Rose Haber and Kevin Li
Midterm Presentation: Light Pollution Measured by the DSS-7
Need: About two thirds of the population of the world and 99% of people in the continental USA and western Europe never see a truly dark starry sky from where they live because of light pollution. Most of them cannot see the Milky Way and for many, the sky never gets darker than it would during natural twilight because so much artificial light brightens the atmosphere. Five to ten billion dollars are spent annually in the United States to fund wasted light, which highly contributes to light pollution Cinzano, 2009.
Knowledge Base- LP: Light pollution is essentially misdirected or misused light Results from inappropriate application of exterior lighting products
Light wastefully escaping into the night sky and causing a glow over urban/suburban areas.
Spectroscopy: Spectroscopy is one way that an astronomer can get information about space. A spectrograph is a device that takes light from a source and separates it by wavelength
Stellar spectroscopy: When stars emit light, they can be broken into spectra with a prism. Solids, liquids and dense gases emit light of all wavelengths, without any gaps. This is called a continuous spectrum. An emission or a bright light spectrum occurs when thin gasses emit light of only a few wavelengths. An absorption or dark line spectrum occurs when a thin gas will absorb light of the same wavelengths it emits if a source of light is behind it.
Spectrograph Fundamentals: The slit on the spectrograph limits the light entering the spectrograph, which allows an astronomer to take a number of spectra from different regions of a source. Light is then collimated or made parallel before hitting a diffraction grating. This separates the light into wavelengths, which can then by focused by a camera mirror into a detector such as a charged-couple device or a CCD imager.
DSS-7: The spectrograph uses a diffraction grating, which has thousands of narrow lines ruled onto a glass surface. It reflects light so no photons are "lost". In order to analyze spectra, a spectrograph, the DSS-7 made by Santa Barbara Instruments, can be used. It is designed to produce a graph of the intensity of light as a function of wavelength, such as this graph on the right. The diagram displays examples of absorption lines for different chemicals, from Australia telescope outreach program. The DSS-7 can reveal these features.
CCD imaging: A charge-coupled device, or CCD, is a silicon semiconductor chip designed to capture light images electronically. To generate electrical power the CCD keeps the charge in individual picture elements, called pixels. To read out the image, the charges are shifted from pixel to pixel across the CCD and read out by an amplifier on one of the edges. A dark frame is an image of the same duration and temperature as the light frame taken with the CCD imager with the lens cap on. During processing, the dark frame is subtracted from the light frame using software to remove the dark current signal.
Eye: The human eye can only see a small part of the electromagnetic spectrum, which is the visible spectrum. The visible spectrum lies between about 400 and 700 nanometers. The human eye has the maximum sensitivity at around 555 nm, which is green.
Outdoor Lighting: The many types of outdoor commercial lighting include: Incandescent lamps, Halogen lamps, Fluorescent lamps, Mercury Vapor lamps, Metal Halide lamps, high-pressure sodium lamps, and low pressure sodium lamps. A mercury-vapor lamp is a gas discharge lamp, which uses mercury in an excited state to produce light. As the main arc strikes and the gas heats up and increases in pressure, the light shifts into the visible range and the high gas pressure causes the mercury emission bands to broaden somewhat. A sodium vapor lamp is a gas discharge lamp, which uses sodium in an excited state to produce light. Such lamps emit light on just one dominant spectral line with other far-weaker lines, and therefore is the easiest to filter out.
Bortle Dark-Sky Scale:
Literature Review- Chalkias: The paper by chal-kEE-ass et al describes a methodology for modeling light pollution using geographical information systems GIS and remote sensing RS technology. Their proposed approach attempts to address the issue of environmental assessment in sensitive suburban areas. Direct light pollution corresponds to optical contact with artificial night light sources, while indirect light pollution corresponds to optical contact with the sky glow above the city. The case study demonstrates high levels of light pollution in suburban areas and its increase over the last decade. X-axis: height from horizon in degrees; y-axis: light emissions
Prugna: This paper reports measurements of zenith night sky brightness and a spectral survey carried out at selected places in Venezuela and Italy. These range from large cities like Florence, to dark sites, such as the Alps. Measurements were carried out visually by means of a simple photometer and spectra from and were obtained by a small spectrograph. The purpose of this paper was to stress the importance and the need of night sky quality monitoring over time to assess the harmful effects of light pollution. The direct monitoring of the night sky quality over time is usually carried out at most observatories, but measurements of night sky brightness at other common places, such as cities, towns and villages, which represent the main polluting sources, are scarce.
Purpose: The purpose of this study was to examine the light pollution in Manhasset, NY as opposed to the lack of pollution in Montauk, NY.
Hypothesis: The null hypothesis states that there is no difference between the light pollution in both areas and the alternate hypothesis states that light pollution will be greater in Manhasset than in Montauk.
Methodology:
Results: Manhasset Zenith Overlapped with Manhasset Zenith with Light Pollution Filter: This is the spectra of Manhasset's Zenith taken with the DSS-7 and the CCD imager without a filter and the spectra of Manhasset's Zenith taken with the DSS-7 and the CCD imager with a light pollution filter. The lower graph is the Manhasset Zenith with the light pollution filter. As you can see, the intensity of the light is decreased using the light pollution filter. There is the greatest decrease of intensity, from Manhasset's Zenith toManhasset's Zenith with the light pollution filter,at the 1100 nm region of the spectra.
Manhasset Zenith Overlapped with Lights: This is a graph of Manhasset's Zenith overlapped with Metal Halide's spectra, Fluorescent's spectra, and Low Pressure Sodium's spectra. The black graph is Manhasset's zenith, the orangish one is Metal Halide, the green one is Fluorescent, and the blue one is Low Pressure Sodium. The Metal Halide spectrum was taken from the Middle School Gym. The Fluorescent light was taken from the High School Gym. The Lower Pressure Sodium light was taken from a Low Pressure Sodium lamp after it was fully turned on.
Montauk Zenith overlapped with Montauk LP filter: This is the spectra of Montauk's Zenith taken with the DSS-7 and the CCD imager without a filter and the spectra of Montauk's Zenith taken with the DSS-7 and the CCD imager with a light pollution filter attached to it.The spectra of both graphs for the most part is the same, but the 1000nm region of the spectra of Montauk's Zenith with the Light Pollution filter is less in intensity than the spectra taken without the light pollution filter.
Manhasset Zenith overlapped with Montauk Zenith: This isthe spectrum of Manhasset's Zenith overlapped with the spectra ofMontauk's Zenith. The lower spectrum, the one with a lower intensity, is the spectra of Montauk's Zenith. You can especially see the difference between the intensity of Manhasset's Zenith and Montauk's Zenith in the 1000nm to the 1200nm region of the spectra.
Discussion: Light pollution filter decreases the intensity of different areas of spectra especially around 1000nm area. Montauk’s spectrum has an overall less intensity than Manhasset’s spectra. Montauk has less light pollution than Manhasset. Manhasset has higher intensity of light at around 1000-1200 nm region. Because it is a suburban area, Manhasset has more light pollution due to all of the houses, and street lighting. On a Bortle Dark-Sky Scale, it even shows Montauk has less light pollution than Manhasset. So far, only used the zeniths of each area. Have yet to image all of the different types commercial outdoor lights due to unavailability at the moment. The missing lights include: Halogen, Mercury-Vapor, and High Pressure Sodium. The human eye is most sensitive to the spectra at 555nm, which is around green part of visible light spectrum. In order to have effective results, light that mostly emit spectra in this zone should be eliminated for ideal viewing.
Conclusion: in conclusion, the data collected, as of now, supports alternate hypothesis. The Manhasset Zenith overlapped with Montauk Zenith shows that the Manhasset night sky is brighter than Montauk and the Manhasset night sky shows more intensity than Montauk, especially in the 1000-1200 nm region. Also, the use of a light pollution filter on the spectrograph decreased the intensity of the spectra at around 1000 nm.
Future Studies: This project can be branched out in many different directions. The eye can be studied in greater detail to determine how and why it is so sensitive to the 555nm spectra. More lights can be imaged to get the best possible spectra that can be filtered out the easiest. The prices of lights need to be analyzed as well, because if change is to be made, it needs to be economical to the government, and the people.