ProceduresCalibrating Your Digital Camera1. Set up a piece of white paper so that it isuniformly illuminated by indirect sunlight. Choose a place where the light isbright, but you should not see any shadows on the paper.
The most importantthing is that the paper is illuminated evenly, with no bright spots or shadows.Choose a time and place during which it is unlikely there will be any changes inlighting.2. Position your digital camera so that the whitepaper fills the entire field of view. The precise distance from the camera tothe paper is not critical.3. Put the camera in manual mode and make thefollowing adjustments:a.
Manually adjust the focus sothat the camera is focused on the white piece of paper. Once you set the focus,do not change it during the calibration.b.
Set the camera’s sensitivity toISO 200.c. Set the aperture to f/2.
8.d. Set the image resolution to alow setting.e. If your camera has a self-timerfeature, set it so that the camera shutter opens a few seconds after you pressthe button to take a picture.
This minimizes shake.4. Now that your camera is focused on the whitepiece of paper, with the settings adjusted correctly, take a series of photosat different shutter speeds, varying by a factor of 2 each time.
(I used:30,15, 8, 4, 2, 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, and1/1,000 sec shutter speeds.)5. Repeat step 4. This will give you two completeseries of calibration photos. You will compare the two sets of photos later inthis procedure.
6. Download all of the calibration photos onto yourcomputer.7. Make two data tables in your lab notebook to keeptrack of the pixel value information for each calibration photo. One data tablewill be for the first set of calibration photos.
The other data table will befor the second set of calibration photos. 8. Measure the average pixel intensity of each photousing ImageJ.a. Start ImageJ.
b. Open the first calibration photousing the “File/Open…” menu command.c.
Click on “Analyze” andselect “Histogram” from the drop-down menu.d. A histogram of the pixel valuesin the photo will open in its own window. You will use this histogram tomeasure the average pixel gray value in each image. e.
Record the Mean, StDev, Min,Max, and Mode in your data tables. StDev is short for “standarddeviation”. Min and Max are short for minimum and maximum, respectively.Mean is another name for the average.
The mean of this histogram is the averagepixel value.f. Click on “File” andselect “Open Next” to open the next image file.Repeat steps 3.d.–3.f. until youhave analyzed all images in both sets of calibration photos.
9. Make a calibration curve by graphing the averagepixel value (the mean of the histogram) on the x-axis and exposure time (inseconds) on the y-axis. Use a logarithmic scale for the x-axis and a normal(linear) scale for the y-axis. Your graph will have two data series, one foreach set of calibration photos. Choose different colors or symbols for eachseries.a.
This is a “semi-log”plot. 10. Look at your graph and compare the calibrationcurves from each set of photos. The two curves should overlap or only beslightly separated. If there is a lot of space between the two calibrationcurves or if one of the curves has a very different shape from the other, youwill need to repeat steps 1–9, making sure that the lighting conditions are thesame for both sets of photos.Taking Skyglow PhotosNow that you have finished calibration, you are readyto measure skyglow. Pick three or four places where you would like to measureskyglow.
Choose places you think will have different amounts of skyglow.a. Make sure it is around the sametime of night and that there are no clouds.2. Travel to your first location with all of yoursupplies.
Pick the one you think will have the most skyglow. In your labnotebook, write down the address of your first location. Include a briefdescription also.3.
Set up your camera to take skyglow photos. Makesure the camera is in full manual mode. It is necessary to use the same camerasettings at each site you visit.
These are the same settings you used forcalibration photos.a. Set the camera’s sensitivity toISO 200.b. Set the aperture to f/2.8.c. Set the image resolution to alow setting.
d. If your camera has a self-timerfeature, set it so that the camera shutter opens a few seconds after you pressthe button to take a picture. This minimizes shake.3. Lay your towel or rag on the ground, then lay thecamera down on it, with the lens pointing toward the sky. If you have a tripod,you can mount the camera on the tripod and then point the camera toward thesky.
4. Double-check that your camera’s field of viewdoes not include the Moon, street lamps, or house lights.5. Take skyglow photos.6. Repeat steps 2–5 for each of the remaininglocations where you plan to measure skyglow.
Using Your Calibration to Measure Skyglow1. Use the ImageJ software to measure the averagepixel value in each skyglow image by following the procedure in step 8 of theCalibrate Your Digital Camera section. Make a data table in your lab notebook,and record the mean, standard deviation, minimum, maximum, and mode of eachpixel value histogram.2. Because all of your skyglow images were takenwith the same camera settings and exposure time, you can use the calibrationcurve to determine an “equivalent exposure time” (EET) for eachskyglow photo.
The EET is how long the exposure time would have to have beenunder calibration conditions to reach the same average pixel value as measuredin the skyglow photo. 3. Convert the average pixel value in each skyglowimage to an EET. Record the EET for each image in your lab notebook.
4. By converting the average pixel values of eachskyglow image into an EET, you can determine how much brighter or darker onelocation is compared to another.5. Determine which of your skyglow locations had thesmallest EET. This is the location with the darkest skyglow.Review of the LiteratureFor most of Earth’s history, our universeof stars and galaxies has been visible in the darkness of the night sky. Fromour earliest beginnings, the display arrayed across the dark sky has inspiredquestions about our universe and our relation to it.
The history of scientificdiscovery, art, literature, astronomy, navigation, exploration, philosophy, andeven human curiosity itself would be diminished without our view of the stars.But today, the increasing number of people living on earth and thecorresponding increase in inappropriate and unshielded outdoor lighting hasresulted in light pollution—a brightening night sky that has obliterated thestars for much of the world’s population. Most people must travel far fromhome, away from the glow of artificial lighting, to experience theawe-inspiring expanse of the Milky Way as our ancestors once knew it.Light pollution is light that isnot being efficiently or completely utilized and is often pointed outwards orupwards and not downwards. Also known as skyglow, light pollution occurs fromboth natural and human-made sources. The natural component of sky glow has fivesources: sunlight reflected off the moon and earth, faint air glow in the upperatmosphere, which results in a permanent low-grade aurora, sunlight reflectedoff interplanetary dust(also known as zodiacal light), starlight scattered inthe atmosphere, and background light from faint, unresolved stars and nebulae,which are celestial objects or diffused masses of interstellar dust and gasthat appear as hazy smudges of light.
Natural sky glow is well quantified.However, in the discussion of sky glow it is mainly human-made sources that areconsidered. Electriclighting also increases night sky brightness and is the human-made source ofsky glow.
Light that is either emitted directly upward by luminaires orreflected from the ground is scattered by dust and gas molecules in theatmosphere, producing a luminous background. It has the effect of reducingone’s ability to view the stars. Sky glow is highly variable depending on theimmediate weather conditions, the quantity of dust and gas in the atmosphere,the amount of light directed skyward, and the direction from which it isviewed. In poor weather conditions, more particles are present in theatmosphere to scatter the upward-bound light, so sky glow becomes a veryvisible effect of wasted light and wasted energy.
Skyglow, while affecting almost everyone, is of most concern to astronomers sinceit reduces their ability to view celestial objects. Sky glow increases thebrightness of the dark areas of the sky, which reduces the contrast of stars orother celestial objects against the dark sky background. Astronomers typicallylike very dry clear dark nights for observing. A typical suburban sky is 5 to10 times brighter at the zenith than the natural sky. The zenith being theangle that points directly upward, or 180°, from the observation point.
In citycenters, the zenith may be 25 or 50 times brighter than the natural background. Thereare three types of skyglow, each falling on the skyglow spectrum. Technicallyspeaking, three main types of light pollution include glare, light trespass andskyglow (in addition to over-illumination and clutter). Glare, from unshieldedlighting is a public-health hazard—especially the older you become.
Glare lightscattering in the eye causes loss of contrast, sometimes blinds you temporarilyand leads to unsafe driving conditions, for instance. Light trespass occurswhen unwanted light enters one’s property, for example, by shining unwantedlight into a bedroom window of a person trying to sleep. Lightpollution doesn’t just affect astronomers. The negative effects of the loss of the night sky might seem intangible.But a growing body of evidence links the brightening night sky directly tomeasurable negative impacts on human health and immune function, on adversebehavioral changes in insect and animal populations, and on a decrease of bothambient quality and safety in our nighttime environment.
Astronomers were amongthe first to record the negative impacts of wasted lighting on scientificresearch, but for all of us, the adverse economic and environmental impacts ofwasted energy are apparent in everything from the monthly electric bill toglobal warming. Thereare ways of measuring sky glow. This is no easy task, because many factors playa role in sky glow. One must not only consider the lighting, but also the angulardistribution of the light emitted from the luminaire, the light reflected fromthe ground and its angular distribution, as well as atmospheric effects ofhumidity and the interaction of light with aerosols (particles in theatmosphere that may be caused by manufactured pollutants, fire, volcaniceruptions, etc.
), all of which can change from moment to moment. Thereare many different ways to help improve the situation. Aside from houses,street lamps are one of the biggest causes of light pollution. The mostpolluting are the lamps with a strong blue emission, like Metal Halide andwhite LEDs. Change from the now widely used sodium lamps to white lamps (MH andLEDs) could produce an increase of pollution in the scotopic and melatoninsuppression bands of more than five times the present levels, supposing thesame photopic installed flux. This increase will worsen known and possibleunknown effects of light pollution on human health, environment and on visualperception of the Universe by humans. There is a measurable criterion toevaluate the lamps based on their spectral emissions and scientists suggestregulatory limits for future lighting.
Thisis an important topic to bring attention to. There are epidemiologicalevidences of increased breast and colon cancer risk in shift workers from lightpollution . An inhibition of the pineal gland function with exposure to theconstant light (LL) regimen promoted carcinogenesis whereas the lightdeprivation inhibits the carcinogenesis. Treatment with pineal indole hormonemelatonin inhibits carcinogenesis in pinealectomized rats or animals kept atthe standard light/dark regimen (LD) or at the LL regimen. These observationsmight lead to use melatonin for cancer prevention in groups of humans at riskof light pollution.
Thereare many different ways to help lessen the amount of light pollution. The mostimportant thing to do is to reduce light escaping your home and to direct theillumination down, not up. These aren’t the hardest things to do and can evensave you money. Using dimmer light switches also can help. Light pollution is aserious issue; it is widespread and has many bad side effects. Additionally it doesn’t just harm scientists;it helps to cause many diseases and conditions. It also affects the sleeppattern of nocturnal animals.
Ichoose to do this topic since I have strong interests in photography andastronomy. I also became more interested in it when I read up on how serious ofan issue light pollution is. I believe that it is a serious issue for everyone.If all directional technology suddenly (i.e Gps, google maps,etc.) failed, wewouldn’t be able to see the night sky to navigate.
In my experiment I will bephotographing different areas’ night skies on multiple nights. I will then runthe through ImageJ and compare and contrast which have more or less skyglow. Myhypothesis is that the area with more street lights will defiantly have moreskyglow than the rest, but the high up areas mainly Vista Point will have less.