaging effect of light pollution is not that it makes faint galaxies and nebulae difficult to spot and photograph (there are ways of overcoming this), but that whole generations of children grow up not knowing what a truly dark sky looks like!

Figure 1. The effect of light pollution on the night sky. This split image shows how artificial light washes out most of the faint detail in the constellation Orion.

Figure 1. The effect of light pollution on the night sky. This split image shows how artificial light washes out most of the faint detail in the constellation Orion.


I am one of those children. I grew up in suburban England (about 60 miles north west of London) where the night sky had a beige/orange tinge, the constellations were difficult to spot and the Milky Way was something you either looked up in a book or ate. I was about 14 when first I saw a proper night sky; on holiday in North West Scotland. I was so fascinated with the sight that an interest in astronomy embedded itself in me and never left! I was lucky, I was still quite young and my interest could be nurtured before the realities of life (exams, chores, jobs…) stepped in. Many aren’t so lucky. I always wonder, how many inquisitive people never experience the joy of observing the universe because of that orange glowing veil of light pollution (LP). It is the barrier that light pollution creates that prompted me to write this post.

I will now concentrate on the issues LP poses to astronomy. Before I do so, I should say that good evidence exists showing that LP can negatively affect human health (such as disrupting sleep cycles) and the natural environment (changing bird migration patterns etc), detailed discussions can be found here. Regarding astronomy, light pollution is

Figure 2. Direct light pollution. These street lights in Atlanta radiate light across a wide area, stargazing near these will be very difficult. Image taken from

Figure 2. Direct light pollution. These street lights in Atlanta radiate light across a wide area, stargazing near these will be very difficult. Image taken from

problematic for two main reasons. (1) Unwanted light can travel directly into your eyes ruining the dark adaption they need to observe faint celestial objects. It can also invade telescopes causing washed out images and unwanted glare. This form of light pollution involves light traveling directly from an unwanted light source (such as a street lamp) to your eye/telescope.

The second source of LP comes from the combined effect of thousands of artificial lights, known as sky glow. Sky glow is form of LP most people are familiar with; the orange tinge that

Figure 3. Skyglow in Manchester. This light is scattering off the atmosphere and falling back to the ground. As a result, the sky looks bright orange. Image taken from

Figure 3. Skyglow in Manchester. This light is scattering off the atmosphere and falling back to the ground. As a result, the sky looks bright orange. Image taken from

in some places can be bright enough to read by! Sky glow exists because the Earth’s atmosphere is not completely transparent, it contains dust, water droplets and other contaminants that scatter man made light moving through it. Some of this light is scattered back down towards the Earth, it is this scattered light that drowns out the distant stars and galaxies. It is a visual reflection of the amount of wasted light energy we throw up into the sky.

You may be thinking that LP spells the end for astronomy in urban areas. Well luckily there are ways around the problem. One way is to  filter it out. The good thing about skyglow is that it is produced mainly by street lamps that use low pressure sodium bulbs. The light from these bulbs  is almost exclusively  orange with 589nm wavelength. Figure 4 shows a spectrum of the light given out by one of the lamps.

Figure 4 - Different colours of light produced by a typical low pressure Sodium street light. The vast majority of the light is orange (589nm) as shown by the bright orange bar. Image taken from:

Figure 4 – Different colours of light produced by a typical low pressure Sodium street light. The vast majority of the light is orange (589nm) as shown by the bright orange bar. Image taken from:

Since this light is comprised of essentially one colour, we can use a simple filter to cut out this wavelength whilst leaving other wavelengths unaffected. In addition, the wavelength of the sodium lights is quite different from the colours produced by many nebulae. Therefore when we filter out the orange light, we don’t also block the light coming from astronomical objects.

So…what am I worrying about then? If light pollution can be overcome by filtering out certain wavelengths of light then astronomy should be possible from anywhere. Well, not quite. Filters are not perfect, even the best filters will block other colours and dim our view of the stars. There is also another reason to worry – street lights are changing. As you may

Figure 5 - LED and sodium streetlights outside my house. LEDs produce light that is harder to block using conventional filters, Sodium lights (seen here as orange) shine lots of light into the sky contributing to sky glow. (Image is my own)

Figure 5 – LED and sodium streetlights outside my house. LEDs produce light that is harder to block using conventional filters, Sodium lights (seen here as orange) shine lots of light into the sky contributing to sky glow. (Image is my own)

already know, street lights are being altered from the sodium bulbs to LEDs. These LEDs are more energy efficient and produce a more natural white light. However, this white light is harder for astronomers to filter out without also blocking light coming from deep space. Luckily, these newer lights are better at directing their glow downwards towards the ground rather than allowing it to leak up into the sky. Figure 5 shows the LED and Sodium lights outside my house. The LED lights appear darker because most of their light is directed towards the ground.

There is still debate in the astronomy community about whether the new street lighting will be beneficial for astronomy. At the moment, LEDs are being introduced slowly so it is difficult to make a clear comparison. My hunch is that when Sodium lights are replaced completely, there will be an improvement in our night skies and finally young people will grow up seeing more of the night sky.

Post by: Daniel Elijah



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Could fruit flies help defeat HPV-derived cancers?

In 2012 528,000 cases of cervical cancer were diagnosed worldwide. In the same year, more than half this number were estimated to have died as a result of this condition. The cause? A virus of the Papillomaviridae family, specifically one of the High Risk Human Papillomaviruses (HR-HPVs). Although mainly associated with cervical cancer in women, HR-HPVs cause an ever increasing number of head and neck, throat and genital tumours in both sexes.

Human Papillomaviruses lack an envelope, a coat made from the membrane of the host cell, possessing only an icosahedral capsid – a sturdy protein bubble that protects the viral DNA within. Viral DNA hijacks the host’s cellular machinery to produce new viral proteins which both continue virus assembly and cause cancer. It is still uncertain exactly how these proteins interact with our cells to cause cancer but some major players and pathways have been identified. Specifically, scientists believe that two particular proteins (the E6 and E7 proteins) may play an important role in this process.

These two E6/7 macromolecules can be referred as “oncoproteins”. Although quite scary, this term simply defines proteins which are involved in mechanisms that could cause a cell to behave abnormally, increasing the chances of them becoming cancerous. Specifically, these two proteins interfere with a wide variety of mechanisms that will trigger conversion to malignancy. Respectively, they either boost or block the activity of p53, Rb and E2F, three molecules that control a cell’s life cycle.

Considering the huge impact such cancers have on human life, it may seem unusual that we are still in the dark about so many aspects of HPV associated pathophysiology. Our limited knowledge is in part due to constraints implicit in this type of research. Specifically, for obvious ethical reasons, researchers are not able to study HPV associated cancers in living human subjects or deliberately induce cancers in subjects. Therefore, they must rely on model systems when studying these disorders. In the past, researches have used artificial keratinocytes (skin’s cells) and mouse models, to understand how processes work in living tissues. However, this work raises a few questions, such as: How do you compare findings in tissue alone to what you would find in a dynamic and complex living system and how well can we compare mouse models to human conditions?


Picture credits: By Botaurus, via Wikimedia Commons – CC BY-SA 2.5 (open access/open use).

We now have an answer to these questions, or at least something that marks the start of a deeper understanding. Researchers at the University of Missouri have been able to successfully develop and use living, fruit fly models. Mojgan Padash’s research team injected fruit flies with the E6 protein along with a human-derived one needed by the E6 to function. The first results show that, although abnormalities in the fruit flies’ skin were noticed, another molecule was needed in order to fully trigger cancer. Following the hypothesis that mutations in a human molecule called Ras, a family of “switch” proteins which activate cell growth-specific genes, the team introduced the latter into the fruit flies. Those “simple” abnormalities turned into malignant cancers, just as they would do in humans.

The results, published in the open access journal PLoS Pathogens, allow scientists to monitor biochemical pathways similar, if not identical, to those found in human sufferers. But why flies and not mice? Although further away from humans, sharing only 60% of the human genome against the 97.5% of mice, flies are easier to use than their murine counterpart. Fruit flies are easier to breed (so to quickly obtain new generations) and their genes can be mutated quicker than mice. Moreover, little to no ethical approval is needed to use them (they can be ordered online, with just one click!) and their easier to monitor development allows researcher to effectively model disease development. These fruit fly models, which are continuously refined and developed, have the potential to help in discovering new molecules involved in such processes.

It comes to no surprise that such information could impact heavily on future treatment, and even the prevention of pathologies caused by this increasingly dangerous family of viruses. So, next time you think about killing a fruit fly in your kitchen … maybe think twice.

Post by: Paolo Arru – @viraleclair

screen-shot-2016-10-10-at-19-43-41Paolo is currently a final year student in Microbiology at the University of Manchester, UK. Science communicator wannabe, he has a keen interest on everything related to HPV, viral oncology and parasitic infections to just say a few. Every bit of his free time is used for planning and getting involved in new projects, baking and getting lost in museums. You can follow him talking about science festivals, geeky stuff and bake off on



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Symbiosis – harmony or harm?

We have all experienced relationships which are beneficial and others that are not. The same can be seen throughout nature. Originally defined by German scientist Heinrich Anton de Bary, symbiosis describes a close association between two species, principally a host and a symbiont, which lives in or on the host. While some partnerships may be advantageous or neutral to one or both parties, others may have a more detrimental effect.

Mutualistic symbiosis:

screen-shot-2016-10-02-at-22-27-45The first of the symbioses involves relationships between two different species which benefit both organisms. Mutualistic symbiosis can involve organisms of all shapes and sizes from stinging ants and bullhorn acacia trees, a relationship where the tree provides the ants with food and shelter in return for protection from herbivores, to the alliance between oxpeckers and zebras, in which the bird enjoys a readily available food source while the zebra has any parasites living on it removed.

One of the most well studied forms of mutualistic symbioses is that of the ruminant (i.e. cattle and sheep etc.), as these organisms play an important role in our agriculture and nutrition. Ruminants host an extensive microbial population in the largest of their four stomachs, the rumen. A mutually beneficial relationship exists between these two organisms because the rumen microbes are able to digest the plant matter consumed by the ruminant. In doing so, they produce fatty acids, which can be used by both parties for energy. Carbon dioxide is also released in this process, providing the rumen microbes with the oxygen-free environment they need to survive (these microbes are predominantly anaerobic so are poisoned by oxygen).

Parasitic symbiosis:

screen-shot-2016-10-02-at-22-27-52In contrast to mutualistic symbiosis, the interaction between two organisms may be less savoury in nature. Parasitic symbiosis describes a relationship between organisms where the symbiont benefits at the expense of its host. Unfortunately for the host, this generally causes it harm, whether this be in the form of disease, reduced reproductive success or even death. The symbiosis between birds, such as the cuckoo and the reed warbler, known as brood parasitism, is a characteristic example of a parasite-host relationship. Rather than building her own nest, the parasitic cuckoo will lay her eggs in a reed warbler’s nest, leaving the warbler to raise this egg along with her own offspring. Once hatched, the cuckoo chick then ejects the warbler’s young from the nest, allowing it to receive all the food that its “adopted” mother provides.

Unsurprisingly, this antagonistic relationship has led scientists to question why warblers raise these parasitic chicks if the practice is so harmful. It has been suggested that cuckoos engage in a kind of “evolutionary arms race” with its chosen host, based on the host’s ability to recognise a parasitic egg. In this ongoing contest, the evolution of a host species to become more adept at spotting and rejecting a parasitic egg may result in a subsequent evolution in the cuckoo to counter this change. This may be to lay eggs with greater similarity to the host’s or to move towards a new host species. Such a process could continue indefinitely.

screen-shot-2016-10-02-at-22-28-01An even more detrimental relationship exists between the parasitoid wasp and its hosts, which include a range of insects from ants to bees. Similarly to cuckoos, these wasps rely on their host to facilitate the development of their young, but do so by either laying their eggs inside the host or gluing them to its body. Once hatched, the wasp larva will feed on the host, usually until it dies.

Commensal symbiosis:

Symbiosis does not necessarily have to be beneficial or detrimental to the host organism. Commensal symbiosis describes a relationship in which one organism benefits while the host is unaffected. This may be in the form of shelter, transportation or nutrition. For example, throughout their lifecycles small liparid fish will “hitch a ride” on stone crabs, providing them with transportation and protection from predators while conserving energy. The crabs, meanwhile, appear to be neither benefitted nor harmed.

One case of commensalism which may come as a surprise involves Candida Albicans, a species of yeast known to cause the fungal infection Candidiasis in humans. Contrary to popular belief, C. Albicans can be pathogenic or commensal depending on which phenotype it has. Under normal circumstances, C. Albicans reside in our gastrointestinal tract undergoing a commensal symbiotic relationship with us (i.e. causing us no harm). This interaction is actually the default existence for C. Albicans. When changes occur in the body’s environment, however, a “switch” in phenotypes to the pathogenic form can occur, placing a temporary hiatus on the usual commensal relationship.

A plethora of symbiotic relationships exist throughout the natural world, from the tiny microbes inhabiting the ruminant gut to the large acacia trees housing ants. They can offer both organisms the harmony of a mutually beneficial association, as is the case with the oxpecker and the zebra, or be parasitic and work in the favour of one player while harming the other, as seen with the parasitoid wasp. In some instances, one organism can gain benefit without impacting the other either positively or negatively. As illustrated by C. Albicans and cuckoos, a symbiotic interaction may change or evolve according to the environment or evolution of the host, respectively. Symbiosis is clearly a highly important aspect of nature which many organisms rely on for survival, and one that will continue to fascinate scientists and non-scientists alike both now and in the future.

Post by Megan Barrett.

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Cakealicious science: The science of baking

screen-shot-2016-09-26-at-08-16-07Food glorious food! Cakes cakes and more cakes! These sweet creations have had people drooling for centuries. There are many variations from rich chocolate to fruit and nut, covered in buttercream or marzipan, stuffed with jam or cream, the choices are almost endless. They’re perfect for big celebrations or just a chilled out half hour with a cup of coffee. But how on earth do they actually work? How can butter, sugar, flour, eggs and baking powder combine to make a delicate mouth-watering sponge?


screen-shot-2016-09-26-at-08-15-46Well science magic anyway. Each key ingredient has its own special role, without which the cake would collapse. The major ingredients need to be roughly of equal weights. First off the sugar and fat are mixed together. During the mixing process air gets caught on the rough surface of the sugar granules and is sealed in by a film of buttery fat, this forms a light fluffy mixture akin to whipped cream. We use caster sugar in this process rather than granulated sugar because it is finer than granulated sugar and therefore has a greater surface area on which to trap air.

screen-shot-2016-09-26-at-08-16-25But sugar does more than just trap air within the cake batter. It softens the flour proteins tenderising the mixture, it also lowers the mix’s caramelisation point, allowing the crust to develop a crisp golden consistency at relatively low temperatures. Finally, sugar also helps keep the cake moist and edible for many days. Most of the moisture in a cake comes from the eggs, which provide the mix with the majority of its liquid. When everything is mixed together the eggs produce a foam which surrounds the air bubbles in the mixture protecting them from the heating process and which is also stiffened by starch in the flour. Proteins in the flour join together creating a network of coiled proteins that we know as gluten. Gluten is key to holding the cake together, it expands during baking and then, when cooling, coagulates and is able to support the cake’s weight.

For the bakers out there you may have noticed that we have missed out the baking powder, this may come across as some voodoo magic but it is basically just dried acid and an alkali. Adding water and heat to this mix allows them to react producing CO2.

Now it’s not just getting the right measurement of ingredients, but it’s also essential to get the temperature of the oven precisely right. Too low and the expanding gas cells coagulate producing a coarse heavy texture leading to the cake sinking, too hot and the outside starts setting before the inside even finishes baking, leading to a volcano-looking cake.

So when you next grab a cupcake just take a little time to appreciate the exact science that went into baking that mouth-watering little treat. So many things that could go wrong it’s a miracle we ever found out how to make these soft icing covered delights.


Post by: Jennifer Rasal




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Woody Plants and pharmaceutics

Take a moment to think about your health over the last year. How often have you taken a painkiller to manage that headache or fever? These powerful tools have the ability to save you from a day of pain, allowing the survival of that long shift at work or half-marathon which has slowly crept up on you. How many relatives or friends have had their health improved through life saving medications such as chemotherapy or anti-depressants. There are a large variety of medications widely used today that have transformed our lives and we would struggle in a world without them. Many are aware that it is advances in medical research which have enabled the development and availability of these. However, it is often forgotten that when developing such drugs scientists will usually take their inspiration from similar compounds found in nature. But where? This article gives much deserved recognition to nature’s own pharmacologists. After all, these magicians are our true heroes.

So, what natural marvels are responsible for these compounds? – mainly plants, animals and fungi. This article will focus primarily on woody plants and their ability to produce useful chemicals. The extraction of compounds from plants goes back years. From tribes making herbal remedies to the scientific extraction of the chemicals we use today. Below are a few examples of how woody plants have completely transformed our lives:


screen-shot-2016-09-19-at-20-04-45Aspirin is a silicate sold as an over the counter medication. Its main purpose is to reduce pain and inflammation. The active ingredient in this common drug originally comes from willow tree bark and has actually been used for about 6000 years. So, how does this drug work? Willow bark contains a substance called salicin which the body transforms into salicylic acid. This acid reduces the production of certain prostaglandins in our nerves. Prostaglandins are produced in response to tissue damage or infection, their role being to facilitate the healing process. However, alongside their healing properties they also cause pain, therefore reducing their production can minimise the pain associated with the healing process. It can subsequently be deduced that willow trees do much more for us than just creating a gorgeous aesthetic landscape!


screen-shot-2016-09-19-at-20-05-23Irinotecan is a chemotherapy medication primarily used to treat colon and rectal cancer. The active ingredients within this medication include camptothecin, pentacyclic quinolines and 10-hydroxycamptothecin, which are derived from Camptotheca Trees, Camptotheca acuminata. The mechanisms by which these compounds interact with the human body are complex. They inhibit DNA topoisomerase I which is important for the replication of cancer cells. It would therefore make sense that without this substance, cancer cannot thrive. This is because type 1 topoisomerases are catalysts for the transient breakage of DNA and for the re-joining of the strands following this during cell replication. Without this catalyst, replication would occur at a very slow rate. Cancer is a devastating disease and advances such as this are hugely important.


Top: Normal heart activity. Bottom: Heart fibrillation

Top: Normal heart activity. Bottom: Heart fibrillation

Digoxin is well established in the treatment of heart arrhythmias including atrial fibrillation. It is extracted from the leaves of the common foxglove plant, Digitalis purpura. It works by slowing down the heart alongside improving ventricle filling which increases the blood supply available for each pump. The heart is one of the most important organs in the body, subsequently reflecting the importance of this medication and its lifesaving qualities.

These are just three examples of how woody plants have transformed our lives. However, there are still many unidentified species that have not yet been discovered in our ecosystems which have the potential to contain life-saving chemicals. In addition, there is the potential for the availability of medication that has fewer side effects to those currently in use. Unfortunately, many biomes are currently being destroyed at such a rate new species, and perhaps medically active chemicals, are being removed before any possible benefits can be uncovered. Therefore, the increased rates of deforestation may be destroying more than just habitats, they may be taking with them a wealth of potentially undiscovered medicines. This is just one more example of why conservation work is so important and I urge that it is taken seriously. Effective conservation is clearly vital to improve the lives of our future generations. It can be concluded that plants have played a huge role in our lives over many generations and continue to help us on a daily basis thus reflecting the importance of conserving them.

Take home message: Next time you take that aspirin in a moment of despair, take a moment to really appreciate the unsung heroes of pharmacy – woody plants. It is a shame that whilst many plants save us, we thank them by cutting them down, destroying biomes and causing extinction.

Post by: Alice Brown



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Are we finished editing CRISPR?

The academic world has been abuzz in the last few years with talk of a new gene editing technology known as CRISPR.  We hear about it on the news and are told that it could one day be a game-changer for modern medicine in terms of genome editing. But, like this article, all new techniques require proofreading and adaptation. So what I’m really wondering is: are we finished editing CRISPR?

CRISPR stands for ‘clustered regularly interspace palindromic repeats’, a mouthful even in the scientific community! CRISPR is a constituent of prokaryotic DNA and is used by these cells as a simple immune system, protecting them against viral attacks. We can imagine prokaryotic DNA as a piece of string (below: labeled as bacterial DNA), with repeated segments (circles) broken up by spacers (rectangles). Bacteria are able to detect invading viral DNA and add short sequences from the viral DNA in between the repeated sequences of their own DNA, creating a catalogue of past infections (a bit like our own immune system). If a virus attacks the same cell again these spacer regions are recognised by a special group of proteins called Cas proteins.  Cas proteins are nucleases which use the CRISPR-incorporated viral DNA segments to chop up the infecting viral DNA and inactivate it.


Scientists have harnessed the power of the CRISPR/Cas9 system by replacing viral DNA spacers with synthetic guide RNA’s that match a specific DNA sequence – this can be anything the scientist wants to modify. Researchers can then direct the Cas9 protein to their selected gene, causing a break in the DNA and the deletion of that region of the gene, ultimately allowing them to control expression of selected genes.

In theory CRISPR has the power to edit and even remove harmful genes associated with both acquired and hereditary diseases. In fact, just this year Anderson and colleagues at MIT demonstrated its potential in mice, correcting a harmful metabolic mutation. So why are we not using CRISPR in the clinics already?

While most people have no issue with treating acquired conditions, such as cancer, in previously healthy people, concerns arise when we talk about germline editing: i.e. editing human embryos prior to birth. From a medical perspective embryo editing could enable children with life threatening and debilitating conditions to lead a ‘normal life’. However, some parents believe that editing their child’s genome will change the child’s identity. Researchers also argue that, not only will germline editing reduce genetic diversity but we also don’t know enough about the genome and its regulation to confidently make such drastic and heritable changes. On a personal note, my main concern is where would germline editing stop? Where do we draw the line at disease state? For example obesity, my own area of research, and its predisposition is now considered as a disease.  The more conditions we begin label as ‘diseases’ the easier it could be to edit for desired traits.

All these issues exist before we even begin to think about the safety aspects of this new technique.  How do we deliver this system effectively into the human body? And, once there, how efficient and specific will it be. For example off target effects have ranged between 0.1-60%, levels still too risky for the clinics.

While acknowledging that CRISPR does have great potential in the future, much editing and rewriting may still be required before we can click submit.

Post by: Stephanie Macdonald


Figure adapted from:


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How to perfect your astro-photos.

In my last post I discussed why astronomers take multiple identical photographs of the same astronomical object in order to reduce the effects of random noise. I discussed how this noise arises and gave examples of the improvements gained by stacking multiple photos together. Of course, reducing random noise within your image is an important first step but, if you really want to obtain the perfect astro image, there is still more to consider. Both your camera and telescope can introduce a number of inconsistencies in your images, these occur to the same extent in every photograph you take, meaning they cannot be cancelled out like random noise can. Here I will discuss what these inconsistencies are and the ways astrophotographers remove them.

So…what are these inconsistencies? Well they come in three types and each must be dealt with separately:

The first of these is a thermal signal which is introduced by the camera. This tends to look like an orange or purple glow around the edge of an image. It develops when heat from the camera excites electrons within the sensor. As we take a photo, these heat-excited electrons behave as though they have been excited by light and produce false sensor readings. This effect gets stronger with increasing exposure time and temperature. The best way to remove this is to take an equal length exposure at the same temperature as your original astro image but with no light entering the telescope/camera (perhaps with the lens cap on). The resulting picture will contain only the erroneous thermal glow. This ‘dark’ frame can then be subtracted from the original image.


Figure 1. The original exposure (showing the constellation Orion at the bottom) shows a strong thermal signal in the top left. By taking a dark frame of equal exposure, we can subtract out the thermal signal, giving a better result.

The next inconsistency is known as bias. This constitutes the camera sensor’s propensity to report positive values even when it has not been exposed to light. This means that the lowest pixel value in your picture will not be zero. To correct this, it’s necessary to shoot a frame using the shortest exposure and the lowest ISO (sensitivity) possible with your kit then subtract it from the original frame. For most modern DSLR cameras, this subtraction has a very small effect but it does increase the contrast for the faint details in the picture – which is particularly important when shooting in low light.

Finally, and arguably the most important image inconsistency of all – uneven field illumination. This problem occurs when the optics within a telescope do not evenly project an image across the camera’s sensor. Most telescopes (and camera lenses) suffer from this problem. A common cause of uneven illumination is dirt and dust on the lens or sensor, which can reduce the light transmitted to parts of the sensor.

This is the objective lens from my telescope before and after cleaning. Although small specs of dust do not seriously affect the overall quality of the image, they can contribute to uneven brightness in the image.

This is the objective lens from my telescope before and after cleaning. Although small specs of dust do not seriously affect the overall quality of the image, they can contribute to uneven brightness in the image.

The final cause of uneven illumination is vignetting, this is a dimming of the image around its edges. Vignetting is normally caused by the telescope’s internal components such as the focus tube and baffles (baffles stop non-focused light entering the camera). These parts of the telescope can restrict the fringes of the converging light from entering the camera. So how do we combat this…keep cleaning the lens? Rebuild the internal parts of the telescope?…no. The answer is simple; take a ‘flat’ calibration frame. All you need to do is take an image of a evenly illuminated object (such as a cloudy sky, white paper, or blank monitor screen). Since you know the original scene is uniformly bright, any unevenness in the brightness of this image must be due to issues with the telescope. You then divide the brightness of the pixels in the original image by the pixels in the flat frame and magically, the unevenness is gone.

For your enjoyment, here’s some examples of flat frames taken from across the Internet, the middle image is from my scope. There are some diabolical flats here; I wonder if it’s even possible to conduct useful astronomy with such severe obstructions in a telescope!

Some examples of flat field frames taken by different telescopes. All these frames show were light is being blocked from reaching the camera sensor. My telescope’s flat frame is the middle picture; it looks good in comparison.

Some examples of flat field frames taken by different telescopes. All these frames show were light is being blocked from reaching the camera sensor. My telescope’s flat frame is the middle picture; it looks good in comparison.

By applying the flat frame correction, the background of the image becomes more even, and dark patches due to dust disappear! No need to clean your scope! (Image taken from

By applying the flat frame correction, the background of the image becomes more even, and dark patches due to dust disappear! No need to clean your scope! (Image taken from

For many people starting to turn their cameras and scopes to the heavens, all of this does sound rather arduous but there is software out there that will automatically combine your star images with the three calibration images and spit out what you want (see Deep Sky Stacker). I was amazed that for reasonably little effort and no extra money, I could improve the quality of my images significantly.

Post by: Daniel Elijah


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